K. Lundmark was the first to speak about supernova explosions in our Galaxy in 1921. He believed that the bright flashes observed in the ancient and Middle Ages were galactic novae and those stars that were later called supernovae. Noting the outbreak of 1054, observed in China, he pointed out that its place is close to the crab nebula - a gas clot of fibrous structure, resembling a crab. It is curious that the American astronomers C. Lampland and J. Duncan also studied this nebula in 1921, and both found that it is systematically expanding, and its expansion duration is almost nine centuries.
It is now easy for us to compare these facts and establish the coincidence of the outburst with the formation of the nebula, but neither Lundmark nor the American researchers have made such a conclusion. Only seven years later, E. Hubble for the first time noted this coincidence in passing, and ten years later, Lundmark already confidently said that the Crab Nebula was formed as a result of the outbreak of 1054. He found the apparent magnitude of the outbreak and the distance to the Crab and obtained its absolute stellar a value that turned out to be much higher than that of a conventional new one. This proved that in 1054 a supernova explosion occurred in the Galaxy. No less important was the establishment of the fact that an expanding nebula remained in its place. The reason for the seventeen-year delay, apparently, was that in the most authoritative ancient Chinese chronicle it was said that "a few inches southeast of the Tian-Kuan, a guest star appeared (as the appearance of stars and comets was called in China)". "Inch" in this case is about one and a half degrees of the arc of the celestial sphere. It was usually believed that the main star of the constellation "Tian-Kuan" ("Heavenly Barrier") was $\zeta$ Taurus (Fig. 23). However, the Crab Nebula is located not to the southeast, but to the northwest of this star. I had to suspect that there was a mistake in the Chinese text.
Rice. 23. The constellation Taurus and its environs.
Degree divisions are marked on the left edge of the map, the thick line with degree divisions is the ecliptic. The boundaries of the constellation Taurus and other modern constellations are outlined with a dotted line, the main stars are indicated by the letters of the Greek alphabet. The configurations of the Chinese constellations are shown in solid lines, their names are given in italics. The Crab Nebula is marked with an X.
But the possibility of error is emphatically rejected by historians of science in ancient China. In 1971, a specialist in ancient Chinese astronomy Ho Ping-yu (Malaysia) and American sinologists F. Paar and P. Parsons pointed out another text with a similar description of the outbreak southeast of the "Tian-Kuan". Therefore, there was no error in the chronicle. We need to look for another reason for the confusion in establishing the location of the outbreak. This seems to have been achieved by the author of this book.
On the ancient Chinese maps of the starry sky, there are almost no constellations with the same names, and only "Tien Guan" turned out to be five: in the modern constellations of Taurus, Virgo, Sagittarius, Gemini and Capricorn. Another of the first researchers of the Chinese system of constellations G. Schlegel in 1875 noted that each of these "Heavenly Barriers" consists of two bright stars, but the main thing - that the line between these barrier stars necessarily crosses the ecliptic - remained unnoticed. But this was the purpose of these special constellations: they played the role of real barriers, blocking in five places the main "celestial highway" - the ecliptic, in the area of \u200b\u200bwhich the movement of celestial bodies takes place: planets, the Sun and the Moon.
Schlegel and others after him considered the second star of the "Tian-Kuan" in Taurus to be a faint star south of Taurus and did not take into account that such a barrier does not cross the ecliptic. This was the mistake that led to confusion in establishing the location of the supernova explosion.
Taurus is also a natural pair of stars that satisfies our requirement. By the way, Hipparchus calls them "horns" of Taurus, which meets with them the luminaries moving along the ecliptic - a role quite similar to the "Heavenly Barrier"! Why hasn't anyone paid attention to Taurus as a natural and, moreover, the main bright component of the "Tian-Kuan"? Because the connection of barriers with the ecliptic was not revealed, and besides, this star was one of the main stars of the neighboring constellation "U-Che" ("Five Chariots"), located on the site of our constellation Auriga. But this was also an insignificant objection, because the "Tian-Kuan" are not entirely independent constellations: in Sagittarius and Gemini they are simultaneously part of neighboring constellations. It's the same with the "Barrier" in Taurus.
It was strictly customary for the Chinese to indicate the position of the "guest star" in relation to the brightest star in the constellation. In the "Tian-Kuan" in Taurus, we must now consider Taurus as such a star, and then the controversial text from the Chinese chronicle receives a clear interpretation: "southeast of Taurus at a distance of several degrees." Southeast of this star, seven degrees from it, is the Crab Nebula.
We will talk a lot more about the Crab Nebula in subsequent chapters, because it has played an exceptional role in astrophysical research. Therefore, of particular interest are detailed information about the flash: its brightness, color, their changes, and other features. However, there are almost no direct comparisons of the brightness of a flared star with anything else. Nevertheless, an attempt to investigate the problem was made in 1942 by the Dutch astronomer J. Oort and the American N. Mayall. They established from Chinese texts that the first time a supernova was noticed on July 4, and it was visible even before dark for 23 days, and at night it was observed until mid-April 1056.
If we take into account that we can see Venus when the Sun has not set, when its brightness exceeds magnitude - 3.5, and the supernova ceased to be visible at night, after its brightness fell to the 5th magnitude, then we get that the star has weakened by 8.5 magnitudes within 650 days, by an average of 1.3 magnitudes per hundred days. But now we know that such a slow rate of decay, combined with the slow expansion of the shell (as seen in the Crab Nebula), is possible only in Type II supernovae.
Oort and Mayall rejected several references to earlier dates for supernova sightings, notably Japanese records from late May, as the supernova was then obscured by the Sun and impossible to see, and three Chinese texts claiming that there was an eclipse of the Sun in 1054. in the daytime and a "guest star" appeared in the "lunar home of Mao" (Pleiades)". The places and moments of all eclipses are accurately calculated in T. Oppolzer's "Canon of Eclipses", and the eclipse referred to took place on the May new moon in South China in the afternoon of May 9, 1054. Now, 40 years after the work of Oort and Mayall, we we can say that both Japanese and Chinese texts did not contain errors: a supernova was seen in May. The modern interpreters were mistaken. But this became clear after information about supernova observations in Armenia was found.
In 1969, Soviet researchers I.S. Astapovich and B.E. Tumanyan was found in the Matenadaran depository of ancient Armenian manuscripts, and in 1975 the astronomical text of Etum Patmich was finally deciphered. In translation, he said that in 1054 "a star appeared on the disk of the Moon when there was a new moon on May 14 in the first half of the night." We already know that according to the modern calendar, the new moon was on May 9, and a little over a day later, as calculations show. The moon is closest to a supernova. This moment could be observed in Yerevan on May 10 at the setting of the moon, which, a day after the new moon, looked like an extremely narrow sickle. But the supernova was almost four lunar diameters below the moon. N.S. Astapovich convincingly showed that this distance near the horizon can be significantly reduced by three optical effects: the horizontal parallax of the Moon, irradiation, and anomalous refraction of the star's light near the horizon. Consequently, the striking sight of a bright star in the vicinity of a crescent moon could be observed.
If Patmich saw a supernova, then the texts that noted its appearance during an eclipse are correct. The fact is that the indication of the "lunar house of Mao" apparently refers only to the Sun, which at the time of the eclipse was indeed in the Pleiades. Perhaps the text noted that in the darkened sky during the eclipse, among the familiar stars, they also saw a “guest star”. When the eclipse ended, it disappeared into daylight, therefore it was still not bright enough and reached its maximum the next day. Until the beginning of July, for almost two months, it could be brighter than -3.5 magnitude and, on occasion, be observed against a blue background of the sky with the Sun not yet set. A long stay at the maximum is also characteristic, as we know, for type II supernovae - this is another argument in favor of such a classification of the outbreak.
In addition to the possible observation of a supernova in Armenia, other circumstances associated with the outbreak of 1054 are now known, the reliability of which is conditional, but they are plausibly combined with other more reliable information about the supernova. These are rock carvings in the northern Arizona desert.
In 1955, the American archaeologist W. Miller discovered there two rock paintings of an unusual plot for North American Indians, namely, containing motifs of a crescent moon and a circle depicting a star (Fig. 24). One drawing was in a cave on White Table Mountain and depicted a young Moon with a bright star on the lower horn, and another, located not far from the first on the wall of the Navajo Canyon, depicted a sickle facing the other way, i.e., the old Moon and a star below it .
Rice. 24. Arizona rock art.
The left drawing was found in the cave of the White Table Mountain and depicts the young Moon approaching the star, the right drawing is on the wall of the Navajo Canyon; old moon and bright star.
The remains of coals in the hearths of the caves and the style of drawings in this part of the canyon showed that the caves were inhabited by the Navajo Indians in the 10th-12th centuries. Most likely, the Indians were amazed by the spectacular spectacle of the proximity of the Moon and the supernova of 1054. The Moon's encounters with the stars in its path occur exactly after 27 days and 7 hours. In particular, the old Moon approached a supernova on June 4, 1054, shortly after it began to be observed in China. This event could correspond to the pattern in the canyon. As for the drawing in the cave, Miller and the astronomers who studied it later believed that the ancient artist turned the image of the Moon upside down, as our contemporaries do when asked by surprise to draw the Moon from memory. To confirm this fact, mass experiments were even arranged, which confirmed the inattention of our contemporaries. Well, as usual, they again blamed the ancient artist for the mistakes.
Rice. 25. Light curves of five galactic supernovae.
Horizontal - phase in days, vertical - apparent stellar magnitudes. 1 - Chinese Supernova 185 2 - Supernova 1006 3 - Supernova 1054, 4 - Brahe's Supernova 1572, 5 - Kepler's Supernova 1604
But comparison with modern man does not stand up to criticism. The moon in the Neolithic era and for a long time after it was for people not a simple night lamp, but also a clock and a calendar. By position in the sky and by phase, it was possible to judge the time of day and the day in lunar month. It was still impossible to confuse the young Moon with the old one, because the young Moon is visible in the evening, and the old one in the morning.
Apparently two different events were depicted. I.S. Astapovich drew attention to the fact that the drawing in the cave, which was considered inverted, corresponds exactly to the May approach of the Moon to the supernova, which was seen on May 10 in Armenia at sunset. But in Arizona, this moment was during the day, the Moon became visible only a few hours later, when it began to set. The distance between her and the star at sunset in Arizona was no longer minimal.
On fig. 25 shows the supposed light curve of the Supernova of 1054. At its maximum, it reached -5th magnitude, and the photometric class was probably II.5.
The search for galactic supernovae
In 1943-1945. Soviet astronomer B.V. Kukarkin and the American astronomer W. Baade independently investigated two more galactic supernovae. These were the brightest outbursts of stars on the eve of the telescopic epoch, known as Tycho Brahe's Nova of 1572 and Johannes Kepler's Nova of 1604. Our contemporaries used comparisons of the brightness of new planets and neighboring stars given in the works of Brahe and Kepler. It is now possible to accurately calculate the magnitudes of the planets for any moment in the past, and the exact magnitudes of stars visible to the naked eye are known. This made it possible to reconstruct the light curves of both bright flares (they are shown in Fig. 25). Korean historical records of New Kepler were also unequally searched for, significantly supplementing European observations. The maximum brightness of the Supernova of 1572, according to our definitions, was -4.5, and that of the Supernova of 1604 was -3.5, i.e., in both cases it reached the brightness of Venus. But the most interesting thing is that their light curves not only turned out to be definitely type I, but both of them corresponded best to the photometric class I.12.
At the sites of outbursts, first at New Kepler, and then at New Brahe, W. Baade discovered faint ragged filamentous nebulae. Although these nebulae differ in detail from the Crab Nebula, it was still a new sign for the search for supernovae in our Galaxy, including those that, for one reason or another, were not observed as flashes in the past. Therefore, it was quite natural to suggest, put forward in 1946 by Oort, that the large filamentous nebula in the constellation Cygnus is also a supernova remnant that had long since slowed down in the interstellar gas. More than three dozen such filamentous nebulae have already been found in the sky. The brightest of them were studied by Soviet astrophysicists G.A. Shain and V.F. Gaza. All of these supernova remnants are thousands of years old.
In 1948, the first strong sources of cosmic radio emission were discovered, and some of them lay in the region of the Milky Way. These sources were named Sagittarius A (later found in the core of the Galaxy), Cassiopeia A and Taurus A. At that time, radio telescopes determined the position of the radio source in the sky very roughly, but still a year later, the Australian radio astronomer J. Bolton and his colleagues discovered that the open earlier, the Taurus A radio source coincides in position with the Crab Nebula.
The study of this radio source at several wavelengths showed that its intensity increases with the transition to longer wavelengths. This was an important fact, the consequences of which were comprehended later. We already know that heated celestial bodies they also emit waves in the radio range, but if the source of radiation is thermal, then its intensity on radio waves decreases with the transition to longer waves. In the case of the Crab Nebula, however, the course of change in the intensity of radio emission with wavelength is different: the intensity increases with increasing wavelength. This shows that the object's radio emission has a non-thermal character. Looking ahead, we note that, in addition to supernova remnants, nonthermal radiation is present in extragalactic sources: radio galaxies and quasars. Weak nonthermal radio emission is also generated by the interstellar medium of spiral arms.
The discovery of non-thermal radio emission from the Crab Nebula prompted the search for supernova remnants using this new feature. In 1952, Baade found a faint filamentous nebula at the site where the radio source Cassiopeia A is observed. Soviet astronomers P.P. Parenago and J.S. Shklovsky suggested that this is also the remnant of a supernova, perhaps even observed in ancient China (in the constellation Cassiopeia, ancient observers saw many outbreaks). Other researchers, such as Minkowski, disagreed with their point of view.
But in 1955, R. Minkowski was able to measure the motion of the clumps of this nebula and found that, despite its dissimilarity to the Crab Nebula, it is also part of a rapidly expanding envelope. He had to withdraw his objections. From the expansion of the nebula, it was possible to determine the age of this supernova. The latest research by Canadian astronomers K. Camper and S. van den Berg indicates the date of the outbreak around 1653 with an uncertainty of about 3 years. This means that it happened quite recently, already after the outbreaks of Supernovae Brahe and Kepler, in the era of the telescopes of Jan Hevelius, but meanwhile, it was not seen in the constellation Cassiopeia, which is always accessible to observations and does not set in the temperate latitudes of our hemisphere. The young supernova discovered by radio astronomy has turned out to be an exceptionally interesting object in many respects.
To date, radio astronomy has made it possible to find 135 nonthermal radio sources belonging to our Galaxy. They are supernova remnants of different ages. Only for relatively young objects, observed in sufficient detail in past centuries by our predecessors, can we determine the type, and sometimes even the photometric class, of a supernova from the light curves.
Supernova observations in antiquity
Scientists have been collecting information about ancient observations of star flares, the appearance of comets and other unusual phenomena for a long time. The first summaries of such data, compiled from Chinese, Middle Eastern and European sources, belong to the French comet researcher A.G. Pingre, who in 1783 published the two-volume work Cometography. He used some Roman and Biblical texts, as well as the first translations of the medieval Chinese encyclopedia "Wenxian Tongkao", compiled by Ma Duanlin, and some other manuscripts, some of which were then lost without a trace during the era of the French Revolution.
Unfortunately, Pingre's list was undeservedly forgotten by both Humboldt and Lundmark. To date, the most complete collection of all phenomena considered, for one reason or another, to be stellar flares, was compiled by the author of this book and included in the international "General Catalog of Variable Stars", regularly updated with new data.
From ancient times to 1700, there are about 200 outbreaks, mainly new stars, and searches in the annals of manuscripts and chronicles continue. Note that, until recently, it was believed that few outbreaks were observed in Europe, the Mediterranean and the Middle East: only 5-7, and the rest were seen in the countries of the Far East. Drawing on the materials of Pingre, Roman chronicles showed that about 25 outbreaks were noted in the West. This is already a serious contribution, which is used for cross-comparison of flare descriptions.
How can supernovae be identified among the observed flares? The three bright galactic supernovae we have discussed in the preceding pages have reached and exceeded magnitude -3.5. And this is not an accident. In order for a star's flare to be easily detected with the naked eye, it must be at least 3rd magnitude. Then it breaks the usual figures of the constellations and catches the eye. A new star will have such a maximum brightness if it is located no further than a thousand light years from us. On the other hand, a supernova that erupted in the most distant part of our Galaxy, if there were no interstellar extinction, would be brighter than zero magnitude and be observed, depending on the type of light curve, from 3 to 8 months. Thus, there is a strong possibility that a flash brighter than magnitude zero is a supernova.
Until recent years, the oldest report that has come down to us about observations of bright stars was the mention of a comet in 2296 BC. e., found by Pingre and contained in the records of oral traditions about the first Chinese ruler Yao. Writing in China arose one and a half millennia later. But a few years ago, J. Mikhanovsky (USA) deciphered a clay tablet of the Sumerians (inhabitants of ancient Mesopotamia), which also recorded the oldest oral legend about the "second deity-sun" that appeared in the southern side of the sky, but soon faded and disappeared. This phenomenon is attributed to 3-4 millennia BC. e. and are associated with a supernova explosion, after which the remnant closest to us remained - the Sail X nebula.
We now have certain and reliable information about an outburst, apparently a supernova, which was seen in China on December 7, 185 AD. e. and was visible until July 186 or 187. Here is how this phenomenon is described: “In the period of Zhong-Qing, in the second year, the 10th moon on the day of Kwei-Hao, an extraordinary star appeared in the middle of Nan-Meng. It was the size of a bamboo abacus and successively showed five colors. Gradually she decreased her brilliance towards the 6th moon after the following year, when she disappeared." This description contains the date of the phenomenon, its duration and place in the sky, its character is indicated: immobility among the stars, weakening of brilliance and change in color. Note that this is the only mention of the phenomenon of 185, other information has not reached us.
The constellation "Nan-Man" is also the Centauri. In Luoyang, the ancient capital of China, it rose three degrees above the horizon and was visible for no more than two hours a night, so the star must be exceptionally bright to be noticed. It was believed that the outbreak was observed for 7 months, but F. Stephenson argues that the corresponding hieroglyph in the text should be translated not as “next year”, but in the sense of “next year”, and estimates the duration at 20 months.
In our opinion, the decisive argument that testifies to the outbreak of a supernova, and not a new star, is the consistent change in the color of the outbreak. New stars hardly change their color, while supernovae are white at their maximum and then successively turn yellow, red, yellow and white again. Since the text speaks of five colors, the first observations refer to the stage white color i.e. to the maximum brilliance.
What was the maximum brightness of a supernova? The text does not provide direct information, but we can calculate it from the duration of the phenomenon. A seven-month visibility of a star near the horizon indicates a stellar magnitude of the flare no higher than -4, and a 20-month one indicates from -4 to -8 magnitude. It turns out a fairly wide choice, which can be limited if you find a supernova remnant.
Four non-thermal radio sources, i.e., supernova remnants, have been found between and Centauri. Located in the middle coincides with a faint filamentous nebula. Recently discovered its thermal X-ray emission - a sign comparative youth supernova remnant. Its age, calculated from the intensity of radio emission, is less than the age of the other three, but exceeds 1700 years, i.e., it turns out to be older than the observed outburst, which should be attributed to the roughness of this method of determining the age. The distance to the remnant is 2-3 kpc, and therefore a type I supernova that exploded at such a distance, after its weakening by interstellar absorption, would reach -4th magnitude, and in the case of type II it would be -2nd magnitude. Apparently, type I is better suited.
Attempts to identify supernova explosions described in ancient texts, "from the back door", using data on galactic supernova remnants, were in great vogue about twenty years ago. Their weak point was the very rough indications of the chronicles on the area of outbreaks. When it became possible somehow to determine the ages of the remains, the imaginary nature of many "identifications" was revealed.
An important role is now played by the search for old texts that contain valuable astronomical information. Particularly instructive in this regard is the history of the study of the Supernova of 1006. This outbreak, observed in the southern constellation of the Wolf, near the horizon, was mentioned in seven Japanese, six Chinese, six European, five Arabic and one Korean chronicles. The chroniclers describing the phenomena were not always professional observers and eyewitnesses, but sometimes there are descriptions of eyewitnesses. Such was the astrologer Ali ben Ridwan, who described in detail the phenomenon of 1006, which he personally saw in his youth. He well remembered the position of the planets when the star appeared, and the American researcher B. Goldstein was able to establish the date and place of this phenomenon in the sky. He obtained similar results from Chinese chronicles.
As in the case of the Supernova of 1054, we are confronted here with the paucity of information about the brightness of the supernova. It is curious, however, that the first description of the supernova on April 28, by Japanese astronomers, noted the blue-white color of the star, and subsequent observers unanimously call the color of the star yellow and golden. Judging by this information, the Japanese saw this supernova even before it reached its maximum brightness. Chinese sources also noted that on May 1, its brightness gradually increased and approached the brightness of Venus. Five sources compare the brilliance of a supernova to that of an incomplete moon, although no one mentions that the star was also seen in the daytime. Of course, in May, the star rose and set late at night. Even if it were equal in brilliance to Venus, it would make a huge impression against the backdrop of a moonless deep night, while we see Venus only at dusk against the bright background of dawn. The shadows from the illumination of the supernova objects also enhanced the impression and served, apparently, as the basis for comparisons with the incomplete Moon. And in fact, a supernova could appear brighter than Venus, but fainter than the Moon in a quarter. Ali ben Ridwan notes that the "size" of the star exceeded Venus by 2.5-3 times. This comparison was "absentee", since the star rose much later than the setting of Venus. The researchers tried to recalculate Ali ben Ridwan's estimate based on old Arabic and modern data on the apparent angular dimensions of Venus, but it turned out to be nonsense. Ali ben Ridwan apparently meant that the star was brighter than Venus by 2-3 magnitudes. Since Venus could have been -3rd magnitude in May evenings, the supernova at its maximum brightness could have been -6th magnitude.
That circumstance; that in July the supernova was supposed to rise in the daytime after noon, but it was not seen against the background of the daytime sky, indicating that it seemed to be weaker than -3.5 magnitudes in this month. When it became visible again at night, it still stood out in brilliance from the surrounding stars. From July to the end of November, Japanese court astronomers reported nine times its visibility to the emperor. Chinese astronomers saw her in the morning in the east until the very end of the year. In 1007 there was no longer any information about a supernova. True, there is a report in one source, which Goldstein translates as a statement that she was seen before 1016, but this is a clear misunderstanding, since in this case the supernova at its maximum would be so bright that it would shine during the day for a long time.
Consideration of the circumstances of the visibility of the supernova speaks in favor of the fact that it was a type I supernova. Among several sources of nonthermal radio emission in the flare region, one was found with traces of gas filaments and with characteristic X-ray emission. In 1979, not far from the center of this supernova remnant, F. Schweitzer and J. Middleditch discovered a blue star of 17th magnitude, which, judging by the spectrum, is a white dwarf.
Looking ahead, we note that by that time, faint blue central stars had already been found and studied in two supernova remnants - in the Crab Nebula and Sails X, which turned out to be blinking at a high frequency - 30 and 10 times per second, respectively. However, no fluctuations in the brightness of the Schweitzer star were found. It could turn out that this star is accidentally projected onto a radio source and is one of the usual objects of the galactic disk in front of or behind the supernova remnant. But, on the other hand, it could also be the first discovered stellar remnant of a Type I supernova! It needed to be sorted out. And in January 1982, from a satellite armed with ultraviolet spectrometers, the spectra of this object from 1200 to 3200 were obtained. The spectra revealed absorption lines belonging to the expanding shell of a supernova remnant located in front of the star; their displacement indicated an expansion velocity of 5,000 to 6,000 km/s. This played a decisive role in establishing the true scheme for the development of type I supernova outbursts.
| Table 13. Galactic supernovae | |||||||
| Supernova, flash year | 185 | 1006 | 1054 | 1181 | 1572 | 1592 | 1604 |
| Constellation | Centaurus | Wolf | Taurus | Cassiopeia | Cassiopeia | Cassiopeia | Ophiuchus |
| Country or part of the world where a supernova was spotted | China | Asia, Africa | Asia, America | Asia | Europe Asia | Korea | Europe Asia |
| Duration of observation, days | 225 | 240 | 710 | 185 | 560 | 100 | 365 |
| Apparent magnitude at maximum | -4 | -6 | -5 | 1 | -4.5 | 2 | -3.5 |
| Photometric class | I type | I.14 | II. 5 | II. 3 | I.12 | ? | I.12 |
| Shell expansion rate, km/s | - | -8 000 | -7 000 | -8 000 | -10 000 | ? | -10 000 |
| supernova remnant | There is | There is | Taurus A "Crab" | 3С 58 | Cassiopeia B | Cassiopeia A | There is |
| Distance to the rest, kps | 2-3 | 4 | 2 | 8 | 5 | 3 | 10 |
It remains for us to tell more about the bright flash of 1181, which was observed mainly in Japan (F. Stephenson counted six chronicles where it was mentioned), as well as in China and Europe. It was visible for half a year, at one time it had a "blue-yellow" color and was equal in brightness to Saturn. The outbreak occurred in the constellation Cassiopeia. The weakening of a supernova by 4 magnitudes in half a year is typical for type II. At the site of the outburst, which was reliably established, there is a non-thermal radio source with a bright core discovered back in 1952 - the "double" of the Taurus A radio source. Recently, a filamentous nebula resembling the Crab Nebula was also found here in a heavily dusty section of the Milky Way. This confirms that the flare belongs to type II supernovae.
How frequent are supernova explosions in the galaxy?
To date, we have a relatively small list of observed supernovae (Table 13); at the same time, 135 radio sources were found that are supernova remnants. Most of the remnants are of great age, located in the Milky Way in areas of strong interstellar extinction. Therefore, their flashes could hardly be seen at all. But among the remains, there were also found those whose outbreaks occurred in the middle of the last century, but were not observed for the reasons indicated above.
Since we ourselves are in the Galaxy, and supernova explosions are not only a grandiose spectacle, but also, as we will see later, an influential factor in our life. solar system, the question of how frequent supernova explosions in the Galaxy is far from being academic, but also vital.
According to the table 11 in Chapter VII, we obtained an interval between supernova explosions in our Galaxy of 110 years with an uncertainty of 60%, i.e., average intervals from 44 to 176 years are possible. These calculations are based on observations of supernovae in other spiral galaxies and are based on the assumption that our star system is of type Sb. If it is of type Sc, then the intervals between flashes should be reduced by a factor of 10. Naturally, such vague conclusions must be verified by a direct study of the frequency of supernova explosions in our Galaxy.
Rice. 26. The location of the seven galactic supernovae in projection onto the main plane of the Galaxy.
Supernovae are marked with the dates of their outbursts. C - the center of the Galaxy, - the Sun, the distance between them is 10 kpc. HI is the boundary of distribution of neutral hydrogen in the Galaxy, HII is the boundary of propagation of ionized hydrogen (i.e., bright gas nebulae).
Recently, H. Tammann tried to calculate the average interval between outbursts for five supernovae of our millennium: 1006, 1054, 1572 and 1604. and Cassiopeia A. Supernova 1181 was rejected by him. These five supernovae are located in a sector that has a central angle of 50 o with a vertex in the core of the Galaxy (ie, the sector is one seventh of the Galaxy, see Fig. 26). If we divide 1000 years by five, we get an interval of 200 years between outbursts in a sector, or, dividing by another 7, we get an interval of 28 years between supernova outbursts for the entire Galaxy. But within the sector there are significant areas where strong absorption of light could hide flares from us. In addition, data on medieval observations have been preserved only for the northern hemisphere of the planet, and therefore flashes in the constellations near the south celestial pole could go unnoticed. We will not go into the details of the corresponding corrections, but only point out that Tammann finally obtained an average interval of 12 years, or 8 supernovae per century, with a possible deviation of 5 flares in one direction or another.
But it would be possible to take a less complicated path. Instead of a sector with its large uncertainties, let us take a neighborhood around the Sun within a radius of 8 kpc. Then, since it has been well studied by optical, X-ray, and radio astronomical methods, we can be sure that it contained only six, young remnants, shown in Table. 13 at least for the last 1800 years, since the outbreak of 185, and in fact for an even longer period. Outside the neighborhood was the Kepler supernova of 1604, which exploded somewhere above the center of the Galaxy.
Note that two of the six supernovae are type II, and the rest are type I. Let's try to find out where supernovae of these types can flare up in the Galaxy. Type I supernovae, judging by outbursts in other star systems, occur at any distance from the center, and more specifically, in the region of distribution of non-ionized hydrogen, which, in essence, is largely a product of the activity of supernovae. As for type II supernovae, they are associated with young stars, the area of distribution of which in galaxies is clearly outlined by luminous gaseous nebulae - clouds of ionized hydrogen.
The radius of propagation of non-ionized hydrogen in the Galaxy is 21 kpc, and that of ionized hydrogen is 16 kpc. Therefore, it is easy to calculate the fraction of our neighborhood with a radius of 8 kpc with respect to the corresponding region of distribution of ionization stages of hydrogen in the Galaxy: 0.15 for non-ionized and 0.25 for ionized. In fact, these are the only factors we need to calculate the average intervals between supernova explosions of both types. Taking the minimum interval of 1800 years, we get 1800:4*0.15 = 67 years for Type I, and 1800:2*0.25 = 225 years for Type II, or, without distinguishing between types, about two supernovae per century. These numbers can be considered correct with an error of up to 50%, but since studies of the radio emission of supernova remnants in a zone with a radius of 8 kpc around the Sun did not reveal other objects younger than 2500 years, the average intervals between outbursts obtained above can be increased by a factor of 1.4, and the number of outbursts reduce by the same amount in a hundred years.
It is interesting to note that the outbursts observed optically over the course of two millennia did not follow each other with approximate uniformity, in "series": one was in the second century, then there was an 8-century break, and in the 11th - 12th centuries there were three outbursts, after which again there was a four-century pause, ending with three outbreaks that followed for 32 years at the turn of the 16th - 17th centuries. Since then, a new four-century pause has been going on. "Series" and "pauses" have no special physical meaning. These are pure accidents in the sequence of a small number of events. One way or another, but during the last four centuries, supernova outbursts occurred outside the neighborhood with a radius of 8 kpc around the Sun. The galaxy "owes" our zone at least two supernovae.
The position of the Solar System in the Galaxy is such that observations of supernova explosions are optically available to us in about half of its volume, and in the rest of the Galaxy the brightness of the flares is muted by interstellar extinction and remoteness to such an extent that even in our time they can be missed and detected after the flare already as radio emitting leftovers.
A supernova explosion is a truly cosmic phenomenon. In fact, this is an explosion of colossal power, as a result of which the star either ceases to exist at all, or passes into a qualitatively new form- in the form of a neutron star or a black hole. In this case, the outer layers of the star are ejected into space. Scattering at high speed, they give rise to beautiful glowing nebulae.
The Crab Nebula gained notoriety in 1758 when astronomers were awaiting the return of Halley's Comet. Charles Messier, the famous "comet catcher" of that time, was looking for a tailed guest among the horns of Taurus, where it was predicted. But instead, the astronomer discovered an elongated nebula, which confused him so much that he mistook it for a comet. In the future, in order to avoid confusion, Messier decided to catalog all the nebulous objects in the sky. The Crab Nebula is catalog number 1. This image of the Crab Nebula was taken by the Hubble Space Telescope. It shows many details: gas fibers, knots, condensations. Today, the nebula is expanding at a speed of about 1,500 km/s, and the change in its size is visible in photographs taken just a few years apart. The total dimensions of the Crab Nebula exceed 5 light years.
The Crab Nebula (or M1 according to the catalog of C. Messier) is one of the most famous space objects. The point here is not its brightness or special beauty, but the role that the Crab Nebula has played in the history of science. The nebula is the remnant of a supernova explosion that occurred in 1054. Mentions of the appearance of a very bright star in this place have been preserved in Chinese chronicles. M1 is in the constellation Taurus, next to the star ζ; on dark transparent nights it can be seen with binoculars. 
The famous object Cassiopeia A, the brightest source of radio emission in the sky. This is the remnant of a supernova that erupted around 1667 in the constellation of Cassiopeia. Strange, but we do not find any mention of a bright star in the annals of the second half of the 17th century. Probably, in the optical range, its radiation was greatly attenuated by interstellar dust. As a result of the last observed supernova in our galaxy, there is still a Kepler supernova. 
Crab nebula in optics, thermal and X-rays. At the center of the nebula is a pulsar, a superdense neutron star that emits radio waves and generates X-rays in its surrounding matter (X-rays shown in blue). Observations of the Crab Nebula at various wavelengths have given astronomers fundamental information about neutron stars, pulsars, and supernovae. This image is a combination of three images taken by the Chandra, Hubble and Spitzer space telescopes. 
The remnant of Tycho's supernova. A supernova erupted in 1572 in the constellation of Cassiopeia. The bright star was observed by the Dane Tycho Brahe, the best astronomer-observer of the pre-telescopic era. The book written by Brahe in the wake of this event was of tremendous ideological significance, because at that time it was believed that the stars were unchanged. Already in our time, astronomers have been hunting for this nebula with telescopes for a long time, and in 1952 they discovered its radio emission. The first photograph in optics was taken only in the 1960s. 
Supernova remnant in the constellation Sails. Most of the supernovae in our Galaxy appear in the plane of the Milky Way, since it is here that they are born and spend their short life massive stars. The fibrous supernova remnants are hard to see in this image due to the abundance of stars and red hydrogen nebulae, but the expanding spherical shell can still be identified by its greenish glow. A supernova in Sails broke out about 11-12 thousand years ago. During the outburst, the star ejected a huge mass of matter into space, but did not completely collapse: in its place was a pulsar, a neutron star emitting radio waves. 
The Pencil Nebula (NGC 2736), part of a supernova shell in the constellation Vela. In fact, the nebula is a shock wave propagating in space at a speed of half a million kilometers per hour (in the picture it flies from the bottom up). Several thousand years ago, this speed was even higher, but the pressure of the surrounding interstellar gas, no matter how insignificant it was, slowed down the expanding shell of the supernova. 
NGC 6962 or Eastern Veil close-up. Another name for this object is the Network Nebula 
The Simeiz 147 Nebula (aka Sh 2-240) is a huge remnant of a supernova explosion, located on the border of the constellations Taurus and Auriga. The nebula was discovered in 1952 by Soviet astronomers G. A. Shain and V. E. Gaze at the Simeiz observatory in the Crimea. The explosion occurred about 40,000 years ago, during which time the expanding material occupied an area of \u200b\u200bthe sky 36 times the area of the full moon! The actual dimensions of the nebula are an impressive 160 light years, and the distance to it is estimated at 3000 light years. years. A distinctive feature of the object is long curved gas filaments, which gave the nebula the name Spaghetti. 
The Medusa Nebula, another well-known supernova remnant, lies in the constellation Gemini. The distance to this nebula is poorly known and is probably about 5,000 light-years. The date of the explosion is also known very approximately: 3 - 30 thousand years ago. The bright star on the right is an interesting variable, eta Gemini, which can be observed (and studied for changes in its brightness) with the naked eye. 
The last of the supernova explosions observed with the naked eye occurred in 1987 in a nearby galaxy, the Large Magellanic Cloud. The brightness of supernova 1987A reached 3 magnitudes, which is quite a lot considering the colossal distance to it (about 160,000 light years); The progenitor of the supernova was a blue hypergiant star. After the explosion, an expanding nebula and mysterious rings in the form of the number 8 remained in place of the star. Scientists suggest that the reason for their appearance may be the interaction of the stellar wind of the predecessor star with the gas ejected during the explosion 
Cycle of gas and dust in the universe
supernova explosion
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Initially, all stars whose brightness suddenly increased by more than 1,000 times were called novae. Flashing, such stars suddenly appeared in the sky, breaking the usual constellation configuration, and increased their brightness at the maximum, several thousand times, then their brightness began to drop sharply, and after a few years they became as weak as they were before the outbreak. The recurrence of flares, during each of which the star ejects up to one thousandth of its mass at high speed, is characteristic of new stars. And yet, for all the grandeur of the phenomenon of such a flash, it is not associated either with a radical change in the structure of the star, or with its destruction. For five thousand years, information has been preserved about more than 200 bright outbursts of stars, if we restrict ourselves to those that did not exceed the brilliance of the 3rd magnitude. But when the extragalactic nature of the nebulae was established, it became clear that the novae that flared in them surpassed ordinary novae in their characteristics, since their luminosity often turned out to be equal to the luminosity of the entire galaxy in which they flared. The unusual nature of such phenomena led astronomers to the idea that such events are something completely different from ordinary new stars, and therefore, in 1934, at the suggestion of American astronomers Fritz Zwicky and Walter Baade, those stars whose flashes reach the luminosities of normal galaxies at their maximum brightness were isolated into a separate, brightest in luminosity and rare class of supernovae.
In contrast to the outbursts of ordinary new stars, supernova outbursts in state of the art Our Galaxy is an extremely rare phenomenon, occurring no more than once every 100 years. The brightest outbreaks were in 1006 and 1054; information about them is contained in Chinese and Japanese treatises. In 1572, the outstanding astronomer Tycho Brahe observed the outbreak of such a star in the constellation Cassiopeia, while Johannes Kepler was the last to follow the supernova in the constellation Ophiuchus in 1604. For four centuries of the "telescopic" era in astronomy, no such flares were observed in our Galaxy. The position of the solar system in it is such that we can optically observe supernova explosions in about half of its volume, and in the rest of it the brightness of the flares is muted by interstellar absorption. IN AND. Krasovsky and I.S. Shklovsky calculated that supernova explosions in our galaxy occur on average once every 100 years. In other galaxies, these processes occur with approximately the same frequency; therefore, the main information about supernovae in the optical outburst stage was obtained from observations of them in other galaxies.
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| EXPLOSION SUPERNOVA CAS A |
Realizing the importance of studying such powerful phenomena, astronomers W. Baade and F. Zwicky, who worked at the Palomar Observatory in the USA, began a systematic systematic search for supernovae in 1936. They had a Schmidt telescope at their disposal, which made it possible to photograph areas of several tens of square degrees and gave very clear images of even faint stars and galaxies. Over the course of three years, they discovered 12 supernova explosions in different galaxies, which were then studied using photometry and spectroscopy. As observational technology improved, the number of newly discovered supernovae steadily increased, and the subsequent introduction of automated search led to an avalanche-like increase in the number of discoveries (more than 100 supernovae per year, with a total number of 1,500). In recent years, large telescopes have also begun searching for very distant and faint supernovae, since their research can provide answers to many questions about the structure and fate of the entire universe. In one night of observations with such telescopes, more than 10 distant supernovae can be discovered.
As a result of the explosion of a star, which is observed as a supernova phenomenon, a nebula is formed around it, expanding at a tremendous speed (about 10,000 km / s). The high expansion rate is the main feature by which supernova remnants are distinguished from other nebulae. In the remnants of supernovae, everything speaks of an explosion of enormous power, which scattered the outer layers of the star and imparted enormous speeds to individual pieces of the ejected shell.
Supernovae by example: Not a single space object has given astronomers as much valuable information as the relatively small Crab corpulence observed in the constellation Taurus and consisting of a gaseous diffuse substance expanding at high speed. This nebula, which is the remnant of a supernova observed in 1054, was the first galactic object with which a radio source was identified. It turned out that the nature of radio emission has nothing to do with thermal radiation: its intensity systematically increases with wavelength. Soon it was possible to explain the nature of this phenomenon. There must be a strong magnetic field in the supernova remnant, which holds the cosmic rays (electrons, positrons, atomic nuclei) created by it, which have speeds close to the speed of light. In a magnetic field, they radiate electromagnetic energy in a narrow beam in the direction of motion. The discovery of non-thermal radio emission from the Crab Nebula prompted astronomers to search for supernova remnants precisely on this basis.
In Fig.: The Crab Nebula. A new sequence of images of the remnant of a huge stellar explosion taken by the Hubble Space Telescope gives astronomers a deeper look into the dynamics of the connection between the small Crab pulsar and the huge nebula it powers. The color photo on the left is a ground-based telescope image of almost the entire Crab Nebula, which formed after a supernova explosion more than 900 years ago. The nebula, 10 light-years across, is located 7,000 light-years away in the constellation Taurus. The green, yellow, and red filaments clustered around the edges of the nebula are the remnant of a star that was ejected into space by the explosion. At the center of the Crab Nebula lies the Crab pulsar, the collapsed core of an exploding star. The blue glow in the interior of the nebula is the light emitted by energetic electrons. The image on the right was taken by the Hubble Space Telescope and represents the interior of the Crab. The pulsar itself is visible as the leftmost of a pair of eveda near the center of the frame. The pulsar is surrounded by a complex of distinct knots and ragged formations. This is one of the sequences of images that Hubble received over the course of several months. It shows that the interior of the Crab Nebula is more dynamic than previously thought.
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| -20,000 years ago. The larger star in a binary system swells up to become a red giant. - The red giant gives off matter to the blue star, and some of it forms a disk. -Two stars merge into one blue star surrounded by a disk of gas. - "Wind" from the star creates a hole in the disk. |
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| -February 1987 A supernova explosion illuminates the inner edge of the ring. -1991-1996 The blast wave and the flow of debris quickly spread in space. -1997 The blast wave reaches the inner edge of the ring, causing pinpoint flares. -2007 Flashes occur along the entire inner edge, forming a luminous ring. |
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| EXPLOSION 1987A |
Pictured: Supernova Cas A. The nebula located in the constellation Cassiopeia turned out to be a particularly powerful source of radio emission - at meter wavelengths, the radio emission flux from it is 10 times higher than the flux from the Crab Nebula, although it is much further than the latter. In optical beams, this rapidly expanding nebula is very weak. The nebula in Cassiopeia is believed to be the remnant of a supernova explosion that took place about 300 years ago.
A system of filamentous nebulae in the constellation Cygnus also showed radio emission characteristic of old supernova remnants. Radio astronomy has helped to find many other non-thermal radio sources, which turned out to be the remnants of supernovae of different ages. Thus, it was concluded that the remnants of supernovae, even tens of thousands of years ago, stand out among other nebulae with their powerful non-thermal radio emission.
As already mentioned, the Crab Nebula was the first object in which X-ray emission was detected. In 1964, it was possible to discover that the source of X-ray radiation emanating from it is extended, although its angular dimensions are 5 times smaller than the angular dimensions of the Crab Nebula itself. From which it was concluded that X-rays are emitted not by a star that once erupted as a supernova, but by the nebula itself.
The multicolored jets criss-crossing the sky in this Hubble Space Telescope image are created by one of the biggest fireworks ever recorded in our galaxy's history, a huge explosion of a massive star. Its light reached Earth 320 years ago. The ragged remnants of a dead star are named Cassiopeia A, or "Cas A" for short. This youngest known supernova remnant in our Milky Way Galaxy lies 10,000 light-years away in the constellation of Cassiopeia. Light from a supernova explosion reached Earth in 1600, and the explosion itself occurred 10,000 years earlier. This photo shows the top edge of the expanding shell of a supernova remnant. Dozens of tiny wisps of matter are visible at the top of the image. Each small lump was originally a small fragment of a star, dozens of times larger than the entire solar system. The star that created them was huge: 15-25 times more massive than our Sun. Such stars usually have a short lifespan, using up their nuclear fuel supply for tens of millions of years (1,000 times faster than our Sun). This stunning image of Cas A allows astronomers to study supernova remnants in detail, showing for the first time that they are made up of small, cooling clumps of gas. This substance will be used to create a new generation of stars and planets. It is possible that our Sun and the planets of the solar system were created from the remnants of a supernova that exploded billions of years ago.
Pictured: Supernova 1987A. Brilliant stars and wisps of gas provide a breathtaking backdrop to the self-destruction of a massive star dubbed Supernova 1987A. Its explosion was observed by astronomers in the Southern Hemisphere on February 23, 1987. This Hubble image shows a supernova remnant surrounded by inner and outer rings of matter in diffuse clouds of gas. This three-color image is a composite of several photographs of the supernova and its neighboring region taken in September 1994, February 1996, and July 1997. Numerous bright blue stars near the supernova are massive stars, each of which is about 12 million years old and 6 times heavier than the Sun. They all belong to the same generation of stars as the one that exploded. The presence of bright gas clouds is another sign of the youth of this region, which is still fertile ground for the birth of new stars. Hubble has discovered rings of glowing gas surrounding the explosion site of supernova 1987A. Perhaps the two rings could be "drawn" by high-energy radiation or particles, similar to how a laser beam of light draws circles on a screen. The source of radiation may be previously unknown stellar remnants of the second component of a star that exploded in 1987. The image taken by Hubble shows a faintly luminous object at the site of the alleged source.
The ring in Hubble's 1994 image [A] shows the glowing ring of gas around supernova 1987A. Image [B] - Recent observations from 1997 by the Hubble Telescope show an increase in the brightness of nodes on the upper right side of the ring. This is the site of powerful collisions between the outwardly moving blast wave and internal parts circumstellar ring. The collisions heat up the gas and make it shine brighter. This is likely the first signal of dramatic and violent collisions that will take place over the next few years, rejuvenating the supernova as a powerful X-ray and radio source. The white crescent-shaped matter in the center is the visible part of the scattered star, rushing at a speed of 3,000 km / s, which is heated by radioactive elements generated when the star exploded.
Supernova influence
Supernovae.
On February 23, 1987, a supernova exploded in our neighboring galaxy, the Large Magellanic Cloud, which became extremely important for astronomers, since it was the first one that they, armed with modern astronomical instruments, could study in detail. And this star gave confirmation of a whole series of predictions. Simultaneously with the optical flash, special detectors installed in Japan and Ohio (USA) registered a stream of neutrino-elementary particles produced at very high temperatures during the collapse of the star's core and easily penetrating through its shell. These observations confirmed the earlier assumption that about 10% of the mass of the collapsing stellar core is emitted as neutrinos at the moment when the core itself collapses into a neutron star. In very massive stars, during a supernova explosion, the cores are compressed to even greater densities and, probably, turn into black holes, but the outer layers of the star are still thrown off. In recent years, indications have appeared that some cosmic gamma-ray bursts are related to supernovae. It is possible that the nature of cosmic gamma-ray bursts is related to the nature of explosions.
Supernova explosions have a strong and diverse effect on the surrounding interstellar medium. The shell of the supernoi, which is thrown off at a tremendous speed, rakes and compresses the gas surrounding it, which can give impetus to the formation of new stars from the gas clouds. A team of astronomers led by Dr. John Hughes of Rutgers University, using observations from NASA's Chandra X-ray Observatory, has made an important discovery that sheds light on how silicon, iron, and other elements are formed in supernova explosions. An X-ray image of the supernova remnant Cassiopeia A (Cas A) reveals clumps of silicon, sulfur and iron ejected from the star's interior during the explosion. The high quality, clarity and information content of the images of the Cas A supernova remnant obtained by the Chandra observatory allowed astronomers not only to determine the chemical composition of many nodes of this remnant, but also to find out exactly where these nodes were formed. For example, the most compact and bright nodes are composed mainly of silicon and sulfur with very little iron. This indicates that they formed deep inside the star, where temperatures reached three billion degrees during the collapse that ended in a supernova explosion. In other nodes, astronomers found a very high content of iron with impurities of a certain amount of silicon and sulfur. This substance was formed even deeper - in those parts where the temperature during the explosion reached higher values - from four to five billion degrees. Comparison of the arrangements in the supernova remnant Cas A of both bright silicon-rich and fainter iron-rich nodes revealed that the "iron" features, originating from the deepest layers of the star, are located at the outer edges of the remnant. This means that the explosion threw the "iron" nodes farther than all the others. And even now, they seem to be moving away from the center of the explosion at a faster rate. The study of the data obtained by Chandra will make it possible to dwell on one of several mechanisms proposed by theorists that explain the nature of a supernova explosion, the dynamics of the process, and the origin of new elements.
Studies have shown that supernovae do not represent a homogeneous group of objects - both spectra and light curves (change in brightness with time) of supernovae differed significantly, the spectral classification divided them into two types: SN I and SN II.
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| The results of 14-hour observations of the supernova remnant Cas A by the Chandra observatory gave the best distribution of heavy elements ejected during the explosion. Upper left is a broadband x-ray image of Cas A. The rest of the images are from silicon ions (upper right), calcium ions (lower left), iron ions (lower right). These elements are part of a gas with a temperature of about 50 million °C. The colors represent the intensity of the X-ray, ranging from yellow (most intense), red and purple to green (least intense). |
| SUPERNOVA CAS A |
Supernovae SN I have very similar spectra (without hydrogen lines) and light curve shapes, while the spectra of SN II contain bright hydrogen lines and are distinguished by a variety of both spectra and light curves. In this form, the classification of supernovae existed until the mid-1980s. And with the beginning of the widespread use of CCD receivers, the quantity and quality of observational material increased significantly, which made it possible to obtain spectrograms for previously inaccessible weak objects, determine the intensity and width of lines with much greater accuracy, and also record weaker lines in the spectra. As a result, the apparently established binary classification of supernovae began to rapidly change and become more complex. Supernovae are also distinguished by the types of galaxies in which they flare up. In spiral galaxies, supernovae of both types flare up, but in elliptical galaxies, where there is almost no interstellar medium and the star formation process has ended, only SN I supernovae are observed, obviously, before the explosion, these are very old stars, whose masses are close to solar. And since the spectra and light curves of supernovae of this type are very similar, it means that the same stars explode in spiral galaxies. The natural end of the evolutionary path of stars with masses close to the sun is the transformation into a white dwarf with the simultaneous formation of a planetary nebula. There is almost no hydrogen in the composition of a white dwarf, since it is the end product of the evolution of a normal star.
Several planetary nebulae are formed annually in our Galaxy, therefore, most of the stars of this mass quietly complete their life path, and only once every hundred years does an SN I type supernova burst. What reasons determine a very special ending, not similar to the fate of other stars of the same kind? The famous Indian astrophysicist S. Chandrasekhar showed that in the event that a white dwarf has a mass less than about 1.4 solar masses, it will quietly "survive" its life. But if it is in a sufficiently close binary system, its powerful gravity is able to “pull” matter from the companion star, which leads to a gradual increase in mass, and when it passes the allowable limit, a powerful explosion occurs, leading to the death of the star.
| SUPERNOVA G11.2-0.3 |
| This image from the Chandra Observatory clearly shows the pulsar at the geometric center of the supernova remnant known as G11.2-0.3. Chandra received strong confirmation that the pulsar was formed by a supernova of 386, recorded by Chinese astronomers. Determining the true age of astronomical objects is very difficult, so historical records of supernovae are of great importance. If this discovery is confirmed, then this pulsar will become only the second pulsar to be accurately associated with a historical event. |
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Supernovae SN II are clearly associated with young, massive stars, in the shells of which hydrogen is present in large quantities. Flashes of this type of supernovae are considered the final stage in the evolution of stars with an initial mass of more than 8-10 solar masses. In general, the evolution of such stars proceeds quite quickly - in a few million years they burn their hydrogen, then helium, which turns into carbon, and then carbon atoms begin to transform into atoms with higher atomic numbers. In nature, the transformations of elements with a large release of energy end in iron, the nuclei of which are the most stable, and no energy is released during their fusion. Thus, when the core of a star becomes iron, the release of energy in it stops, it can no longer resist gravitational forces, and therefore begins to quickly shrink, or collapse. The processes that occur during collapse are still far from being fully understood. However, it is known that if all the matter of the core turns into neutrons, then it can resist the forces of attraction - the core of the star turns into a "neutron star", and the collapse stops. In this case, huge energy is released, which enters the shell of the star and causes expansion, which we see as a supernova explosion. From this, one would expect a genetic link between supernova explosions and the formation of neutron stars and black holes. If the evolution of the star before this happened “quietly”, then its shell should have a radius hundreds of times greater than the radius of the Sun, and also retain enough hydrogen to explain the spectrum of SN II supernovae.
Pulsars. The fact that after a supernova explosion, in addition to an expanding shell and various types of radiation, other objects remain, it became known in 1968 due to the fact that a year earlier, radio astronomers discovered pulsars - radio sources, the radiation of which is concentrated in separate pulses, repeating after a strictly defined period of time. Scientists were struck by the strict periodicity of the pulses and the shortness of their periods. The greatest attention was paid to the pulsar, whose coordinates were close to the coordinates of a very interesting nebula for astronomers, located in the southern constellation of Sails, which is considered the remnant of a supernova explosion - its period was only 0.089 seconds. And after the discovery of a pulsar in the center of the Crab Nebula (its period was 1/30 of a second), it became clear that pulsars are somehow connected with supernova explosions. In January 1969, a pulsar from the Crab Nebula was identified with a faint star of magnitude 16, changing its brightness with the same period, and in 1977, a pulsar in the constellation Parycos was also identified with a star.
The periodicity of the radiation of pulsars is associated with their rapid rotation, but not a single ordinary star, even a white dwarf, could rotate with a period characteristic of pulsars - it would be immediately torn apart by centrifugal forces, and only a neutron star, very, dense and compact, could to stand before them. As a result of the analysis of many options, scientists came to the conclusion that supernova explosions are accompanied by the formation of neutron stars - a qualitatively new type of objects, the existence of which was predicted by the theory of evolution of stars of large mass.
Black holes. The first proof of a direct connection between a supernova explosion and the formation of a black hole was obtained by Spanish astronomers. As a result of the study of radiation emitted by a star orbiting a black hole and the Nova Scorpii 1994 binary system, it was found that it contains large amounts of oxygen, magnesium, silicon and sulfur. There is an assumption that these elements were captured by it when a nearby star, having survived a supernova explosion, turned into a black hole. Supernovae (particularly Type Ia supernovae) are among the brightest stellar objects in the universe, so even the most distant ones can be explored with the equipment currently available. Many Type Ia supernovae have been discovered in relatively nearby galaxies. Sufficiently accurate estimates of the distances to these galaxies made it possible to determine the luminosity of supernovae that burst out in them. If we assume that distant supernovae have the same average luminosity, then according to the observed magnitude at maximum brightness, one can also estimate the distance to them. Comparison of the distance to the supernova with the removal rate (redshift) of the galaxy in which it flared up makes it possible to determine the main value characterizing the expansion of the Universe - the so-called Hubble constant.
Even 10 years ago, values for it were obtained that differed by almost two times - from 53 to 100 km/s Mpc, today the accuracy has been significantly increased, as a result of which a value of 72 km/s Mpc is accepted (with an error of about 10%) . For distant supernovae, the redshift of which is close to 1, the relationship between the distance and the redshift also makes it possible to determine quantities that depend on the density of matter in the Universe. According to Einstein's general theory of relativity, it is the density of matter that determines the curvature of space, and, consequently, the future fate of the Universe. Namely: will it expand indefinitely or will this process ever stop and be replaced by contraction. Recent studies of supernovae have shown that most likely the density of matter in the universe is insufficient to stop the expansion, and it will continue. And in order to confirm this conclusion, new observations of supernovae are needed.
A supernova, or supernova explosion, is the process of a colossal explosion of a star at the end of its life. In this case, huge energy is released, and the luminosity increases billions of times. The shell of the star is ejected into space, forming a nebula. And the nucleus shrinks so much that it becomes either , or .
The chemical evolution of the universe proceeds precisely thanks to supernovae. During the explosion, heavy elements are ejected into space, which are formed during a thermonuclear reaction during the life of a star. Further, from these remnants are formed with planetary nebulae, from which, in turn, stars with planets are formed.
How does an explosion happen?
As you know, a star releases enormous energy due to a thermonuclear reaction occurring in the core. A thermonuclear reaction is the process of converting hydrogen into helium and heavier elements with the release of energy. But when the hydrogen in the bowels ends, the upper layers of the star begin to collapse towards the center. After reaching a critical point, the matter literally explodes, compressing the core more and more and carrying away the upper layers of the star with a shock wave.
In a rather small volume of space, so much energy is generated in this case that part of it is forced to carry away a neutrino, which has practically no mass.
Type Ia supernova
This type of supernova is not born from stars, but from. An interesting feature is that the luminosity of all these objects is the same. And knowing the luminosity and type of the object, you can calculate its speed from. The search for type Ia supernovae is very important, because it was with their help that the accelerating expansion of the universe was discovered and proved.
Maybe tomorrow they will flare up
There is a whole list that includes supernova candidates. Of course, it is quite difficult to determine exactly when the explosion will occur. Here are the closest known ones:
- IK Pegasus. The double star is located in the constellation Pegasus at a distance of up to 150 light years from us. Its companion is a massive white dwarf, which has already ceased to produce energy through thermonuclear fusion. When the main star turns into a red giant and increases its radius, the dwarf will begin to increase the mass due to it. When its mass reaches 1.44 solar, a supernova explosion may occur.
- Antares. A red supergiant in the constellation Scorpius, 600 light years from us. Antares is accompanied by a hot blue star.
- Betelgeuse. Antares-like object is located in the constellation Orion. The distance to the Sun is from 495 to 640 light years. It is a young star (about 10 million years old), but it is believed that it has reached the phase of carbon burnout. Already within one or two millennia, we will be able to admire the explosion of a supernova.
Impact on the Earth
A supernova, exploding nearby, of course, cannot but affect our planet. For example, Betelgeuse, exploding, will increase the brightness by about 10 thousand times. For several months, the star will look like a shining point, similar in brightness to the full moon. But if any pole of Betelgeuse is facing the Earth, then it will receive a stream of gamma rays from the star. The auroras will increase, the ozone layer will decrease. This can be very Negative influence for the life of our planet. All these are only theoretical calculations, what will actually be the effect of the explosion of this supergiant, it is impossible to say for sure.
The death of a star, just like life, is sometimes very beautiful. An example of this is supernovae. Their flashes are powerful and bright, they outshine all the luminaries that are nearby.
I tested the capabilities of the new camera by attaching it to a 40 cm telescope. He chose the spiral galaxy NGC 613, located 80 million light-years away in the constellation Sculptor, a major constellation in the southern hemisphere, to shoot. Buzo shot the galaxy for an hour and a half with a 20-second shutter speed to avoid being exposed to the lights of the city. For the first 20 minutes, the photos looked the same.
And then Buzo noticed a bright dot at the end of one of the arms of the galaxy and realized that something extraordinary was happening. But he could not determine what exactly, and turned to professionals for help.
After examining the images, astronomer Melina Bersten and her colleagues from the Institute of Astrophysics in La Plata realized that
Boso managed to fix the rarest event - a supernova explosion.
During a supernova explosion, the luminosity of a star increases sharply by four to eight orders of magnitude, and then the explosion slowly fades. The explosion is accompanied by the ejection of a significant mass of matter from the outer shell of the star into interstellar space. As a rule, supernovae are observed after the fact, that is, when the event has already occurred and its radiation has reached the Earth. The blast wave, which was recorded on Buzo's camera, can only be observed in the first few hours. Photographing an explosion is difficult, as it is impossible to predict when it will occur. So far, no one has been able to do this. According to Bursten, the chance of such a discovery is one in 10, if not 100 million.
However, Buzo managed to fix the very beginning of this process.
Victor Buso/Gaston Folatelli
In fact, some researchers have already begun to wonder how true theoretical models supernova explosion,” explains Bursten, who led the study. —
Buzot's observations are extremely valuable, even the lottery is easier to win than to do something like that."
“It’s like winning the space lottery,” confirms astrophysicist Alexei Filippenko of the University of California at Berkeley, who has been involved in observing the supernova after the explosion. The observation data were published on February 21 this year in the journal Nature, scientists mentioned Buzo among the co-authors.
“Buzot's data are exceptional,” Filippenko notes. “This is a great example of a partnership between amateur and professional astronomers.”
Within two months of the discovery of the supernova, dubbed SN 2016gkg, astronomers observed it with the Keck and Lick Observatory telescopes. Based on the discovery and further observations, Bursten and her colleagues determined that the supernova was part of a binary star system that had lost its outer layers of gas, retaining only a mostly helium core. The spectral data showed it to be a Type IIb supernova - a massive star that had already lost most of its mass before the explosion.
The team calculated that SN 2016gkg had about 20 times the mass of the Sun, but by the time of the explosion, the star had lost 3/4 of its mass. Now that SN 2016gkg has gone supernova, it has shrunk to five solar masses.
The long-awaited visual data will help astronomers get more information about the star's structure just before it exploded, as well as information about the explosion itself.
“Professional astronomers have been waiting for something like this for a long time,” says Filippenko. “Observations of the stars in the first moments of the explosion provide information that cannot be directly obtained in any other way.”
In November 2017, Gazeta.Ru talked about another unusual discovery -
Which has already survived several explosions and refuses to fade.
Supernova iPTF14hls was discovered by astronomers during the Palomar Transient Factory astronomical survey in September 2014. A few months later, astronomers from the Las Cumbres Observatory in the United States noticed that the star stopped fading and began to become brighter. After reviewing the archival data, the researchers found that a supernova in the same place was discovered in 1954. Somehow, she survived the explosion and continued to shine, and then exploded again 50 years later.
According to researchers, before the explosion, the mass of the star was 50 times the mass of the Sun. The scale of the star's explosion may be related to its unusual behavior, they suggest. Supernova iPTF14hls may be the first example of a pulsating pair-unstable supernova discovered.
“According to this theory, it is possible that the star was so massive and hot that it created antimatter in its core when it exploded. This could be the reason that the star was unstable and experienced several flares over the years of its existence, the researchers suggest. - Such explosions are believed to have been possible only on early stage the existence of the universe and today should no longer occur. It's like meeting a dinosaur."
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