Crab in the constellation Taurus

Crab -shaped nebula is one of the most famous celestial objects. A huge number of the most important astronomical discoveries are connected with it! There is no nebula in the sky, better known and studied and at the same time more mysterious. And the story of its study is like a detective novel.

Monument to the imagination

For the first time, this nebula was observed in 1731 by the English physicist and amateur astronomer John Bevis. He outlined the nebula in the atlas "Uranography of the British", which was going to publish. But the publisher went bankrupt and Bevis died without waiting for publication. Only half a century later, in 1786, Bevis cards (without mentioning his name!) Was entered the star satin published in London. By that time, the nebula re -opened Charles Messier, an astronomer at the court of King Louis XV.

Messier brought the nebula to the catalog under the first number and gave the designation M1. William Gershel believed that it was a distant star cluster, and if he had a larger telescope, he would have seen separate stars in a foggy spot. Lord Ross had such a telescope, but he could not see a single star in the M1 nebel. However, Ross did two important things. Firstly, I found that the nebula has a strange fibrous structure. Secondly, with an even more careful examination, the nebula seemed like a crab to him, and Ross called her crab-shaped. Under this name, the nebula is also known today - a monument to the imagination that can make out anything in a foggy spot.

The first riddles of crab -shaped nebula

In 1892, the British astronomer William Roberts first photographed crab -shaped nebula, and the American astronomer Vesto Slifer in 1913 received its first spectrograms. Unlike other gas tummen, the range of crab turned out to be continuous. Against this background, bifurcated radiation lines were visible. The continuous spectrum (with absorption lines) usually have stars, but here the nebula was radiated! Why was the spectrum turned out to be continuous, not linear?

The riddle of radiation of a crab lasted a long time. Moreover, it became almost insoluble when in 1936 it was proved that the crab nebulae was in the sky exactly in the place where the brightest “gesture star” broke out in 1054, which could be seen even in bright sunlight for several months.

Now such the brightest flashes are called supernova. The name was invented in the 1930s Walter Baada and Fritz Zvikki, who worked in American observatories. “Let,” they said, “very bright new stars are called supernova.” The name is quite meaningless, that's why, probably, it took root. Just like a crab.

In the work of Baada and Zvikki, published in 1934, there were many correct ideas. They approached the problem of supernova as theorists, but used all the observation material at their disposal. They began, however, not with the riddle of supernova. They were interested in the problem of the origin of space rays no less urgent in those years. For the first time, Baada and Zvicki connected two phenomena and concluded: cosmic rays can be generated with supernova flashes.

The second idea of ​​Baada and Zvikki was even more interesting and, so to speak, even more correctly. They predicted that neutron stars are born with supernova flashes.

In 1934, there were no right ideas about how the stars evolve. Neutron was opened only two years earlier. The theory of nuclear transformations practically did not exist. The idea of ​​Baada and Zvikki looked like science fiction, albeit scientific.

Is the southern star the rest of the flash?

While Baada and Zvikki investigated the crab units, the American astronomer Rudolf Minkovsky studied two weak stars, which have long been observed against the background of M1. One of the stars, as he hoped, could be the desired object - the “cinder” of the flashed star. Minkovsky found out that the southern star is moving at a speed of more than 100 km/s. What made the star fly at such a speed?

The spectrum of the southern star turned out to be even more amazing. There were no lines in it at all! No: neither absorption, nor radiation. Nevertheless, Minkovsky came to the conclusion: the nebula is heated by the southern star. He was mistaken.

In 1948, John Bolton pointed out an error. He found in the sky four bright sources of radio emission. One of them was located in the constellation Taurus. A year later, Bolton specified the coordinates of the source and announced that they exactly coincide with the position of crab -shaped nebula. It turned out that the crab -shaped nebula is emitting too much in the radiodiapason, much more than in optics. So, the southern star does not heat the nebula? So, its radio emission has a different nature?

Why does the nebula radiate?

This contradiction was allowed in 1953 by the Soviet astrophysicist Joseph Shklovsky, suggesting that in the crab nebula, not gas emits, but electrons moving in a magnetic field with almost light speeds. This radiation is called synchrotron. Ultraletivistic electrons, "entangled" in the magnetic field of crab -shaped nebula, are radiated in all ranges of wavelengths and in all directions. The idea was simple and explained the observation data so naturally that they did not even object to it.

No one returned to the riddle of the southern star in those years. But the star became even more mysterious than it was! If the radiation of the crab uninvited nebula is synchrotron, then the gas is not necessary to heat the gas, and therefore there is no need to assume that a hot star is in the nebula. And the size of the southern star Minkovsky calculated precisely in the assumption that the star was very hot. Everything crumbled ...

Electrons of high energy could remain in the nebula and from the time of the outbreak. Zvikki also wrote about this when he explained the origin of space rays. But this assumption was refuted in 1956 by the Soviet astrophysicist Solomon Pikelner. The electrons responsible for the radio emission of the crab -shaped nebula do not lose energy very quickly, they really could remain after the flash and survive to this day. But the electrons responsible for optical radiation should have lost the entire supply of energy over a hundred years! The flash occurred nine centuries ago. Electrons, the radiation from which it reaches our time, could not arise during the outbreak - they appeared in the nebula much later. In the crab nearest nebula, there should be a “gun”, which continuously shooting fast electrons. Where is this gun? One of two: either electrons are accelerated in the nebula itself, or their source is the southern star.

X -ray window

In 1962, the Aerobee rockets first raised an X -ray detectors to a height of a hundred kilometers. In the first flight, a powerful source of cosmic X -ray radiation in the constellation Scorpio was discovered, and another source was discovered during the second flight, and it was located in the direction of the crab -shaped nebula.

But what was radiated: all the nebula or the famous southern star? Devices of that time did not have good resolution, with their help it was impossible to obtain the image of the nebula in the X -ray range and highlight the radiation of the southern star.

The idea of ​​verification was proposed by Joseph Shklovsky. On July 7, 1964, a rather rare event was supposed to occur - an eclipse of crab -shaped nebula by the moon. If the X -ray source is not the nebula, but the star, then the moon will close it instantly, and X -ray radiation will disappear. If all the nebula radiates, then the source will begin to weaken gradually, as the moon crawls to the nebula. The full eclipse will last 12 minutes, then the source will appear again.

At the time of turning on the device on Aerobee, the speed of the photon account was 300 pulses per second, smoothly decreased, and two minutes later the source disappeared. It became clear: not the southern star radiates, but the nebula!

With renewed vigor, the old contradiction made itself felt. In the nebula, there must necessarily be an injector of relativistic electrons. And in it they have not yet found anything but the southern star! The crab nebula brows every second in all ranges of electromagnetic waves thousands of times more than the sun. In the neutron star (if, as Baada and Zvikki suggested, the southern star - neutron) could not be such powerful sources of energy. Where do they get in a dead and cooled ball?

The solution was proposed in 1964 by the Soviet astrophysicist Nikolai Kardashev. The star, the outbreak of which led to the phenomenon of the "star of the guest", possessed a magnetic field and rotated around the axis. In 1054, she exploded. The shell scattered, and the core has become a neutron star. The shell carried with it the power lines of the magnetic field. The neutron star rotates quickly, and the power lines are wound on it, like a drum. The magnetic field passing through the nebula becomes a similar spiral, the branches of which are twisted more tightly. The magnetic field increases, magnetic pressure grows. And the pressure of the magnetic field pushes the plasma in the nebula, makes it expand faster.

However, the decision of Kardashev did not explain where the ultra -peelativist electrons responsible for radiation in the nebula. Not from a neutron star! In 1964, there was still a strong and unexplored prejudice: a neutron star is a dead body.

Pulsar in crab -shaped nebulae

In 1968, the British radi -Anthony Hugaish and his graduate student Joeelin Bell opened the first radio pulsar 1 , which turned out to be a neutron star. But if, as Baada and Zvikki claimed, the southern star in Crab is neutron, then she, in theory, could be a pulsar!

A year later, Australian radiostronomers opened a pulsating radio source in crab -shaped nebula, the coordinates of which exactly coincided with the position of the southern star. The discovery was expected, but, nevertheless, became a sensation. Pulsar in the crab nearest nebulae turned out to be a recordly small period of repetition of impulses - only 33 milliseconds.

In the winter of 1968, it became obvious to everyone that neutron stars were finally discovered. Moreover, the idea of ​​Baada and Zvikki was brilliantly confirmed that neutron stars are formed with supernova flashes, during a catastrophic collapse.

But a natural question arose: if the radio emission of the southern star is so pulsing, why does this not happen either with optical or x -ray radiation?

Maybe and the observers said, we did not think about it. Indeed, it never occurred to anyone to look for quick pulsations at the optical star and, especially from the X -ray source. There were no new missile starts. A group of American scientists, led by Edwin Boldt, re -processed the results of the missile flight in March 1968, taking into account the fact that the variable of the X -ray source may be fast. And they found a variable - exactly the same as that of the radio pulsar, with a period of 33 milliseconds.

The embarrassed observers decided to rehabilitate themselves to the end: finding a quick optical variability in the southern star. In January 1969, at the Stuard Observatory at the University of Arizona, a series of optical observations was carried out by using photographs that could fix the quick fluctuations of shine, and opened the first optical pulsar.

The frosty January nights of 1969 ended the thirty -five -year -old epic of the search for a neutron star in a crab -shaped nebula.

***

Crab -shaped nebula is a truly unique object. Supernova 1054 was seen in the light of the sun. The first gaseous residue of the explosion of the supernova discovered by astronomers was a crab -shaped nebula. The first residue of Supernova, for which it was possible to determine age, was a crab. The first residue in which internal activity was discovered was a crab. The first residue in the center of which is an optical star: crab. The southern star in Crab is the first object, which was suspicious that it was a neutron star. One of the first radio sources found in the sky was a crab. One of the first open x -rays is Crab. It was even lucky that the crab nebula is regularly overshadowed by the moon - the observations of the ecloth allowed the first to determine the dimensions of the X -ray source. Pulsar in crab rotates faster than many famous pulsars.

A whole panopmic of astrophysical anomalies! And finally: Supernova 1054 flared up at a distance of “only” six thousand light years from the sun. After all, the flash could occur on the opposite edge of the galaxy. Who knows how science would develop then - and not only astrophysical. Many discoveries would be late, or maybe they would not have been made at all!

Pavel Amnuel

1 See: Amnuel P. The Far Lights of the Universe. Fryazino: century-2, 2007.