Astronomers from the Moscow state University have uncovered one of the secrets of the birth of white dwarfs

© Francesco MereghettiДвойная star system HD 49798 in the constellation the Poop in the representation of the artistAstronomers from the Moscow state University have uncovered one of the secrets of the birth of white dwarfs© Francesco Mereghetti

Astrophysicists from Russia and Italy revealed the mysterious nature of the binary system HD 49798 in the constellation of the Stern, proving that one of its inhabitants is a young white dwarf, whose matter is compressed gradually, and not a neutron star, as believed by some scientists. Their findings were published in the journal MNRAS.

«This discovery has two important meaning. On the one hand, there was a mysterious system. For several years astronomers argue that there is a white dwarf or a neutron star? We explained, though perhaps it is not so important for astrophysics as a whole. On the significance of the discovery can be compared with the disclosure of cunning crimes detective — although the event is local, the audience still interesting,» — says Sergey Popov, an astrophysicist from the State astronomical Institute named after Sternberg, Moscow state University.

The majority of relatively small stars, like the Sun in size, ends not with a Bang a supernova and become a white dwarf – small and super-dense ball of superhot exotic matter continues to glow for many hundreds of millions of years due to heat trapped in their depths.

Scientists long enough I think that the young white dwarfs gradually shrink after a reset, the outer shells of a dead star, «slimming» to a few hundred kilometers in the first million years of its independent existence. Evidence of this, as explained by Popov, has still not been able to find, as the majority of white dwarfs is considerably older than a million years, and astronomers did not have accurate data on their diameter in order to «see» the compression process.

Russian and Italian astrophysics under the leadership of Popov was able to get the first evidence that such compression does occur, watching the mysterious binary star HD 49798 in the constellation the Poop, distant from us by about 2100 light years.

The facility was opened in 1964, Argentine astronomers initially thought that they were dealing with an unusual white subcortical, in the depths of which contained an unusually little hydrogen. In the future, scientists found that HD 49798 is a double star, one half of which is the «normal» body, and the second neutron star or a white dwarf.

The controversy aroused unusually high frequency of rotation of the second object – it completes one rotation around its axis in just 13 seconds. This is a normal value for neutron stars, but a record high anomaly for a white dwarf, which is rather hard to explain.

Moreover, recently, scientists have discovered that the rotation of the second halves of HD 49798 is accelerating, which probably suggests that the white dwarf or neutron star is actively «stealing» the matter of his neighbour, accumulating it on its surface. It is extremely difficult to explain in the context of both versions of the nature of this star, which further drove the astronomers to a standstill.

Russian astrophysicists have found an explanation for all these oddities, paying attention to how changing the properties of stars when they transform and in neutron stars, and white dwarfs.

And that, and the other process have one thing in common – the volume of stars dramatically decreases and its density increases sharply. The decrease in the volume of stars, according to «school» the law of conservation of angular momentum will lead to the fact that the speed of rotation will increase.

Accordingly, a rapid increase in the speed of rotation of the second half HD 49798 can be explained by the fact that this star is compressed and its volume is gradually reduced. Following this idea, Popov and his team figured out how to shrink a white dwarf of similar size and age, and compare the computer model with real data.

As shown by these calculations, the white dwarf age of 2 million years expected to contract at a rate of approximately one centimeter per year, which perfectly matches the kind of pace increases the rotation speed of the second halves of HD 49798. Accordingly, we can say that now astronomers had an example of «young» white dwarf, the study of which, as I hope the authors will help us better to understand their nature

«There is a second meaning of the opening. Dozens of years it was clear that the young white dwarfs are compressed. The phase of compression «live» we have never seen. And the uniqueness of the system, which we watched, was the fact that the white dwarf was like «glowing» due to the flow of matter from the neighboring star. Most importantly, it highlighted so neatly that it did not affect its rotation, and this is the rarity system. In other pairs of white dwarfs and main sequence stars, accretion is much more powerful: it defines how the white dwarf is spinning, why notice the «beauty of compression» it is impossible», — concluded Popov.