In mid-October 2017, the whole world was hotly discussing an important scientific event. Scientists announced the first-ever detection of a gravitational-wave burst from the fusion of two neutron stars. This was done with the help of the LIGO interferometer, with the help of which the first gravitational bursts from the fusion of black holes were observed, for which three famous physicists were awarded the Nobel Prize.
The peculiarity of the October discovery was that after the gravitational signal, a response was also received in the electromagnetic range-gamma, optical, radio, and x-ray. One of the important conclusions of the discovery was the confirmation of the hypothesis that it is in such processes in the Universe that most elements are produced heavier than iron-gold, lanthanides, uranium and others. The discovery made by LIGO was the topic of the interview that famous astrophysicist Stephen Hawking gave to BBC journalist Pallaba Gosh. This interview, as the author notes, was the last for Hawking. The scientist died on March 14.
Tell me, how important is the discovery of the fusion of two neutron stars?
This is a real achievement. This is the first ever detection of a gravitational-wave source with an electromagnetic response. It confirms that short gamma-ray bursts occur when neutron stars merge. It gives a new opportunity to determine distances in cosmology and tells about the behavior of matter with an incredibly high density.
What will the electromagnetic waves tell us about this merger?
Electromagnetic radiation indicates the exact position of the source in the sky. In addition, it tells us about the red shift of the object (the shift of the spectral lines to the long-wave side). Gravitational waves indicate to us the photometric distance. Together, these measurements give us a new way of measuring distances in cosmology. This is the first example of what will become a new cosmological scale of distances. The substance inside the neutron star is much denser than anything we can produce in the laboratory. The electromagnetic signal from the merging neutron stars can tell us about the behavior of matter with such an ultrahigh density.
Will this discovery tell us how black holes form?
The fact that black holes can be formed by the fusion of two neutron stars was known from theory. But this event was its first verification, the first observation. The fusion probably leads to the formation of a rotating, supermassive neutron star, which then collapses into a black hole.
This is very different from other ways of forming black holes, such as a supernova explosion or during the accretion of a normal star substance onto a neutron star. Careful data analysis and theoretical modeling on supercomputers will give broad opportunities for understanding the dynamics of formation of black holes and gamma-ray bursts.
Will the measurements of gravity waves provide a deeper understanding of how space-time and gravity work, and thus change our view of the universe?
Yes, without a shadow of a doubt. An independent cosmological scale of distances can give an independent verification of cosmological observations, or there may be many surprises. Gravitational-wave observations allow us to test the general theory of relativity in those cases when the gravitational field is strong and very dynamic. Some believe that the general theory of relativity needs to be improved in order to avoid the introduction of dark energy and dark matter. Gravitational waves provide a new way to search for signs of possible deviations from the general theory of relativity. The appearance of a new observation window in the universe usually leads to unexpected events that can not be predicted. And we are all three of our eyes, or rather the ears, as we just woke up to hear the sound of gravitational waves.
Can the fusion of neutron stars be one of the few ways, or the only way that gold will form in the universe? Can it explain why there is so little gold on Earth?
Yes, the collision of neutron stars is one of the ways of gold formation. It can also be produced by fast neutron capture during supernova explosions. Gold is small everywhere, not only on Earth. The reason for its rarity is that the maximum binding energy of the nucleus is iron, which makes it harder to form elements heavier than it. In addition, for the formation of such stable heavy nuclei as gold, it is required to overcome a strong electromagnetic repulsion.