In mid-October 2017, the whole world was hotly discussing an important scientific event. Scientists have announced the first ever detection of a gravitational wave burst from the merger of two neutron stars. This was done using the LIGO interferometer, which previously observed the first gravitational bursts from merging black holes, for which three famous physicists were awarded the Nobel Prize.
A feature of the October discovery was that after the gravitational signal, a response was 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 of the elements heavier than iron are born - gold, lanthanides, uranium and others. The LIGO discovery was the topic of an interview with the famous astrophysicist Stephen Hawking to BBC journalist Pallab Ghosh. This interview, as the author notes, was Hawking's last. The scientist died on March 14.
How important is it to detect the merger 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 GRBs occur when neutron stars merge. It provides a new way of determining distances in cosmology and tells about the behavior of matter with incredibly high density.
What will the electromagnetic waves from this merger tell us?
Electromagnetic radiation tells us the exact position of the source in the sky. In addition, it tells us about the redshift of the object (shift of spectral lines to longer wavelengths). Gravitational waves tell 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 the new cosmological distance scale. The matter inside a neutron star is much denser than anything we can produce in a laboratory. The electromagnetic signal from merging neutron stars can tell us about the behavior of matter with such super-high density.
Does this discovery tell us how black holes form?
The fact that black holes can form when two neutron stars merge was known from theory. But this event was her first test, her first observation. The merger likely results in the formation of a spinning, supermassive neutron star, which then collapses into a black hole.
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This is very different from other ways black holes form, such as a supernova explosion or during the accretion of material from a normal star onto a neutron star. Thorough data analysis and theoretical modeling on supercomputers will provide ample opportunities to understand the dynamics of the formation of black holes and gamma-ray bursts.
Will measurements of gravitational waves provide a deeper understanding of how spacetime and gravity work, and thus change our understanding of the universe?
Yes, without a shadow of a doubt. An independent cosmological distance scale can provide an independent verification of cosmological observations, and it can conceal many surprises. Gravitational wave observations allow us to test general relativity in cases where the gravitational field is strong and very dynamic. Some believe that general relativity needs more work to avoid the introduction of dark energy and dark matter. Gravitational waves provide a new way to look for signs of possible deviations from general relativity. The emergence of a new observational window into the Universe usually leads to unexpected surprises. And we all three our eyes, or rather ears, because we just woke up to hear the sound of gravitational waves.
Could the merging of neutron stars be one of the few ways, or the only way, through which gold is formed in the universe? Can it explain why there is so little gold on Earth?
Yes, colliding neutron stars is one way gold is formed. It can also be produced by fast neutron captures in supernova explosions. Gold is scarce everywhere, not only on Earth. The reason for its rarity is that the maximum binding energy of the nucleus falls on iron, which makes it difficult to form elements heavier than it. In addition, strong electromagnetic repulsion must be overcome to form stable heavy nuclei such as gold.
Nikolay Khizhnyak