The collision of two neutron stars, located several billion light-years away, gave rise to one of the most powerful gamma-ray bursts recorded by the ALMA radio telescope in the Chilean Atacama Desert. We are now 20 billion light-years from the galaxy in which these stars are located.
Neutron stars are super-dense cores left after the explosion of massive stars, and when they collide, a powerful explosion occurs, the result of which is called a kilonova. The name hints that the energy produced by this can be a thousand times greater than the energy emitted by a supernova. Gravitational waves are produced and gamma-ray beams are emitted in two opposite directions.
The described event was recorded on November 6, 2021 by the European Space Agency’s INTEGRAL orbital X-ray and gamma-ray observatory – it sent a signal that activated NASA’s Swift satellite. Cataloged as GRB 211106A, the burst lasted less than two seconds, and the kilonova afterglow lasted much longer.
The afterglow is amenable to study. Gamma waves accelerate the electrons contained in the gas at the collision site, and the energy emitted by these electrons peaks in the millimeter range – from which you can judge the total energy of the explosion. Using the data obtained by ALMA, it was found that with the gamma-ray burst GRB 211106A, energy was released in the range from 2 × 1050 up to 6×1050 erg, which makes it one of the most powerful in the history of observations (1 erg is a unit of work and energy in the CGS system, equals 10-7 J).
Image Source: Nidhi Yashwanth / pixabay.com
The collision of stars took place from 6.3 billion to 9.1 billion years ago, and now, taking into account the expansion of the universe, the “native” galaxy of these stars is 20 billion light-years away from us. Gravitational waves from a source at such a distance could not be detected – too far. But scientists have studied in detail the afterglow of a gamma-ray burst: it starts in a narrow beam, and then gradually expands. In this case, the beam opening angle reached 16°, and this is one of the largest values for a short gamma-ray burst. The researchers are lucky because the beam can only be fixed when it is directed at us, which means that the wider it is, the more likely we are to see it.
Such events are important for space chemistry: such collisions of stars form heavy elements, including silver, gold and platinum. As scientists have calculated, the mass of gold formed in this case can reach from 3 to 13 Earth masses.
The report of scientists about the event will be published in a scientific journal Astrophysical Journal Letters.
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