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[EN VIDÉO] Gamma-ray bursts: Collisions of neutron stars brighten up the universe Gamma-ray bursts are the brightest events in the universe in the electromagnetic spectrum. We can observe one a day on average across the sky, and they occur in distant galaxies. There are two types, short and long. This video explains the nature of short bursts.
Many advances in astronomy result from the opening of a new window of observation in a new band of the electromagnetic spectrum. X-rays have revealed stellar black holes, infrared rays the interior of stellar nurseries, and decimeter radio waves the Milky Way’s arm structure.
This is one of the reasons for the design of the Atacama Large Millimeter/submillimeter Array (Alma). Another, complementary, is that the network of radio telescopes thus constructed makes it possible to perform aperture synthesis and therefore have a very large virtual instrument without having to create it.
Today we learn that the Alma radio telescope network was used for a major premiere observing the astrophysical processes associated with kilonovae at millimeter and submillimeter radio regimes. Keep in mind that these are neutron star collisions, first discovered in the form of brief gamma-ray bursts, and the nature of which we have only recently been able to determine, although we are not sure. doubted for decades. The energy released is colossal, making gamma-ray bursts the brightest phenomena in the cosmos.
In this artist’s video, two neutron stars of small dimensions but very high density merge and explode into a kilonova. This particularly rare event leads to the emission of gravitational waves and short gamma-ray bursts. The two emissions were actually observed on August 17, 2017 by Ligo-Virgo and Fermi/Integral, respectively. Various detailed observations made with ESO telescopes have confirmed the nature of this object – a kilonova – located in the galaxy NGC 4993, some 130 million light-years from Earth. This type of objects is the main source of heavy chemical elements like gold and platinum in the universe. ©ESO
Key to this determination was the rise of multi-messenger astronomy with the simultaneous detection of gravitational waves by Ligo and Virgo from source GW170817, which is clearly associated in the sky with emissions of both X- and gamma-ray electromagnetic waves (GRB 170817A) – observed by the Chandra and Fermi satellites – than in the visible with the Las Cumbres Observatory, to name just those instruments.
Collisions of neutron stars producing gold and platinum
This time, astrophysicists have published an article in The Astrophysical Journal Letters, a version of which is freely available on arXiv, that talks about the brief gamma-ray burst GRB 211106A observed on November 6, 2021 – as the name Gamma Ray Burst suggests. As with the source of gravitational waves (gravitational wave) observed on August 17, 2017, the collision of the neutron stars is due to the fact that the two compact stars have been losing energy in the form of gravitational waves at an accelerating rate, causing them to inexorably and rapidly collide with each other.
The fusion must have produced not only thermonuclear reactions that caused the formation of heavy elements like gold and platinum, but also a collimated beam of particles at very high velocities that also produced an equally collimated beam of high-energy gamma-ray photons. The earth happened to pass this beam like an observer illuminated by a lighthouse.
The beam of particles and gamma photons that injects itself into the interstellar medium, excites it and forces the matter within to glow in response. This remanent radiation was first detected in the spectral band accessible to Alma. Prior to this instrument, millimeter telescopes were not sensitive enough to detect this afterglow, as GRBs are often observed billions of light-years from the Milky Way. We therefore only observe the old GRBs and also suspect that they became more frequent during the first billion years of the history of the cosmos for reasons still unknown. In fact, GRB 211106A occurred when the observable universe was only 40% of its current age. But even if the kilonovae in the gamma are clearly visible from afar, this is no longer the case with the much weaker residual radiation.
When only GRB 211106A’s X-ray counterpart was initially spotted with the Swift satellite, astrophysicists believed the kilonova could still have come from a nearby galaxy, although it was unclear whether it could be assigned by Hubble visible observations could – probably due to the presence of a large amount of dust on the line of sight near the GRB.
But finally, thanks to Alma, it was possible to find a faint and distant galaxy where the gamma-ray burst took place. From the determined distance it had to be concluded that it was one of the strongest GRBs discovered so far …
Alma, together with observations from the JWST (James Webb Space Telescope), should make it possible to go even further in the study of short gamma-ray bursts.
The recognition saga around GW170817. For a fairly accurate French translation, click the white rectangle at the bottom right. Then the English subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose French. © Science vs. Cinema
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