ALMA captures the effects of neutron star mergers

ALMA Radio Observatory (Atacama Large Millimeter/submillimeter Array) for the first time recorded millimeter radiation from the GRB 211106A flare caused by the collision of two neutron stars. Scientists have already confirmed that this explosion was one of the most powerful short gamma-ray bursts ever observed in the history of astronomy.

Nature of short gamma-ray bursts

Gamma-ray bursts represent the brightest and most high-energy events in the Universe. In just a few seconds, they emit more energy than our Sun in billions of years of its life.

A short gamma-ray burst in the artist’s image. Source: NRAO/AUI/NSF

By duration, all gamma-ray bursts are divided into short and long bursts. Short bursts are associated with events such as collisions of supercompact objects (neutron stars and/or black holes). According to scientists, they are responsible for the formation of the heaviest elements in the Universe, such as gold and platinum. These substances are synthesized during the nuclear reactions accompanying the collision of neutron stars.

Also, during short gamma-ray bursts, a large amount of energy is released in the form of gravitational waves, and the resulting explosion is accompanied by jets moving at near-light speeds. When one of the jets turns out to be directed towards the Earth, astronomers record a short pulse of gamma radiation, which gave the name to such events.

Most powerful gamma-ray burst in history

The problem of studying short gamma-ray bursts is related to the fact that their average duration is only a few tenths of a second. After the flash, an afterglow is formed, which occurs due to the interaction of jets with the surrounding gas — however, it is quite difficult to detect it. Until today, astronomers have registered only a few short gamma-ray bursts in the radio range, and not a single such event in the millimeter range.

Animation showing the radiation from the GRB 21106A gamma-ray burst. Source: ALMA (ESO/NAOJ/NRAO), T. Laskar (Utah), S. Dagnello (NRAO/AUI/NSF)

The more significant the data obtained by ALMA. Initially, the gamma-ray burst GRB 211106A was recorded by the Swift Space Observatory. But, while the telescope was able to detect the accompanying X-ray radiation, it failed to identify the galaxy itself, in which the stars merged.

After that, astronomers used ALMA. Observations carried out by the observatory in the millimeter range made it possible to determine that GRB 211106A was significantly further than the initial estimates. The burst occurred just 5.5 billion years after the Big Bang. Taking into account the expansion factor of the Universe, the distance to it is now about 20 billion light years. This means that GRB 211106A is one of the most powerful gamma-ray bursts in the history of astronomy.

Earlier we talked about how astronomers managed to detect the source of isolated short gamma-ray bursts.

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