Scenario proposes a new way to destroy a star |  Urania

While searching for the source of a powerful gamma-ray burst (GRB), an international team of astrophysicists may have found a new way to destroy stars.

Although most gamma ray bursts (GRBs) It is formed by the explosion of massive stars or by fusion Neutron starsScientists conclude that GRB 191019A formed as a result of the collision of stars or star debris in the dense surrounding environment. supermassive black hole in the old heart galaxies. This demolition-like environment points to a long-supposed—but never before seen—way to destroy a star and generate GRBs.

Test results have been left published June 22, 2023 in Nature Astronomy.

For every hundred events that fit into the traditional classification scheme for gamma ray bursts, there is at least one strange case that baffles us. said Wen Fei Fong, Northwestern astrophysicist and co-author of the study. However, it is these strange events that tell us the most about the amazing variety of explosions that the universe is capable of.

Discovering these unusual phenomena in dense star systems, especially those that surround supermassive black holes at the cores of galaxies, is undoubtedly exciting. said Giacomo Fragione, Northwestern astrophysicist and co-author of the study. This remarkable discovery gives us a tantalizing glimpse into the complex dynamics at work in these cosmic environments, making them factories for events that would otherwise be considered impossible.

Most stars end their lives in one of three predictable ways, depending on their mass. Stars with relatively low mass, such as our Sun, shed their outer layers with age, and as a result become white dwarfs. Stars with more mass burn brighter and explode in catastrophic explosions supernovae, which creates extremely dense objects such as neutron stars and black holes. The third scenario occurs when two of these stellar remnants form a binary system and eventually collide with each other.

However, a new study shows that there may be a fourth option.

Our results show that stars can meet their death in some of the denser regions of the universe, where they can be pushed to collide – said the paper’s lead author Andrew Levan, an astronomer at Radboud University. It’s exciting to understand how stars die and to answer other questions, such as what unexpected sources they might produce gravitational wavesWe can detect it on Earth.

Old galaxies, long past their prime, contain few, if any, massive stars. However, their cores are full of stars and very dense stellar remnants such as white dwarfs, neutron stars, and black holes. Astronomers have long suspected that in the turbulent hive of activity surrounding the supermassive black hole, it would be only a matter of time before two stellar objects collided to produce GRBs. However, evidence of such collisions has remained elusive.

On October 19, 2019, astronomers observed the first signs of such an event when Quick Observatory He detected a bright gamma-ray burst that lasted just over a minute. Any GRB lasting more than two seconds is considered long. Such flares are usually caused by the collapse of stars at least 10 times the mass of our Sun.

Then scientists used it Gemini South Telescope in Chile for long-term observations of the fading GRB glow.

Through these observations, astronomers were able to locate the GRB in an area less than 100 kilometers away light years From the core of an ancient galaxy – very close to its supermassive black hole. Interestingly, the researchers found no evidence of a similar supernova that would have left its mark in the light recorded by Gemini South.

The absence of such a supernova indicates that this explosion is not the typical result of a massive star collapse, explains Jillian Rastenjad, a member of the research group that did the calculations to verify the presence of a supernova accompanying long GRB 191019A. . GRB 191019A’s location in the heart of its host galaxy points to a suspected but unproven theory about the origin of gravitational-wave emission sources.

In typical galactic environments, long gamma-ray bursts caused by the collision of stellar remnants such as neutron stars and black holes are extremely rare. However, the cores of ancient galaxies are anything but ordinary. There may be a million or more stars in an area a few light years across. This extremely dense collection of stars can lead to accidental collisions, especially under the influence of the massive gravity of the supermassive black hole, which disrupts the motion of the stars and sends them in different directions. Eventually, these disobedient stars will cross their paths and merge, creating a gigantic explosion that can be seen from vast cosmic distances.

Virtually all of our predictions about the environment in both short and long GRBs are undermined by this event said Anya Nugent, the researcher responsible for principal modeling of the host galaxy. Long GRBs have not yet been observed in galaxies as old and lifeless as those hosting GRB 191019A. By contrast, short GRBs from mergers were not previously thought to be closely associated with the nuclei of their host galaxies. The discovery of this phenomenon in the heart of a quiet, ancient galaxy opens up new promising horizons for formation dual systemswhich has been rarely observed until now.

It is possible that such events occur routinely in similarly crowded regions of the universe, but so far they have gone unnoticed. One possible reason for their concealment is that the centers of galaxies are filled with dust and gas, which can obscure both the initial gamma-ray burst and the resulting afterglow. However, GRB 191019A may be a rare exception, allowing astronomers to detect the flare and study its effects in detail.

Although this event is the first of its kind to be detected, it is possible that there could be more, hiding behind large amounts of dust near their galaxies. Fung said. Indeed, if this long-lasting event results from the fusion of compact organisms, it contributes to a population of GRBs that defies our conventional classifications.

Scientists working to detect more such events hope to match the detection of gamma ray bursts with the corresponding detection of gravitational waves. This combination will provide more information about the true nature of these phenomena and confirm their origin – even in the most extreme environments.

Agnes Nowak

more information:

Source: Northwestern

Pictured: Artist’s impression of a gamma-ray burst. Source: Gemini International Observatory / NOIRLab / NSF / AURA / M. Garlick / M. Zamani

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