The center of an ancient galaxy

The center of an ancient galaxy

Scientists can go back to the drawing board. Because apparently we still don’t fully understand how long gamma-ray bursts see daylight.

Gamma ray bursts are the most energetic phenomenon in the universe. They are in fact nothing more than violent high-energy gamma-ray bursts that last from a few milliseconds to a few minutes. Astronomers have long assumed that gamma ray bursts come in two “flavors”: short GRB and long GRB, both of which have different origins. Um… is that too short-sighted? In recent years, researchers have seen gamma-ray bursts originate in a different way than expected. And now there is a surprising third example.

For nearly two decades, astrophysicists have believed that short GRBs are caused by neutron star mergers. The collision of neutron stars can then produce what is called a kilonova. An explosion in which heavy elements such as gold are discarded. Long GBRs would only be produced by the collapse of massive stars, resulting in a supernova.

The center of an ancient galaxy
In a new study, researchers examined the aftermath of a gamma-ray burst captured on October 19, 2019 by Neil Gerrell Express Observatory. They did it with Southern GeminiTelescope in Chile Scandinavian optical telescope On the Canary Island of La Palma and the Hubble Space Telescope. It leads to an amazing discovery. The long gamma-ray burst appears to be coming from the center of an ancient galaxy. And this is very strange. As mentioned earlier, long GRBs are usually formed in the collapse of massive stars. And let them be lost in the center of ancient galaxies. Massive stars are typical of young galaxies.

An artist’s impression of a long-period gamma-ray burst near the center of an ancient galaxy. Image: Gemini Observatory International/NOIRLab/NSF/AURA/M. Garlick/M. my time

Three ways
The new observation turns our understanding of how long gamma-ray bursts are generated on its head. And this is not the first time. Last year, for example, researchers discovered another long type of GRB produced by neutron star mergers. In this case, two large stars, which have been orbiting each other their entire lives, eventually turned into neutron stars and collided with kilonovas. This is while it was assumed that only short GRBs could be associated with a kilonova. This theory can go straight to the trash. And now, in 2023, it looks like long GRBs may be forming in a third way.

The researchers rule out that the long GRB originated from the collapse of a massive star (as is usually thought). That’s because supernovae usually emit bright light, which astronomers fail to notice.

Instead, the team suspects that the long GRB spotted in the center of the ancient galaxy was caused by the merger of two separate neutron stars. In this case, unlike last year’s study, it’s not about neutron stars that have been orbiting each other for a long time, but about two separate stars that suddenly met each other. “We think that neutron stars are being pushed together by the gravity of many surrounding stars at the center of the galaxy,” said lead researcher Andrew Levan, of Radboud University.

Things are busy
This is not a crazy theory at all. It’s very busy in the middle of the galaxies. There are hundreds of thousands of ordinary stars, white dwarfs, neutron stars, black holes, and dust clouds all orbiting a supermassive black hole. In all, there are more than ten million stars and objects crammed into about four light-years. “This is an area comparable to the distance between our Sun and the next star,” Levan explains. “So the chance of a collision in the galactic center is much higher than it is in our own cosmic backyard.”

Whether it was actually two colliding neutron stars is not entirely clear at the moment. So researchers remain cautious. For example, the long GRB in the center of the ancient galaxy could also have been created by other colliding objects, such as black holes or white dwarfs. In the future, the team hopes to detect more long GRBs that act in sync with gravitational waves. This will enable them to produce more definitive data about the origin of the radiation.

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