Have you ever thought that stars could disappear? How could they disappear? Huge stars gathered together in space, get a little too close to each other and bam! There is a huge explosion, visible for billions of light years, and the stars disappear.

GRB 191019A: THE STAR DESTROYER
On 19 October 2019, astronomers detected the source of one such event, called GRB 191019A. The first sign was a prolonged gamma-ray burst (GRB) lasting about a minute. (That's a long time in GRB terms, but there is evidence that some last much longer. However, most are only a few seconds to a few microseconds long). Neil Gehrels Swift Observatory detected it immediately.
Astronomers then spent months studying the fading afterglow of the GRB source. They used the International Gemini Observatory, as well as the Nordic Optical Telescope and the Hubble Space Telescope. The observations revealed a stellar death scene in the crowded heart of a galaxy some 3 billion light years away.

Observers described it as an almost demolition derby-like collision of stellar remnants and stars in the chaotic neighbourhood of the supermassive black hole at the centre of the galaxy. The source of the GRB flare was only 100 light years from the heart of the galaxy. The source turned out to be very close to the central supermassive black hole.
"These new results show that stars can meet their demise in some of the densest regions of the Universe, where they can be dragged into collisions," said Andrew Levan, lead author of a paper on the GRB and its source.
"This is exciting for understanding how stars die and for answering other questions, such as what unexpected sources might create the gravitational waves we can detect on Earth."

According to Levan, what makes this event so unusual is that it occurred in a very old galaxy. "Our follow-up observation told us that the explosion was most likely caused by the merger of two compact objects, rather than the collapse of a massive star," Levan said.
"By pinning its position to the centre of a previously identified old galaxy, we have obtained the first teasing evidence of a new way for stars to meet their demise."

An ageing galaxy is not where you would expect to find such huge fireworks. That's because the time for star formation is long past. Most of the giant stars have already died in supernovae. But its core can be the perfect place for the remains of stars to be destroyed in collisions.

The central regions of many old galaxies are home to large stellar populations. According to some estimates, more than a million stars are concentrated in a region just a few light-years across. There are also clouds of gas and dust, as well as a population of stellar remnants, such as black holes and neutron stars, which are the result of the death of massive stars.
All these objects gather around the central supermassive black hole. It does not take much time to bring two stellar objects (whether nearby stars or remnants) together under the gravitational pull of the central black hole.
Within a second, the two objects orbit each other; a second later they collide and produce a massive explosion, which we recognise as a long-lived GRB. There is also a burst of gravitational waves followed by a flash of light.

Astronomers have not seen many of these long-collisional GRBs in normal galaxies, but they probably occur more often than anyone thinks. The galaxy cores where they form are often obscured by clouds of gas and dust, which masks the initial GRB flare and the subsequent flare. Fortunately, GRB 191019A occurred more or less "in the open", which gave observers a chance to watch it for quite a long time.

GRB 191019A is the first observed event containing stellar remnants in the environment of a crowded galaxy core. Now that Levan and others know what to look for, they want to find more. Their hope is to pair a GRB detection with a corresponding gravitational wave detection, which will reveal more about their true nature and confirm their origin in even the darkest environments.
Fortunately, existing observatories, as well as new facilities such as the Vera C. Rubin Observatory, can play a role in this.

"Studying gamma-ray bursts like this is a great example of how the field is really evolving with many facilities working together, from the detection of the GRB, to the discovery of afterglows and distances with telescopes like Gemini, to the detailed study of events with observations across the electromagnetic spectrum," Levan said.

 

Source: https://www.sciencealert.com/