If you’re an evil genius supervillain looking to strike terror into your enemy with a big messy space cablooie, here’s a novel way to do it. Smash up some remnants of old stars right in front of your nemesis. The result will be a delightfully large, bright explosion, as well as an additional gamma-ray burst visible across the Universe. And it will scare everyone to commit your evil intentions.
To do this, of course, one must have extremely strange powers. These don’t exist outside of comics. But in the real universe there are ways to do this. You just need these massive stellar objects crammed together in space. Then they get a little too close and – it’s their fault! a massive explosion visible billions of light-years away.
GRB 191019A: the Star Destroyer
On October 19, 2019, astronomers focused on the source of one such event called GRB 191019A. The first clue was a long-term gamma-ray burst (GRB) that lasted about a minute. (That’s long in the GRB range, although there is evidence that some last much longer. However, most are only a few seconds to a few microseconds long.) Neil Gehrel’s Swift Observatory spotted it immediately. Months later, astronomers observed the fading afterglow from the GRB source. They used the International Gemini Observatory, as well as the Nordic Optical Telescope and the Hubble Space Telescope. The observations revealed stellar death in the crowded heart of a galaxy some 3 billion light-years away.
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Artist’s rendering of the SWIFT satellite capturing a gamma-ray burst. Photo credit: NASA
Observers described it as an almost demolishing derby-like collision of stellar debris and stars in the chaotic neighborhood of the galaxy’s central supermassive black hole. The source of the GRB flash was just 100 light-years from the heart of the galaxy. It turned out to be in close proximity to the central supermassive black hole. “These new results show that stars can die in some of the densest regions of the Universe where they can be collided,” said Andrew Levan, lead author of a paper on the GRB and its source. “It’s exciting for understanding how stars die and for answering other questions, like what unexpected sources could produce gravitational waves that we might detect on Earth.”
Search for Star Destroyers in unusual locations
What is unusual about this event, according to Levan, is that it took place in a very old galaxy. “Our follow-up observation showed us that the outburst was not a collapsing massive star, but most likely the merger of two compact objects,” Levan said. “By pinpointing its location at the center of a previously identified ancient galaxy, we had the first compelling evidence of a new path in which stars face their demise.”
Diagram showing the evolution of stars under most circumstances. GRB 191019A reveals another way of destroying stars or stellar remnants. Photo credit: NASA
In an aging galaxy one does not necessarily expect fireworks of this magnitude. This is because the prime time of star formation is long past. Most giant stars have already died as supernovae. However, its core could be a perfect place for the destruction of stellar debris in collisions. The central regions of many old galaxies harbor large stellar populations. By some estimates, more than a million people crammed into a region just a few light-years across. There are also clouds of gas and dust, as well as a population of stellar debris – the black holes and neutron stars that result from the deaths of massive stars.
All of these objects swarm around the central supermassive black hole. It wouldn’t take much to bring two stellar objects (be they nearby stars or remnants) together under the gravitational influence of the central black hole. For a second, two objects spin around each other; Next time, they collide and create a violent burst, which we consider a long-lasting GRB. There is also a burst of a gravitational wave followed by a flash of light.
Looking for more GRBs
Astronomers haven’t seen many of these protracted collisional GRBs in normal galaxies, but they’re probably more common than anyone thought. The galactic cores in which they occur are often obscured by clouds of gas and dust that obscure the initial GRB flash and subsequent afterglow. Luckily, GRB 191019A happened more or less “in the clear,” giving observers a chance to watch it for quite some time.
GRB 191019A is the first observed event to involve stellar remnants in a crowded galaxy core environment. Levan and others would like to find more of these now that they know what to look for. Their hope is to compare a GRB detection with a corresponding gravitational-wave detection, which would reveal more about their true nature and confirm their origins in even the direst of environments.
Ruby Observatory at dusk in May 2022. This observatory will be incredibly useful for studying the afterglow of GRBs from massive star deaths as well as from collisions in distant galaxies. Credit: Ruby Obs/NSF/AURA
Fortunately, the current observatories, along with future facilities like the Vera C. Rubin Observatory, can play a role. “Studying gamma-ray bursts like these is a great example of how the field is really advancing through the collaboration of many institutions, from discovering the GRB to discovering afterglows and distances with telescopes like Gemini to analyzing events in detail with observations across the electromagnetic spectrum,” Levan said.
For more informations
Unprecedented opportunity to destroy a star
A long-term gamma-ray burst of dynamic origin from the core of an ancient galaxy (ArXiv PDF)