Many stars orbit near Sagittarius A*, the supermassive black hole at the center of the Milky Way. In some galaxies, some of these stars are ripped apart when they get too close to the supermassive black hole. Other stars change color due to incredible gravitational effects. And in a few cases, the stars are just slingshot into intergalactic space. S5-HVS1 is one of these stars.
As reported in a paper available on the pre-print server arXiv, yet to be peer-reviewed, an international group of scientists serendipitously spotted a hyper-velocity star as they were studying interesting objects for the Southern Stellar Stream Spectroscopic Survey (S5). And they are not joking when they call it hyper-velocity. The star is moving at a staggering 1,017 kilometers per second (2.275 million miles per hour). It covers the distance between New York and Sydney in just 15.7 seconds.
To move at that speed, much faster than your average star, something must have accelerated it. The team of researchers tried to estimate where the star could have possibly come from, and based on their analysis the most likely explanation is the core of the Milky Way. And, well, it is very easy to point the finger at Sagittarius A*.
If our friendly neighborhood supermassive black hole is indeed the culprit, the star was probably kicked away with a velocity of roughly 1,800 kilometers per second (over 4 million miles per hour) and has been slowly slowing down on its travels for about 4.8 million years. The star, which is a standard hydrogen-fusing or "main sequence" object, is located roughly 30,000 light-years from Earth.
While this is the fastest main-sequence star ever discovered, it is not a unique object. Astronomers have discovered dozens of these stars, although most of them appear to have been accelerated out of the galaxy by events other than interactions with Sagittarius A*. Researchers suggest that if one of the two stars in a binary system goes supernova, it could give enough of a kick to push its companion away, beyond the disk of the Milky Way.
But stars aren't just being kicked out. Researchers have also discovered stars coming into the galaxy from smaller companions of the Milky Way. They too could have been accelerated by a supernova or perhaps even a supermassive black hole that we are yet to observe.