Looking at all the stars in the night sky, you’d never notice that one of them wasn’t from around here. Astronomers have now found that a star right near the supermassive black hole at the center of the Milky Way likely originated in a smaller galaxy that ours devoured.
The Milky Way is home to more than 100 billion stars, and while the vast majority of them were born and raised here, some seem to have migrated in from other galaxies. Most of these intergalactic interlopers are found in the Milky Way’s “halo,” on the very outskirts of the galaxy. But in a new study, Japanese astronomers have discovered one that’s about as central as is possible.
Smack-bang in the middle of the Milky Way is a supermassive black hole known as Sagittarius A*. It’s a busy neighborhood, but new stars aren’t thought to be born there often, because this monster exerts extreme forces on its surroundings. Astronomers at Miyagi University of Education were studying where these stars had migrated from, when they discovered one had taken a much longer journey than anticipated.
The star in question is known as S0-6, and it lies a little under 11 light-years from the black hole itself. The astronomers have been watching its movements for eight years, using the Subaru Telescope in Hawaii. Their studies found that the star is more than 10 billion years old – and most intriguingly, was a pretty well-traveled old timer.
The chemical composition of S0-6 didn’t match other stars nearby, or even within the Milky Way itself. Instead, it’s a much closer match to stars found in small galaxies that orbit our own, like the Small Magellanic Cloud and the Sagittarius Dwarf galaxy. The researchers hypothesize that S0-6’s home galaxy was swallowed up by the Milky Way during what seems to be a pretty regular occurrence, although it wasn't known that these stars could end up so deep in the middle.
That origin story indicates the star must have traveled a bare minimum of 50,000 light-years to end up in its current location. But the real figure is likely much higher, as it would have slowly spiraled in over billions of years rather than making a beeline for the center.
Discovering S0-6’s weirdness isn’t the end of the story, of course – on the contrary, it means astronomers will be motivated to study it even closer, to help answer more questions.
“Did S0-6 really originate outside the Milky Way galaxy?” said Shogo Nishiyama, lead author of the study. “Does it have any companions, or did it travel alone? With further investigation, we hope to unravel the mysteries of stars near the supermassive black hole.”
The research was published in the journal Proceedings of the Japan Academy, Ser. B, Physical and Biological Sciences.
Source: Subaru Telescope
