At the center of the Milky Way galaxy, a swarm of stars orbits a supermassive black hole.
These are S stars, objects of astronomical fascination and wonder. Among other things, many of the puzzles surrounding them are their origins.
The vicinity of a supermassive black hole is thought to be too extreme and turbulent to allow star formation, so astronomers believe that any stars hanging there must have come from somewhere else. I believe that.
Now, a team led by astrophysicist Shogo Nishiyama of Miyagi University of Education has determined the origin of one of these stars, named S0-6, and it is clear that it is not a star from around here. found.
In fact, S0-6 appears to come from entirely outside the Milky Way, making it the first star in the galactic center found to have an extragalactic origin story.
In fact, S Star is a lot of fun. They have long looping elliptical orbits around the supermassive black hole Sagittarius A* that reach mind-boggling speeds. The fastest star discovered so far in the Milky Way is an S star, which can reach speeds of up to 24,000 kilometers (15,000 miles) per second as it plummets around a black hole.
The S star was also part of a long, decades-long observation and analysis campaign to demonstrate general relativity at one of the most extreme scales ever. Therefore, it is very interesting to learn more about how physics works.
But Nishiyama and his colleagues wanted to know where the stars actually came from in the first place. They carefully studied S0-6 over eight years using the Subaru Telescope, an optical and infrared observatory in Hawaii.
First, they measured the star’s velocity and orbit and found accelerations that supported its orbit around Sagittarius A*. S0-6 is located just 0.04 light years from the black hole.
They then carefully analyzed the light emitted by the star, looking for bright and dark lines on the spectrum. These lines are created by elements that absorb and emit light at specific wavelengths, and can reveal the chemical composition of the star itself.
Older stars have lower amounts of heavy elements than younger stars, so this information helps astronomers estimate a star’s age. But a star’s composition can also help reveal its origin, since stars born at the same time in the same location usually have similar chemical profiles.
The researchers found that S0-6’s spectrum is significantly lacking in heavy elements, giving it an estimated age of about 10 billion years.
However, the amounts and proportions of these elements are most similar to stars outside the Milky Way, namely in the dwarf galaxies that orbit it, such as the Sagittarius dwarf spheroid and the Small Magellanic Cloud.
These galaxies are currently being swallowed very slowly by the Milky Way, so it’s not unexpected that some of their stars might end up here. And we also know that the Milky Way has swallowed quite a few other galaxies during her 13.6 billion year lifespan.
Many relics of these subsuming galaxies exist within the Milky Way. S0-6 presents the first observational evidence that their remains may have made their way toward the galactic center.
That has not yet been confirmed, but at least we know that the chemical evolution of S0-6 was quite different from that of other stars at the center of the galaxy. Of course, as always, more research needs to be done.
“Did S0-6 really originate outside the Milky Way?” Nishiyama says.. “Does it have companions or did it travel alone? Through further investigation, we hope to unravel the mysteries of stars near supermassive black holes.”
This study Japan Academy Proceedings Series B.