The margins of the Milky Way are holding the galaxy’s oldest stars. In this particular region, researchers have recently identified a rather surprising cosmic retirement collective, namely a group of young stars.
What is even more surprising is that the spectral analysis seems to imply that the young stars come from an extragalactic place. The stars are allegedly not containing the same material as the Milky Way, but hold elements from two closely located dwarf galaxies known as the Magellanic Clouds. Those galaxies are on a crash trajectory with our own Milky Way.
The finding suggests that a surge of gas expanding from the galaxies is approximately half as far from colliding into the Milky Way as earlier believed.
“This is a puny cluster of stars—less than a few thousand in total—but it has big implications beyond its local area of the Milky Way,” says main discoverer Adrian Price-Whelan, a researcher at the Flatiron Institute’s Center for Computational Astrophysics in New York City.
The recent stars could help scientists understand more about the Milky Way’s background. These stars may, for instance, show if the Magellanic Clouds crashed with our galaxy in the past.
Prince-Whelan and his colleagues introduced their discoveries on January 8th at the American Astronomical Society meeting in Honolulu. Their finding was published previously in The Astrophysical Journal, as well as the later spectroscopic analysis of the stars, on December 5th, and December 16th, respectively.
Discovering clusters of stars is a rather difficult task because our galaxy is filled with radiant orbs. Some stars may seem to be close together in the night sky, but they are actually located at impressively different distances from Earth. Other stars may momentarily be close to one another but move on in opposite directions. Estimating which stars are, in fact, gathered together asks for numerous accurate measurements over time. The recently found cluster is relatively young at 117 million years old and is on the far edges of the Milky Way.
“It’s really, really far away,” Price-Whelan says. “It’s further than any known young stars in the Milky Way, which are typically in the disk. So right away, I was like, ‘Holy smokes, what is this?'”
Searching for an Answer
David Nidever, assistant professor of physics at Montana State University in Bozeman, conducted a research on the metal content of the 27 brightest stars in the cluster. Similar to the Magellanic Stream, the stars were composed of low quantities of metal.
The scientists suggest that the cluster took shape as gas from the Magellanic Stream traveled through the gases around the Milky Way. The process created a drag-force that compacted the Magellanic Stream gas, and together with tidal forces from the galaxy‘s gravitational pull, compressed the gas enough to create a star formation. With time, the stars moved and ended up in the Milky Way.
“If the Magellanic Stream is closer, especially the leading arm closest to our galaxy, then it’s likely to be incorporated into the Milky Way sooner than the current model predicts,” Nidever says. “Eventually, that gas will turn into new stars in the Milky Way’s disk. Right now, our galaxy is using up gas faster than its being replenished. This extra gas coming in will help us replenish that reservoir and make sure that our galaxy continues to thrive and form new stars.”
The enhanced numbers could even provide an answer for the debate over whether the Magellanic Clouds have passed through the Milky Way before. Finding a clue to this mystery will help astronauts better comprehend the background and properties of the Milky Way.