Cosmology

Baby Stars are Swarming Around the Galactic Center

The vicinity of Sagittarius A* (Sgr A*), the supermassive black hole at the Milky Way’s center, is hyperactive. Stars, gas, and dust zip around the black hole’s gravitational well at thousands of kilometers per hour. Previously, astronomers thought that only mature stars had been pulled into such rapid orbits. However, a new paper from the University of Cologne and elsewhere in Europe found that some relatively young stars are making the rounds rather than older ones, which raises some questions about the models predicting how stars form in these hyperactive regions.

Astronomers have known about the highly mobile stars surrounding Sgr A* for over thirty years now. They even have their own categorization, known as S stars. However, researchers lacked the equipment to analyze the age of some of these stars, and theories pointed to older, dimmer stars being the most likely to survive near a black hole.

But then, as it does so often with science, evidence that challenged the old and dim star theory began to pile up. Twelve years ago, researchers found an object they believed was a cloud of gas that was in the process of being eaten by Sgr A*. More recently, evidence has begun to hint that that gas cloud might surround a newly born star, known as a “Young Stellar Object” (YSO) in astronomy jargon.

Video showing the motion of stars around Sgr A*, from the corresponding author of the new paper.
Credit – Florian Peißker YouTube Channel

As Sgr A* started to receive more observational time with more powerful telescopes over the years, researchers were able to focus in on other interesting objects, the paper describes dozens of potential YSOs in the vicinity of the previously known S stars. Interestingly, they also seem to follow similar orbits.

Those orbits have the new YSOs zipping in front of the black hole at thousands of kilometers per hour, much faster than typical star formation theories allow. Maybe some intricacy of the black hole’s gravitational field is causing this dramatic motion, or maybe there is some other unknown aspect of stellar formation that can account for these fast-moving young stars, but for now, how they are formed remains a mystery.

However, the researchers made another interesting discovery as part of their work. They found that these YSOs, along with their S star counterparts, orbit in very well-defined formations. In a press release from the University of Cologne, they compare this to how bees from the same hive fly in formation when together. In this case, the black hole appears to be forcing them into this common formation, though other explanations could also account for it, and that analysis wasn’t part of the current research.

Fraser digs into the long term future of our supermassive black hole.

The pattern they formed was three-dimensional, so it wasn’t as simple as one stellar object following the orbital path of another around the black hole. However, the complexity still needs to be studied in detail, and theories that would account for this new information about orbital patterns are hard to come by.

As more telescope time on increasingly powerful systems is devoted to watching one of the most intriguing parts of our galaxy, there will be plenty of data for future astronomers to puzzle over. But for now, this is a step toward understanding the hyperactive world around Sgr A* and the world of stellar birth more generally and how extreme forces play a role in both.

Learn More:
University of Cologne – High-speed baby stars circle the supermassive black hole Sgr A* like a swarm of bees
Peißker et al. – Candidate young stellar objects in the S-cluster: Kinematic analysis of a subpopulation of the low-mass G objects close to Sgr A*
UT – Three Baby Stars Found at the Heart of the Milky Way
UT – Baby Stars Discharge “Sneezes” of Gas and Dust

Lead Image:
Image of the galactic center, including Sgr A*
Credit – NASA/JPL-Caltech/ESA/CXC/STSci

Andy Tomaswick

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