Researchers Discover Supermassive Black Hole in Neighboring Galaxy

A team of Harvard astrophysicists discovered a supermassive black hole at the center of the Large Magellanic Cloud, the Milky Way’s closest galactic neighbor.

The research, published in January in the Astrophysical Journal, challenges long-standing assumptions about the origins of hypervelocity stars and concludes that the Large Magellanic Cloud harbors a black hole with a mass of approximately 600,000 solar masses.

Previously, researchers thought that hypervelocity stars — stars moving at extreme speeds — signified an interaction with Sagittarius A*, the black hole located in the center of our Milky Way galaxy. That was until Jiwon “Jesse” Han, a fourth-year graduate student at the Harvard-Smithsonian Center for Astrophysics, noticed that one of these hypervelocity stars was not headed towards the galaxy center.

“I realized that one of the stars wasn’t going to the galaxy center, and that was sort of the beginning of this new and different project. So, I just took all the stars and checked if these actually all went to the galactic center and it turns out they didn’t,” Han, the lead author of the study said. “Half of them tracked through our galactic center, and then the other half went to our nearest galaxy, the Large Magellanic Cloud.”

“That was a big aha moment for us, of like, ‘oh, wait a second, we could be learning about the LMC here, not just our own galaxy,’” said Scott A. Lucchini, another researcher on the project and a postdoctoral fellow at the Center For Astrophysics.

To confirm his hypothesis of the LMC origin of the hypervelocity stars, Han collected data about the 3D locations and velocities of the stars, then ran a series of simulations and compared the two data sets to learn more about the mass of the black hole. Using Newton’s Laws of Motion, Han was able to track the past trajectory of these hypervelocity stars.

Not only did the research answer the question of where the stars came from, but whether “our closest galactic neighbor,” as Han called it, would have a supermassive black hole at its center.

“This in particular has been an open question as long as we’ve known the LMC’s existence,” Han said. “So it’s a very old question, and I think the answer is yes, and I think that's a significant answer.”

Warren R. Brown, an astrophysicist at the Smithsonian Astrophysical Observatory and a collaborator on the study, said that astronomers have long theorized about the presence of black holes in dwarf galaxies but had lacked direct observational evidence, until Han’s observation.

“It was Jesse that pointed out that one cause of that could be the signature that you’d expect of these high-velocity stars escaping the Large Magellanic Cloud,” Brown said.

Han said that despite all they’ve learned, “the most important question” of the black hole’s location has yet to be answered.

“We can basically prove the existence of it, but we don't know where it is, and the obvious follow-up work is to identify it, and X-ray photons and radio waves, and pinpoint it, just like we have done with our galactic center,” Han said.

This discovery offers a new avenue for studying black holes beyond our own galaxy. Other potential follow-up studies include further investigating the characteristics of the LMC’s central black hole, and whether similar black holes exist in other nearby dwarf galaxies.

“As long as it involves that level of creativity and agency in your work, I think that’s what really keeps it fun,” Han said. “And sometimes, at the end of the day, you discover a supermassive black hole.”

—Staff writer David D. Dickson can be reached at david.dickson@thecrimson.com.

—Staff writer Ella F. Niederhelman can be reached at ella.niederhelman@thecrimson.com.