A team led by UC Berkeley astronomers discovered what may be the first free-floating black hole found in the Milky Way galaxy.

However, according to researcher and campus associate professor of astronomy Jessica Lu, the data collected by the team was not entirely consistent with black holes. This suggests OB110462, the object the team identified, could also be a neutron star.

OB110462 was discovered through gravitational microlensing, which is a method used to discover objects with a strong gravitational field because they distort and briefly brighten the light of a distant background star, according to a campus press release.

“But not just black holes act as gravitational lenses,” Lu said in an email. “Anything with mass can lens a background star, including stars themselves or even planets.”

After studying the metrics from five microlensing occurrences, the team found that OB110462 appeared to be a “compact object,” a stellar remnant such as a neutron star or black hole, according to the campus press release. Lu added that additional measurements from the Hubble Space Telescope and more complicated models by the team will help clarify whether the mass is a neutron star or a black hole.

Lu also said that there is another team researching the object. According to the campus press release, the teams had discrepancies in the motions of foreground and background objects, and the other team strictly identified the mass as a black hole.

“In science, it is always good to have independent teams working on the same problem to be sure we get to the truth,” Lu said in the email. “While both teams are confident we have a dark, free-floating compact object, time – and new data – will tell whether it is definitely a black hole.”

However, Lu stated that the collection of astrometric data — which is important to the understanding of black holes — is often limited due to technological constraints and long telescope time.

Lu said in the email that finding more black holes requires advances in engineering, data science, statistical modeling and computation in order to improve telescope imaging and simulations of the galaxy’s population of black holes. 

The discovery has led the team to predict there are an estimated 100 million black holes in the Milky Way galaxy — one of which is likely 70-120 light-years from Earth, according to Lu.

Lu added that the more black holes the team discovers, the easier it will be to pinpoint the distance of the black holes from Earth.

“There are so many basic questions we still don’t know about the population of black holes in our own Milky Way,” Lu said in the email. “So there is a lot of work for astronomers to do at this frontier.”

Anna Armstrong and Ananya Rupanagunta contributed to this report.