They suggest how to observe the second closest supermassive black hole to Earth

Three million times the mass of the Sun. That is what a black hole housed in the Leo I dwarf galaxy occupies. Its discovery was made at the end of 2021 by an independent team of astronomers and now two astrophysicists suggest a way to look at it.

The group that discovered it last year identified how the stars increased their speed as they approached the center of the galaxy, which is a evidence of the presence of a black hole. Now, CfA astrophysicists Fabio Pacucci and Avi Loeb suggest a new way to verify the existence of this supermassive black hole in a study published in the journal Astrophysical Journal Letters.

«Black holes are very elusive objects and sometimes they enjoy playing hide-and-seek with us,” says Fabio Pacucci, lead author of the study. “Light rays cannot escape their event horizons, but the environment around them can be extremely bright, if enough material falls into their gravitational well. But if a black hole accumulates no mass, instead it emits no light and becomes impossible to find with our telescopes.”

This is the challenge with Leo I, a dwarf galaxy so devoid of gas available to accumulate that it is often described as a “fossil.” The researchers suggest that a small amount of mass lost by stars wandering through the black hole could provide the accretion rate needed to observe it.

Doing so would be “groundbreaking” as it is the second closest supermassive black hole to Earth after the one at the center of our galaxy. The rarity of this one is that it has a mass very similar to that housed in the Milky Way, but it is a thousand times less massive than ours.

“In the case of Leo I,” Loeb continues, “we would expect a much smaller black hole. Instead, appears to contain a black hole several million times the mass of the Sun, similar to the one that houses the Milky Way. This is exciting because science often advances further when the unexpected happens.”

When asked when we can expect an image of the black hole, Pacucci answers that we still “we have not arrived”. The team has obtained observing time at the Chandra X-ray Space Telescope and the Very Large Array Radio Telescope in New Mexico and is currently analyzing the new data.