Astrophysicists hunt for second-closest supermassive black hole to Earth

The Milky Way's companion galaxy, Leo I, appears as a faint blob to the right of the bright star, Regulus. Credit: Scott Anttila Anttler.
Decades of studies show that most massive galaxies harbor a supermassive black hole at their center, with the mass of the black hole being one tenth of the total mass of the surrounding spheroid of stars.
Two astrophysicists from the Center for Astrophysics | Harvard and the Smithsonian have proposed a method to observe what could be the second-closest supermassive black hole to Earth. The supermassive black hole, which is home to the Leo I dwarf galaxy, has a mass three million times that of the Sun.
The Leo I* supermassive black hole was first proposed by an independent team of astronomers in late 2021. The astronomers observed that the stars gained speed as they approached the center of the galaxy, but it was impossible to directly image the galaxy. emission from the black hole.
Now, CfA physicists Fabio Pacucci and Avi Loeb propose a new method to confirm the presence of the supermassive black hole.
Fabio Pacucci, lead author of the ApJ Letters study, said: "Black holes are very elusive objects, and sometimes they like to play hide-and-seek with us. Light rays cannot escape their event horizons, but the environment around them surrounding it can be extremely bright, if enough material falls into its gravitational well. But if a black hole isn't accumulating mass, it emits no light and is impossible to find with our telescopes."
"This is the challenge of Leo I, a dwarf galaxy so devoid of gas available for accretion that it is often described as a 'fossil'. So should we give up any hope of observing it? Perhaps not."

"In our study, we suggest that a small amount of mass lost by stars wandering around the black hole could provide the accretion rate needed to observe it. Old stars become very large and red, which we call red giant stars. "Red giants often have strong winds that carry a fraction of their mass into their surroundings. The space around Leo I* appears to contain enough of these ancient stars to make it observable."