Two astrophysicists from the Harvard-Smithsonian Center for Astrophysics have proposed a way to observe the second-closest supermassive black hole to Earth: a giant black hole 3 million times the mass of the Sun in the dwarf galaxy Leo I. A supermassive black hole I* named Leo was first proposed by an independent group of astronomers at the end of 2021. The team observed that stars accelerate as they approach the center of the galaxy, suggesting the presence of a black hole, but directly viewing the radiation from the black hole was impossible.

Now CfA astrophysicists Fabio Pacucci and Avi Loeb propose a new way to test for the existence of a supermassive black hole; Their work is described in a study published today. Astrophysical Journal Letters.

“Black holes are very elusive objects and sometimes they like to play hide and seek with us,” says Fabio Pacucci, lead author of the ApJ study. Literature. “Light rays cannot travel beyond the event horizon, but the environment around them can be extremely bright if enough material falls into the gravitational wells. But if a black hole does not form mass, it will instead emit light and become impossible to find with our telescopes.”

That’s the problem with Leo I, a gas-deprived dwarf galaxy ready to collect, often referred to as a “fossil.” So shall we despair of observing it? Maybe not, say astronomers.

“In our study, we hypothesized that the small amount of mass lost by stars orbiting a black hole could provide the accretion rate necessary to observe it,” explains Pacucci. “Older stars become very large and red—we call them red giants. Red giants typically have strong winds that carry some of their mass into the environment. The space around Leo I* seems to contain enough of these older stars to make it observable.”

“Observing Leo I* can be groundbreaking,” says study co-author Avi Loeb. “This will be the second-closest supermassive black hole located at the center of our galaxy, after the black hole in a galaxy with a very similar mass but a thousand times smaller than the Milky Way. This fact questions everything we know about it. “How massive black holes evolve together. How can a child this big be born from a weak father?”

Decades of research have shown that the largest galaxies have a supermassive black hole at their centers, and the black hole’s mass is only one-tenth of the total mass of the stellar sphere that surrounds it.

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

So when can we expect the appearance of a black hole?

“We haven’t gotten to that point yet,” Pacucci says.

The team received telescope data from the Chandra X-ray Observatory and the Very Large Array Radio Telescope in New Mexico and is currently analyzing the new data. “Leo I* plays hide and seek, but it emits too much radiation to go unnoticed for a long time,” Pacucci says.