Astrophysicists search for the second-closest supermassive black hole

The ultra-faint companion galaxy to the Milky Way, Leo I, appears as a faint patch to the right of the bright star, Regulus. Credit: Scott Anttila Asta

Two astrophysicists at the Harvard-Smithsonian Center for Astrophysics have suggested a way to observe what could be the second-closest supermassive black hole to Earth: a giant 3 million times the mass of the Sun, hosted by the dwarf galaxy Leo I.

The supermassive black hole, labeled Leo I*, was first proposed by an independent team of astronomers in late 2021. The team noted that stars increased in speed as they approached the center of the galaxy (evidence for a black hole), but emitting images directly from the black hole was not possible.

Now CfA astrophysicists Fabio Pacucci and Avi Loeb suggest a new way to verify the existence of the supermassive black hole; their work is described in a study published today in the 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 Letters ApJ to 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.” So will we give up any hope of observing it? Maybe not, astronomers say.

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

“Looking at Leo I* could be groundbreaking,” says Avi Loeb, co-author of the study. “It would be the second closest supermassive black hole after the one at the center of our galaxy, with a very similar mass but housed in a galaxy a thousand times less massive than the Milky Way. This fact challenges everything we know about how galaxies and their central supermassive black holes coevolve. How did such a big baby end up being born to a skinny father?

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 a percent of the total mass of the surrounding spheroid of stars.

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

So when can we expect an image of the black hole?

“We’re not there yet,” says Pacucci.

The team has obtained the time from the telescope at the space-borne Chandra X-ray Observatory and the Very Large Array radio telescope in New Mexico and is currently analyzing the new data.

Pacucci says, “Leo I* is playing hide-and-seek, but he’s emitting too much radiation to stay unnoticed for long.”

More information:
The accumulation of RGB star winds may reveal the supermassive black hole in Leo I, The letters of the astrophysical journal (2022). DOI: 10.3847/2041-8213/ac9b21

Provided by the Harvard-Smithsonian Center for Astrophysics

Citation: Astrophysicists Search for Second Closest Supermassive Black Hole (November 28, 2022) Accessed November 28, 2022 at hole.html

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