MADRID, November 28 (EUROPA PRESS) –
Two astrophysicists at the Center for Astrophysics | Harvard and Smithsonian have suggested a way to look at what it could be the second closest supermassive black hole to Earth.
A giant 3 million times the mass of the Sun, housed in the Leo I dwarf galaxy, the black hole Leo I star, it was first proposed by an independent team of astronomers in late 2021. The team noted that the stars increased in speed as they got closer to the center of the galaxy (evidence for a black hole), but directly imaging 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 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.”
“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 get very big 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 star appears to contain enough of these stars old to be observable”.
“Looking at Leo I star could be innovative”, 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 they coevolve.” galaxies and their central supermassive black holes. 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 houses the Milky Way. This is exciting because science often 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 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.
Pacucci says: “Leo I star is playing hide-and-seek, but emits too much radiation to remain unnoticed for long.”