Why is this black hole so different? It may provide important clues to solve astronomical mysteries

The hunt is on for the second-closest supermassive black hole to Earth in a neighboring galaxy.

(Illustration: Leo 1, a dim companion galaxy of the Milky Way, may be hiding a huge supermassive black hole. Image source: Scott Anttila Anttler)

Astronomers may finally be able to find a giant supermassive black hole they suspect is lurking in a nearby dwarf galaxy.

This behemoth may be the second closest supermassive black hole to Earth after Sagittarius A at the center of the Milky Way, located in the companion galaxy Leo 1. This nearby supermassive black hole is called Leo 1. Its existence was first proposed in 2021 when astronomers noticed that stars accelerated as they approached the center of the dwarf galaxy. While this was good evidence in favor of the existence of a supermassive black hole, astronomers were disappointed to find that they could not directly obtain radiation images of Leo 1 to prove its existence.

Now two researchers have proposed a solution: "Black holes are very elusive objects, and they sometimes play hide-and-seek with us," Fabio Panucci, an astrophysicist at the Harvard Smithsonian Center for Astrophysics and the lead author of the study, said in the report. "Light cannot escape their event horizons, but the environment around them can become very bright - if enough matter falls into the gravity well. But if the black hole does not gain mass, on the contrary, it will not emit light and cannot be found by our telescopes."

Right now, the situation with Leo 1 is that the dwarf galaxy doesn't provide enough gas to feed a supermassive black hole, making it inactive and unconfirmed to exist. But Panucci and a colleague suggest that the black hole may be enjoying an alternative daily diet and has taken in enough matter to convince scientists of its existence.

"We propose that a small amount of mass lost from stars floating around the black hole could provide the metabolic rate data necessary to observe the black hole," Panucci said. "Old stars become very large and red - we call them red giants. Red giants often produce strong winds that carry a small amount of mass into the environment. The space around Leo 1 seems to hold enough ancient stars to allow for observation."

According to Avi Loeb, an astrophysicist also at the Harvard-Smithsonian Center for Astrophysics, if the high-tech technology works, the Leo 1 observations could be groundbreaking.

In particular, the discovery would solve another astronomical mystery: whether a dwarf galaxy could harbor such a large supermassive black hole. (Scientists estimate that Leo 1 is probably about three million times more massive than our sun; the Milky Way's black hole (Sgr A*) is only slightly larger, at about four million times more massive.)

"This could be the second-closest supermassive black hole to us after the center of our Milky Way, with a mass similar to our own, but from a galaxy a thousand times less massive than our own," Loeb said in the report. "This fact challenges our understanding of the co-evolution of galaxies and their central supermassive black holes. How could such a massive entity emerge from a tiny parent body?"

For example, the supermassive black holes at the center of the Milky Way and most galaxies have a mass about one-tenth that of the stars around them. The existence of the dwarf galaxy Leo 1 completely deviates from this ratio.

"In the case of LEO 1, we expected to see a smaller black hole," Loeb said. "However, LEO 1 showed a black hole that is several million times more massive than our sun, similar to the black holes in our Milky Way. This is exciting because science advances when the unexpected happens."

Panucci said astronomers still have a long way to go to characterize Leo 1, but he and his team have gained time with the space-based Chandra X-ray Observatory and the Very Large Array radio telescope in New Mexico to unravel the theoretical cosmic behemoth.

"Leo 1 is playing hide-and-seek with us, but it's emitting so much radiation that it leaves so many unsolved mysteries," Panucci said.

The team's research was published in a paper published Monday (November 28) in the Astrophysical Journal.

Related knowledge translation: A galaxy is a system composed of stars, stellar remnants, interstellar gas, dust, and dark matter, which are bound together by gravity. The word comes from the Greek galaxias (γαλαξίας), which literally means "milky", referring to the Milky Way that contains the solar system. Galaxies have an average of about 100 million stars, ranging from dwarf galaxies with less than 100 million stars to the largest known galaxies-supergiant systems with 100 trillion stars, each of which moves around the center of mass of the galaxy. Most of the mass of a typical galaxy is in the form of dark matter, and only a few percent of the mass is in the form of stars and nebulae. Supermassive black holes are common features in the centers of galaxies.

BY:Robert Lea

FY: Zhuohua

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