- Quasars and their embedded supermassive black holes are exceedingly bright. We often see them at very large distances, corresponding to a time in the early history of our universe.
- Quasar H1821+643 is the closest known quasar to Earth within a galaxy cluster. It’s about 3.4 billion light-years away. So we’re seeing it at a time not so long ago.
- This quasar’s supermassive black hole appears to be underachieving, despite having some attributes like the quasars in the early universe, such as powerful jets and high levels of radiation. It’s underachieving in the sense that it isn’t affecting its surroundings as much as astronomers expected it would.
The supermassive black hole in the center of our Milky Way galaxy is about 4 million times our sun’s mass. But the black hole embedded in quasar H1821+643 – 3.4 billion light-years away – is some 4 billion times our sun’s mass. As the closest quasar known within a galaxy cluster, H1821+643 was the focus of a new study performed in both X-rays and radio. Astronomers collaborated, using the Earth-orbiting Chandra X-ray Observatory and the Very Large Telescope, or VLT, in Chile. And, on March 21, 2024, upon releasing the results of their study, they called the black hole in H1821+643 an underachiever.
They said that, although this giant black hole is responsible for high levels of radiation and powerful jets, it’s not affecting its surroundings as greatly as many of its black hole counterparts in other galaxies.
The international team of researchers published their peer-reviewed findings in the Monthly Notices of the Royal Astronomical Society on January 27, 2024.
Closest quasar to Earth in a galaxy cluster
Quasars are extremely bright, up to 1,000 times brighter than our home galaxy, the Milky Way. The intense radiation from quasars is thought to be due to the supermassive black holes found at the hearts of most galaxies. Quasars in the early universe tend to be exceedingly “hungry.” They are pulling in material from their surroundings, creating conditions for high levels of radiation and powerful, superluminal jets.
But some supermassive black holes are pulling in surrounding material more slowly than others. They outburst energy on a regular basis, preventing the superheated gas that surrounds them from cooling down. This has two effects. One is the limiting of star formation in the host galaxy. The other is a limit on how much material the black hole consumes.
Underachieving black hole
But when it comes to supermassive black holes in quasars that are in galaxy clusters, like H1821+643, there is still a lot for astronomers to learn. And this black hole appears to be underperforming. As lead author Helen Russell of the University of Nottingham in the U.K. noted:
We have found that the quasar in our study appears to have relinquished much of the control imposed by more slowly growing black holes. The black hole’s appetite is not matched by its influence.
Overall, the new study suggests that quasars may have less influence on their host galaxy, and even the galaxy cluster, than previously thought.
Observing with Chandra
So, how did the researchers determine this? With Chandra, they looked at the hot gas that surround the black hole, quasar and host galaxy. The hot gas emits weak X-rays, while the X-rays from the quasar and black hole are much stronger. Strong enough that they obscured the astronomers’ observations of the gas X-rays. So the researchers had to remove the stronger X-rays from the composite images. In doing so, the researchers could measure how much influence the X-rays from the black hole and quasar had on its surroundings.
As it turned out, not that much. The density of hot gas was higher in the vicinity of the black hole and quasar, but the temperatures lower than expected. Why? The researchers said it’s because there are less outbursts of energy from the black hole than they thought there would be. Usually, those bursts would help prevent the gas from cooling down. But instead, the gas is cooling down and flowing toward the center of the galaxy cluster.
Most supermassive black holes have a much larger influence on their neighborhood. So this particular black hole is underperforming, you could say. As the paper described it,
The active galactic nucleus appears to be underheating the core of this cluster.
The paper also noted that the black hole may be undersized, or it may be going through a period of underheating. Additional observations may help to determine which is the case.
Bottom line: A black hole in a quasar 3.4 billion light-years away is powerful but underachieving, according to astronomers using NASA’s Chandra X-ray Observatory.
Source: A cooling flow around the low-redshift quasar H1821+643
Read more: What are black holes?
Read more: Closest black holes yet in famous Hyades star cluster?
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