Astronomers have found that dust-obscured supermassive black holes are likely to grow and release huge amounts of energy when inside galaxies that are expected to collide with a neighboring galaxy. The new work, led by researchers from the University of Newcastle, has been published in the journal Monthly Notices of the Royal Astronomical Society.
Galaxies, including our own Milky Way, contain supermassive black holes at their centers. They have a mass equivalent to millions or even billions of times that of our sun. These black holes grow by “eating” the gas that falls on them. However, what drives gas near black holes to cause this to happen is an ongoing mystery.
One possibility is that when galaxies are close enough to each other, they are likely to be gravitationally pulled toward each other and “merge” into one larger galaxy.
In the final stages of its journey to the black hole, the gas lights up and releases a huge amount of energy. This energy is usually detected using visible light or x-rays. However, the astronomers who conducted this study were only able to detect the growing black holes using infrared light. The team used data from many different telescopes, including the Hubble Space Telescope and the infrared Spitzer Space Telescope.
Researchers have developed a new technique to determine how likely it is that two galaxies that are so close together are expected to collide in the future. They applied this new method to hundreds of thousands of galaxies in the distant universe (looking at galaxies that formed 2 to 6 billion years after the Big Bang) in an effort to better understand the so-called “cosmic noon”, a time when most of the expected The occurrence of growth in the galaxy of the universe and the black hole.
Understanding how black holes grew during this time is key to modern galactic research, especially because it could give us insight into the supermassive black hole residing within the Milky Way, and how our galaxy has evolved over time.
Being so far away, only a few of the noonday cosmic galaxies meet the criteria required to obtain accurate measurements of their distances. This makes it very difficult to tell with high accuracy whether any two galaxies are very close together.
This study presents a new statistical method to overcome previous limitations of measuring the exact distances of galaxies and supermassive black holes in the cosmic noon. It applies a statistical approach to determining the distances of galaxies using images at different wavelengths and removes the need for spectral distance measurements for individual galaxies.
Data from the James Webb Space Telescope over the coming years are expected to revolutionize infrared studies and reveal more secrets about how these dusty black holes grow.
“Our new approach looks at hundreds of thousands of distant galaxies with a statistical approach and asks how likely it is that any two galaxies are close together and very likely to be on a collision course,” says Sean Dougherty, a postgraduate student at the University of Newcastle and lead author of the paper.
Chris Harrison, co-author of the study, states, “These supermassive black holes are very difficult to find because the X-ray light, which astronomers typically use to find these growing black holes, is blocked, and is not detected by our telescopes. But these black holes themselves can be found.” It uses infrared radiation, which is produced by the surrounding hot dust.
He adds: “The difficulty in finding these black holes and in making accurate measurements of the distances explains why this finding has been so difficult previously in identifying distant cosmic noon galaxies. With the JWST we expect to find more of these hidden growing black galaxies. The holes. The JWST will be much better at finding them.” “So we’ll have a lot more to study, including the hard-to-find ones. From there, we can do more to understand the dust that surrounds them, and find out how many are hidden in distant galaxies.”
Sean L. Dougherty et al., AGNs in galaxy pairs are obscured at the cosmic noon: Evidence from probabilistic manipulation of optical redshifts, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad1300
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