Title: Supermassive Black Holes Hidden by Dust are More Likely to Grow and Release Tremendous Energy During Galaxy Collisions, New Research Reveals
Subtitle: Newcastle University Study Sheds Light on the Growth of Dust-Enshrouded Black Holes in Distant Galaxies
Date: May 8, 2023
Scientists from Newcastle University have uncovered new evidence suggesting that supermassive black holes concealed by dust have a higher probability of growing and emitting immense amounts of energy when their host galaxies are expected to collide with neighboring galaxies. The findings, published in the Monthly Notices of the Royal Astronomical Society, contribute to a better understanding of the evolution of galaxies and the role of black holes within them.
Supermassive black holes, which possess masses millions or even billions of times greater than that of our Sun, reside at the center of galaxies, including our own Milky Way. These black holes enlarge their size by devouring gas that spirals into them. However, what triggers the gas to approach close enough to be consumed by the black holes, has long puzzled astronomers.
One possibility explored by the researchers is that when two galaxies come into close proximity, their gravitational forces cause them to merge and form a larger galaxy. During the final stages of this merging process, the gas ignites and generates an enormous amount of energy. Traditionally, this energy has been detected using visible light or X-rays. However, the team behind the recent study could only observe the growing black holes by analyzing the infrared light emitted from them. To do so, the researchers utilized data obtained from various telescopes, including the Hubble Space Telescope and the infrared Spitzer Space Telescope.
Developing a novel technique, the scientists were able to gauge the likelihood of two galaxies being in close proximity and on a trajectory to collide. This methodology was subsequently applied to hundreds of thousands of galaxies in the distant universe, observing galaxies that formed between 2 to 6 billion years after the Big Bang. The aim was to gain deeper insights into the “cosmic noon,” a pivotal period when significant galaxy and black hole growth is believed to have occurred.
Understanding the growth of black holes during this phase is crucial for modern galactic research, as it could provide invaluable insights into the supermassive black hole residing within our Milky Way and the evolution of our own galaxy.
Due to their considerable distance, only a small number of the observed cosmic noon galaxies met the criteria necessary for precise distance measurements. Consequently, accurately determining whether two galaxies are in close proximity became an arduous task.
Nonetheless, the research team introduced a new statistical approach to overcome this limitation. They leveraged images captured at various wavelengths and used a statistical analysis to determine the distances between galaxies, negating the need for spectroscopic distance measurements for individual galaxies.
Furthermore, the upcoming James Webb Space Telescope (JWST) is anticipated to revolutionize infrared studies and unlock more mysteries concerning the growth of these enigmatic dust-shrouded black holes.
Lead author of the study and Newcastle University postgraduate student, Sean Dougherty, explained, “Our novel approach looks at hundreds of thousands of distant galaxies with a statistical approach and asks how likely any two galaxies are to be close together and so likely to be on a collision course.”
Co-author Dr. Chris Harrison emphasized the challenges faced in locating these supermassive black holes, “These supermassive black holes are very challenging to find because the X-ray light, which astronomers have typically used to find these growing black holes, is blocked and not detected by our telescopes. But these same black holes can be found using infrared light, which is produced by the hot dust surrounding them.”
Dr. Harrison added, “With the JWST, we are expecting to find many more of these hidden growing black holes. JWST will be far better at finding them; therefore, we will have many more to study, including ones that are the most difficult to find. From there, we can do more to understand the dust that surrounds them and find out how many are hidden in distant galaxies.”
The study titled “Obscured AGN enhancement in galaxy pairs at cosmic noon: evidence from a probabilistic treatment of photometric redshifts” was authored by Sean L Dougherty, C M Harrison, Dale D Kocevski, and D J Rosario.
Reference: Dougherty, S. L., Harrison, C. M., Kocevski, D. D., & Rosario, D. J. (2023). Obscured AGN enhancement in galaxy pairs at cosmic noon: evidence from a probabilistic treatment of photometric redshifts. Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stad1300.