Astronomers at Newcastle University and Colby College have developed a new technique to determine how likely it is that two galaxies are very close together and are expected to collide in the future. They’ve applied this method to hundreds of thousands of galaxies in the distant Universe in an attempt to better understand the so-called cosmic noon, a time when most of the Universe’s galaxy and black hole growth is expected to have taken place.
Dust-obscured supermassive black holes are more likely to grow and release tremendous amounts of energy when they are inside colliding galaxies. Image credit: University of Hawai’i at Mānoa.
Supermassive black holes grow by accreting gas that falls on to them. However, what drives the gas close enough to the black holes for this to happen is an ongoing mystery.
One possibility is that when galaxies are close enough together, they are likely to be gravitationally pulled towards each other and merge into one larger galaxy.
In the final stages of its journey into a black hole, gas lights up and produces a huge amount of energy. This energy is typically detected using visible light or X-rays.
However, Newcastle University astronomer Chris Harrison and colleagues were only able to detect the growing black holes using infrared light.
They analyzed data from many different telescopes, including the NASA/ESA Hubble Space Telescope and NASA’s Spitzer Space Telescope.
They developed a new technique to determine how likely it is that two galaxies are very close together and 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 formed 2 to 6 billion years after the Big Bang) in an attempt to better understand the so-called cosmic noon.
Understanding how black holes grew during this time is fundamental in modern day galactic research, especially as it may give us an insight into the supermassive black hole situated inside the Milky Way, and how our galaxy evolved over time.
As they are so far away, only a small number of cosmic noon galaxies meet the required criteria to get precise measurements of their distances.
This makes it very difficult to know with high precision if any two galaxies are very close to each other.
“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,” said Newcastle University astronomer Sean Dougherty.
Data arriving from the NASA/ESA/CSA James Webb Space Telescope over the coming years is expected to revolutionize studies in the infrared and reveal even more secrets about how these dusty black holes grow.
“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,” Dr. Harrison said.
“But these same black holes can be found using infrared light, which is produced by the hot dust surrounding them.”
“The difficulty in finding these black holes and in establishing precise distance measurements explains why this result has previously been challenging to pin down these distant ‘cosmic noon’ galaxies.”
“With Webb we are expecting to find many more of these hidden growing black holes.”
“Webb 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 findings were published in the Monthly Notices of the Royal Astronomical Society.
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Sean L. Dougherty et al. Obscured AGN enhancement in galaxy pairs at cosmic noon: evidence from a probabilistic treatment of photometric redshifts. MNRAS, published online May 8, 2023; doi: 10.1093/mnras/stad1300
