Recent research conducted by astronomers from the University of Southampton and an international team revealed that approximately 35% of supermassive black holes in the universe are concealed from view, an increase from previous estimates of 15%. The findings suggest that a vast population of these cosmic giants remains hidden, shrouded by thick clouds of gas and dust.
Using data from NASA's Infrared Astronomical Satellite (IRAS) and the Nuclear Spectroscopic Telescope Array (NuSTAR), scientists were able to peer through obscuring material to identify hundreds of probable hidden black holes. The combined infrared and high-energy X-ray observations were crucial in confirming the existence of numerous previously overlooked black holes, according to Science Magazine.
"This is the first time we have a highly refined census of black holes growing by consuming interstellar material surrounding them," said Professor Poshak Gandhi, a co-author of the study published in The Astrophysical Journal. "We've found that many more are lurking in plain sight—hiding behind dust and gas rendering them invisible to normal telescopes."
Supermassive black holes, which can have masses equivalent to millions or even billions of suns, are typically found at the centers of large galaxies, including the Milky Way. However, many remain hidden from view, making it difficult to confirm their presence.
"Even when hidden, the surrounding dust absorbs and re-emits this light as infrared radiation, revealing their presence," explained Professor Gandhi, as reported by Space.com. By analyzing the infrared emissions detected by IRAS, researchers could identify the heat signatures of the obscuring clouds around the black holes.
To confirm the existence of these hidden black holes, the team used NuSTAR, which can detect high-energy X-rays capable of penetrating thick gas clouds. "X-rays provide a complementary view peering through the veiling gas, much like a medical X-ray scan allows a doctor to peer through to our insides," said Gandhi, according to IFLScience.
The discovery of this vast population of hidden supermassive black holes has implications for understanding galaxy evolution. Determining the number of hidden black holes compared to known ones may help understand how they grow to such sizes. Feeding supermassive black holes can influence their host galaxies by affecting star formation rates through feedback mechanisms.
For instance, if too much material falls toward a black hole, it can "start coughing up the excess and firing it back out into the galaxy," producing galaxy-wide winds that snuff out star formation. This process can slow down or even halt the formation of new stars in the surrounding galaxy.
"If our galaxy, the Milky Way, did not have a supermassive black hole, we would see many more stars in the sky," said Gandhi. This suggests that black holes can limit a galaxy's size by drawing it toward a gravitational center or consuming vast quantities of star-forming dust.
"It amazes me how useful IRAS and NuSTAR were for this project, especially despite IRAS being operational over 40 years ago," said Peter Boorman, an astrophysicist at Caltech and study co-author. "This shows the value of the legacy of telescope archives and the benefit of using various instruments with different wavelengths of light."
The researchers believe that the techniques used in this study may help astronomers determine how common supermassive black holes are in the universe and understand their role in galaxy formation. The technique may even help scientists learn more about the heart of our own Milky Way and paint a better picture of how galaxies evolve.
The article was written with the assistance of a news analysis system.