JWST reveals surprising scarcity of supermassive black holes

Using the James Webb Space Telescope, a team of astronomers peered roughly 10 billion years into the past to look for hidden supermassive black holes.
Chris Young
An artist's impression of a black hole.
An artist's impression of a black hole.

Pitris / iStock 

A team of astronomers used the James Webb Space Telescope (JWST) to discover that the early universe was between 4 and 6 billion years old and had fewer supermassive black holes than previously believed.

The team used Webb to study a region of space known as the Extended Groth Strip, near the Big Dipper constellation. The well-known region contains an estimated 50,000 galaxies, and it is the first time it has been studied by an observatory as powerful as JWST.

Using Webb, they could peer behind dust clouds and shed new light on ancient black holes. They were also surprised to encounter far fewer in their observations than anticipated.

James Webb continues to peer further than ever before

In a press statement released by the University of Kansas, Allison Kirkpatrick, team leader, explained that "our observations were taken in last June and December, and we were aiming to characterize how galaxies looked during the heyday of star formation in the universe. This is a look back in time of 7 to 10 billion years in the past."

The team used Webb's Mid-Infrared Instrument (MIRI) instrument to peer behind dust in galaxies that existed up to 10 billion years ago. They published their findings in a new paper in preprint server ArXiv.

Surprisingly, the team found far fewer active galactic nuclei than they expected. An active galactic nucleus, or AGN, is a type of supermassive black hole that heats the surrounding material it is "eating", creating massive amounts of radiation. They are so bright they often outshine all the stars in their host galaxy.

As Webb can peer much further into the past, the team expected to find many new AGNs compared to previous surveys of the same region. Instead, they only discovered a handful of previously unobserved AGNs.

"The results looked completely different from what I had anticipated, leading to my first major surprise," Kirkpatrick explained. "One significant revelation was the scarcity of rapidly growing supermassive black holes. This finding was prompting questions about the whereabouts of these objects."

Kirkpatrick added that previous growth rates for supermassive black holes, based on observations of the region by the Spitzer Space Telescope, may have been overstated because the telescope only allowed astronomers to observe the brightest and fastest-growing examples.

Shedding new light on Sagittarius A*

The new findings suggest that the early universe may have been more stable than previously thought.

"The study's findings suggest that these black holes are not growing rapidly, absorbing limited material, and perhaps not significantly impacting their host galaxies," Kirkpatrick said. "This discovery opens up a whole new perspective on black-hole growth since our current understanding is largely based on the most massive black holes in the biggest galaxies, which have significant effects on their hosts, but the smaller black holes in these galaxies likely do not."

The researchers believe the new findings may also shed new light on the evolution of our galaxy, the Milky Way.

Astronomers have wondered whether it may have once had an AGN at its heart. The new research doesn't provide a conclusive answer, but it hints at the Milky Way's ancient past.

The black hole at the center of our galaxy, Sagittarius A*, is known to swallow surrounding matter at an incredibly slow pace.

"Our black hole seems quite uneventful, not displaying much activity. One significant question regarding the Milky Way is whether it was ever active or went through an AGN phase," Kirkpatrick continued. "If most galaxies, like ours, lack detectable AGN, it could imply that our black hole was never more active in the past. 

"Ultimately, this knowledge will help constrain and measure black hole masses, shedding light on the origins of black holes growing, which remain an unanswered question," she added.

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