Supermassive black holes are much more common in the universe than believed

There are objects in our universe so dense that not even light escapes through them. These oddities, known as supermassive black holes, can weigh billions of times more than our sun.

Scientists have long known that such behemoths lurk in galactic centers. Yet new results indicate that 35% of these giants may be obscured by heavy blankets of dust, rather than the 15% that was previously estimated.

Detecting supermassive black holes

Professor Poshak Gandhi from the University of Southampton is a co-author of the analysis. Researchers believe their deeper census has broad implications for galaxy evolution.

They studied hidden black holes using data from NASA’s InfraRed Astronomy Satellite and the NuSTAR X-ray telescope, operated by NASA/JPL.

By comparing infrared and X-ray signals, they uncovered powerful sources that had slipped past earlier surveys.

Supermassive black holes – the basics

Supermassive black holes are colossal cosmic objects found at the centers of most galaxies, including Sagittarius A* in our Milky Way.

Unlike their stellar-mass cousins, which form from collapsing stars, supermassive black holes tip the scales at millions to billions of times the mass of our Sun.

Despite their enormous mass, they occupy relatively compact regions in space. Scientists believe they formed in the early universe, possibly from the merging of smaller black holes and dense gas clouds.

Over billions of years, they grew by devouring nearby matter and merging with other black holes during galactic collisions.

These black holes exert an immense gravitational pull, influencing the behavior of stars, gas, and even entire galaxies around them.

When matter spirals into a supermassive black hole, it heats up and emits powerful radiation, creating phenomena like quasars – some of the brightest objects in the universe.

Why many black holes were missed

“Black holes are the most mysterious objects in the universe and are present everywhere – yet we still don’t fully know how they evolve. If we didn’t have a supermassive black hole in our Milky Way galaxy, there might be many more stars in the sky,” said Prof. Gandhi.

Some black holes fuel active galaxies. Others lurk in silence. But even quiet ones leave clues, if we know where to look.

By looking at how gas and dust emit light after being heated, the researchers were able to spot many more black holes. These black holes glow brightly with infrared radiation, even if the dust hides their visible light.

Supermassive black holes affect galaxies

The research team showed that supermassive black holes don’t just sit there. They actively shape their galaxies.

“Black holes also influence the galaxies they live in, this happens because they are surrounded by massive clouds of gas and dust and can consume vast amounts of material,” explained Dr. Peter Boorman, the study’s lead author and a researcher at Caltech in Pasadena, California.

When a black hole takes in more matter than it can handle, it ejects the surplus back into the galaxy. This outflow can scatter the gas clouds where new stars are forming, ultimately reducing the galaxy’s star formation rate.

The gas blown outward can stop new stars from forming. So the galaxy’s future depends, in part, on how the black hole behaves.

How they spotted the hidden ones

“Though black holes are dark, surrounding gas heats up and glows intensely, making them some of the brightest objects in the universe,” explained Prof. Gandhi.

Most traditional telescopes can’t see through dense gas. That’s where X-rays and infrared come in.

Even when obscured, surrounding dust absorbs the light and re-emits it as infrared radiation, making these objects detectable.

X-rays offer a complementary perspective, penetrating the veiling gas much like a medical X-ray reveals structures inside the human body.

That combination of data helped the team update their census. They now believe over a third of growing black holes may be hidden in plain sight.

Why this matters now

This shift changes more than just numbers. It changes how we model the life cycle of galaxies and the role that supermassive black holes play in shaping them.

Each black hole’s appetite affects the material around it. If it eats too fast, it might blast gas outward. That gas is the same stuff new stars need in order to form.

And since the process of feeding and ejecting happens over long timescales, it could explain why some galaxies suddenly stop making stars.

Earlier work underestimated the number of obscured black holes. This new count shows we were missing a large piece of the puzzle.

What’s next for black hole research

The team’s work fits into a growing effort to understand what’s going on behind the dust. New surveys, will take this further by combining X-ray, optical, and infrared data over large portions of the sky.

Scientists hope to identify even more hidden black holes and understand how they affect their host galaxies.

In the meantime, researchers know one thing: black holes are even more common than we thought. And the tools we use to find them matter just as much as the theories we build around them.

The study is published in The Astrophysical Journal.

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