Supermassive black holes have masses of more than a million suns – but their growth has slowed as the universe has aged

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Supermassive ****** holes have masses of more than a million suns – but their growth has slowed as the universe has aged

****** holes are remarkable astronomical objects with

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that nothing, not even light, can escape them. The most gigantic ones, known as “supermassive” ****** holes, can weigh millions to billions times the mass of the Sun.

These giants

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. Our own galaxy, the Milky Way,

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in its heart as well.

So, how do these supermassive ****** holes become super massive? To answer this question,

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looked back in time across the universe’s 13.8 billion-year history to track how supermassive ****** holes have grown from the early days to today.

We constructed a model of the

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of supermassive ****** holes spanning the past 12 billion years.

How do supermassive ****** holes grow?

Supermassive ****** holes grow primarily in two ways. They can consume gas from their host galaxies in

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, and they can also

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when two galaxies collide.

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An artist’s illustration of an accreting supermassive ****** *****. The central ****** ***** is ******, while its surrounding gas heats up and shines to produce light. Nahks Tr’Ehnl (Penn State)

When supermassive ****** holes consume gas, they

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, a type of high-energy light invisible to the ****** eye. You’ve probably heard of X-rays at the dentist, where they are sometimes used to examine your teeth.

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generally have lower energies than medical X-rays.

So how can any light, even invisible X-rays, escape from ****** holes? Strictly speaking, the light is not coming from the ****** holes themselves, but from the gas just outside them. When gas gets pulled toward a ****** *****, it heats up and shines to produce light, like X-rays. The more gas a supermassive ****** ***** consumes, the more X-rays it will produce.

Thanks to the data accumulated over more than 20 years from three of the most powerful X-ray facilities ever launched into space –

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,

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and

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– astronomers can capture X-rays from a large number of accreting supermassive ****** holes in the universe.

This data allows our research team to estimate how fast supermassive ****** holes grow by consuming gas. On average, a supermassive ****** ***** can consume enough gas to amount to about

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each year, with the exact value depending upon various factors.

For example,

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that a ****** *****’s growth rate, averaged over millions of years, is strongly connected to the mass of all the stars in its host galaxy.

How often do supermassive ****** holes merge?

Besides feeding on gas, supermassive ****** holes can also grow by merging with each other to form a single, more massive ****** ***** when galaxies collide.

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can predict about how often these events happen. These simulations aim to model how the universe grows and evolves over time. The countless galaxies flying through space are kind of like bricks, building up the universe.

These

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galaxies and the supermassive ****** holes they host can undergo multiple mergers across the span of cosmic history.

Our team has tracked these two growth channels – gas consumption and mergers – using X-rays and supercomputer simulations, and then combined them to construct this overall growth history, which maps the growth of ****** holes across the universe over billions of years.

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that supermassive ****** holes grew much faster billions of years ago, when the universe was younger.

Back in the early days, the universe contained more gas for supermassive ****** holes to consume, and supermassive ****** holes kept emerging. As the universe aged, the gas was gradually depleted, and supermassive ****** ***** growth slowed. About 8 billion years ago, the number of supermassive ****** holes stabilized. It hasn’t increased substantially since then.

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An illustration of a merger of two supermassive ****** holes. Scott Noble (NASA GSFC)

When there isn’t enough gas available for supermassive ****** holes to grow by accretion, the only way for them to get larger is through mergers. We didn’t see very many cases of that in our growth history. On average, the most massive ****** holes can accumulate mass from mergers at a rate up to the mass of the Sun every several decades.

Looking forward

This research has helped us understand how over 90% of the mass in ****** holes has accumulated over the past 12 billion years.

However, we still need to investigate how they grew in the

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to explain the remaining few percentages of the mass in ****** holes. The astronomical community is starting to make progress exploring these early supermassive ****** holes, and we hope to find more answers soon.

This article is republished from

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, a nonprofit, independent news organization bringing you facts and analysis to help you make sense of our complex world.

It was written by:

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,

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and

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,

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.

Read more:

Fan Zou receives funding from the U.S. National Science Foundation, the Chandra X-ray Center and Penn State.

W. Niel Brandt receives funding from the U.S. National Science Foundation, the Chandra X-ray Center, and Penn State.

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#Supermassive #****** #holes #masses #million #suns #growth #slowed #universe #aged

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