How the universe's first black holes changed cosmic history

New observations from the James Webb Space Telescope reveal that some of the earliest supermassive black holes launched winds powerful enough to sweep gas clean out of their host galaxies. Dr Tiago Costa, NUAcT Fellow in the School of Mathematics, Statistics, and Physics, explains why many of the Universe's first massive galaxies stopped forming stars far earlier than expected.

Contents:

1. The first supermassive black holes...
2. When black holes outshine galaxies
3. What is a quasar?
4. Using JWST to put theory to the test
5. No gas today, no stars tomorrow
6. A new chapter in galaxy evolution
7. Looking back to understand today's universe

The first supermassive black holes...

Today's universe is relatively quiet, with the peak of cosmic star formation around ten billion years ago now well behind us.

In contrast, the early universe was a hive of activity. Galaxies were assembling rapidly out of cosmic gas and colliding with one another at an extraordinary rate. Stars were forming at a remarkable pace — typical galaxies churned out stars at a rate of tens to hundred times faster than the Milky Way does today — and the first supermassive black holes ballooned, some attaining astonishing masses equivalent to more than a billion suns within one billion years from the Big Bang.

Yet astronomers have long puzzled over a strange pattern. Some of these young galaxies seemed to ‘retire’ almost as soon as they got going, with unexpectedly massive galaxies shutting down star formation within the universe's first two billion years.

But excitingly, an international team including myself has now uncovered a key piece of the puzzle.

When black holes outshine galaxies

While black holes themselves emit no light, the material falling into them can give rise to some of the brightest sources in the universe, known as ‘active galactic nuclei’. As gas spirals toward a supermassive black hole, it heats to millions of degrees and radiates copious amounts of energy across the spectrum. The most luminous of these nuclei are referred to as quasars.

One of the main objectives of the James Webb Space Telescope (JWST) is to understand how galaxies came to host supermassive black holes, and how these may, in turn, influence their host galaxies across cosmic time.

The JWST serves thousands of astronomers around the world. It studies multiple critical stages in the history of our universe, from the first galaxies forming after the Big Bang to the evolution of our own solar system. The space-based telescope follows a complex path that combines an orbit around the Sun with a continuous loop around a point in space where the combined gravity of the Sun and Earth keeps it in position.

Using JWST, the team found that powerful winds driven by quasars were far more common, and far more violent, in the early universe than previously thought.

Rendering of the James Webb Space Telescope (JWST).

What is a quasar?

Quasars are the brightest active galactic nuclei in the universe. Through a telescope, a quasar  looks like a simple, faint point of light at first glance, a bit like an ordinary star. But in reality, it's an intricate, luminous system: a dark heart — the supermassive black hole — encircled by a swirling disc of gas which spirals inward.

Quasars don't just shine, they interact violently with their host galaxies. For decades, astrophysicists have suspected that a quasar's radiation could drive vast streams of gas out of its parent galaxy, reshaping it by stripping away the raw material needed to form new stars. This idea has long featured in computer simulations of galaxy evolution, but confirming it observationally — particularly in the earliest galaxies — has proved difficult.

Using JWST to put theory to the test

For years, my research has delved into modelling how quasars shape galaxy evolution.

My simulations have predicted that bright quasars in the young universe should often generate outflows capable of ejecting gas out of their host galaxies at thousands of kilometres per second. JWST's sensitivity and ability to detect the optical emission released by interstellar gas make it possible to test that prediction directly, by observing quasars as they began to light up the Universe more than 13 billion years ago.

Our international team studied 27 quasars, dating from roughly one billion years after the Big Bang. Six showed exceptionally powerful galaxy-scale winds, travelling at up to 8,400 kilometres per second — around 5,000 miles per second, fast enough to go around the Earth in under 5 seconds.

More striking still was how common these extreme outflows turned out to be: compared with quasars in the more recent universe, they appeared at least four times more often and carried around 100 times more kinetic energy.

One of my simulations predicting strong winds from a simulated early quasar. Photo credit: Costa et al. 2024.

No gas today, no stars tomorrow

Stars form when cold gas clouds within galaxies collapse under their own gravity. Strip away enough of that gas, and star formation slows down — or stops altogether. Astronomers call this ‘quenching’.

The newly observed quasar winds offer a natural explanation for why some of the earliest massive galaxies shut down so quickly.

Rather than simply running out of fuel, they may have had their gas reservoirs blasted away by the energy released as their central black holes grew.

The idea itself isn't new, but this is some of the strongest direct evidence that suggests that it actually happened in the early universe.

Astronomers have long predicted that early quasars should drive powerful winds through their host galaxies. Seeing that confirmed, and finding the outflows even more extreme than expected, marks a striking validation of the theory.

A new chapter in galaxy evolution

The findings help resolve one of modern astronomy's biggest puzzles: the surprising number of massive galaxies that already looked ‘mature’ when the universe itself was still young, their stars formed in a rapid burst before star formation mysteriously ground to a halt.

Rather than galaxies simply exhausting their gas supply naturally, it now looks like growing supermassive black holes actively shut down star formation by blasting material out into intergalactic space from the earliest stages of galaxy evolution.

The next challenge is understanding the details. Why do only some quasars show these extreme winds? What physical processes drive them? How long do the outflows last, and how do they affect neighbouring galaxies as well as their own?

The answers will sharpen the theoretical models astronomers build to reconstruct how galaxies like our own Milky Way came to be.

Looking back to understand today's universe

One of JWST's greatest strengths is its ability to look so far back in time. Because light takes billions of years to reach us, observing the most distant quasars lets astronomers witness events from when the Universe was less than five per cent of its current age.

The discovery that quasar-driven winds were both common and exceptionally energetic suggests supermassive black holes played a far bigger role in shaping the young Universe than previously appreciated. Far from being passive residents at galactic centres, these early black holes may have acted as cosmic architects — deciding when galaxies could keep building stars, and when they would fall silent.

You might also like…

• find out more about Dr Tiago Costa, NuACT Fellow in the School of Mathematics, Statistics, and Physics
• learn more about the James Webb Space Telescope (JWST)
• read the blog: discover how our researchers used JWST to discover what a hidden veil of dust near a supermassive black hole tells us about our universe
• discover what the James Webb Space Telescope (JWST) is exploring about our universe
• explore the incredible work carried out by our School of Mathematics, Statistics, and Physics