Quasars cloaked in dust found less than a billion years after Big Bang

Astronomers have discovered a hidden population of quasars – supermassive black holes blazing from the universe’s childhood – wrapped in cosmic dust.

Using a clever one-two punch of telescopes, researchers first flagged suspiciously luminous galaxies with Japan’s Subaru Telescope, then aimed NASA’s James Webb Space Telescope (JWST) at them to see what the dust was concealed.

The payoff: seven objects blazing like quasars less than a billion years after the Big Bang, but so dust-shrouded that earlier surveys had missed them.

It’s the first time astronomers have confirmed bright, dust-obscured quasars at such early times. The result effectively doubles the census of luminous quasars from the “Cosmic Dawn,” suggesting voracious black holes were at least twice as common then as we thought.

Quasars regulate star birth

Nearly every large galaxy today harbors a supermassive black hole at its center. Most lie quiet, but when gas spirals in, friction heats the material to extraordinary temperatures, and the black hole lights up as a quasar – outshining its entire galaxy.

That storm of radiation can blow out or heat gas, regulating how stars form. In other words, to understand how galaxies came to be, you need to understand their central black holes.

There’s a lingering puzzle, though: supermassive black holes were already in place very early on. Finding more of them at Cosmic Dawn sharpens the question of how they formed so fast – did they grow from many small “seeds” left by the first stars, or collapse directly from large gas clouds under special conditions?

A key clue is how many existed. If luminous quasars were more common than previously realized, rapid black hole growth may have been widespread rather than rare.

Cosmic fog conceals quasars

Historically, quasar searches relied on ultraviolet light, which early quasars emit in abundance. Thanks to the expansion of the universe, that UV appears to us as visible light. The catch? Ultraviolet is easily absorbed by dust, and young galaxies are dusty places. If a quasar sits inside a dusty host, much of its UV never escapes.

That’s why the team changed tactics. They started with the Subaru Telescope’s Hyper Suprime-Cam survey (HSC-SSP), which had already revealed a trove of unusually bright galaxies in the distant universe. But those galaxies lacked the telltale “broad emission lines” that usually confirm an active black hole.

Gas racing around the black hole at thousands of miles per second creates broad lines; their width is a smoking gun.

Enter JWST. Because infrared light passes through dust far better than ultraviolet, JWST’s Near-Infrared Spectrograph (NIRSpec) can look where older instruments were effectively blind.

Seven hidden quasars light up

Between July 2023 and October 2024, the team used NIRSpec to take spectra of 11 of the brightest Subaru-selected galaxies. In seven of them, the broad emission lines popped – undeniable signatures of quasars.

These are the first confirmed examples of dust-obscured but luminous quasars at Cosmic Dawn. JWST has recently found a menagerie of fainter, compact objects nicknamed “Little Red Dots,” many of which host black holes. These are dimmer than the classic early quasars. The new finds are the full-power kind – just veiled.

Brightness like no other

Peering into the spectra, the researchers estimated that each newly revealed quasar shines with the energy of a few trillion suns. They are powered by black holes a few billion times the mass of the Sun. That makes them comparable to the brightest unobscured quasars already known from the same era.

The difference comes from dust. It blocks about 70 percent of visible light and nearly all ultraviolet – 99.9 percent – before escape. No wonder earlier UV-based searches overlooked them.

“This discovery was only possible with the unique combination of two powerful telescopes,” said lead author Yoshiki Matsuoka from Ehime University. “The Subaru Telescope’s wide and sensitive survey allowed us to spot rare, luminous galaxies, and JWST was able to catch the faint infrared light from the hidden quasars.”

“This shows how effective the approach of ‘Discover with Subaru Telescope, explore with James Webb’ can be.”

Doubling the headcount at Cosmic Dawn

By comparing how many dust-obscured quasars they found with the tally of previously known, unobscured ones, the team concluded that bright quasars in the early universe are at least twice as common as previously thought.

That jump in number density has ripple effects. Black hole growth, galaxy evolution, and even the reionization of the universe all depend on how much quasar light was present and how it shaped its surroundings.

A richer, dustier population of early quasars also hints that black hole feeding frenzies often unfolded inside messy, rapidly forming galaxies – exactly the kind of environments where dust would thrive.

Peering deeper with ALMA

Finding the hidden quasars is step one. Now the team wants to see how they differ – if at all – from their dust-free cousins.

JWST’s spectra contain a forest of emission lines from different elements; their relative strengths and shapes act like diagnostic tools for the temperature, density, and motion of gas near the black hole. Are the obscured quasars blasting stronger winds? Are they embedded in thicker, more turbulent cocoons?

The researchers will also use ALMA, the Atacama Large Millimeter/submillimeter Array, to map cold gas and dust in the host galaxies. ALMA can reveal if galaxies hold star-forming gas, how it moves, and whether quasars stir or expel it.

In parallel, the team plans to expand the hunt to less luminous galaxies to see how far down the iceberg of hidden black holes goes. A new JWST program is already on the calendar, with observations slated to begin early next year.

A crowded early cosmos

Quasars are nature’s lighthouses, and the earliest ones are beacons from a time when the first galaxies were assembling.

By switching to infrared eyes and following up the brightest dusty suspects, astronomers have revealed a whole cohort of lighthouses we didn’t know were there. The universe at a billion years old just got more crowded – and a lot more interesting.

The study is published in The Astrophysical Journal.

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