James Webb Space Telescope Finds Possible Supermassive Black Hole in GHZ2 350 Million Years After the Big Bang

The James Webb Space Telescope has provided a team investigating the small, remote galaxy GHZ2 with evidence of a supermassive black hole that is actively feeding. Observed only 350 million years after the Big Bang, the object could force a rethink of how the earliest black holes came into existence.

A record-breaking candidate in a tiny galaxy

GHZ2 emerged in Webb observations in 2022 as one of numerous exceptionally remote galaxies. Its light has taken roughly 13.4 billion years to arrive at Earth, allowing astronomers to view it when the universe was still very young.

The galaxy stood out not because it was faint, but because it was unexpectedly bright in particular infrared colours. These colours act as signatures of the atoms within GHZ2 and suggested that an exceptionally energetic process is taking place at its centre.

The new analysis suggests that GHZ2 may host the most distant supermassive black hole ever identified, turning a blurry dot into a critical test case for early-universe physics.

The research team posted its study on the arXiv preprint server on 4 November, where it is awaiting peer review. The analysis uses observations from two of Webb’s major instruments, the Near Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI). Combined, they enable scientists to separate the galaxy’s light into a spectrum and examine it in detail, line by line.

Interpreting the light: what emission lines reveal

Galaxies do not emit an even, smooth glow alone. They also produce narrow peaks of brightness at precise wavelengths, known as emission lines. Such lines occur when atoms or ions are excited before releasing their energy as light.

In GHZ2, these peaks are exceptionally powerful, with several belonging to a category known as “high-ionisation lines”. They indicate gas exposed to extremely energetic radiation.

The spectrum of GHZ2 shows high-energy emission that ordinary young stars struggle to generate, pointing toward a more exotic power source at its heart.

One signal in particular drew immediate notice: a prominent C IV line created by triply ionised carbon, meaning carbon atoms that have lost three electrons. Producing carbon in this state requires a substantial supply of highly energetic photons.

Massive, hot stars are capable of ionising gas, but their effects have limits. The C IV line seen in GHZ2 is stronger than standard models of star-forming galaxies can readily account for. An active galactic nucleus (AGN), in contrast - where gas circulates around and falls into a supermassive black hole - naturally produces radiation this hard.

A composite system: stars and a harsher source

The researchers constructed detailed models combining light from conventional stars with the light predicted from an AGN. They adjusted these models repeatedly to establish which mix best reproduced Webb’s observations.

They concluded that energetic star formation alone could explain many of the visible and near-infrared features. Yet the carbon line, along with several other high-ionisation signals, consistently demanded another, more intense radiation source.

This strongly suggests that GHZ2 is a “composite” galaxy, in which a young stellar population and a feeding black hole shine at the same time.

• Star formation accounts for most low- and mid-energy emission lines.
• High-ionisation lines, particularly C IV, support the presence of an active black hole.
• GHZ2 probably contains both vigorous star formation and a central AGN.

However, the evidence is not completely clear-cut. GHZ2 does not show certain familiar AGN markers commonly found in nearby galaxies, including particular line ratios and mid-infrared features. As a result, alternative explanations remain possible.

It may contain extraordinarily massive, short-lived stars, with masses hundreds or thousands of times that of the Sun, which could generate harder radiation than ordinary stars. Alternatively, its early stellar population may operate differently from stars in present-day galaxies, altering the expected emission-line pattern.

Why an early black hole creates such a problem

If GHZ2 does contain a supermassive black hole at this point in cosmic history, it presents a challenging question: how could it have become so massive so rapidly?

Black holes begin small before growing through the consumption of gas, dust and stars, or through mergers with other black holes. At an age of 350 million years, however, the universe has had little time to assemble an object millions of times the Sun’s mass.

GHZ2 lands right in the middle of a fierce debate about whether the first black holes started tiny and grew explosively, or began life already heavy.

Astronomers generally consider two principal possibilities:

Type of seed	Origin idea	Growth challenge
Light seed	Remnants of the first generation of massive stars, a few tens to hundreds of solar masses	Must grow extraordinarily quickly and almost continuously to reach millions of solar masses so early
Heavy seed	Direct collapse of huge gas clouds, starting at tens of thousands to hundreds of thousands of solar masses	Requires rare circumstances in which gas collapses without first breaking up into normal stars

GHZ2 may serve as a natural laboratory for assessing these possibilities. Should future observations establish the black hole’s mass and accretion rate, astronomers could determine whether a light seed could realistically have grown so large within only a few hundred million years, or whether a heavy seed offers the more plausible explanation.

Next observations with Webb and ground telescopes

Although the existing data are striking, they still permit some uncertainty. The team is seeking deeper, sharper spectra for several important emission lines, requiring additional observing time with Webb.

Observations at higher resolution could disentangle overlapping lines and lower measurement noise, offering a more precise picture of the gas around the galactic centre. This would help establish whether the ionising radiation genuinely matches AGN signatures rather than unusual starlight.

The researchers also intend to use the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe far-infrared lines and cold gas. These data can show how much gas is available to sustain both star formation and the black hole, as well as whether that gas is turbulent or orderly.

If GHZ2’s AGN is confirmed, it would set a new distance record for a supermassive black hole and offer a benchmark for early-galaxy models.

Understanding the terminology

Several important terms can help non-specialists interpret the result.

An active galactic nucleus is the luminous central area surrounding a supermassive black hole that is currently accreting matter. As gas spirals towards the black hole, it becomes hot and releases enormous quantities of radiation across the spectrum, from X-rays to infrared.

Ionisation is the removal of electrons from atoms. The more electrons an atom loses, the higher its ionisation state and the more energetic the required radiation. Lines produced by triply ionised carbon therefore act as a signpost saying, “intense energy source at work here.”

Redshift describes the extent to which the expansion of the universe has stretched light from remote objects. GHZ2’s substantial redshift means that light originally emitted in the ultraviolet has shifted into the infrared, precisely the light Webb was built to detect.

What GHZ2 could mean for our view of the early universe

Results of this kind feed directly into computer simulations of the first galaxies. Modellers seek to reproduce systems such as GHZ2 by beginning with conditions shortly after the Big Bang, then allowing gravity and gas physics to evolve.

If simulations repeatedly cannot create a GHZ2-like galaxy containing a supermassive black hole by 350 million years, it would indicate missing physics. This might involve more efficient flows of gas, more common mergers, or additional ways for heavy seeds to form.

There may also be indirect effects on the speed at which galaxies enrich themselves with heavier elements. Active black holes can produce powerful outflows that expel gas from young galaxies. This feedback influences later star formation and could change when and where subsequent generations of stars - and eventually planets - are able to form.

For the moment, GHZ2 remains on a sort of cosmic “most wanted” list. As Webb and ALMA continue observing it, astronomers aim to establish whether this dim point of light really contains the earliest known supermassive black hole, or whether an even more unusual process is occurring in one of the universe’s first galaxies.