To the uninitiated, astronomers’ interest in ancient black holes might seem like an obsession. Why spend so much time, energy, and resources looking back billions of years just to detect the nearly undetectable? They do it because ancient black holes hold unique clues to understanding the modern Universe.
As far as astronomers can tell, large galaxies like ours host supermassive black holes (SMBHs) in their centers as if they’re anchoring them. These enormously massive objects can have tens of billions of solar masses. Astronomers have thought that SMBHs grow so massive during galaxy mergers. However, the JWST has found these massive objects when the Universe was very young. In 2024, the JWST detected a black hole with about 1.6 million solar masses at the center of a galaxy called GN-z11. It’s about 13.4 billion years old, meaning it formed only about 400 million years after the Big Bang.
SMBHs this large so soon after the Big Bang pose a challenge to our standard models of cosmology. There simply wasn’t enough time for them to accrete enough mass and grow this large. The discovery of ancient SMBHs suggests that they formed by direct collapse of massive gas clouds or that accretion was much more rapid in the very early Universe. Scientists know that conditions in the early Universe were different, which could open the door to understanding these confounding early black holes.
When SMBHs are actively accreting material, they emit light and are called active galactic nuclei (AGN). The most luminous AGNs are called quasars, and they emit more light across the electromagnetic spectrum, outshining entire galaxies like our Milky Way. Astronomers need to find more of these ancient black holes and gather more evidence. However, despite their luminosity, that’s not an easy task. Many of these objects are concealed behind massive amounts of gas and dust in an accretion ring.
Researchers working with ALMA have developed a new way to detect quasars. Their research, “Warm gas in the vicinity of a supermassive black hole 13 billion years ago,” was published in Nature Astronomy. Professor Ken-ichi Tadaki of Hokkai-Gakuen University in Sapporo, Japan, is the lead author. Their work is focused on JADES-GS-z14-0, an extremely distant and ancient galaxy discovered by the JWST in 2023.
While the SMBH in the research isn’t the oldest one ever detected, it’s important for another reason. This is the most detailed look astronomers have ever gotten of the hot molecular gas in the vicinity of such an ancient SMBH. The hot gas indicates that the SMBH is actively accreting material, which could provide clues to how it, and others of its type, grew to be so massive in such a short period of time.
“The findings help us understand how black holes grow from tiny seeds in the early universe to supermassive black holes and the challenges posed by dust and gas that can obscure them,” said study co-author Dr. Takafumi Tsukui from Australia National University. “Many supermassive black holes may lie concealed within dusty regions of the early universe, simply undetected.”
Quasars blaze with intense light, which makes them hard to miss. However, seeing into the inner regions around them is difficult. The research team used ALMA’s high-resolution capability to reveal for the first time the mechanisms that heat the gas within a few hundred light years of the SMBH. The physical conditions near a black hole are extreme, and these observations can help scientists understand them.
“We discovered that intense X-ray radiation emitted by the material spiralling around the black hole, along with strong winds and shock waves, heat the gas to energy states far higher than what’s typically seen in normal galactic environments, where the main source of energy comes from the ultraviolet radiation from stars,” Dr. Tsukui said. “As the radio waves observed by ALMA are not easily absorbed by dust, our technique becomes a powerful tool for discovering hidden supermassive black holes.”
This schematic shows the quasar’s composition, which consists of a compact disk, a starburst disk and an outflow component. It shows that XDR (X-ray-dominated regions) heating dominates as the heating mechanism in the central region of the quasar, whereas shock heating becomes dominant in regions slightly farther away. Image Credit: Tadaki et al. 2025.
At the heart of this research is ALMA’s ability to observe carbon monoxide (CO) at high energy states, termed “high-J emissions.” CO molecules exist in different energy states with different molecular line emissions. The molecules exist in different rotational energy states, and each state can be expressed by a quantum number termed J. Whenever a carbon monoxide molecule transitions to a lower energy state (from J to J-1, for example), it emits a photon with a specific wavelength/frequency.
In this work, ALMA detected photons emitted by CO molecules transitioning from J = 13–12 and from J = 14–13. These are high-J transitions, and they have particular attributes. They require high temperatures of several hundred degrees Kelvin, and they trace gas that’s warmer and denser than lower-J transitions. Critically, they emit in high frequencies in the sub-millimetre range. That makes them detectable by ALMA.
This figure shows how emissions reveal the morphology of the distant, luminous quasar. (a) shows the 1.4 mm continuum, (b) shows the CO J = 13–12 emission, (c) shows the CO J = 14–13 emission, and (d) shows the CO luminosity ratio. The dashed magenta line shows the effective radius of the compact disk. Image Credit: Tadaki et al. 2025.
“The breakthrough in our research comes from specifically targeting radio emissions from carbon monoxide molecules in higher energy states, which uniquely reveals the hot gas conditions in the immediate vicinity of the supermassive black hole,” Dr Tsukui said.
This work shows that astronomers can use ALMA to detect the hot gas that is otherwise obscured by dust around quasars. By finding more of these ancient black holes, researchers hope to understand how they’ve grown so large in the modern Universe.
More:
Research: Warm gas in the vicinity of a supermassive black hole 13 billion years ago
Press Release: Discovery of ‘Hot Gas’ near a Supermassive Black Hole 12.9 Billion Years Ago: New Possibilities for Finding Hidden Black Holes in the Early Universe
Press Release: New discovery promises to reveal hidden black holes across the universe