The James Webb Telescope may have discovered the oldest and most distant supermassive black hole ever observed

Astronomers using the James Webb Space Telescope (JWST) may have discovered the most distant supermassive black hole ever observed. Hosted by the galaxy GHZ2, this massive object is so far away that astronomers have observed it only 350 million years after the Big Bang.

The team’s study, which was uploaded to the preprint server arXiv on November 4 but has not yet been peer-reviewed, used observations from JWST’s near-infrared spectrometer and mid-infrared instruments. These instruments cover a wide range of wavelengths and can detect ultraviolet and optical light originally emitted by distant galaxies and extended into the infrared by the expansion of the universe.

“GHZ2 existed when the universe was very young, and the supermassive black hole and its host galaxy had a relatively limited amount of time to grow together,” Oscar Chávez Ortiz, a doctoral candidate in the astronomy department at the University of Texas at Austin and lead author of the study, told Live Science in an email. “While black holes and galaxies are clearly coevolving in the local universe, the detection of such systems at this early age raises the question of how supermassive black holes gain mass so rapidly.”

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There are two main hypotheses for how these supermassive black holes form so early, Chavez-Ortiz said. They are either “light seeds” that grow unusually fast, or “heavy seeds” that start with a large mass and get a head start.

secret of the line

Since the discovery of GHZ2 was reported in 2022, astronomers have used JWST to find many distant galaxies. But GHZ2 stands out because its spectrum is comprised of very strong “emission lines,” or bright bands of light emitted when the electrons of certain atoms or ions receive energy and release energy at specific wavelengths. These lines contain clues about the process that powers GHZ2.

“We are observing emission lines that require a lot of energy to produce, known as highly ionizing lines,” Jorge Zabala, an assistant professor in the astronomy department at the University of Massachusetts Amherst and a co-author of the study, told Live Science in an email.

Zavala explained that current understanding of gas ionization – the heating of gases that turns atoms into ions by losing or gaining electrons – is based primarily on nearby star-forming regions and typically does not take into account powerful highly ionizing lines. These lines and the relationships between them are commonly seen in active galactic nuclei (AGNs). The AGN contains an actively feeding black hole at its center and much higher energy radiation.

An important clue was the detection of the C IV λ1548 emission line. This emission line results from triple ionized carbon, that is, a carbon atom that has lost three electrons. “Removing three electrons requires a very strong radiation field, and it is very difficult to achieve that in stars alone,” Chávez-Ortiz said. AGN naturally generates these high-energy photons. The strength of this line strongly suggests the presence of an actively feeding black hole in GHZ2, motivating the researchers to conduct a detailed analysis.

mixed system

Because GHZ2 is an unusual system that challenges existing models, researchers needed to develop a detailed model to match its unique behavior and understand the contributions of both stars and AGNs to the galaxy’s light. This process involved iteratively testing and improving the model to ensure that it accurately represented the properties of the galaxy.

Their analysis revealed that visible light spectral lines can be explained by star formation alone, but that particularly strong carbon lines require the presence of AGNs. This discovery suggested that some of the galaxy’s light showed a contribution from a hungry supermassive black hole.

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However, Zavala pointed out that GHZ2 lacks some other indicators of AGN. This means that a large part of the galaxy may be driven by stars. If those stars were supermassive, hundreds to thousands of times more massive than the Sun, or if star formation in GHZ2 occurred in a very different way than we currently understand.

Another possibility is that some of the galaxy’s light comes from regular stars and some from more exotic sources such as supermassive stars or AGNs.

To further confirm AGN activity, the researchers plan to acquire more JWST observations and collect high-resolution spectra of some emission lines. Additionally, observations from the Atacama Large Millimeter/Submillimeter Array covering far-infrared spectral lines could improve the sensitivity of the dataset.

If confirmed, GHZ2 would house the most distant supermassive black hole ever confirmed. Detecting signs of AGN activity in this galaxy would provide a rare natural laboratory for testing competing “light seed” and “heavy seed” models of black hole formation and growth just a few hundred million years after the Big Bang.