Webb’s Little Red Dots may reveal how giant black holes formed soon after the Big Bang

The launch of NASA’s James Webb Space Telescope (JWST) in 2021 pushed the horizon of seeing the early universe, unveiling cosmic events just a few hundred million years after the Big Bang. Among the most striking discoveries are supermassive black holes—some reaching 100 million times the mass of our sun.

“Finding black holes in the early universe is such a surprise because it goes against the standard model of how the universe is building structure from small pieces, or ‘light seeds,’ to big pieces or ‘heavy seed,'” said Volker Bromm, a professor of astronomy in the College of Natural Sciences and co-director of the Cosmic Frontier Center at The University of Texas at Austin.

Bromm has co-authored a study on curious astronomical objects discovered by the JWST called Little Red Dots (LRD), published in the Astrophysical Journal.

LRD are extremely compact, emitting highly-redshifted light with unusual spectral characteristics that defy easy explanation. Bromm and colleagues compared and found good agreement with JWST LRD data to models that employed a “heavy seed” hypothesis of black hole formation.

Black hole ‘heavy seeds’

Astronomers call the heavy seeds direct collapse black holes (DCBH), hypothesized to form from the speedy collapse of huge primordial clouds of hydrogen and helium gas. This line of thought contrasts the “light seed” hypothesis of black hole formation, a slower process where a massive star burns out all its nuclear fuel and collapses into a remnant black hole, with a mass a few tens to 100 times that of the sun.

The Little Red Dots appear at the tail end of DCBH formation.

“Little Red Dots are now thought to be powered by supermassive black holes surrounded by a massive cocoon, a gas cloud of high-density material,” Bromm said.

Supercomputing behind the breakthrough

Bromm secured allocations on the Lonestar6 and Stampede3 supercomputers at the Texas Advanced Computing Center (TACC) through the University of Texas Research Cyberinfrastructure program, opening the door for researchers across UT System to harness world-class advanced computing power.

Volker used the supercomputers to develop the models that started with initial conditions of what the universe was like about half a million years after the Big Bang, gleaned from prior data on the Cosmic Microwave Background Radiation.

“Lonestar6 and Stampede3 were absolutely key to this modeling and achieving this level of realism,” Bromm said. “The moment you couple dark matter with baryons (luminous materials), you get into a realm that is completely nonlinear. These facilities support the only way to solve this super complex problem.”

Bromm and colleagues used the galaxy formation code Ancient Stars and Local Observables by Tracing Halos (A-SLOTH) to populate the early universe with DCBHs and compare that to standard stellar remnant star seed models. They found better agreement with DCBH models vs. stellar remnant seeds in matching observed LRD population statistics and host dark matter halo properties.

Little Red Dot genetics

The researchers deconstructed the observational data from JWST on LRD using what they called a “genetic technique,” where the data is broken up into its progenitors.

“We do a merger tree of the LRD history from the very beginning. It’s like constructing the history of one person, going back millions of years and tracking all descendants,” they noted.

Building on this, Bromm and colleagues incorporated key astrophysical objects and processes, such as dark matter halos, adding primordial gas to elucidate questions on how the gas forms stars, their life cycle and energy output, supernova feedback, and the resulting enrichment with heavy chemical elements.

This is analogous to modeling the deep history of a person living today, tracing every ancestor and the defining moments that shaped their lives to understand who that person is today.

While not directly used in the simulations, Bromm acknowledged that artificial intelligence played a supporting role in the larger effort to extract the key properties of the Little Red Dot population from JWST imaging data.

Cosmic challenge

“The big challenge now is intricately a supercomputing problem—to understand the data coming from the JWST on the first galaxies, starting with the primordial universe, and moving time forward to solve this coupled set of differential equations,” Bromm said.

He added that another great challenge for theoretical astronomers is connecting data from JWST on the “luminous universe,” matter we can see, with the properties of dark matter: “To make this connection between the visible and the underlying dark matter universe, supercomputing is key.”

“Philosophically, it’s fantastic that now humans are in a position to understand the entirety of nearly 14 billion years of cosmic history,” Bromm concluded. “This is a breathtaking extrapolation of our own lifetimes, and ultimately a gift from supercomputing to put this all together.”