The Synchronous Evolution of Black Holes and Stars: A Shift in Galactic Formation Theories

2024-03-21 22:30:16

The transition in star formation and black hole growth rates at redshift decreases from regimes where positive feedback dominates to later epochs when feedback is predominantly negative. credit
Stephen Burroughs, Rosemary Wise and Mitch Bagelman

The James Webb Space Telescope’s discovery of early galaxies with massive black holes challenges traditional theories of galaxy formation, suggesting the synchronous evolution of black holes and stars, a finding that could reshape our understanding of cosmic evolution.

Astronomers have long sought to understand the early universe, and thanks to the James Webb Space Telescope (JWST), a critical piece of the puzzle has been created. The telescope’s infrared-detecting “eyes” spotted an array of small, red dots, identified as some of the earliest galaxies formed in the universe.

This surprising discovery isn’t just a visual wonder, it’s a clue that could reveal the secrets of how galaxies and their enigmatic black holes began their cosmic journey.
“James Webb’s amazing discovery is that not only does the universe have the very compact and bright objects in the infrared, but they are probably regions where giant black holes already exist,” explains JILA fellow and professor of astrophysics at the University of Colorado Boulder Mitch Bagelman. “It is considered impossible.”

Bagelman and a team of other astronomers, including Joe Silk, a professor of astronomy at Johns Hopkins University, published their findings in The Astrophysical Journal Letterssuggesting that new theories of galactic creation are needed to explain the existence of these supermassive black holes.

“Something new is needed to reconcile the theory of galaxy formation with the new data,” explains Silk, lead author of the potentially groundbreaking study.

The traditional story of the formation of the galaxy

Astronomers have in the past posited a somewhat orderly evolution when thinking about how galaxies form. Conventional theories stated that galaxies form gradually, gathering together over billions of years. In this slow cosmic evolution, the stars were thought to emerge first, illuminating the primordial darkness.

“The idea was that you went from this early generation of stars to the galaxies that are really dominated by stars,” Begelman adds. “And then, towards the end of that process, you start building these black holes.”

Supermassive black holes, those enigmatic and powerful entities, are believed to have appeared after the first stars, growing quietly in the galactic core. They were seen as regulators, occasionally springing into action to moderate the formation of new stars, thus maintaining galactic balance.

Challenging conventional wisdom

Thanks to JWST’s “Little Red Dot” observations, researchers discovered that the first galaxies in the universe were brighter than expected, as many showed stars coexisting with central black holes known as quasars.

“Quasars are the most luminous objects in the universe,” explains Meshi. “They are the products of gas accretion on massive black holes in the nuclei of galaxies that create enormous lights, which surpass their host galaxies. They are like monsters in the cuckoo’s nest.”

Seeing the coexistence of stars with black holes, researchers quickly realized that conventional theories of galaxy formation had to be flawed. “(This new data) looks like (the process) is reversed, that these black holes formed together with the first stars, and then the rest of the galaxy followed,” Begelman says. “We say that the growth of the black hole, in the beginning, promotes the stars. And only later, when the conditions change, it turns into a state of extinguishing the stars.”

From the newly proposed process, the researchers found that the link between star formation and black hole formation appears to be closer than expected, as each initially boosted the growth of the other through a process known as positive feedback.

“Star formation accelerates the formation of massive black holes, and vice versa, in an inextricably linked violent, birth-death interaction that is the new beacon of galaxy formation,” says Silk.

Then, after nearly a billion years, the nurturing giants became oppressive, depleting the gas reservoirs in their galaxies and shutting down star formation. This “negative feedback” resulted from energy-saving outflows – strong winds that stripped gas from galaxies, starving them of the material needed to form new stars.

A new galactic timeline

Armed with the discovery of the nurturing behavior of black holes, the researchers proposed a new timeline for the transition from positive to negative feedback in early galaxy formation. By looking at the spectrum of light and the various chemical signatures emitted by these “little red dots,” the researchers suggested that this change occurred about 13 billion years ago, a billion years after the Big Bang, a period astronomers classify as “z ≈6.”

Identifying this age of transition helps astronomers target specific periods in the universe’s history for observation. This could guide future observational strategies using telescopes like JWST and others to study the early universe more effectively. Additionally, by understanding when this change occurred, astronomers can better contextualize the characteristics of modern galaxies, including size, shape, stellar composition, and activity level.

Innovative process validation

To verify this new theory of cooperative galactic formation between the stars and black holes, and provide further insight into the processes involved, computer simulations are needed.

“It will take some time,” Bagelman says. “Current computer simulations are quite primitive, and you need high resolution to understand everything. It requires a lot of computing power and is expensive.”

Until then, there are other steps the astronomy community can take to review and verify this new theory.

“The next steps will come from improved observations,” adds Silk. “JWST’s full power to probe the spectra of the most distant galaxies will be unleashed over the next few years.”

Both Bagelman and Silk are optimistic that the rest of their field will adopt their proposed idea.

“As far as I know, we are the first to go in this extreme direction,” adds Begelman. “Over the years I’ve pushed the envelope with my collaborators working on this problem of black hole formation. But JWST shows us that we haven’t thought outside the box enough.”

For more information on this study, see The primordial race between black holes and galaxies.