March 1, 2024

How black holes went from creation to star extinction

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The transition in star formation rates and black hole growth as redshift decreases from regimes where positive feedback dominates to a later epoch when feedback is largely negative. Credit: Steven Burrows, Rosemary Wyse and Mitch Begelman.

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The transition in star formation rates and black hole growth as redshift decreases from regimes where positive feedback dominates to a later epoch when feedback is largely negative. Credit: Steven Burrows, Rosemary Wyse and Mitch Begelman.

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 emerged. The telescope’s infrared detection “eyes” detected a series of small red dots, identified as some of the first galaxies formed in the universe.

This surprising discovery is not just a visual marvel, it is a clue that could unlock the secrets of how galaxies and their enigmatic black holes began their cosmic journey.

“James Webb’s surprising discovery is that not only does the Universe have these very compact, infrared-bright objects, but they are also likely regions where enormous black holes already exist,” explains Mitch Begelman, JILA fellow and professor of astrophysics at the University of California. Colorado in Boulder. “This was considered impossible.”

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

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

The traditional history of galaxy formation

Astronomers had already postulated a somewhat orderly evolution when thinking about how galaxies formed. Conventional theories held that galaxies form gradually, clumping together over billions of years. In this slow cosmic evolution, stars were thought to emerge first, illuminating the primordial darkness.

“The idea was to move from this initial generation of stars to galaxies that became dominated primarily by stars,” adds Begelman. “So at the end of this process, you start to build these black holes.”

Supermassive black holes, these enigmatic and powerful entities, were believed to appear after the first stars, growing silently in the galactic core. They were seen as regulators, occasionally stepping in to moderate the formation of new stars, thus maintaining galactic balance.

Challenging conventional wisdom

Thanks to observations of “little red dots” by JWST, researchers discovered that the Universe’s first galaxies 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 Silk. “They are products of the accumulation of gas in massive black holes in the cores of galaxies that generate immense luminosities, outshining the 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 [the process is] flipped, that these black holes formed along with the first stars, and then the rest of the galaxy followed,” says Begelman. “We’re saying that black hole growth, in principle, promotes stars. And only later, when conditions change, does this switch to a mode of turning off the stars.”

From this newly proposed process, researchers discovered that the relationship between star formation and black hole formation appeared closer than expected, as each initially amplified the growth of the other through a process known as feedback. positive.

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

Then, after nearly a billion years, the nurturing giants became suppressive, depleting the gas reservoirs in their galaxies and extinguishing star formation. This “negative feedback” was due to energy-conserving outflows – powerful winds that drove gas out of galaxies, depriving them of the material needed to create new stars.

A new galactic timeline

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

Identifying this transitional epoch helps astronomers pinpoint specific periods in the history of the Universe for observation. It could guide future observation strategies using telescopes like JWST and others to study the early universe more effectively. Furthermore, by understanding when this change occurred, astronomers can better contextualize the characteristics of modern galaxies, including size, shape, stellar composition and level of activity.

Validating a new process

To validate this new theory of collaborative galaxy formation between stars and black holes, and provide more information about the processes involved, computational simulations are needed.

“This will take some time,” says Begelman. “Current computer simulations are quite primitive and you need high resolution to understand everything. It takes a lot of computing power and it’s expensive.”

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

“The next steps will come from improved observations,” adds Silk. “The full power of JWST to study the spectra of the most distant galaxies will be unleashed in the coming years.”

Both Begelman and Silk are optimistic about the rest of their field adopting the proposed idea.

“As far as I know, we are the first to go in this extreme direction,” adds Begelman. “I was pushing the limits over the years with my collaborators working on this problem of black hole formation. But JWST shows us that we don’t think outside the box enough.”

More information:
Joseph Silk et al, Which Came First: Supermassive Black Holes or Galaxies? JWST information, The letters from the astrophysical journal (2024). DOI: 10.3847/2041-8213/ad1bf0. …847/2041-8213/ad1bf0

Diary information:
Astrophysical journal letters

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