A Mystery about the Universe’s First Black Holes May Be Solved at Last

A Mystery about the Universe’s First Black Holes May Be Solved at Last

A Mystery about the Universe’s First Black Holes May Be Solved at Last

Astrophysicist Priyamvada Natarajan’s groundbreaking theory about starless black hole formation gains support from new observations

In the quest to understand the universe's earliest epochs, astronomers have encountered a perplexing enigma: colossal black holes that appear to have reached maturity astonishingly quickly. This mystery might finally be unraveling, thanks to the pioneering work of astrophysicist Priyamvada Natarajan, who proposed that black holes could form directly from collapsing gas clouds, bypassing the need for stars.

Natarajan’s approach to studying black holes is akin to that of a biologist examining a thriving ecosystem. As a graduate student, she revolutionized the field by analyzing black holes collectively, much like studying species within a rainforest. Now at Yale University, her focus remains on the genesis and evolution of these enigmatic objects, which are so dense that they devour all matter and light within their grasp.

Traditionally, black holes are born from the remnants of massive star explosions, growing by consuming nearby gas. However, observations of supermassive black holes in the early universe hinted at a more complex picture. In 2006, Natarajan and her colleagues proposed a bold theory: gas disks could collapse directly into massive black holes without first forming stars. This idea has now found support through joint observations by the James Webb Space Telescope (JWST) and the Chandra X-ray Observatory, which discovered a distant, luminous black hole aligning with Natarajan’s predictions.

“It’s definitely a very strong case in favor of these heavy black hole seeds,” notes Raffaella Schneider, an astrophysicist at Sapienza University of Rome. “[Natarajan] having proposed this idea really helped the community to enlarge our view on the different possibilities that can occur.”

A Conversation with Priyamvada Natarajan

What inspired your interest in black holes and their origins?

I’ve always been drawn to the universe’s invisible entities. My work focuses on understanding dark matter, dark energy, and black holes on a fundamental level. These objects are incredibly alluring and enigmatic, reminding us of the limits of our knowledge and the breakdown of known physical laws.

Over recent decades, black holes have transitioned from theoretical constructs to observable phenomena, becoming central to our understanding of galaxy formation. The universe is teeming with black holes of various sizes, making it crucial to understand their origins.

What mysteries remain about black hole formation?

Typically, black holes are the remnants of dying stars. Massive stars collapse under gravity, leaving behind black holes. This origin story is well established.

However, around twenty years ago, we discovered extremely massive black holes—up to a billion times the mass of the sun—when the universe was only one to two billion years old. Given the known growth rates of black holes, there wasn’t enough time for these tiny seeds to grow into such giants. This wasn’t just an anomaly; there was an entire population of supermassive black holes in the early universe, creating a significant puzzle.

Researchers began exploring if black holes could feed faster than previously thought, but evidence was lacking. I wondered if we could start with larger seeds. My team hypothesized that a gas disk could collapse directly into a black hole if radiated by nearby stars, bypassing star formation. These direct-collapse black holes would be significantly larger at birth, quickly growing into the massive black holes observed.

How was your theory received?

Initially, there was skepticism. Critics questioned if the process was efficient enough to occur in the universe. At the time, we couldn’t observe these early epochs directly. But the promise of the JWST kept us motivated. We theorized that a direct-collapse black hole would be temporarily more massive than the stars in its galaxy, producing a distinct observational signature.

Even with advanced telescopes like JWST and Chandra, we couldn’t directly observe early black hole seeds. However, we hoped to find indirect evidence via gravitational lensing. We focused on the galaxy cluster Abell 2744, hoping its gravitational lensing would reveal a hidden galaxy with the predicted signature.

What was the outcome?

Last year, I received an exciting call from astrophysicist Akos Bogdan, who had analyzed Chandra’s observations of galaxies behind Abell 2744. He had found a galaxy spectrum matching our predictions from 2017. It was an astonishing moment, providing compelling evidence for direct-collapse black holes.

While there may be other ways to form black hole seeds, this discovery opens up numerous exciting questions. We’re now investigating other potential pathways and their unique signatures.

How did it feel to find evidence supporting your theory?

 imaged with NASA’s Chandra X-ray Observatory (purple) and infrared data from NASA’s James Webb Space Telescope (red, green, blue).

This is the thrill of being an astrophysicist: seeing theoretical ideas confronted with observational data. We live in an extraordinary time where predictions can be validated within a lifetime, truly making this a golden age of cosmology. I am deeply grateful for this opportunity.