As astronomers delve into the early chapters of the universe's story, they've stumbled upon a trove of massive black holes that seem to have grown faster than previously believed possible.
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This image contains the most distant black hole ever detected in x-rays, a result that may explain how some of the first supermassive black holes in the universe formed. The extremely distant black hole is located in the galaxy UHZ1, imaged with NASA’s Chandra X-ray Observatory (purple) and infrared data from NASA’s James Webb Space Telescope (red, green, blue). X-ray: NASA/CXC/SAO/Ákos Bogdán; Infrared: NASA/ESA/CSA/STScI; Image Processing: NASA/CXC/SAO/L. Frattare & K. Arcand |
Priyamvada Natarajan is like a cosmic biologist, studying the lives of these unusually large black holes. These objects are so dense that they trap everything, including light, within their grasp. Back when Natarajan was an astronomy grad student, she was among the first to treat black holes as populations rather than solitary objects, likening them to studying bats in a rainforest. Now, as an astrophysicist at Yale University, Natarajan continues her research, particularly focusing on understanding how these black holes come into existence.
Traditionally, black holes are thought to form after massive stars explode, gradually growing as they consume nearby gas. But some observations of supermassive black holes in the early universe suggest there might be more to the story. In 2006, Natarajan and her colleagues proposed a radical idea: that disks of gas could directly collapse into unusually massive baby black holes without forming a star first. Recently, a joint observation by the James Webb Space Telescope (JWST) and the Chandra X-ray Observatory spotted a distant, glowing black hole that seems to confirm Natarajan's theory.
"It's a strong case supporting these heavy black hole seeds," says Raffaella Schneider, an astrophysicist at Sapienza University of Rome. "[Natarajan] proposing this idea really broadened our understanding of the different possibilities that could happen."
Natarajan talked to Scientific American about how these recent observations align with her proposal for "direct-collapse black holes" and what they reveal about the origins of these entities.
[Below is an edited transcript of the interview.]
What sparked your interest in studying black holes and how they form?
I've always been drawn to the unseen aspects of the universe. My work mainly revolves around understanding the nature of dark components like dark matter, dark energy, and black holes on a fundamental level. These objects are incredibly mysterious and intriguing to me. They highlight the boundaries of our knowledge, the places where our understanding of physics reaches its limits.
In recent decades, black holes have transitioned from abstract mathematical concepts to tangible objects we can observe. They've become central to our understanding of how galaxies form. The universe is teeming with black holes of all sizes, making them a crucial part of our cosmic inventory. Thus, understanding their origins is a fundamental question we're still exploring.
What gaps exist in our understanding of how black holes form?
Traditionally, we believed black holes form when massive stars die. When these stars collapse under their own gravity, they leave behind a compact object known as a black hole. That's the generally accepted origin story.
About twenty years ago, as we began peering deeper into the universe with missions like the Sloan Digital Sky Survey, we stumbled upon a handful of incredibly massive black holes—some reaching up to about a billion times the mass of the sun—when the universe was merely one to two billion years old. Given how quickly we know black holes tend to consume matter, there simply wasn't enough time for the tiny seeds formed from the explosions of the first stars to grow into these colossal black holes. Over the following years, we discovered that these were not isolated anomalies; there existed an entire population of supermassive black holes in the early universe. And that's when the puzzle started to unfold.