While probing the dawn of the universe for the origins of ancient galaxies, the James Webb Space Telescope uncovered something unexpected lurking at their cores—a discovery that might reshape our view of the early cosmos.
Scientists have long thought that galaxies evolved first, while the black holes at their center formed after from the collapse of large stars. Recent observations by Webb, however, tell a different story. The telescope captured evidence of supermassive black holes evolving first, without a host galaxy to feed them.
The Webb observations may finally provide an answer to a celestial chicken-or-the-egg question, suggesting that ancient black holes did not need to consume large amounts of surrounding gas and dust to grow to their enormous sizes.
“This is a remarkable finding,” Roberto Maiolino, a researcher from the University of Cambridge and co-author of two studies published in Nature and the Monthly Notices of the Royal Astronomical Society, said in a NASA statement. “It’s a paradigm shift, a total revisiting of the classical scenarios of how black holes form and grow.”
A look back in time
One of the first tiny glowing flecks of infrared light that Webb found, named Abell2744-QSO1 (QSO1), dates back to just 700 million years after the Big Bang (5% of its current age). The prototypical Little Red Dot is gravitationally lensed by the galaxy cluster Abell 2744. That makes it an ideal target, as it appears magnified and triply imaged.
Initial observations of QSO1 showed that it may be a supermassive black hole around 40 million times the mass of the Sun, surrounded by a cloud of glowing hydrogen and helium gas. However, scientists couldn’t be sure if the black hole was really that massive.
“Before now, all of the mass measurements of black holes in the early universe have been indirect, based on assumptions from what we know about them in the local universe. We didn’t know if those assumptions really apply to the distant universe,” Francesco D’Eugenio, a researcher at the University of Cambridge and co-author of the studies, said in a statement.
Weighing the beast
Image: NASA, ESA, CSA, Lukas Furtak (Ben-Gurion University); Image Processing: Alyssa Pagan (STScI)To confirm the mass of the black hole, the team behind the study traced the effects of its gravity on the gas swirling around it and mapped the distribution of various elements in the gas. Using Webb’s Near Infrared Spectrograph (NIRSpec), the scientists found that the gas orbits a central point in the same way that planets in our solar system orbit the Sun. This phenomenon is known as Keplerian motion.
“This is important because it tells us that most of the mass of QSO1 is concentrated in the black hole at the center,” Ignas Juodžbalis, a graduate student at Cambridge University and lead author of one of the studies, said in a statement. “If the mass were more distributed, as it would be if there were a lot of stars, the gas would not have this perfect Keplerian rotation.”
Since Keplerian motion is governed by laws of gravity, the team used the velocity measurements of the surrounding gas to directly calculate the mass of the black hole. “This is a phenomenal result,” Maiolino said. “It is the first direct measurement of a black hole mass within the first billion years after the Big Bang, and it is consistent with the previous measurements.”
The results revealed that not only is the black hole supermassive, at 50 million times the mass of the Sun, but it also makes up around two-thirds of QSO1’s total mass. Supermassive black holes generally make up only a small fraction of the total mass of their host galaxies. The discovery revealed a proportion between the supermassive black hole and its galaxy that’s thousands of times greater than in nearby galaxies.
The findings suggest that this black hole was born a big boy rather than forming from a collapsing star and feeding on its surrounding gas to grow to its massive size. The chemical composition of QSO1 also showed that it is made up almost entirely of hydrogen and helium, with very little of the heavier elements like oxygen normally found in a galaxy rich with stars and stellar debris.
“It seems that we have found a black hole that does not have a substantial host galaxy and that has predated stellar processes,” Juodžbalis said. “This is very exciting because it is evidence for primordial black holes or direct collapse black holes, which have been theorized but not confirmed.”
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