While investigating the origins of ancient galaxies at the dawn of the universe, the James Webb Space Telescope discovered something unexpected lurking in their cores, a discovery that could change our view of the early cosmos.
Scientists have long thought that galaxies evolved first, while the black holes at their centers formed after the collapse of large stars. However, Webb’s recent observations tell a different story. The telescope captured evidence that supermassive black holes evolved first, without a host galaxy to feed them.
Webb’s observations may finally provide an answer to the celestial chicken-or-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,” said Roberto Maiolino, a researcher at the University of Cambridge and co-author of two studies published in Nature and the Monthly Notices of the Royal Astronomical Societysaid in a nasa statement. “It is a paradigm shift, a total revision of the classical scenarios of how black holes form and grow.”
A look back in time
One of the first bright little specks of infrared light that Webb found, called Abell2744-QSO1 (QSO1), It 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 Abell 2744 galaxy cluster. That makes it an ideal target, as it appears magnified and imaged three times.
Initial observations of QSO1 showed that it may be a supermassive black hole about 40 million times the mass of the Sun, surrounded by a cloud of incandescent hydrogen and helium. However, scientists couldn’t be sure if the black hole was really that massive.
“Until now, all mass measurements of black holes in the early universe have been indirect, based on assumptions about 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
To confirm the mass of the black hole, the team behind the study tracked the effects of its gravity on the gas rotating around it and mapped the distribution of various elements in the gas. Using Webb’s near-infrared spectrograph (NIRSpec), scientists discovered that the gas orbits a central point in the same way that the 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 QSO1’s mass is concentrated in the central black hole,” Ignas Juodžbalis, a graduate student at the University of Cambridge 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 many stars, the gas would not have this perfect Keplerian rotation.”
Since Keplerian motion is governed by the laws of gravity, the team used 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 the mass of a black hole within the first billion years after the Big Bang, and is consistent with previous measurements.”
The results revealed that the black hole is not only supermassive, with 50 million times the mass of the Sun, but also makes up about 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 ratio between the supermassive black hole and its galaxy that is 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 surrounding gas to grow to its massive size. The chemical composition of QSO1 also showed that it is composed almost entirely of hydrogen and helium, with very little of the heavier elements like oxygen normally found in a galaxy rich in stars and stellar debris.
“It seems that we have found a black hole that does not have a substantial host galaxy and that predates stellar processes,” Juodžbalis said. “This is very exciting because it is evidence of primordial black holes or direct collapse black holes, which have been theorized but not confirmed.”
