Free Astronomy Magazine November-December 2024

20 NOVEMBER-DECEMBER 2024 Black holes play an important role in the lifecycle of all galaxies, but there are major uncertainties in our un- derstanding of how galaxies evolve. In order to gain a complete picture of the link between galaxy and black hole evolution, the researchers used Hubble to survey how many black holes exist among a popula- tion of faint galaxies when the uni- verse was just a few percent of its current age. Initial observations of the survey re- gion were re-photographed by Hub- ble after several years. This allowed the team to measure variations in the brightness of galaxies. These variations are a telltale sign of black holes. The team identified more black holes than previously found by other methods. The new observational results sug- gest that some black holes likely formed by the collapse of massive, pristine stars during the first billion years of cosmic time. These types of stars can only exist at very early times in the universe, because later- More black holes than expected in the early Universe by NASA − Ray Villard W ith the help of NASA’s Hubble Space Telescope, an international team of researchers led by scientists in the Department of Astronomy at Stock- holm University has found more black holes in the early universe than has previously been reported. The new result can help scientists understand how supermassive black holes were created. Currently, scien- tists do not have a complete picture of how the first black holes formed not long after the big bang. It is known that supermassive black holes, that can weigh more than a billion suns, exist at the center of several galaxies less than a billion years after the big bang. “Many of these objects seem to be more mas- sive than we originally thought they could be at such early times — either they formed very massive or they grew extremely quickly,” said Alice Young, a PhD student from Stock- holm University and co-author of the study published in The Astro- physical Journal Letters . generation stars are polluted by the remnants of stars that have already lived and died. Other alternatives for black hole formation include collapsing gas clouds, mergers of stars in massive clusters, and “pri- mordial” black holes that formed (by physically speculative mecha- nisms) in the first few seconds after the big bang. With this new infor- mation about black hole formation, more accurate models of galaxy for- mation can be constructed. “The formation mechanism of early black holes is an important part of