Hubble Discovers More Black Holes Than Expected in the Early Universe

Using NASA’s Hubble Space Telescope, an international team of researchers led by scientists from Stockholm University’s Department of Astronomy has discovered more black holes in the early universe than previously reported. This new result may help scientists understand how supermassive black holes were created.

Currently, scientists do not have a clear idea of ​​how the first black holes formed shortly after the Big Bang. Supermassive black holes, which can weigh more than a billion suns, are known to exist at the centers of several galaxies less than a billion years after the Big Bang.

“Many of these objects appear to be more massive than we originally thought at such remote times: either they formed very massively or they grew extremely rapidly,” said Alice Young, a doctoral student at Stockholm University and co-author of the study published in Letters from the Astrophysical Journal.

Black holes play an important role in the life cycle of all galaxies, but there are large uncertainties in our understanding of how galaxies evolve. To get a complete picture of the link between galaxy evolution and black hole evolution, the researchers used Hubble to study the number of black holes in a population of faint galaxies when the universe was only a few percent of its current age.

The first observations of the region studied were photographed again by Hubble after several years. This allowed the team to measure the variations in the brightness of the galaxies. These variations are a telltale sign of the presence of black holes. The team identified more black holes than had been discovered previously by other methods.

The new observational results suggest that some black holes likely formed from the collapse of massive, intact stars during the first billion years of cosmic time. These types of stars can only exist in very early epochs of the Universe, because the stars of the next generation are polluted by the remains of stars that have already lived and died.

Other hypotheses for black hole formation include the collapse of gas clouds, the merger of stars in massive clusters, and “primordial” black holes that formed (by physically speculative mechanisms) in the first seconds after the Big Bang. With this new information about black hole formation, more accurate models of galaxy formation can be constructed.

“The mechanism of formation of the first black holes is an important part of the puzzle of galaxy evolution,” said Matthew Hayes of Stockholm University’s Department of Astronomy and lead author of the study. “With black hole growth models, calculations of galaxy evolution can now be placed on a more physical basis, with a precise scheme of how black holes emerged from the collapse of massive stars.”

Astronomers are also conducting observations with NASA’s James Webb Space Telescope to look for galactic black holes that formed shortly after the Big Bang, to understand their mass and where they were located.