The three panels show an ever-shrinking region of the PRIMER galaxy field. The first image shows a vast area of ​​galaxies against the black background of space. The second image shows a smaller region of the field, revealing galaxies in greater detail with a variety of shapes and colors. The final image shows the ZS7 galaxy, showing the emission of ionized hydrogen in orange and doubly ionized oxygen in dark red. Image credit: ESA/Webb, NASA, CSA, J. Dunlop, D. McGehee, P.G. Pérez-González, Huebler, R. Maiolino et al. Astronomers have found supermassive black holes, with millions to billions of solar masses, in most massive galaxies in the local universe, including the Milky Way. These black holes are likely to have had a profound effect on the evolution of the galaxies in which they reside. However, scientists still do not fully understand how these objects became so massive. The discovery of massive black holes in the first billion years after the Big Bang suggests that this growth must have happened very rapidly and very early. Now, the James Webb Space Telescope is shedding new light on the growth of black holes in the early universe. The new Webb observations provide evidence that two galaxies and their massive black holes were merging when the universe was only 740 million years old. The system is known as ZS7. The study was published in the Monthly Notices of the Royal Astronomical Society. Massive black holes that are actively accumulating material have unique spectroscopic signatures that allow astronomers to identify them. For very distant galaxies like those studied here, these signatures are inaccessible from the ground and can only be observed with Webb. “We found evidence of extremely dense, fast-moving gas close to the black hole, as well as hot, highly ionized gas illuminated by the high-energy radiation that black holes typically produce during their accretion phase,” explained lead author Hannah Obler of the University of Cambridge in the UK. “Thanks to his unprecedentedly sharp imaging capabilities, Webb also enabled our team to spatially separate the two black holes.”

The team found that one of the two black holes has a mass 50 million times that of the Sun. “The mass of the other black hole is probably similar, but this second black hole is much more difficult to measure because it is buried in a dense gas,” explained team member Roberto Maiorino of the University of Cambridge and University College London in the UK. “Our results suggest that mergers exist as an important pathway for black holes to grow rapidly, even at the dawn of the universe,” explained Professor Ebler. “Together with other Webb discoveries of active massive black holes in the distant universe, our results also show that massive black holes have shaped the evolution of galaxies since the very beginning.” “The mass of the star in this system we studied is similar to that of the Large Magellanic Cloud, which is our neighbour,” said team member Pablo G. Pérez González of the CSIC/INTA Center for Astrobiology (CAB) in Spain. “You can try to imagine how the merger evolution of galaxies would be affected if each galaxy had a supermassive black hole as massive as or more massive than the Milky Way.” The research team also discovered that gravitational waves are also produced when two black holes merge. Such phenomena will be detectable by next-generation gravitational wave observatories such as the upcoming Laser Interferometer Space Antenna (LISA) mission, which was recently approved by the European Space Agency and will be the first space-based observatory dedicated to the study of gravitational waves. “Webb’s results show that light stellar systems that can be detected by LISA should be much more common than previously thought,” said Nora Luetzgendorff, LISA lead project scientist at the European Space Agency in the Netherlands. “We will probably need to adjust our models to accommodate LISA speeds in this mass range. This is just the tip of the iceberg.” The discovery is based on observations made as part of the Galaxy Assembly by NIRSpec Integral Field Spectroscopy program. The research team was recently tasked with a new flagship program in Webb’s observing cycle 3, a detailed study of the relationship between massive black holes and their host galaxies over their first billion years. A key part of this program is a systematic search for black hole mergers and their characterization. The effort will determine the rate at which black hole mergers occur in the early cosmic epoch and evaluate the role of mergers in the early growth of black holes and the occurrence rate of gravitational waves since the ancient past.

source: https://dx.doi.org/10.1093/mnras/stae943