An international team of astronomers has found the most distant astronomical object ever: a galaxy called HD1, about 13.5 billion light-years from Earth, was able to form its first stars with astonishing speed. These stars belong to the first generation of stars in the universe that has not yet been directly observed. Additionally, HD1 may contain the first supermassive black hole at its center with a mass of about 100 million times that of the Sun. Two articles devoted at once to this discovery, which can be read on the website of electronic preprints, are also published in the Astrophysical Journal and Monthly Notices of the Letters of the Royal Astronomical Society.
The HD1 galaxy was found after more than 1200 hours of observation with the ground-based telescopes Subaru, VISTA, the UK Infrared Telescope and the Spitzer Space Telescope.
“It was very difficult to find HD1 among over 700,000 objects,” says Japanese astronomer Yuichi Wonderne of the University of Tokyo, who discovered the galaxy and is the lead author of the paper in the Astrophysical Journal. “The observed redshift of HD1 is surprisingly accurate with the expected features of this galaxy 13.5 billion light-years away, and I had goosebumps when I found it.”
A team of astronomers then performed multiple checks with the ALMA radio telescope complex in the Chilean Atacama Desert to confirm an estimate of its distance and age to this object. The distance separating the Sun from HD1 is 100 million light-years longer than that recorded in the previous record holder and the farthest galaxy candidate, GN-z11. In this case z means redshift, GN-z11 has a redshift of z=11.1 while HD1 has z>12-13. The redshift of the characteristic spectral lines of chemical elements is a manifestation of the Doppler effect in the Universe with receding galaxies, it makes it possible to estimate distances from Earth to distant objects.
Two theories have been proposed to explain the unusually rapid birth of the HD1 galaxy in the Universe: According to the first, massive stars initially formed from gas accumulations experiencing processes of merger and compression-collapse, and then formed a supermassive black. hole through multiple engagements; According to another theory, stellar galaxies formed around supermassive black holes that first appeared at their centers.
“Answering questions about the nature of a source this far away can be difficult,” said Italian theoretical astrophysicist Fabio Pacucci of Harvard University and the Smithsonian Astrophysical Observatory, lead author of the MNRAS paper and co-author of the ApJ paper. reconnaissance.. “It’s like guessing the nationality of a ship from its flag when you look from the shore, and the ship itself is in the middle of a storm and is obscured by a dense fog. Perhaps in this case it is possible to distinguish the colors and shape of the flag, but this whole picture will be incomplete. Ultimately, there is a long analytical work to be done by gradually eliminating completely illogical scenarios.
HD1 shines very brightly in the ultraviolet range. Pacucci believes this indicates that some kind of high-energy processes are taking place there, possibly continuing several billion years after the observations.
Initially, researchers assumed that HD1 was a more or less ordinary galaxy with a sudden burst of star formation, so stars are born there at a very high rate. However, by counting how many stars HD1 produces per unit time, the scientists simply got an “incredible” figure: HD1 was supposed to produce more than a hundred stars per year; this is at least an order of magnitude higher than the expected rate of star formation for this type of galaxy. . This led to the conclusion that normal, ordinary HD1 stars cannot form this way.
“The first populations of stars in the universe were much larger, brighter, and hotter than modern ones,” explains Pacucci. – And if we assume that stars formed in HD1 are among the first – the so-called population III stars [в данном случае последовательность звезд традиционно отсчитывается от конца]Then everything becomes clear. Population III stars emit much more ultraviolet light than ordinary stars; This could explain HD1’s increased, even extreme, luminosity in the ultraviolet range.”
The first giant stars in the HD1 galaxy must have formed at least 300 million years after the Big Bang.
However, a supermassive black hole could also explain HD1’s extraordinary luminosity: if it absorbs large amounts of surrounding gas, a bright accretion disk is formed around it, emitting high-energy photons. If that’s true, then astronomers are observing the oldest supermassive black hole they’ve ever known, beating the previous record by a wide margin and forming much more recently to the Big Bang than the previous record holder.
“The black hole in HD1 formed just a few hundred million years after the Big Bang and must have grown at an unprecedented rate,” says renowned astronomer Avi Loeb. Harvard-Smithsonian Center for Astrophysics, is also the co-author of the article at MNRAS. “Once again, nature has been more resourceful than we thought.”
“Astronomers see a lot of ultraviolet there, but they can’t say yet exactly what they’re seeing: stars or a supermassive black hole?” Ru RAN. “More likely, these are stars that will later turn into a black hole, because alternative hypotheses – for example, the formation of supermassive black holes from primary ones – seem so weak so far, they simply cannot come up with a good mechanism of their formation. Most likely, everything “The first interstellar cloud clusters are millions of solar masses that split into very large stellar associations and then into galaxies. The first stars devoid of heavy elements probably formed 100-200 million years after the Big Bang.”
Although the maximum emission of the most distant stars is in the ultraviolet part of the spectrum, the redshift correction allows scientists on Earth to observe in the infrared and submillimeter ranges through two “windows”.
“Certainly, the discovery of an ancient galaxy is a recent achievement that deserves the closest attention,” says Boris Stern. “Now the James Webb Space Telescope is just getting started and needs to find dozens of similar objects, but this record will still precede it. The previous one took several years.
In the future, the research team is scheduled to make HD1 observations using NASA’s new James Webb Space Telescope to determine how far this object is from Earth. If current calculations prove correct, HD1 would be recognized as the most distant and oldest galaxy ever recorded. The same observations will allow scientists to look deeper into HD1’s properties and confirm whether one of the aforementioned theories of the formation of the first galaxies is correct.