Farthest galaxy: Astronomers have found what may be the most distant object ever seen

A galaxy called HD1 appears to be about 33.4 billion light-years away, making it the most distant object ever seen — and its extreme brightness amazes researchers


Apr 7, 2022

HD1, shown in red, is the most distant galaxy astronomers have ever seen

Harikane et al.

A galaxy called HD1 may be the most distant object astronomers have ever seen. Its astonishing brightness is hard to explain and could be due to a massive black hole at its center or to the formation of extremely massive primordial stars, both of which are confusing our understanding of the early Universe.

Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics in Massachusetts, and his colleagues found HD1 by searching large public data sets from several of the most powerful telescopes available. They then observed it again with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Those observations showed that HD1 is about 33.4 billion light-years away, more than a billion light-years further than the previous most distant object ever observed, a galaxy called GN-z11. Such a distance is possible, despite the universe being only about 13.8 billion years old, because of the accelerating expansion of the cosmos.

The galaxy is extraordinarily bright in ultraviolet wavelengths, meaning anything that produces its light is likely to be extremely hot. There are two possible ways for it to shine so brightly: either it is undergoing a burst of star formation much larger than we would expect for the galaxy’s relatively small size, or it is home to an active supermassive black hole.

If the answer is a starburst, HD1 should produce about 110 times the mass of the sun in stars every year. “This is very big, it’s an insane number,” Pacucci says. “One explanation is that this galaxy may not form normal stars, but these primordial stars that are much more massive and much hotter than normal nearby stars.” We have never seen such primeval stars.

The other explanation is that HD1 could contain an unexpectedly colossal supermassive black hole. “The observation of a black hole with a mass of 100 million suns so early in the history of the universe would be really groundbreaking, because we really wouldn’t be sure how to form it,” Pacucci said. Black holes take time to grow, and HD1 is so distant that we see it as it was only 330 million years after the Big Bang, so it’s unclear how a black hole could have grown so large so quickly.

We need more observations to be sure of HD1’s extreme distance and to figure out why it’s so bright, Pacucci says. “Right now we are expanding the capabilities of our current observatories very thinly.” The researchers were given observation time with the James Webb Space Telescope to observe HD1, as well as two other objects called HD2 and HD3 that appear to be nearly as far away.

References magazine: The Astrophysical JournalDOI: 10.3847/1538-4357/ac53a9; MNRASin the press

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