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Hot on the heels of the most distant star ever seen, astronomers have found a new record-breaking galaxy, whose light comes to us from about 300 million years after the Big Bang. The galaxy, known as HD1, replaces GN-z11 as the farthest known object in the universe, by a good 100 million years. Given that looking back into the cosmos is looking into the past, if the observations are confirmed, HD1 will be the oldest known galaxy.
The new paper describing the discovery, published in The Astrophysical Journal, reports two objects further than GN-z11. HD1 and HD2. More observations are necessary to confirm their exact distance but what has been found so far points to galaxies at the extreme end of our observational capabilities (at least for the next few months, c'mon JWST!).
“It was very hard work to find HD1 out of more than 700,000 objects,” lead author Yuichi Harikane, from the University of Tokyo who discovered the galaxy, said in a statement. “HD1's red color matched the expected characteristics of a galaxy 13.5 billion light-years away surprisingly well, giving me a little bit of goosebumps when I found it.”
The galaxies were discovered from 1,200 hours of data from the Subaru Telescope, VISTA Telescope, UK Infrared Telescope, and Spitzer Space Telescope. The huge observational data set provided compelling data on the distance. Follow-ups using the Atacama Large Millimeter/submillimeter Array (ALMA) further strengthened the evidence.
The team plans to use the JWST, whose science mission starts in June, to confirm HD1's distance and better understand the nature of this galaxy – because this object is weird.
It is just too bright in ultraviolet light. In a companion paper, published in the Monthly Notices of the Royal Astronomical Society, Harikane and co-authors question further the nature of these distant sources. They have two possible explanations, both equally challenging to square with our current models.
In one explanation, the source could be a quasar, a supermassive black hole at the center of a distant galaxy or protogalaxy gobbling up so much material so quickly that the forces at play make said material so hot it outshines the galaxy. If this was the case, it would have to be a supermassive black hole of about 100 million solar masses, something very challenging to have so early in the universe, but not impossible. For comparison, the one at the center of the Milky Way is 4.6 million solar masses.
The other option is that the object is a starburst galaxy. As the name suggests, these objects are experiencing an incredible phase of star formation. For this galaxy, it would need 100 new stars the mass of the Sun born every year. This is 10 times higher than expectations; again not impossible but certainly difficult to explain.
“Answering questions about the nature of a source so far away can be challenging,” added lead author of the second paper, Fabio Pacucci, an astronomer at the Center for Astrophysics. “It’s like guessing the nationality of a ship from the flag it flies, while being far away ashore, with the vessel in the middle of a gale and dense fog. One can maybe see some colors and shapes of the flag, but not in their entirety. It’s ultimately a long game of analysis and exclusion of implausible scenarios.”
JWST, as well as the Nancy G. Roman Telescope, and further infrared observatories such as the Japanese GREX-PLUS are expected to find more of these extremely distant galaxies from the dawn of the universe.
