Hot on the heels of the discovery of “Earendel”—the most distant single star at 12.9 billion light-years distant—comes the announcement today that astronomers have now found the most distant galaxy.
Called HD1 and discovered by Japanese astronomers using a bevy of telescopes across the globe, this ultra-remote exists at a staggering 13.5 billion light-years away.
That’s a mere 300 million years after the “Big Bang” that is thought to have created the Universe.
It’s thought that HD1 may be home to the Universe’s very first stars, known as Population III stars, which until now have never been observed.
Here’s everything you need to know about HD1:
HD1 is really far away. It breaks the record held by a galaxy called GN-z11 was discovered in 2017 at 13.4 billion light-years away and takes astronomers even closer to the “Big Bang.”
This is time-travel of the highest order—HD1 no longer exists, but its light is still traveling in our direction.
Published today in The Astrophysical Journalthe paper outlines just how HD1 was found using 1,200 hours of observation data taken by the Subaru Telescope, VISTA Telescope, UK Infrared Telescope and Spitzer Space Telescope.
“It was very hard work to find HD1 out of more than 700,000 objects,” says Yuichi Harikane, the astronomer who discovered HD1. “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.”
HD1 is red because very old light it is stretched over time as it travels through space. Red light has the longest wavelength. Since the Universe is expanding, very distant galaxies appear to move away from us at greater speeds than closer galaxies. Their light is therefore even redder.
What’s surprising about HD1 is its extreme luminosity, It’s extremely bright in ultraviolet light and therefore thought to be a very active star-forming galaxy. It’s estimated to be forming more than 100 stars every single year.
However, that’s 10 times higher a rate than scientists expected. Is HD1 producing an earlier generation of stars astronomers know nothing about. “The very first population of stars that formed in the Universe were more massive, more luminous and hotter than modern stars,” said Fabio Pacucci, an astronomer at the Center for Astrophysics and lead author of an accompanying paper also published today in the Monthly Notices of the Royal Astronomical Society Letters. “If we assume the stars produced in HD1 are these first, or Population III, stars, then its properties could be explained more easily. In fact, Population III stars are capable of producing more UV light than normal stars, which could clarify the extreme ultraviolet luminosity of HD1.”
HD1 was discovered after more than 1,200 hours of observing time with the Subaru Telescope, VISTA Telescope, UK Infrared Telescope and Spitzer Space Telescope. The team then conducted follow-up observations using the Atacama Large Millimetre/submillimetre Array (ALMA) to confirm the distance, which is 100 million light years further than GN-z11, the current record-holder for the furthest galaxy.
Doubting their findings, the team used the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope array in Chile to confirm HD1’s distance. “The significance of the signal is 99.99%,” said Akio Inoue, a professor at Waseda University, who led the ALMA observations. “If this signal is real, this is evidence that HD1 exists 13.5 billion light-years away, but we cannot be sure without a significance of 99.999% or more.”
So for now HD1 is regarded as a “candidate” galaxy until it’s confirmed by a different team of scientists using different equipment or methods. That’s how science works. “Answering questions about the nature of a source so far away can be challenging,” said Pacucci. “It’s ultimately a long game of analysis and exclusion of implausible scenarios.”
It’s possible that HD1 is a black hole, which itself would still be an incredible discovery. “Forming a few hundred million years after the Big Bang, a black hole in HD1 must have grown out of a massive seed at an unprecedented rate,” says Avi Loeb, an astronomer at the Center for Astrophysics and co-author on the MNRAS study . “Once again, nature appears to be more imaginative than we are.”
Cue the James Webb Space Telescope, which will be used later this year to peer at HD1 to confirm its existence and suss-out its physical properties. In fact, HD1 has already been selected as a target for its cycle 1 observations.
“If the spectroscopic observation confirms its exact distance, HD1 will be the most distant galaxy ever recorded, 100 million light-years further away than GN-z11,” said Harikane. “We are looking forward to seeing the Universe with the James Webb Space Telescope.”
Wishing you clear skies and wide eyes.