Since the Renaissance astronomer Galileo Galilee first studied the heavens using a telescope he built himself, astronomers have been pushing the boundaries of what they can observe. After centuries of progress, they have been able to study and catalog objects in all but the earliest periods of the Universe. But thanks to next-generation instruments and technologies, astronomers will soon be able to observe the “Cosmic Dawn” era – ca. 50 million to billion years after the Big Bang.
In recent years, astronomers have made discoveries that preview what this will be like, the most recent of which is the galaxy candidate known as HD1. This galaxy is about 13.5 billion light-years from Earth (32.2 billion light-years in terms of “proper distance“), making it the farthest ever observed. This discovery implies that galaxies existed as early as 300 million years after the Big Bang, a finding which could have drastic implications for astronomy and cosmology!
The team was made up of scientists from the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo, the National Astronomical Observatory of Japan (NAOJ), University College London (UCL), the Kapteyn Astronomical Institute, the NASA Goddard Space Flight Center, the Harvard-Smithsonian Center for Astrophysics (CfA), the Harvard Black Hole Initiative, the Space Telescope Science Institute (STScI), and multiple research institutes and universities.
Previously, the record for the most distant galaxy went to GN-z11, which was discovered by astronomers Pascal Oesch and Gabriel Brammer of the Cosmic Dawn Center, which is part of the Niels Bohr Institute in Copenhagen. The discovery was made using data from the Hubble Space Telescope’s Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and the Spitzer Space Telescope’s Great Observatories Origins Deep Survey (GOODS).
However, GN-z11 was at the very limit of these telescopes’ detection capabilities. The discovery of HD1 was made possible thanks to 1,200 hours of observation time conducted by multiple telescopes and observatories worldwide. These included the Subaru Telescope and the UK Infrared Telescope at the Mauna Kea Observatory in Hawaii; the Spitzer Space Telescope; and the Visible and Infrared Survey Telescope for Astronomy (VISTA) telescope at the Paranal Observatory in Chile.
Yuichi Harikane, an assistant professor of astrophysics with the ICRR, led the team that discovered HD1. “It was very hard work to find HD1 out of more than 700,000 objects,” explained Harikane in a recent ICRR press release. “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 team then conducted follow-up observations using the Atacama Large Millimeter/submillimeter Array (ALMA) to confirm HD1’s distance. These results supported their previous findings, showing that HD1 was a particularly bright object 13.5 billion years ago – making it a strong galaxy candidate. Akio Inoue, a professor at Waseda University, led the ALMA observations. As he indicated:
“We found a weak signal at the frequency where an oxygen emission line was expected. The significance of the signal is 99.99%. 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 99.9999% or more.”
Observational information on HD1 is still limited, meaning its physical properties are not yet well-constrained. For instance, scientists are not yet certain if its brightness results from it being a very active star-forming galaxy or an active black hole. Either possibility presents exciting opportunities for future observations with next-generation telescopes. HD1 was selected as a target for the cycle 1 observations with the James Webb Space Telescope (JWST), which is expected to gather its first light by the summer.
Beyond potentially establishing a new distance record, the possibility that HD1 is an early galaxy has considerable implications for astronomers and cosmologists. Basically, it would demonstrate that bright objects already existed in the Universe just 300 million years after the Big Bang. This is inconsistent with current models of galaxy formation and cosmic evolution, which theorize that the first galaxies didn’t emerge until roughly one billion years after the Big Bang.
However, recent observations that pushed the limits of our current instruments have forced scientists to reconsider this. Said Yuichi Harikane, who will be leading these 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. We are looking forward to seeing the Universe with the James Webb Space Telescope.”
The paper that describes their findings will appear in the April 8th issue of The Astrophysical Journal.