Shining only ~ 300 million years after the Big Bang, it could be home to the oldest stars in the universe or an oversized black hole. An international team of astronomers, including researchers at the Center for Astrophysics Harvard & Smithsonian have located the most distant astronomical object: a galaxy. Named HD1, the candidate galaxy is about 13.5 billion light-years away and is described today (April 7, 2022) in The Astrophysical Journal. In an accompanying paper published in the Monthly Notices of the Royal Astronomical Society Letters, scientists have begun to speculate about what exactly the galaxy is. The team proposes two ideas: HD1 can form stars at an astonishing rate and possibly even host the stars of Population III, the first stars in the universe – which, to date, have never been observed. Alternatively, HD1 may contain an oversized black hole about 100 million times the mass of our Sun. “Answering questions about the nature of a source so far away can be challenging,” says Fabio Pacucci, lead author of the MNRAS study, co-author of the paper on the ApJ and an astronomer at the Center for Astrophysics. “It is like guessing the nationality of a ship from the flag it carries, while it is on a distant shore, with the boat in the middle of a storm and dense fog. One can see some colors and shapes of the flag, but not all of them. It is, after all, a long game of analyzing and excluding improbable scenarios. HD1 is extremely bright in ultraviolet light. To explain this, “some energy processes are happening there or, even better, they happened a few billion years ago,” says Pacucci. Researchers initially speculated that HD1 was a typical star-bursting galaxy, a galaxy that produces stars at a high rate. But after calculating how many stars HD1 produced, they got “an incredible pace – HD1 would form more than 100 stars each year. “This is at least 10 times higher than what we expect for these galaxies.” It was then that the team began to suspect that HD1 might not be forming normal, everyday stars. “The first star population to form in the universe was larger, brighter and hotter than modern stars,” says Pacucci. “If we assume that the stars produced in HD1 are these first stars or Population III, then its properties could be more easily explained. In fact, the stars in Population III are capable of producing more ultraviolet light than normal stars, which could clear up the HD1’s extreme UV brightness. An oversized black hole, however, could also explain the HD1’s excellent brightness. As it devours huge amounts of gas, high-energy photons can be emitted from the area around the black hole. If that were the case, it would be by far the earliest oversized black hole known to mankind, observed much closer in time to the Big Bang than the current record holder. The Timeline displays the first candidate galaxies and the history of the universe. Credits: Harikane et al., NASA, EST and P. Oesch / Yale “HD1 would represent a giant baby in the delivery room of the early universe,” said Avi Loeb, an astronomer at the Center for Astrophysics and co-author of the MNRAS study. “It breaks the highest quasar shift in the record almost twice, a remarkable achievement.” HD1 was discovered after more than 1,200 hours of observation with the Subaru Telescope, the VISTA Telescope, the United Kingdom Infrared Telescope and the Spitzer Space Telescope. “It was very hard work to find HD1 from more than 700,000 objects,” said Yuichi Harikane, an astronomer at the University of Tokyo who discovered the galaxy. “The red color of HD1 matched the expected characteristics of a galaxy 13.5 billion light-years away, which left me a little chilled when I found it.” The team then made subsequent observations using the Atacama Large Millimeter / submillimeter Array (ALMA) array to confirm the distance, which is 100 million light-years away from GN-z11, the current record holder for the farthest galaxy. Using the James Webb Space Telescope, the research team will soon be looking at HD1 again to verify its distance from Earth. If current calculations turn out to be correct, HD1 will be the most distant — and oldest — galaxy ever recorded. The same observations will allow the team to dig deeper into the identity of HD1 and confirm whether one of its theories is correct. “Forming a few hundred million years after the Big Bang, a black hole in HD1 must have grown out of a huge seed at an unprecedented rate,” says Loeb. “Once again, nature seems to be more imaginative than we are.” Bibliographical references: “A Search for H-Dropout Lyman Break Galaxies at z ~ 12-16” by Yuichi Harikane, Akio K. Inoue, Ken Mawatari, Takuya Hashimoto, Satoshi Yamanaka, Yoshinobu Fudamoto, Hiroshi Matsuo, Yoichi Tamura, Pratika Dayal, LY Aaron Y , Anne Hutter, Fabio Pacucci, Yuma Sugahara and Anton M. Koekemoer, April 7, 2022, The Astrophysical Journal. DOI: arXiv: 2112.09141 “Are the recently discovered sources of z∼13 abandonment galaxies with starfish or quasars?” by Fabio Pacucci, Pratika Dayal, Yuichi Harikane, Akio K. Inoue and Abraham Loeb, April 7, 2022, .DOI: arXiv: 2201.00823 About the Astrophysics Center Harvard & Smithsonian Astrophysics Center The Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask – and ultimately answer – humanity’s biggest unanswered questions about the nature of the universe. The Astrophysics Center is headquartered in Cambridge, MA, with research facilities throughout the United States and around the world.
