The newly-discovered galaxy, named HD1, existed when the Universe was just 330 million years old.
HD1 (red object). Image credit: Harikane et al., arXiv: 2112.09141.
“Observing the first galaxy formation is one of the main goals in the modern astronomy,” said Dr. Fabio Pacucci, an astronomer at the Harvard & Smithsonian Center for Astrophysics and the Black Hole Initiative at Harvard University, and his colleagues.
“One of the most straightforward approaches to achieve this goal is to observe forming galaxies directly in the early Universe.”
“Large telescopes currently in operation have yielded the most distant objects so far,” they added.
“These highest redshift objects have posed various interesting questions for astronomy. For example, the most distant quasars at redshift z > 7 raised a serious problem to form blackholes as massive as one billion solar masses in the limited cosmic time.”
“Thus, searching for the most distant objects is not only the simplest frontier of the knowledge of human beings but also has a great power to reveal the formation physics of various objects in the early Universe.”
HD1 is located some 13.5 billion light-years away and may be home to the oldest stars in the Universe.
“HD1 is extremely bright in ultraviolet light,” Dr. Pacucci said.
“Some energetic processes are occurring there or, better yet, did occur some billions of years ago.”
At first, Dr. Pacucci and colleagues assumed HD1 was a standard starburst galaxy, a galaxy that is creating stars at a high rate.
But after calculating how many stars HD1 was producing, they obtained an incredible rate — HD1 would be forming more than 100 stars every single year. This is at least 10 times higher than what we expect for these galaxies.
That’s when the astronomers began suspecting that HD1 might not be forming normal, everyday stars.
“The very first population of stars that formed in the Universe were more massive, more luminous and hotter than modern stars,” Dr. Pacucci said.
“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.”
Timeline displays the earliest galaxy candidates and the history of the Universe. Image credit: Harikane et al., arXiv: 2112.09141 / NASA / EST / P. Oesch / Yale University.
A supermassive black hole, however, could also explain the extreme luminosity of HD1.
As it gobbles down enormous amounts of gas, high energy photons may be emitted by the region around the black hole.
If that’s the case, it would be by far the earliest supermassive black hole known to humankind, observed much closer in time to the Big Bang compared to GN-z11, the current record-holder for the furthest galaxy.
“HD1 would represent a giant baby in the delivery room of the early Universe,” said Professor Avi Loeb, an astronomer at the Harvard & Smithsonian Center for Astrophysics.
“It breaks the highest quasar redshift on record by almost a factor of two, a remarkable feat.”
The discovery is described in two papers published in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society Letters.
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Yuichi Harikane et al. 2022. A Search for H-Dropout Lyman Break Galaxies at z~12-16. ApJ, in press; arXiv: 2112.09141
Fabio Pacucci et al. 2022. Are the Newly-Discovered z∼13 Drop-out Sources Starburst Galaxies or Quasars? MNRASL, in press; arXiv: 2201.00823
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