Not more than two weeks after scientists announced the discovery of the farthest star ever observed, another group of astronomers has announced they have spotted the farthest galaxy ever seen. Coined HD1, the galaxy candidate is some 13.5 billion light-years away from Earth.
Writing in the Astrophysical Journal, the team proposed two theories as to the nature of the astronomical object. The first is that HD1 could be forming stars at an astounding rate and maybe even be home to Population III stars, the universe’s very first stars — which, until now, have never been observed. While no confirmation of those stars currently exists, the group put forward the hypothesis due to the extremely bright ultraviolet-light signature of HD1. Alternatively, HD1 may contain a supermassive black hole about 100 million times the mass of our Sun.
“I don’t like putting discoveries in a ranking, because the work of every scientist is fundamental for our advancement as human beings, however, if the redshift of HD1 is further confirmed, its study would offer a mind-blowing opportunity to study the universe as it was 13.5 billion years ago,” Fabio Pacucci, lead author of the study and an astronomer at the Center for Astrophysics at Harvard & Smithsonian, told ZMEScience.
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 Millimeter/submillimeter Array (ALMA) to confirm the distance, which is 100 million light-years farther than GN-z11, the previous record-holder for the most distant galaxy.
Upon first glance, the research team believed the object was a standard starburst galaxy that already produces stars at a high rate. However, after more calculations, they found that HD1 was producing an insane amount of stars, more than would be feasible for a normal starburst. Each year, HD1 would be forming more than 100 stars, ten times the number that one would expect from a standard starburst galaxy.
“This rate, for a galaxy like HD1, is extremely large, far from our theoretical expectations,” Pacucci said. “If this galaxy were to be producing more primordial stars, which are heavier, hotter, and produce more ultraviolet light than normal stars, then the explanation of HD1’s observational properties would be easier. If, in the future, HD1 is confirmed as a starburst of Pop III stars, or if such primordial star formation is detected in other galaxies with the James Webb Space Telescope (JWST), that would be a transformative discovery for astrophysics.”
Though that luminosity could also be caused by a supermassive black hole. If that is the case, HD1 would be by far the earliest supermassive black hole known to man. If that hypothesis is proven true, it would be about 100 million times the size of our Sun. By size comparison, the black hole at the center of the Milky Way is approximately four million solar masses. While giant, it certainly wouldn’t be the largest in space.
“We now know that supermassive black holes of some tens of billions of solar masses are out there,” Pacucci said. “Compared to these behemoths, the black hole in HD1 would be relatively small. This is not surprising, because black holes need time to grow, a long time. And HD1 could be shining only 330 million years after the Big Bang, not leaving enough time to grow. If HD1 is indeed at redshift 13, and if it hosts a 100 million solar masses black hole, it would provide a tremendous opportunity to place constraints on how black holes formed and grew in the very first phases of the evolution of the universe.”
The next step for the research team will be to study HD1 in further detail with the JWST to obtain a spectrum of the source and conclusively determine its nature.
“(The discovery is) like using a time machine, seeing the first bursts of stars forming, possibly the first supermassive black holes being assembled,” Pacucci said. “All these processes would ultimately end up creating everything that we see around us today, including our own bodies! In addition, this would be, by far, the farthest object that a human eye ever witnessed.”