The furthest object we’ve ever seen – a very young galaxy

Astronomers have caught a glimpse of a galaxy which, at 13.5 billion light-years away, they believe to be the most distant object yet seen.

The type of galaxy, which is named HD1, remains to be figured out. According to their observations, it’s either an incredibly young galaxy, filled with stars from the birth of the universe – or it contains a supermassive black hole, 100 million times bigger than our Sun.

It was found after 1,200 hours of observation with four different telescopes: 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, an astronomer at the University of Tokyo, Japan, who discovered the galaxy.

“HD1’s red colour matched the expected characteristics of a galaxy 13.5 billion light-years away surprisingly well, giving me goosebumps when I found it.”

The researchers then confirmed the galaxy’s distance using the Atacama Large Millimetre/Submillimetre Array. They’ll be following up with the James Webb Space Telescope for a final verification.

If the James Webb confirms the observation, HD1 will unseat GN-z11’s record as the most distant object – by roughly 100 million light-years.

The extra data will also be useful for figuring out which of the two theories about the galaxy are correct.

“Answering questions about the nature of a source so far away can be challenging,” says Fabio Pacucci, an astronomer at the Harvard & Smithsonian Center for Astrophysics, US.

“It’s like guessing the nationality of a ship from the flag it flies, while being faraway ashore, with the vessel in the middle of a gale and dense fog. One can maybe see some colours and shapes of the flag, but not in their entirety. It’s ultimately a long game of analysis and exclusion of implausible scenarios.”

The central clue is HD1’s brightness: it’s emitting a lot of ultraviolet light. Pacucci says that this means “some energetic processes are occurring there or, better yet, did occur some billions of years ago”.

This could be explained by HD1 being a starburst galaxy – a type of galaxy where stars are forming very quickly. But to explain its brightness, Pacucci says that HD1 would have to be forming stars at “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.”

Meaning that the galaxy could be very, very young.

“The very first population of stars that formed in the universe were more massive, more luminous and hotter than modern stars,” says Pacucci. “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.”

But the UV light could also be caused by a supermassive black hole. This would be an exciting result too – it’d be the earliest supermassive black hole we know about.

“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, also an astronomer at the Harvard & Smithsonian.

“Once again, nature appears to be more imaginative than we are.”

The galaxy is described in a paper in the Astrophysical Journal, and the two theories about its identity are published in the Monthly Notices of the Royal Astronomical Society Letters.