Astronomers have spotted the farthest cosmic object ever: a galaxy 13.5 billion light-years away.

Last week, researchers released big news: Hubble had captured light from the farthest star ever to exist in the first billion years after the universe’s birth. Now astronomers come in a new study again with a record-breaking discovery. Because this time, researchers have stumbled upon the most distant galaxy ever.

HD1

The galaxy has been given the name HD1 and is located about 13.5 billion light-years away. Astronomers tracked down this distant cosmic object after more than 1,200 hours of gazing at the night sky using the Subaru Telescope, VISTA Telescope, UK Infrared Telescope and Spitzer Space Telescope. “Picking out HD1 from over 700,000 objects was a lot of hard work,” recalls discoverer Yuichi Harikane. “HD1’s red color matched surprisingly well with the expected features of a galaxy more than 13.5 billion light-years away, which gave me a bit of goosebumps.”

Galaxy HD1, the red object. Image: Harikane et al.

To confirm the distance, the team conducted follow-up observations using the Atacama Large Millimeter/submillimeter Array (ALMA). Indeed, HD1 is a whopping 100 million light-years further from us than galaxy GN-z11; the previous record holder.

Extremely bright

What is particularly striking is that HD1 is extremely bright in ultraviolet light. How is that possible? “There are some energetic processes taking place there,” explains researcher Fabio Pacucci. “Or, better yet, that happened several billion years ago.”

starbust galaxy

Initially, the researchers assumed that HD1 is a standard starburst galaxy that produces stars at a rapid rate. But after calculating how many stars HD1 gives birth to, the researchers make an astonishing discovery. The galaxy appears to form more than 100 stars every year. “This is at least ten times higher than what we expect from Starbusts,” said Pacucci.

This timeline shows the first galaxies and the history of the universe. Image: Harikane et al., NASA, EST and P. Oesch/Yale

Population III stars

The team has two theories so far. On the one hand, HD1 could potentially be home to population III stars; the very first stars in the universe that have never been observed to date. “The very first population of stars to form in the universe was more massive, brighter, and hotter than contemporary stars,” explains Paccuci. “Assuming that the stars produced in HD1 represent this first population of III stars, their properties could be more easily explained. Population III stars are able to produce more UV light than normal stars, which explains the extreme ultraviolet brightness of HD1.”

More about the Population III stars
As mentioned, Population III stars are the very first stars to form after the Big Bang. These stars had very short lives – possibly several hundred thousand years – but have been important for the ‘evolution’ of the universe. These stars quickly convert light elements into heavier elements, such as oxygen, nitrogen, carbon and iron. Without these elements we would not have existed, because they are very important for the origin of life. These primordial stars have not yet been observed. But they may become detectable if they are magnified very strongly by gravitational lenses, giving hope for future observations.

However, the researchers have another theory. Alternatively, HD1 could also host a supermassive black hole about 100 million times the mass of our sun.

supermassive black hole

Such a supermassive black hole could also explain HD1’s extreme brightness, according to the researchers. As the black hole swallows massive amounts of gas, high-energy photons may be emitted from the area around it. If so, this would be by far the earliest supermassive black hole discovered to date.

Research into HD1 continues. For example, the team plans to re-study the distant galaxy using the recently launched James Webb telescope to verify its distance from Earth. If current calculations prove correct, HD1 will officially go down in the books as the farthest – and oldest – galaxy ever discovered. The same observations allow the team to dig deeper into HD1’s identity and confirm whether any of their proposed theories are correct.