A team of astronomers has found what could be the most distant galaxy ever spotted. Named HD1, it is about 13.5 billion light-years away – which is to say it is quite close to the 14 billion year old Big Bang. 

The finding shows that bright systems like HD1 can be really, really ancient, existing as early in the Universe as 300 million years after the Big Bang! If the James Webb Telescope confirms HD1's exact distance, it will be indeed the most distant galaxy humans have ever found.

Astronomers look for distant galaxies to understand how and when they formed in the early Universe. As the speed of light is constant and has a limit, it takes time for the light from distant objects to reach us. The light of an object one billion light-years away left that object one billion years ago – in other words, it had to travel one billion years to reach us! This is why astronomers, when looking at distant objects in space, are studying objects far in time, in the deep past.

HD1, spotted at 13.5 billion light-years away, demanded a lot of work to be found. A team of international astronomers analysed over 1,200 hours of observation data from the Subaru, VISTA, UK Infrared and the Spitzer telescopes to put it all together. 

It was, in some ways, the same as looking for a (red) needle inside a huge haystack: to find HD1, astronomers had to look beyond more than 700,000 space objects! These very distant galaxies usually get redder and redder the more distant they are, because the waves of light "stretch" out from our point of view the farther they are from us. And the more these waves get stretched, the closer they are to the red colour of the electromagnetic spectrum, a phenomenon astronomers call "redshift". 

HD1 is very bright, and astronomers are stunned that such bright objects existed so early in the Universe. As the theory of galaxy formation does not account for this kind of phenomena, the next step will be to find out how this specific galaxy was born – or whether it is indeed a galaxy: it could even be an active black hole. The team hopes the James Webb Space Telescope will help solve that mystery.

Image: Image created using data from the VISTA telescope. The red object in the center of the zoom-in image is HD1. Credits: Harikane et al.