Discovery of HD1, the most distant galaxy from Earth

This is a new record that takes us far in space and time. This was reported on April 7, 2022 in the journal by researchers from Harvard (USA). Astrophysical Journal discovery of the most distant galaxy ever observed. HD1 is 13.5 billion light-years away. This is 100 million more than the reigning champion GNz11. And this is especially close to the beginning of the universe, since it was only about 300 million years old when the image of this galaxy began to move towards us … It took 1200 hours of observation with four instruments, Subaru Telescope (Hawaii), VISTA (Atacama Desert, Chile) , the Infrared Telescope of the United Kingdom (Hawaii) and, finally, the Spitzer Infrared Space Telescope, decommissioned at the end of 2020. The measurements were taken in the infrared, because due to the expansion of the Universe, all distant objects are moving away from us. And the further they go, the faster they disappear. This escape velocity is at the heart of the Doppler effect, which shifts their light towards longer wavelengths corresponding to infrared.

The mythical first stars of the universe

However, if we were close to HD1, hence without the Doppler effect, it would glow strongly in the ultraviolet. And this intensity intrigues researchers. To explain this, the team considers two equally interesting hypotheses… According to the first, the necessarily very young galaxy HD1 will form new stars at an incredible rate: about 100 stars per year. In comparison, the Milky Way makes less than 10 per year. Better: it could have been the mythical so-called population III stars that first lit up the universe and have never been observed. “The very first generation of stars to form in the universe was more massive, brighter, and hotter than today’s stars.explains on the Harvard University website Fabio Pacucci, the main author of the article. If we assume that those formed in HD1 are these early stars, or Population III, then its properties could be easily explained. Because they are capable of producing more ultraviolet light than the next, hence the exceptional brightness of the HD1.” A hypothesis put forward by Hakim Atek of the Paris Institute of Astrophysics and a member of the Origin and Evolution of Galaxies group,this young galaxy may simply be forming more massive stars and thus brighter, but not population III. HD1 is very massive for such a young galaxy. Perhaps several generations of stars lived in it. Population III has a very short lifespan, a few million years.

A black hole with a mass of one hundred million solar

The second hypothesis suggests the presence in the center of the galaxy of a supermassive hole with a mass of about 100 million solar masses. The ultraviolet radiation will be emitted by huge amounts of gas accelerated to the speed of light before disappearing into the black hole. On the one hand, the presence of such a star would not be so surprising: most galaxies have one at the center, starting with the Milky Way, which contains a black hole with a mass of 4 million solar masses. On the other hand, how to explain that such a quantity of matter has accumulated in such a short time?! The mechanism has yet to be figured out…

James Webb in Search

The sequel is now owned by the James Webb Space Telescope, which will be up and running soon. “For now, HD1 is more of a candidate for the “most distant galaxy” than a verified observation. The measurements taken by Fabio Pacucci are promising but need to be confirmed by JWST.” notes Hakim Atek. Therefore “HD1” will be added to James Webb’s menu along with GNz11. But many other distant galaxies should join this list. “The tool will allow us to go back even further, at least 100 million light years from where we are today. And above all, it will save us from bias due to the fact that HD1 measurements were made from the ground. Only the brightest and therefore most massive galaxies are available. However, they remain an exception: the Universe at the beginning of its existence was mainly populated by galaxies of very small masses, less luminous. They are much better suited for detecting the light of very early stars.”concludes Hakim Atek.

Leave a Comment