Astronomers had goosebumps: the most distant galaxy ever detected, coming from the remote ages of the universe 13.5 billion years ago, is described Friday in a study whose results remain to be confirmed by further observations.
A galaxy 13.5 billion light years away
It took more than 1,200 hours of observing the sky, using four telescopes, to find “HD1”, a very luminous object whose “red color surprisingly corresponded to the characteristics of a galaxy located at 13.5 billions of years”, explains its discoverer Yuichi Harikane, in a press release published on the sidelines of the study by The Royal Astronomical Society.
An intuition that additional data, collected by the Alma observatory in Chile, have corroborated: HD1 is located 100 million years further than GN-z11, so far holder of the record for the most distant galaxy.
The galaxy HD1 would therefore have been born only 300 million years after the Big Bang, a period of the primitive universe. And the light that emanates from it would have traveled for 13.5 billion years to reach the Earth.
” I had goosebumps “
To determine its age, scientists measured the redshift of its original light. As the universe expands, the space between objects expands. And the more we go back in the past, the more these objects are distant and the more their light stretches, shifting towards increasingly red wavelengths.
“When I found this red, I had goosebumps,” says the astrophysicist from the University of Tokyo, one of the authors of the study published in Astrophysical Journal.
Stars never observed or a supermassive black hole?
But there is a catch: scientists have also measured an exceptionally strong intensity of ultraviolet radiation there, the sign of an activity that theoretical models of galaxy formation have not considered.
The authors of the study then put forward two hypotheses: the young galaxy would have been a particularly fertile ground for the formation of stars, producing around 100 of them per year – a rate ten times higher than expected. These could be so-called “population III” stars that astronomers have never observed before. These first generations of stars were “more massive, brighter and hotter than ‘modern’ stars”, according to Fabio Paccuci, of the Harvard Astrophysics Center (United States), main author of the study, quoted in the press release.
The James Webb Telescope to the rescue
Another track: the presence of a supermassive black hole in the heart of the galaxy. Who by engulfing gigantic quantities of gas would emit powerful radiation in the ultraviolet. But for that, the black hole would have to be 100 million solar masses. “Reaching such a mass in such a short time is not very credible,” comments astrophysicist Françoise Combes, from the Paris-PSL Observatory, who did not participate in the study.
To remove the unknowns, the HD1 galaxy was selected as a target for the James Webb Space Telescope and its unparalleled ability to see the very distant universe.