Astronomers are competing to see who gets the furthest in the past. Last week, a group using the Hubble Space Telescope announced it had discovered possibly the most distant and oldest star ever seen, dubbed Earendel, which shone 12.9 billion years ago, a mere 900 million years after the Big Bang.
Now another international group of astronomers, pushing Earth’s largest telescopes to their limits, has announced that it has discovered what appears to be the oldest and most distant collection of starlight ever seen: a reddish blob dubbed HD1 that was pouring out massive amounts of starlight. prodigious amounts of energy just 330 million years after the Big Bang. This epoch of time has not yet been explored. Another smear, HD2, looks almost equally distant.
While waiting for the opportunity to observe these spots with the new James Webb Space Telescope, astronomers can only guess what they might be — galaxies, quasars, or possibly something else entirely. But whatever they are, they say, they can shed light on a crucial phase in the cosmos when it evolved from pure primordial fire to become planets, life, and us.
“I am as electrified as a child who sees the first firework in a magnificent fireworks display,” said Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics. “It is very possible that this is one of the first faint glows of light to illuminate the cosmos in a spectacle that ended up creating every star, every planet and even every flower we see around us today, more than 13 billion years later. “
Pacucci was one of a team led by Yuichi Harikane of the University of Tokyo that spent 1,200 hours using various ground-based telescopes to search for very early galaxies. Their findings were published Thursday in The Astrophysical Journal and Monthly Notices of the Royal Astronomical Society. Their work was also reported earlier this year by Sky & Telescope magazine.
In the expanding universe, the farther an object is from us, the greater the speed at which it is moving away from us. In the same way that the sound of an ambulance moving away changes to a lower pitch, movement causes light from an object to change to redder wavelengths. In search of the most distant galaxies, astronomers examined about 70,000 objects, and HD1 was the reddest they could find.
“HD1’s red color matched surprisingly well the predicted features of a galaxy 13.5 billion light-years away, which gave me goosebumps when I encountered it,” Harikane said in a statement released by the Center for Astrophysics.
But the standard of excellence for cosmic distances is the “redshift”, or redshift, derived by taking a spectrum of the object and measuring how much the wavelengths emitted by the characteristic elements have increased or shifted towards the red.
Using the Atacama Large Millimeter/submillimeter Array, or Alma — an array of radio telescopes located in Chile — Harikane and his team achieved a non-definitive redshift of 13 for HD1, which means that the wavelength of light emitted by an atom of oxygen will stretch to 14 times its resting wavelength. The redshift of the other spot was not determined.
This dated the supposed galaxy to just 330 million years since time began, right in the middle of the period targeted by the Webb telescope, which will also be able to confirm the redshift measurement.
“If the redshift measured by Alma can be confirmed, this will indeed be a spectacular object,” commented Marcia Rieke of the University of Arizona, one of the principal investigators on the Webb telescope.
According to the story told by astronomers, the road that led to the universe as we know it began about 100 million years after the Big Bang, when hydrogen and helium created in the primordial explosion began to condense to form the first stars, known as stars. of Population 3 (Populations 1 and 2, which have larger amounts of heavier elements, are present in galaxies today).
Such stars composed solely of hydrogen and helium have never been observed and must have been much larger and more luminous than the stars present in the universe today. They would have reached very high temperatures and died in a short time in supernova explosions that then kick-started the chemical evolution that polluted the pristine universe with elements like oxygen and iron, which make us up.
Pacucci said they initially thought HD1 and HD2 were called starburst galaxies, which expand with new stars. But, after further research, they found that HD1 appeared to be producing stars at more than ten times the speed these galaxies usually do.
Another possibility, Pacucci said, is that these galaxies were giving birth to the very first ultraluminous Population 3 stars themselves. But astronomers have a hard time explaining how a black hole could have reached such dimensions at such an early point in cosmic time.
Had he been born that way, in the chaos of the Big Bang, or was he simply stupendously hungry?
“HD1 would represent a gigantic baby in the delivery room of the early universe,” said Avi Loeb, co-author of Pacucci’s paper.
Translation by Clara Allain
