(Paris) Astronomers have observed star clusters in the Universe so dense that their mass and light played a key role in the evolution of their galaxy at the time of the cosmic dawn, according to a study published Monday in the journal Nature.
“It’s impressive, we don’t see anything like this in the contemporary local Universe,” Angela Adamo, professor in the astronomy department at Stockholm University, explains to AFP.
The study she carried out with an international team identified five globular protoclusters with remarkable characteristics, in a dwarf galaxy from the early ages of the Universe, 460 million years after the Big Bang.
Discovered in 2018 in images from the Hubble Space Telescope, Cosmic Gems Arc is the most distant ever observed, more than 13.2 billion light years away. In the middle of the so-called reionization era, when the intense activity of the first stars and galaxies will illuminate the Universe.
This cosmic dawn is one of the playgrounds of the new James Webb space telescope, which has an even sharper eye than that of Hubble. Where the latter distinguished a faint arc of red light, the James Webb reveals “a very young galaxy, with very young star clusters inside,” according to Ms. Adamo.
“This is really the first time that we can observe this type of object at this distance”, and therefore at such a distant time, explains to AFP Adélaïde Claeyssens, postdoctoral researcher in the astronomy department in Stockholm and co -signatory of the study.
This observation should help to understand the “formation of star clusters that we still observe in the nearby universe –– which are now very old – and their influence on the formation of galaxies,” she adds.
“In our Milky Way, we see about 170 globular clusters, but there were thousands of them,” before they were dispersed or broken up by the galaxy’s expansion, says Ms. Adamo. Above all, the survivors inside the Milky Way disk do not weigh much, with an “insignificant” mass compared to all the stars that populate it.
While conversely, the five star clusters observed in Cosmic Gems Arc are real heavyweights, together representing around 30% of the galaxy’s mass. “This tells us that the Universe is very different,” at that time, according to the astronomer.
Very dense, these star clusters are each concentrated in a very small diameter, less than the approximately four light-years separating our Sun from its nearest star, Proxima Centauri. “Imagine there are a million stars,” in this space, says Ms. Adamo.
With massive stars within them, whose mass would be 5,000 to 10,000 times that of the Sun, according to a recent study by the University of Geneva. “We know that these massive stars produce a lot of radiation,” and that in this way, “they influence how galaxies form stars and how gas is distributed around galaxies.”
In the same way, these very massive stars, at the end of their short lives, created black holes, some of which could be the supermassive objects found today at the heart of many galaxies.
These observations open “a kind of window” into the genesis of galaxies, according to the study’s astronomers. To find out more, we will need to find other future globular clusters at the time of the cosmic dawn, and be able to study them in more detail.
“The James Webb will help find some,” according to Professor Adamo, but astronomers are waiting for the arrival of the ELT (Extremely Large Telescope) from the European Southern Observatory “to help understand the physical processes at work in these galaxies.
“Another five years of waiting” before we better understand what was happening more than 13.2 billion years ago.
