[ad_1]
Evidence that the first generation of stars existed in the universe has come to light thanks to observations made by the James Webb Space Telescope (JWST). The proof is found in one of the most distant galaxies known.
The galaxy, named GN-z11, was discovered by the Hubble Space Telescope in 2015 and, before the launch of the James Webb Space Telescope, was considered the most distant galaxy known. With a redshift of 10.6, it makes more sense to talk about how long it has existed, rather than how far away it is. That’s because we see GN-z11 as it was only 430 million years after the Big Bang because of the time it took for its light to travel to our corner of the cosmos. By comparison, the current universe is 13.8 billion years old.
As such, GN-z11 was a prime target for JWST to study. Now, two new papers describe profound discoveries about GN-z11 that reveal vital details about how galaxies that existed in the early universe could have grown.
GN-z11 is the most luminous galaxy known at this particular redshift, and indeed this has become a common theme for the high-redshift galaxies that JWST now finds almost regularly in the early universe. Many of them appear much brighter than our models of galaxy formation predict they should be. Those predictions are based on the standard model of cosmology.
Related: James Webb Telescope Detects Oldest ‘Dead’ Galaxy in Known Universe, and Its Death Could Challenge Cosmology
Now, new JWST observations appear to have shed light on what’s going on.
An astronomy team, led by Roberto Maiolino of the University of Cambridge, has tested GN-z11 with JWST’s two near-infrared instruments, the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrometer (NIRSpec). The researchers discovered evidence of the first generation of stars, called Population III stars, as well as a supermassive black hole that is engulfing enormous amounts of matter and growing at an enormously accelerated rate.
Scientists can calculate a star’s age based on its abundance of heavy elements, which would have been formed by previous generations of stars that lived and died, flinging those heavy elements into space where they are eventually recycled in star-forming regions to form new. stellar bodies. The youngest stars that have formed over the past five or six billion years are known as Population I stars and have the highest abundance of heavy elements. Our sun is a population I star. Older stars contain fewer heavy elements because there were fewer generations of stars before them. We call these Population II stars and they live in the oldest regions of our galaxy, the Milky Way.
Population III stars, however, have until now been purely hypothetical.
These would have been the first stars to form and, as there were no other stars before them, they would have contained no heavy elements and would have been formed solely from the pristine hydrogen and helium forged during the Big Bang. It is also believed that these early stars were extremely luminous, with masses equivalent to at least several hundred suns.
Although astronomers have not yet directly seen Population III stars, Maiolino’s team detected indirect evidence of them in GN-z11. NIRSpec observed a mass of ionized helium near the edge of GN-z11.
“The fact that we see nothing but helium suggests that this mass must be quite pristine,” Maiolino said in a statement. “This is something that theory and simulations expected in the vicinity of particularly massive galaxies of these epochs: that there should be pockets of pristine gas surviving in the halo, and these could collapse and form Population III stars.”
This helium gas is being ionized by something that produces enormous amounts of ultraviolet light, something inferred to be Population III stars. Potentially, the observed helium is material left over from the formation of those stars. The amount of ultraviolet light needed to ionize all that gas requires about 600,000 solar masses of stars in total, shining with a combined luminosity 20 trillion times brighter than our sun. These figures suggest that distant galaxies like GN-z11 would have been more adept at forming massive stars than galaxies in the modern universe.
Meanwhile, according to a second set of results, Maiolino’s team also found evidence of a two-million-solar-mass black hole at the heart of GN-z11.
The team also detected a powerful sleet of radiation flowing from the accretion disk of matter rotating around the black hole, as well as ionized chemical elements normally found near accreting black holes. It’s the most distant supermassive black hole yet discovered, the team says, and its gluttonous appetite causes its accretion disk to become dense and hot, and glow brightly. This, combined with the Population III stars, is what makes GN-z11 shine so brightly, the researchers believe, without breaking standard cosmology as some have prematurely claimed.
The study on the ionized helium group and population III stars has been accepted for publication in the journal Astronomy & Astrophysics, and a preprint can be published. found here. Meanwhile, the study on the NIRCam black hole observations was published on January 17 in the journal Nature.
Originally published in space.com.