Webb Detects Pristine Helium Clump in GN-z11’s Halo

GN-z11 is an exceptionally luminous galaxy that existed when our Universe was only 420 million years old, making it one of the earliest and most distant ever observed.

This two-part graphic shows evidence of a gaseous clump of helium in the halo surrounding galaxy GN-z11. In the top portion, at the far right, a small box identifies GN-z11 in a field of galaxies. The middle box shows a zoomed-in image of the galaxy. The box at the far left displays a map of the helium gas in the halo of GN-z11, including a clump that does not appear in the infrared colors shown in the middle panel. In the lower half of the graphic, a spectrum shows the distinct ‘fingerprint’ of helium in the halo. The full spectrum shows no evidence of other elements and so suggests that the helium clump must be fairly pristine, made of hydrogen and helium gas left over from the big bang, without much contamination from heavier elements produced by stars. Theory and simulations in the vicinity of particularly massive galaxies from these epochs predict that there should be pockets of pristine gas surviving in the halo, and these may collapse and form Population III star clusters. Image credit: NASA / ESA / CSA / Ralf Crawford, STScI.

GN-z11 is an early but moderately massive galaxy located in the constellation of Ursa Major.

First discovered in 2016 with the NASA/ESA Hubble Space Telescope, this galaxy is estimated to date from when the Universe was only 420 million years old, or 3% of its current age.

GN-z11 is around 25 times smaller than our Milky Way and has just 1% of our Galaxy’s mass in stars.

Surprisingly, the galaxy hosts a supermassive black hole of about 1.6 million solar masses that is rapidly accreting matter.

Using the Near-Infrared Spectrograph (NIRSpec) instrument on the NASA/ESA/CSA James Webb Space Telescope, University of Cambridge astronomer Roberto Maiolino and colleagues detected a gaseous clump of helium in the halo surrounding GN-z11.

“The fact that we don’t see anything else beyond helium suggests that this clump must be fairly pristine,” Dr. Maiolino said.

“This is something that was expected by theory and simulations in the vicinity of particularly massive galaxies from these epochs — that there should be pockets of pristine gas surviving in the halo, and these may collapse and form Population III star clusters.”

Finding the never-before-seen Population III stars — the first generation of stars formed almost entirely from hydrogen and helium — is one of the most important goals of modern astrophysics.

These stars are anticipated to be very massive, very luminous, and very hot.

Their expected signature is the presence of ionized helium and the absence of chemical elements heavier than helium.

The formation of the first stars and galaxies marks a fundamental shift in cosmic history, during which the universe evolved from a dark and relatively simple state into the highly structured and complex environment we see today.

“In future Webb observations, we will explore GN-z11 in greater depth, and we hope to strengthen the case for the Population III stars that may be forming in its halo,” the astronomers said.

The findings will be published in the journal Astronomy & Astrophysics.