Spotted: Galaxy protocluster in the early universe with hot gas cloud

While observing a galactic protocluster in the early universe, using W. M. Keck Observatory on Maunakea in Hawaiʻi, astrophysicists discovered a scorching gas cloud surrounding the protocluster. 

A galactic protocluster way ahead of its time

This scorching gas is in close contact with a region that consists of a significant collection of galaxies named COSTCO-I. Observed when the cosmos was around 11 billion years younger, COSTCO-1 is assumed to be of a time when the gas that occupied most of the space outside the observable galaxies, called the intergalactic medium, was comparatively much cooler. In the course of this era, called the "Cosmic Noon," galaxies in the cosmos were at the peak of forming stars; Cold gasses filled the galaxies' stable environment they required to form and grow, with temperatures of around 10,000 degrees Celsius. 

Overall, the cauldron of gasses related to COSTCO-I seems ahead of its time, burning in a hot, complex state; its temperature somewhat resembling the modern-day intergalactic medium, which has temperature measuring from hundred thousand to more than ten million degrees Celsius, often referred to as the "Warm-Hot Intergalactic Medium" (WHIM). 

This was the very first-time astrophysicists discovered a patch of ancient gas with characteristics pretty much similar to the modern-day intergalactic medium; to date, it is the earliest known component of the universe that managed to reach the temperature of the present-day WHIM. 

First bubble of the boiling cosmic stew

The research, led by a team from Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, part of the University of Tokyo), is published in The Astrophysical Journal Letters.

"If we think about the present-day intergalactic medium as a gigantic cosmic stew that is boiling and frothing, then COSTCO-I is probably the first bubble that astronomers have observed, during an era in the distant past when most of the pot was still cold," said Khee-Gan Lee, an assistant professor at Kavli IPMU and co-author of the paper.

COSTCO-I was observed by the team when the universe was only 1/4th of its present age. The total mass of the galaxy protocluster is similar to the mass of more than 400 trillion Sun and is several million lightyears old. 

"We were surprised because hydrogen absorption is one of the common ways to search for galaxy protoclusters, and other protoclusters near COSTCO-I do show this absorption signal," said Chenze Dong, a Master's degree student at the University of Tokyo and lead author of the study. "The sensitive ultraviolet capabilities of LRIS on the Keck I Telescope allowed us to make hydrogen gas maps with high confidence, and the signature of COSTCO-I simply wasn't there."