A new study published in Astrophysical Journal Letters, A group of international researchers led by the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) reported that they have discovered the first signs that certain parts of the universe are being heated to temperatures similar to the intergalactic gaseous medium. atoms in the universe now reside.

The vast majority, about 90%, of all atoms in the universe can be found in the intergalactic gas that fills the space between visible galaxies. This intergalactic medium is currently hot and complex, with temperatures ranging from 100,000 degrees Celsius to 10 million degrees Celsius, which researchers refer to as the “warm-hot intergalactic environment” (WHIM).

However, more than 10 billion years ago, when galaxies in the universe were at the peak of star formation, most of the intergalactic medium existed at relatively lower temperatures below 10,000 degrees Celsius, creating a more predictable and stable phase.

An international research team led by IPMU Kavli PhD student Chenze Dong and project assistant professor Hee-Gang Lee has discovered that the farthest region of the universe is heated to temperatures more typical than today’s WHIM, when the universe is only 3 billion years old. . This region is a giant galaxy cluster known as “COSTCO-I”, with a total mass of more than 400 trillion solar masses and several million light-years across, also discovered by a team from Li and Kavli IPMU. Researchers in 2022

This figure compares the hydrogen absorption observed near the COSTCO-I galaxy primordial cluster (top panel) with the expected absorption in the presence of the first cluster. The typically large mass and size of protocluster galaxies cast a large shadow when observed at a specific wavelength of 121.6. nm, caused by neutral absorption hydrogen associated with the primary cluster gas. However, no absorption shadow was found in the COSTCO-I region.

“We were surprised by its absence because hydrogen absorption is one of the common ways to search for galaxy primordial clusters, and other first clusters near COSTCO-I show this absorption signal,” Dong said.

The absence of neutral hydrogen following the initial cluster indicates that the gas in the primary cluster must have been heated perhaps a million degrees above the cold state then expected for the intergalactic medium in the Universe.

“If we think of today’s intergalactic environment as a giant cosmic stew boiling and bubbling, COSTCO-I was probably the first bubble in the distant past observed by astronomers at a time when most of the pot was still cold,” Lee said.

“WHIM’s properties and origin remain one of the biggest questions in astrophysics right now, and being able to look at one of WHIM’s first hotbeds will help reveal the mechanisms that cause intergalactic gas to boil into the modern foam. There are several options for how this might happen, but “This could either be gas warming as they collide with each other in gravitational collapse, or giant radio jets pumping energy from supermassive black holes in the protocluster.”

“COSTCO-I is interesting even in terms of protocluster evolution. Astronomers often look for first clusters in galaxies or the intergalactic medium to find them. However, COSTCO-I cannot be found by these conventional methods. A future PFS study could look for more protoclusters like COSTCO-I and try to find them. can reveal its evolution,” said Rieko Momose, co-author and JSPS Research Fellow at overseas.

The intergalactic medium is the gas reservoir that feeds the galaxy’s raw materials, and hot gas behaves differently from cold gas in how easily they can enter galaxies to form stars. Being able to directly study the growth of WHIM in the early universe allows astronomers to build a complete picture of galaxy formation and the life cycle of the gas that feeds it.

Kavli IPMU astronomers are currently actively participating in the development of a powerful new multi-object spectrograph known as the Subaru Prime Focus Spectrograph (PFS) for the Subaru 8.2-metre telescope on Maunakea. With Subaru PFS, astronomers will be able to map volumes 40 times larger than in the current study and examine the properties of gas in hundreds of primordial clusters of galaxies.