The birth of a cluster of galaxies observed in the early Universe

This image shows the proto-cluster around the Spider's Web galaxy at a time when the Universe was only 3 billion years old.

A huge reservoir of hot gas in a cluster of forming galaxies was detected using the ALMA (Atacama Large Millimeter-Submillimeter Antenna Array) telescope of the European Southern Observatory (ESO) installed in Chile.

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This is the most distant detection of hot gas associated with the formation of clusters to date, which again shows the precocity of the formation of such structures in the Universe.

• Galaxy clusters are among the largest known structures in the cosmos.
• They can be made up of tens or even thousands of galaxies.
• Our Milky Way is part of a set of about thirty galaxies called the Local Group.

The galaxies formed by clusters are surrounded by an intra-cluster medium (MIA) which permeates the space between them.

While the physics of galaxy clusters is generally well understood, the earliest phases of MIA formation are not well documented. In fact, MIAs had only been studied in nearby fully formed galaxy clusters.

Cosmological simulations had predicted the presence of hot gas in [forming] galaxy clusters for more than a decade, but observations failed to confirm it, says Elena Rasia of the Italian Institute of Science. x27;Astrophysics (INAF) of Trieste, in an ESO press release.

The team led by Luca Di Mascolo of INAF has achieved the feat of detecting and d to study an MIA in a cluster of galaxies in the early days of the Universe.

You should know that the gas in the MIA is often much heavier than the galaxies themselves .

Some clusters of galaxies are so massive that they can collect gas which heats up as they fall towards the cluster, the researchers explain in a statement published by ESO.

To confirm the presence of such a gas in a forming cluster, the scientists selected one of the candidates well known to astronomers: the Spider's Web proto-cluster, located at a time when the Universe was only 3 billion years old.

The discovery of a large reservoir of hot gas in this proto-cluster would indicate that the system is on its way to becoming a true cluster of long-lived galaxies rather than dispersing, the scientists note.

Italian astronomers detected the Cobweb's MIA through what is known as the Sunyaev-Zeldovich thermal effect.

This effect occurs when light from the cosmic microwave background – the residual radiation from the big bang – passes through the MIA. When this light interacts with the fast-moving electrons in the hot gas, it gains some energy, and its color or wavelength changes slightly, the researchers say.

“At the correct wavelengths, the Sunyaev-Zeldovich thermal effect thus appears as a shadow effect of a cluster of galaxies on the cosmic microwave background. »

— Luca Di Mascolo, INAF

It was by measuring these shadows on the cosmic microwave background that astrophysicists were able to deduce the existence of the hot gas, estimate its mass and map its shape.

“Thanks to its unparalleled resolution and sensitivity, ALMA is the only facility currently capable of performing such a measurement for distant progenitors of massive clusters. »

— Luca Di Mascolo, INAF

The present work has determined that the Cobweb proto-cluster contains a vast reservoir of hot gas at a temperature of a few tens of millions of degrees Celsius.

Previously, cold gas had been detected in this proto-cluster, but the mass of hot gas discovered in this new study exceeds that of cold gas by several thousand times. This discovery shows that the Spider's Web cluster of galaxies is indeed expected to transform into a massive galaxy cluster in about 10 billion years, with its mass increasing by at least a factor ten, the researchers note.

“The hot thermal component will destroy much of the cold component during the x27; system evolution, and we are witnessing a delicate transition. […] This system confirms through observation long-standing theoretical predictions about the formation of the largest gravitationally bound objects in the Universe.

— Tony Mroczkowski, co-author of the article and researcher at ESO

The arrival of the European Giant Telescope from ESO, which will come into operation in 2027, will help better understand structures such as the Spider's Web with new state-of-the-art instruments that will better describe the galaxies within.

The details of this study are published in the journal Nature.