Huge cluster of galaxies found in ancient universe

(ORDO NEWS) — Astronomers have studied a group of galaxies located more than 12 billion light-years away from us. The cluster is remarkable in that it is at a little-studied intermediate stage of formation.

Scientists have known about the large protocluster SPT2349−56 for years. It contains one of the most active star formation zones, but it was not possible to more accurately estimate the total stellar mass of the entire system due to too dim light.

Without these data, it was impossible to say whether active star formation was the result of favorable conditions or a direct consequence of the massiveness of the entire system.

The authors of the new study conducted observations in the deep optical and infrared ranges, analytically improved the accuracy of the data, identified new galaxies, determined their mass, and using computer simulations confirmed that the supercluster is at a little-studied stage of formation.

Clusters of galaxies are the nodes of the “cosmic web”, the large-scale structure of our universe. These knots are “linked” to each other by galactic threads, and relatively empty spaces stretch between them.

It is known that these clusters were formed due to small differences in the density of the primary matter of the Universe, which we see in the CMB.

The relic radiation is well studied, as well as the large clusters of galaxies that formed over time, because these are the fundamental “building blocks” of the Universe. But scientists still lack observational data to build accurate computer models of how the density fluctuations created such massive structures.

“Modern” clusters of galaxies are clearly visible, because in the process of their formation, the intergalactic gas heated up and now glows in the X-ray range.

But at distances of ten billion light years (at a redshift greater than 2), the radiation becomes almost indistinguishable, so ancient objects are searched for through mapping the sky in the infrared and submillimeter ranges.

In recent years, a method has become popular, which was developed for the study of cosmic microwave background radiation. It involves large-scale scanning of the sky in the submillimeter and millimeter range with an accuracy of several arc minutes. So many candidates were found for further study, including SPT2349-56.

Huge cluster of galaxies found in ancient universe
CMB map according to the Planck space observatory. The red stripe in the center is light from the Milky Way, the disk of our galaxy

Over the years, astronomers have learned a lot about this object, but the latest observations using Hubble and the infrared camera of the Spitzer telescope have significantly improved the accuracy of the data and revealed new galaxies in it.

The protocluster SPT2349-56 is now known to contain more than 30 submillimeter galaxies, i.e. galaxies in the process of merging with a high rate of star formation. And a few dozen more indistinguishable galaxies ( LBG – and LAE – galaxies).

Analysis of the interstellar gas has shown that the galaxy is in the final stages of star formation. And the forecast of their further development coincides with the observational data for clusters closer to us.

In general, SPT2349-56 is indeed a protocluster of galaxies at a little-studied intermediate stage in the evolution of such objects. The rate of star formation in it exceeds 10 thousand solar masses per year. We see it as it was when the universe was only a few billion years old. The galaxies there are younger than our Milky Way.

Despite the fact that the object was chosen for further study because of its brightness, the galaxies that compose it are themselves ordinary – not too bright and massive. The only exception was C6 , which is at the center of a merger of 20 galaxies and is expected to be the cluster’s brightest galaxy.

More precisely, it has become, but the light of these events will reach us in hundreds of millions of years. The main conclusion of the study is that star formation proceeds there in the same way as in more studied and close to us clusters.


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