Thus A Cluster Emerges From The Cosmic Web (Cosmology)

An international team of astronomers used the National Science Foundation’s Green Bank Telescope and NASA’s Chandra X-ray Observatory to capture a snapshot of a massive cluster around the time it began to emerge from the cosmic web, nearly 10 billion. Years ago. The study is published in Mnras

A sort of reverse dive: so we can imagine the emergence of any cosmic structure from the cosmos itself. However, this representation is only part of the story, the fruit of a limited perspective. Observing, for astronomers, means focusing attention on phenomena that appear luminous, that is, involving baryon matter . In the formation of cosmic structures, however, light comes almost last. To this, then, it must be added that seeing what was bright when the universe was little more than just born is no small feat.

In an article currently being published in Monthly Notices of the Royal Astronomical Society , a group of scientists managed to capture the light of a cluster of galaxies just as it ignited and emerged from the cosmic web. The cluster is called Idcsj1426 + 3508, is located at redshift 1.75 and its light has traveled almost 10 billion years to reach us.

Let’s start from the beginning: the light does not come first, we said. The texture of the cosmos is in fact woven from dark matterwhich, through gravity, we can imagine as a spider’s web with some more or less large densities: these are the attractors of baryon matter. When an imposing structure such as a cluster begins to form, it is therefore the dark matter that first prepares a comfortable lair in which the baryon matter – the gas – can begin to thicken as it is gravitationally attracted. It therefore seems like a dip in the opposite direction, that of light, because the gas that heats up proportionally to the increase in its density begins to ignite slowly, becoming visible. This is how astronomers were able to measure the properties of Idcsj1426 + 3508, and they did so in an era and with unprecedented precision.

A snapshot that, thanks to the comparison of the properties of the gas of Idcsj1426 + 3508 with those of its most plausible descendants of the present day – those observed in the nearby universe – scientists have been able to evolve over time to predict the history of its future and tumultuous evolution.

Stefano Andreon (researcher of INAF from Brera and first author of this study) observing a very high redshift cluster with the Green Bank Telescope from his home studio

«Everywhere, except in the center, the temperature will become warmer despite the entry of new cold gas from the peripheral regions» explains Stefano Andreon , INAF researcher at the Brera site and first author of the study. The center of the cluster, therefore, will retain its properties unchanged over time despite the tumultuous and hostile environment, maintaining a delicate balance between the perturbations generated by the entry of matter and a response mechanism – in astronomical jargon, feedback– not yet identified. Just outside the center, however, the gas in the newly born cluster seems to be colder than that of today’s clusters, while in the outermost regions the situation is reversed. In order to become similar to his great-grandchildren, therefore, Idcsj1426 + 3508 will have to go through a mechanism that warms the innermost regions, while the external regions cool down and the center remains almost unchanged over time.

The possibility of going so far back in time with extreme precision was offered by the joint use of the Chandra telescope – which, observing at X-ray frequencies, “sees” the density of the tenuous gas that permeates the cluster – and the Mustang2 chamber of the Green Bank Telescpe ( GBT ), in West Virginia, which made it possible to measure the thermal agitation of the gas – which astronomers and physicists call pressure – at various points in the cluster. The data showed that the gas gets hotter as the distance from the center increases, going from 50 to 150 million degrees Celsius.

“But a swallow doesn’t make spring,” Andreon continues. “The evolution of galaxy clusters is probably diverse, which is why we are observing, and inviting colleagues to observe, other clusters that begin to emerge from the cosmic network, in the hope of identifying, in addition to individual differences, a common general pattern” .

“Of course we are interested in how clusters evolve over time, not just to understand their astrophysics and associated phenomenology,” adds Charles Romero , researcher at the Green Bank Observatory and the University of Pennsylvania and co-author of the study. “The evolution of clusters, in fact, is a fundamental step in being able to study the evolution of the universe and cosmology using the clusters of galaxies themselves as tracers”.

Featured image: Image of the cluster Idcsj1426 + 3508 in which the hot gas in the periphery is colored red, the colder gas in the center is blue. Credits: Gbt / Chandra / Sdss / Andreon / Cigan

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Provided by INAF

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