Galaxy protoclusters identified using the Planck and Herschel space telescopes

The Planck all-sky map at submillimetre wavelengths with the protoclusters indicated as black dots. The inset images showcase some of the observations made by Herschel’s SPIRE instrument (Image ESA and the Planck Collaboration/ H. Dole, D. Guéry & G. Hurier, IAS/University Paris-Sud/CNRS/CNES)
The Planck all-sky map at submillimetre wavelengths with the protoclusters indicated as black dots. The inset images showcase some of the observations made by Herschel’s SPIRE instrument (Image ESA and the Planck Collaboration/ H. Dole, D. Guéry & G. Hurier, IAS/University Paris-Sud/CNRS/CNES)

An article published in the journal “Astronomy & Astrophysics” describes the results of a research carried out by combining the observations made with ESA’s Herschel and Planck space telescopes. The purpose was to find protoclusters, the precursors of today’s galaxy clusters seen in the distant past when the universe was only three billion years. This will help to understand how these huge groups of tens, hundreds and even thousands of galaxies formed and evolved.

The Planck Surveyor and the Herschel Space Observatory are twins, meaning they were launched together on May 14, 2009 on a Ariane 5 rocket. Both of them reached the area called L2, where the combination of the gravitational force of Earth and Sun balance the centrifugal force creating a situation of stability.

Both missions are now finished but the observations made over the years can be the subject of lengthy analyzes. In the case of the research on protoclusters, only now the results have been published. They were obtained by combining the skills of the Planck and Herschel space telescopes, which were equipped with different instruments which in this case were used in a complementary manner.

The main purpose of the Planck Surveyor was to observe the cosmic microwave background (CMB) radiation, of which an accurate map was created. It analyzed the entire sky in nine different wavelengths ranging from infrared to radio waves. It couldn’t make precise observations of specific areas but they were sufficient to identify 234 brilliant sources. They had characteristics that suggested they were far away so they appeared as they were in the early universe.

At that point, the Herschel came space telescope into action and was able to make observations with a much higher resolution in the field of infrared submillimetre wavelengths. Most of the sources detected by Planck proved consistent with dense concentrations of galaxies in the the early universe.

In young galaxies that form those protoclusters, it was possible to see gas clouds forming stars at a rate that ranged from a few hundred to 1,500 solar masses per year. Today, in the Milky Way stars are born at the average rate of just one solar mass per year.

The fact that already in the early stages of their formation so many stars were born in galaxies is surprising. It’s a very interesting result for this innovative approach that combined the skills of two space telescopes. This is only the first phase of the research because now more studies will be carried out also using other telescopes. It will be possible to study in detail the evolution of galaxy clusters, also to understand the role of dark matter.



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