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Hubble revealed strange blue “spots” of young stars

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The astrophysicists working on the riddle of black matter they are looking for dwarf galaxies containing dark matter but which are likely very faint from having escaped a previous detection. the standard cosmological model predicts the existence of a large number of these galaxies dwarfs around large galaxies such as the Milky Way.

It is possible to hunt these dwarf galaxies, and more generally faint galaxies near our galaxy using radio telescopes like those of the network of Very large matrix in New Mexico (United States). Technically it is a question of studying radiation Radio from clouds from gasFor instance through the famous line 21 cm from hydrogen. Several promising gas clouds that could be associated with faint dwarf galaxies were therefore discovered by the group ofastronomers led by Elizabeth Adams of the Dutch Radio Astronomy Institute.

These gas clouds were thought to be associated with the Milky Way and most of them probably are. But when teams – with researchers such as David Sand, associate professor of astronomy at Arizona, or Michael Jones, postdoctoral researcher atObservatory for Arizona Stewards and lead author of an article on these clouds and deposited in free access on arXiv – I wanted to search stars associated with them and the dwarf galaxies, they had surprises.

Thus, an unprecedented association of young blue stars forming a group called DRY 1 and observed with telescope Hubble was actually in thecluster of galaxies of the Virgin. Located at an estimated distance of between 48 and 72 millionlight yearsit was discovered by the famous French astronomer Carlo Messier (1730-1817) known for creating the famous catalog of deep-sky objects that bears his name.

Two hypotheses for the origin of the mysterious “blue spots”

Other observations made with Hubble and the instruments of the VLT of Eso in Chile revealed the existence of ” patches similar projects with features never seen before. Therefore, most of the stars in each system are very blue and very young, rich in heavy elements that astrophysicists call metals which are, in fact, simply nuclei different from those ofhydrogenL’helium it’s theirs isotopesall immersed in clouds that contain very little atomic hydrogen forming well at the end of the structures the size of a dwarf galaxy.

The article on arXiv reports five blue “spots” that are distant from the Milky Way and distant galaxies in the cluster of Virginwith which they are potentially associated, from a distance of up to 300,000 light years.

The presence almost exclusively of blue stars, therefore young, with n yellow dwarf Where is it red dwarf truly detectable, it indicates that the star formation is recent. However, the presence of many metals indicates that the gas from which these stars formed must have been in a large and ancient galaxy that has had time to chemically evolve with several generations of stars in nucleosynthesis stellar and finish their life in supernova, thus expelling the products of this nucleosynthesis into galaxies. We should therefore see, as in the Milky Way, red dwarfs and yellows in abundance.

To resolve this paradox, two theories can be invoked, all involving masses gas expelled from a large galaxy. The first takes on the effect of tidal forces exerted by one large galaxy on another, forces that would then have ripped off gas. The other theory concerns a galaxy rapidly colliding with a mass of hot plasma in the galaxy cluster. It can be shown that the shock produces a pressure capable of rapidly stripping a mass of gas from the galaxy. We therefore speak of an effect called dynamic pressure stripping (piston pressure stripping in English).

The researchers are more oriented towards the second hypothesis because, in order to obtain blobs despite everything that are very isolated from the surrounding galaxies, they must move quickly, which is not compatible with the hypothesis of the mechanism with tidal forces.

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