Galaxies expelled from their clusters

Thanks to the use of public data, provided by the Virtual Observatory, two Russian astronomers have found that the compact elliptical galaxies may have been expelled from their clusters are formed and where they once lived. The researchers believe that their discovery could shed light on the structure and evolution of this class of objects. The results were published in Science.
Thanks to the use of public astronomical data collected in the archives of the Virtual Observatory (VO), two astronomers Russians, Igor and Ivan Zolotukhin Chilingarian the Sternberg Astronomical Institute at Moscow State University, currently working at the Center for Astrophysics (CfA) at Harvard and the Institut de Recherche en Astrophysique et Planétologie, Toulouse, France, respectively, have identified some galaxies that may have been expelled from their clusters as a result of the gravitational interaction with their fellow neighbors. According to the authors, the results of this study, published in Science, may shed light on the structure and evolution of elliptical galaxies compact.


Credit: ESA/Hubble

Astronomers believe that there are many planets that are not visible and isolated that roam freely in space, dispersed in our galaxy, it is not gravitationally bound to any star. In addition, there are dozens of stars known to have been expelled at high speed (of this we have already discussed in another article) and even a star cluster that contains millions of stars escaped the gravity of the giant elliptical galaxy M87 located in Virgo Cluster. All these objects have in common one thing: they have left their systems due to a series of gravitational perturbations.
Until 2006, scientists knew only 6 cases of extremely compact elliptical galaxies, such as Andromeda galaxy M32 satellite of nearby objects that seem so small nuclei ‘stripped’ of ordinary galaxies. These stellar systems have been identified mainly in the vicinity of giant galaxies present in the central regions of giant galaxy clusters. Numerical simulations have shown that these compact elliptical galaxies could be the remains of ancient mergers of galaxies that have remained, in fact, ‘stripped’ of their core due to strong tidal interactions with a more massive galaxy. In 2009, Chilingarian identified 20 other rare cases of this type was found in 2013 while the first compact elliptical located at a great distance from a massive galaxy. At the time, it was not immediately understand where it came from nor where it was formed as a result of a tidal interaction. Therefore, it was necessary to look for other objects of this type.
To carry out their research, Chilingarian Zolotukhin and analyzed a large amount of astronomical data of some surveys, such as the Sloan Digital Sky Survey (SDSS) and the GALEX (GALEX), which are made public through the initiative of the Virtual Observatory . This allowed the authors to identify 195 new compact elliptical galaxies. Most of them, as you would expect, are in clusters or groups of massive galaxies and only 11 are isolated, dispersed in space at distances of the order of a few million light years from clusters closer. “We wondered how we could explain this phenomenon,” says Chilingarian.
Although they are isolated, these compact elliptical galaxies show properties similar to those which are present in the clusters, which implies that they must have had a common origin in the past. Astronomers believe that a massive galaxy initially take away the outer parts of a smaller galaxy falling toward the cluster of galaxies, leaving behind only a compact nucleus; subsequently, the gravitational interaction of a third galaxy expels this residual nucleus in space. Similar processes occur in the central regions of the Milky Way, for example, Sagittarius A *, the supermassive black hole in our galaxy, can scagliar via one of the two stars that are part of a binary system that has moved much closer and possibly ‘absorb’ the other companion. “This is the same phenomenon that, however, takes place on different scales. In other words, in a sort of slingshot effect, during an interaction with three bodies that lighter flies away from the system,” adds Zolotukhin.
To support their hypothesis, the researchers calculated what should be the escape velocity of the compact elliptical galaxies to escape the gravitational pull of its clusters. We know, for example, that to escape the earth’s gravitational attraction, a rocket must travel at a speed exceeding 11 km / sec, while to leave the Solar System Earth orbit that speed becomes greater than 42 km / sec. The calculations of researchers indicate that in the case of an elliptical galaxy compact the escape velocity becomes approximately 2500 km / sec. “These galaxies have a lonely future in front of them because they were exiled from their clusters where they were formed and enjoyed a time,” says Chilingarian. “But this, perhaps, will help them survive in some way because it would otherwise be forced to spiral up to be destroyed by the most massive objects in the course of about a billion years.”
Chilingarian Zolotukhin and now hope that their discovery could shed light on the structure and evolution of elliptical galaxies compact because they believe that these objects do not contain dark matter, the enigmatic component of the Universe which is the ‘cosmic skeleton’ that makes stable various types of galaxies. It is the first time that such a discovery is achieved using only public data. This is a new era in the field of astronomical research in which any user who has an internet connection can use a file accessible and perhaps make a discovery without the need to physically travel to reach an astronomical observatory.

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