The international team of astronomers has found that dull massive galaxy Dragonfly 44 ( “Dragonfly 44″) in the constellation Coma Berenices, is composed almost entirely of dark matter, according to The Independent.
Research galaxies never cease to amaze astronomers. So, in spite of a significant breakthrough in the technique of producing deep high resolution images, an entire class of objects is fraught with many still unexplored interesting features and presents new surprises
This special class -. Galaxies of low surface brightness
Galaxy of low surface brightness – it is a system, in many ways similar to the “normal” galaxies, but it has a very low surface brightness, even in the most central areas. At this point it is already obvious that the low brightness of the galaxy may be of different shapes and sizes. There are a dwarf and a giant system of low brightness.
In particular, there is an amazing class of giant galaxies, low brightness, the characteristic dimensions of which exceed the size of the Milky Way 10 times!
As such systems could be formed, it is still not completely clear. The study of these galaxies, in particular, held and Russian scientists. New low-brightness galaxies surprise was in 2014, when Pieter van Dokkum of Yale University and colleagues found in the Coma Cluster of galaxies 47 ultradiffuznyh low brightness, comparable in size to the size of the Milky Way. These objects had an old stellar population and had a spheroidal shape.
In terms of parameters, this class of objects most resembled dwarf spheroidal galaxies, for example, of the Local Group of galaxies close to the M101. But the impressive size found ultradiffuznyh galaxies did not allow them to be considered a dwarf. Of particular interest in these galaxies stems from the fact that, judging by the extremely low surface brightness, they have a very small total mass of stars. If the bulk of these objects was just stellar population, they would be destroyed by the tidal accumulation of forces.
The astronomers decided to conduct detailed studies of these galaxies, to obtain an accurate estimate of mass. To this end, they got the measurement of stellar kinematics of one of the largest sample ultradiffuznyh spheroidal galaxies – Dragonfly 44. Work was adopted in Astrophysical Journal Letters
The first author of the work of Pieter van Dokkum said:. “Very soon after the opening, we realized that this galaxy must be much more massive than the eye can see. It is so few stars that it would be torn to pieces if something is holding her together. ” In addition, the astronomers were also deep image of the galaxy. The observations were made at the two telescopes – Gemini and Keck Observatory. Both telescopes are located in Hawaii. Astronomers lucky and monitoring took place with different weather conditions. To obtain reliable spectral data scientists took 33.5 hours of observations, which were carried out over six nights.
Evaluation of the dispersion of stellar velocities of 47 km / s puzzled astronomers. “It is amazing, but the stars are moving at speeds that far exceed expectations for such a dim galaxy. This means that the Dragonfly 44 contains a huge share of invisible masses “, – said study co-author Roberto Abraham of the University of Toronto
The estimated total mass of the galaxy is close to the mass of the Milky Way.. And at a fraction of dark matter accounts 98% within a radius containing the half-luminosity galaxies,
and 99.9% if extrapolated to the much larger virial radius, within which the average density the substance is 200 times higher than the critical density of the universe, the next of cosmological models.
As noted by the authors, a preliminary analysis of the data for other smaller ultradiffuznym galaxies sample shows lower values of the velocity dispersions, indicating smaller dynamic weight.
Such a large and dense cluster of dark matter, according to astrophysicists, can explain how this galaxy and its other “sverhtemnye” cousin opened in the last two years, there may be a number of large clusters of galaxies, which should have long ago break them apart
«The opening of this galaxy -. a great gift for scientists studying dark matter. It has no “extra” objects like stars and gas, it is composed almost entirely of dark matter, which we can learn. Before we only knew of the existence of dwarf galaxies of this type, and the discovery of galaxies, similar to Dragonfly 44, but closer to us, it helps us to know what the dark matter and the look of its particles “- concludes van Dokkum
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