10Jun2018

Astronomers Discover Six New Galaxies That Have No Stars

Астрономы обнаружили шесть новых галактик, в которых нет звезд

Dark galaxy is a hypothetical object of galactic dimensions that contains very little or does not contain stars. This discovery changes the entire ballgame. How can this exist?

When you meet the term “galaxy”, the first thing that comes to mind is the magnificent view of vortices in outer space, filled with stars and glowing clouds of cosmic gas. However, scientists-astrophysicists were able to find something extraordinary – a few “empty” galaxies that existed only in the early Universe, inside of which contains a very small amount of stars or does not contain at all.

These starless galaxy known under the term “dark galaxy”, they represent a striking example of an early moment in the process of galactic formation. According to present models, such galaxies were a very common thing in the early periods of the Universe when no stars complicated the process of forming new stars.

Since dark galaxies contain no stars, and only consist of gas and more dense matter, they do not emit light in the visible range, so they are so difficult to detect and to study. For the time of astronomical observations was discovered only a few candidates for the title of “dark galaxy”. Detection of six new candidates could help scientists understand what exactly is a dark galaxy in fact and to clarify their role in the formation of normal galaxies.

Six dark galaxies was discovered by astronomers from the Swiss Federal Institute of technology (Swiss Federal Institute of Technology, ETH) in Zurich, using a combination of old and new technologies of observation. This technique relies on observations of quasars, the brightest objects in the Universe, which constitute the immediate environment of supermassive black holes, located generally in the Central regions of galaxies.

Quasars, due to the heating of matter passing through the event horizon of a black hole, emit bright light, a big enough part of which falls on the ultraviolet light. This ultraviolet light is absorbed by the hydrogen atoms and makes them glow. And this is a secondary glow of hydrogen is nazanie alpha-Dini Lyman (Lyman-alpha line).

If the dark galaxy, which is rich in hydrogen, is near a galaxy with a bright quasar at its center, it will act as a space filter and an alpha-hydrogen lines are clearly seen in the light of the quasar. This method has already been used in 2012 to identify dark galaxy candidates by means of a telescope Very Large Telescope of the European southern Observatory.

In 2014 at the VLT telescope was a new instrument, the Multi Unit Spectroscopic Explorer MUSE. This allowed astronomers to look into space much further than was previously possible and allowed us to identify several new dark galaxies. With the help of the MUSE instrument, astronomers investigated six areas adjacent to a bright quasar, and each observation was conducted for 10 hours.

The MUSE instrument has allowed scientists to conduct a full spectral analysis of light. In this set, we allocated more than 200 sources of alpha-hydrogen lines which could not be normal galaxies, in the depths of which are the processes of star formation.

Yet scientists have no hard evidence that discovered “empty” area are dark galaxies. There are some other possible explanations of the observed phenomena. And the final points over “i” will allow to place only further observations, made with the VLT telescope equipped with the MUSE instrument.  Source:Silver Stars

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