In the so-called dark age of the Universe's history it had to fill theoretically predicted, but until recently detected dark galaxy. It is believed that they served as a building material for modern bright, full of stars, galaxies, providing them with a large amount of gas, which subsequently formed the current light.

At the top of the surroundings of the quasar HE 0109-3518 in its natural form, below - emitting dark galaxies (blue line) and quasar (red). (Here and below illustrate ESO, DSS 2, S. Cantalupo.)

In those days, the universe was filled with hydrogen, helium and relict radiation. The stars and the more quasars and other bright sources have not "cut out" from the clouds of gas.

It is clear that without the bright light sources to find objects that are almost 13 billion light-years, was not easy. But "Very large telescope (VLT) succeeded. Why? The dark ages ended not simultaneously: there have already appeared the quasars and other galaxies was still quite dark. And nearby quasars became their dark neighbors - or, rather, their dark gas.

It, according to astronomers, and they saw, finding the most notorious dark galaxy.

"Our approach to the detection of dark galaxy is simple: to cover its dazzling light, " explains Simon Lilly, one of the authors of the report. We were looking for fluorescent glow of gas in the dark galaxies that are illuminated by ultraviolet radiation close to them very bright quasar. Light quasar makes dark galaxy to glow due process similar to the one that lit white lit UV lamp..."

Of course, I had to make a series of very long exposures to detect extremely weak fluorescent glow dark galaxies as the illumination of objects at a distance of more than 10 billion light years. As a highlight was used particularly bright quasar HE 0109-3518. With receiver FORS2 astronomers have built a map of the area of the sky around HE 0109-3518, trying to find UV glow emitted by gaseous hydrogen, which falls intense radiation.

The expansion of the Universe leads to the fact that when this he'arah reaches VLT, it is observed as a shade of visible violet light. This radiation of atoms of hydrogen known as radiation Lyman-alpha. It was formed in the transition of electrons in hydrogen atoms from the second to the first (lowest) level of energy and lies in the ultraviolet region of the spectrum. Because of the expansion of the Universe is the wavelength of light traveling from the object, stretched at movement in space, and the further spreading wave, the more it stretches. Because the red color corresponds to the greatest wavelength of light perceived by the human eye, the process is represented as a shift in wavelength toward the red end of the spectrum (hence the term "red shift"). Kvazar HE 0109-3518 is located at redshift z = 2,4, and UV-radiation of dark galaxies is shifted in the visible region of the spectrum. To select wavelength shifted fluorescence emission, researchers have developed a narrow-band filter with a wide bandwidth of 4 nm. He was centered on a wave of about 414,5 nm (violet shade, where and must shift the wavelength of Lyman-alpha emission at z = 2,4.

In the end, after years of searching I found immediately about a hundred gaseous objects on the destruction of several million light-years from the galaxy. Then there was a long analysis of whether any of them glow of gas called the ongoing process of gassing their own stars, and who was illuminated only by the ultraviolet radiation of the galaxy. The last object was twelve - and this is the real dark galaxy. Estimated mass of gas in each of them is equal to about a billion Solar masses that galaxy's not much, but at the first stage of evolution of the Universe, to mass mergers and acquisitions, other and could not be.

Also, was able to show that, compared with the typical zvezdoobrazovaniya galaxy, which is at the same stage of its history, the efficiency of star formation in a dark galaxy a hundred times lower (the efficiency of star formation is defined as the ratio of the mass of newly formed stars to the mass of gas, from which stars can form). It turned out that these objects would need about 100 billion years for their gas turned into a world - term, more than seven times greater than the time elapsed from the beginning of existence of the Universe. The result is consistent with recent theoretical research has concluded that due to low metal content-rich gas of low-mass halos at high red shifts may differ very low intensity of star formation.

Based on the materials of the European space Agency.