What Galaxy is surrounded by a halo, it is clear long ago. The question was, what is its main component. X-ray telescope space-based Chandra and other instruments revealed that the gas component of the halo that extends over a huge distance, by weight not inferior to all the stars of our Galaxy combined.

Hot gas halo extends more than 100 KPC from the periphery of the Galaxy and includes not only the milky Way, but the Large and Small Magellanic Clouds. (Here and below Fig. NASA / CXC / M.Weiss / Ohio State / A.Gupta et al.)

A group of five astronomers using data from telescopes Chandra, XMM-Newton and Astro-EII, set rather strict limitations on the weight and temperature of hot gas component of the galactic halo, and the space it requires. To do this, the researchers used an observation telescopes for distant extragalactic x-ray sources: radiation from them most efficiently absorbed the oxygen ions that are part of this halo.

The temperature of the main part of the gas was not above 2 500 000 To no less than 1 000 000 To, that is hundreds of times hotter than the surface of the Sun, but close to the temperature of the solar corona. This is more than was thought in a number of previous studies have investigated only warm gas component of the galactic halo, with temperatures from 100 000 to 1 000 000 K. the authors of work, that's too high a temperature of hot gas was the reason for such a late discovery: other groups sought mostly gas with lower temperatures.

"We know that the gas surrounding the Galaxy, and we know its temperature, " says the study's lead author anjali Gupta from Ohio state University (USA). That is the big question is how big is this halo and how it massively".

By combining data from different x-ray telescopes, scientists have come to conclusion, that "weighs" halo around 60 billion solar masses. Its density is small, about ~10-4 cm-3. The length of the outside of our Galaxy could be hundreds of thousands of light years, and more. Pets also that we are talking about the total for the whole local group of galaxies environment. Even if true the lowest score - 100 PDA (360 000 light-years), the size of the halo is many times greater than the diameter of the visible galactic disk (100 000 light years).

By the way, the assessment of 60 billion solar masses rather conservative: a precise combination of oxygen and hydrogen in the galactic halo is unknown, but because astronomers have preferred a comparatively low value.

Despite this assumption, even in its current form, the study capable in large part to resolve the issue of hidden mass, at least in respect of our Galaxy. Earlier, according to different estimates, up to half of normal baryonic matter did not come to the attention of astronomers, without revealing itself nor the stars, nor in the interstellar gas within the galactic disk.

A study published in the Astrophysical Journal Letters; Preprint available here.

Prepared according to NASA.