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X-Ray Milky Way Still Waits For Galileo To Come
May 3, 2006 13:29


Russian astrophysicists Mikhail Revnivtsev and Sergei Sazonov suggested new hypothesis, explaining origin of almost all kinds of x-ray radiation in our Galaxy.

  Scientists fail to find sources for about 70% of our Galaxy’s x-ray radiation, detected by means of orbiting observatories. Such radiation is detected as continuous diffuse x-ray glow. The example for this type of radiation is a large cloud of low-density gas. However, gas hypothesis meets several explanation difficulties. Hot gas particles move at enormous speeds, and thus tend to escape the Galaxy’s gravity. That is why hot gas should leave the Galaxy very quickly, thus there should be a source for compensating gas losses at a constant basis. Supernovas can be regarded as such sources, but the number of already detected stars is significantly lower than predicted. Mikhail Revnivtsev and Sergei Sazonov from Russian Institute for Space Research (ISR), currently employed in Max Planck Institute for Astrophysics in Germany, give following explanation for background x-ray radiation: our Galaxy has numerous sources of x-ray radiation, which modern equipment cannot detect separately. The situation reminds of visible diffuse glow of the Milky Way – only Galileo’s telescope successfully showed that it was joint glow of numerous individual stars.

To confirm their hypothesis the authors compared data of two sky surveys, one of which was infrared (performed by COBE (Cosmic Background Explorer) satellite, launched in 1989) and the other was x-ray (performed by RXTE (Rossi X-ray Timing Explorer) satellite, orbiting our planet since 1995). Both surveys showed similar radiation intensity peaks. Major part of infrared radiation, detected by COBE, comes from numerous old and cold stars – red dwarfs, which implies that Galaxy’s diffuse x-ray radiation is linked with stars too.

Physicists suggested two possible sources for such radiation, first is white dwarfs, which usually are parts of duplex systems and form so called cataclysmic variables. White dwarfs are known for absorbing matter of accompanying stars. Stellar matter heats up and emits x-ray radiation. White dwarfs origin from stars with mass similar to our Sun’s – such stars are larger than red dwarfs and their evolution is faster. But these two star types should have similar distribution in space. Ordinary “active” stars are considered to be another source for this type of radiation. Solar corona’s matter is known to be as hot as several million degrees and to emit x-rays, which  become more intensive during solar flares. Of course, x-ray intensity is weaker than that of visible solar radiation, but total x-ray radiation of hundreds of millions of stars can be a significant contribution to general x-ray background of the Milky Way. Expert estimations claim our Galaxy having over a million cataclysmic variables and about a billion active stars, which 100 times exceeds usual estimations. However, some physicists report that our Galaxy shelters over ten million cataclysmic variables.

Abovementioned hypothesis eliminates contradictions between expected and observed supernova flares ratio. But it won’t easily conquer expert’s approval. “New Scientist” magazine reports that described mechanisms are unable to provide necessary intensity for x-ray radiation.

To prove the hypothesis those, who doubt, need x-ray telescopes of new generation – they are very sensible and have high resolution. NASA currently develops “Constellation X” telescope system including x-ray satellites, which are expected to make a breakthrough in x-ray techniques – just as Galileo did in optics.


Kizilova Anna

Tags: Russian Scientists     

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