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Saturday, November 10, 2012

Detected giant halo surrounding the Milky Way

The estimated mass is comparable to that would add all the stars in the galaxy, said Yair Krongold, researcher at the Institute of Astronomy at UNAM, and member of the international team that made the discovery.

Mexico City. An international group of astronomers, which owns Krongold Yair Herrera, a researcher at the Institute of Astronomy (IA) of the UNAM, detected a gigantic halo of hot gas surrounding the Milky Way.

With the Chandra X-ray Observatory of NASA scientists found evidence, consisting of a huge cloud of gas extends hundreds of thousands of light years away, and has a mass comparable to that add up all the stars in the galaxy. The group consists of the astrophysical Indian Anjali Gupta and Smita Mathur of Ohio State University, and colleagues Yair Krongold, Mexican IA, UNAM, the Italian Fabrizio Nicastro, and Center.

Astrophysics at Harvard University and the Institute Smithson, and Massimiliano Galeassi of the University of Miami in Coral Glabes. The results of their work were published in the September issue of The Astrophysical Journal. Matter is a contemporary of the Milky Way and heated during its formation, Krongold said in an interview.

"It reached a very high temperature when they collapsed to form the galaxy has heavy elements, in particular oxygen from stars, as in the Big Bang that created the universe was only hydrogen and helium. Then strong winds of the stars threw the material out, "he said. Before the screening, scientists already imagined, but so far have failed to have evidence of their existence.

Solution to the "missing matter"

For decades, astronomers have had the problem of the "missing matter", which called baryonic, because it comes from heavy subatomic particles, the baryons. "If we measure the amount of matter in the universe than the theory predicts Big Bang nucleosynthesis, and compare it to the one we see today in the nearby universe, about 50 percent is lost, "said Krongold.

By comparing the amount predicted by the Big Bang to the information inferred from the cosmic microwave background (remaining energy of the universe is very young), agree, and so does the amount observed in the distant Universe, "but at distances close to us, we lose evidence of matter gradually. In general, the amount in galaxies is one fifth of the total, and the rest is in the middle Intergalactic "he explained.

The latter is captured by the specialists through the absorption of hydrogen at very large distances, over 10 thousand 500 million light years from Earth. "But at closer distances not seen that stuff, that's the mystery of the so-called 'lost'. Do not know where half because we see our planet from just 40 to 50 percent of it, "

"About 20 percent are in galaxies. In the space between the latter, at a temperature less than 100 000 degrees Celsius, we found about another 30 percent of the nearby universe, which, added to that of the galaxies represents about 50 percent of that indicated by the Big Bang. The question is where the rest is ", raised Krongold, whose response is directed to the giant halo surrounding the Milky Way.

Collate theoretical models with reality
The galaxies are formed by gravitational collapse, at the time that the Gravity pulls a cloud of matter collapses and it meets in the center denser elements forming stars. Models of galaxy formation predict that as constitute the material collapses, but a big part of it falls, but is shocked and heated to very high temperatures.

"Theoretical models predict that this material is in the intergalactic medium, but to millions of degrees Celsius, and this temperature is difficult to detect. We now know that in addition to being high, is very dim, is between galaxies and has a small density, although a large volume. "

The halo has a density of about 100 atoms per cubic meter. "Virtually empty. If you see a great distance is great, because the volume is considerable, although the density is low. Only be detected with X-ray radiation, "he said.

Detect the shadow

To detect the halo, scientists observed by Chandra eight quasars (very bright celestial objects and distant), who served as headlights with light emitted toward Earth. Captured light absorption that produces that matter, something like a shadow from the latter, which can be captured with the X-ray source

"The matter of the halo cannot be observed directly, we have to see the little shadow which is to quasars. The halo clouds the X-ray light coming from quasars, which are very bright. We realize that our galaxy around dimly shadowed the light from Quasars. So we infer their existence, "said Krongold.

To measure the temperature, it was found out how ionized oxygen. "We found that it is six or seven times, that is, if the neutral oxygen has eight electrons, is so hot that you have started six or seven. The halo is like a fireball, but dim, around the galaxy, it is a few million degrees, similar to the temperature of the center of the Sun.”

As for his size, has a diameter of at least several hundred thousand light years, while the Milky Way has about 100 thousand light years across. "Our galaxy is like a tiny part in the core of a very faint cloud," he said.

"Now you begin to solve the problem, then we show that the missing mass is there. To be sure, we must make more precise measurements in order to know the quantity of matter ".

So begin new observations with Chandra, and devoted two weeks of telescope observing time to observe one of the eight quasars and shadow that darkens its light halo. The new

Results will be ready within two years.

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