Archive for October 25, 2012

Astronomers Report Dark Matter ‘Halos’ May Contain Stars, Disprove Other Theories

October 25, 2012 Leave a comment

Could it be that dark matter “halos” — the huge, invisible cocoons of mass that envelop entire galaxies and account for most of the matter in the universe — aren’t completely dark after all but contain a small number of stars? Astronomers from UCLA, UC Irvine and elsewhere make a case for that in the Oct. 25 issue of the journal Nature.

Astronomers have long disagreed about why they see more light in the universe than it seems they should — that is, why the infrared light they observe exceeds the amount of light emitted from known galaxies.

When looking at the cosmos, astronomers have seen what are neither stars nor galaxies nor a uniform dark sky but mysterious, sandpaper-like smatterings of light, which UCLA’s Edward L. (Ned) Wright refers to as “fluctuations.” The debate has centered around what exactly the source of those fluctuations is.

“The dark matter halo is not totally dark,” Wright said. “A tiny fraction, one-tenth of a percent, of the stars in the central galaxy has been spread out into the halo, and this can produce the fluctuations that we see.”

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Quasar May Be Embedded In Unusually Dusty Galaxy

October 25, 2012 Leave a comment

Hubble Space Telescope view of one of the most distant and luminous quasars ever seen. Credit: NASA/ESA/M. Mechtley, R. Windhorst, Arizona State University

Hubble astronomers have looked at one of the most distant and brightest quasars in the universe and are surprised by what they did not see: the underlying host galaxy of stars feeding the quasar. The best explanation is that the galaxy is shrouded in so much dust that the stars are completely hidden everywhere. Astronomers believe that the James Webb Space Telescope will reveal the galaxy.

All but the very first galaxies contain some dust—the early universe was dust-free until the first generation of stars started making dust through nuclear fusion. As these stars aged and burned out, they filled interstellar space with this dust as they lost their atmospheres. The quasar dates back to an early time in the universe’s history—less than one billion years after the big bang—but was known to contain large amounts of dust from previous sub-millimeter observations. What surprised the researchers is how completely the dust is shrouding starlight within the galaxy—none of the starlight seems to be leaking out from around the quasar.

The team speculates that the black hole is devouring the equivalent mass of a few suns per year. It may have been eating at a more voracious rate earlier to bulk up to an estimated mass of three billion solar masses in just a few hundred million years.

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World’s Most Advanced Mirror For Giant Telescope Completed

October 25, 2012 Leave a comment

Credit: Ray Bertram/UA

Scientists at the UA and in California have completed the most challenging large astronomical mirror ever made. The mirror will be part of the 25-meter Giant Magellan Telescope, which will explore planets around other stars and the formation of stars, galaxies and black holes in the early universe.

By the standards used by optical scientists, the “degree of difficulty” for this mirror is 10 times that of any previous large telescope mirror. The mirror surface matches the desired prescription to a precision of 19 nanometers – so smooth that if it were the size of the continental U.S., the highest mountains would be little more than a half-inch high.

This mirror, and six more like it, will form the heart of the 25-meter Giant Magellan Telescope, providing more than 380 square meters, or 4,000 square feet, of light-collecting area.

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NASA’s NuSTAR Spots Flare From Milky Way’s Black Hole

October 25, 2012 Leave a comment

Focused high-energy X-ray view. Image credit: NASA/JPL-Caltech

NASA’s newest set of X-ray eyes in the sky, the Nuclear Spectroscopic Telescope Array (NuSTAR), has caught its first look at the giant black hole parked at the center of our galaxy. The observations show the typically mild-mannered black hole during the middle of a flare-up.

“We got lucky to have captured an outburst from the black hole during our observing campaign,” said Fiona Harrison, the mission’s principal investigator at the California Institute of Technology (Caltech) in Pasadena. “These data will help us better understand the gentle giant at the heart of our galaxy and why it sometimes flares up for a few hours and then returns to slumber.”

Compared to giant black holes at the centers of other galaxies, Sgr A* is relatively quiet. Active black holes tend to gobble up stars and other fuel around them. Sgr A* is thought only to nibble or not eat at all, a process that is not fully understood. When black holes consume fuel — whether a star, a gas cloud or, as recent Chandra observations have suggested, even an asteroid — they erupt with extra energy.

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A 84-Million Star Color-Magnitude Diagram Of The Milky Way Bulge

October 25, 2012 Leave a comment

VISTA gigapixel mosaic of the central parts of the Milky Way. Credit: ESO/VVV Consortium

Astronomy & Astrophysics published the first analysis of a catalog of 84 million individual stars in the Milky Way bulge as a part of the VVV ESO public survey. This gigantic data set allows building the largest, deepest, and most accurate color-magnitude diagram ever produced, containing more than ten times more stars than any previous study.

The bulge of the Milky Way is a large central concentration of ancient stars that is predominantly observed from the southern hemisphere. Understanding the formation and evolution of the bulge is fundamental for deciphering the properties of our Galaxy. In the bulge of the Milky Way, very faint individual stars can be observed, allowing astronomers to separate stellar populations based on age, kinematics, and chemical composition. However, the bulge is centered on the stellar disk of the Milky Way, where most of the stars, gas, and dust of our Galaxy is concentrated. This makes observations of the bulge very challenging because they are affected by crowding, extinction by interstellar dust, and the depth effect of stars being at a range of distances from us.

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