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Posts Tagged ‘astrophysical journal’

SDO and STEREO Spot Something New On the Sun

April 10, 2012 Leave a comment

One day in the fall of 2011, Neil Sheeley, a solar scientist at the Naval Research Laboratory in Washington, D.C., did what he always does – look through the daily images of the sun from NASA’s Solar Dynamics Observatory (SDO).

But on this day he saw something he’d never noticed before: a pattern of cells with bright centers and dark boundaries occurring in the sun’s atmosphere, the corona. These cells looked somewhat like a cell pattern that occurs on the sun’s surface — similar to the bubbles that rise to the top of boiling water — but it was a surprise to find this pattern higher up in the corona, which is normally dominated by bright loops and dark coronal holes.

Sheeley discussed the images with his Naval Research Laboratory colleague Harry Warren, and together they set out to learn more about the cells. Their search included observations from a fleet of NASA spacecraft called the Heliophysics System Observatory that provided separate viewpoints from different places around the sun. They describe the properties of these previously unreported solar features, dubbed “coronal cells,” in a paper published online in The Astrophysical Journal on March 20, 2012 that will appear in print on April 10.

Full Story: http://www.nasa.gov/mission_pages/sunearth/news/solar-plumes.html

Black Holes Grow By Eating Binary Star Partners


A study led by a University of Utah astrophysicist found a new explanation for the growth of supermassive black holes in the center of most galaxies: they repeatedly capture and swallow single stars from pairs of stars that wander too close.

Using new calculations and previous observations of our own Milky Way and other galaxies, “we found black holes grow enormously as a result of sucking in captured binary star partners,” says physics and astronomy Professor Ben Bromley, lead author of the study, which is set for online publication April 2 in Astrophysical Journal Letters.

“I believe this has got to be the dominant method for growing supermassive black holes,” he adds. “There are two ways to grow a supermassive black hole: with gas clouds and with stars. Sometimes there’s gas and sometimes there is not. We know that from observations of other galaxies. But there are always stars.”

Full Story: http://unews.utah.edu/news_releases/how-black-holes-grow/

Chandra Finds Fastest Wind from Stellar-Mass Black Hole

February 22, 2012 Leave a comment

Image Credit: NASA/CXC/M.Weiss

Image Credit: NASA/CXC/M.Weiss

Astronomers using NASA’s Chandra X-ray Observatory have clocked the fastest wind yet discovered blowing off a disk around a stellar-mass black hole. This result has important implications for understanding how this type of black hole behaves.

The record-breaking wind is moving about 20 million mph, or about 3 percent of the speed of light. This is nearly 10 times faster than had ever been seen from a stellar-mass black hole.

Stellar-mass black holes are born when extremely massive stars collapse. They typically weigh between five and 10 times the mass of the sun. The stellar-mass black hole powering this super wind is known as IGR J17091-3624, or IGR J17091 for short.

“This is like the cosmic equivalent of winds from a category five hurricane,” said Ashley King from the University of Michigan, lead author of the study published in the Feb. 20 issue of The Astrophysical Journal Letters. “We weren’t expecting to see such powerful winds from a black hole like this.”

Full Story: http://www.nasa.gov/mission_pages/chandra/news/H-12-056.html

Largest Driver of Galaxy Growth Challenged

January 11, 2012 Leave a comment

A Hubble Space Telescope study of massive galaxies two to three billion years after the Big Bang has uncovered two remarkable results that challenge the common lore that major mergers play a dominant role in growing galaxies over a wide range of cosmic epochs.

Astronomers led by University of Texas at Austin graduate student Tim Weinzirl and associate professor Shardha Jogee will present their findings, recently published in The Astrophysical Journal, today at the 219th meeting of the American Astronomical Society in Austin.

Weinzirl and Jogee studied 166 of the most massive galaxies present only a few billion years after the Big Bang , selected from the GOODS NICMOS survey headed by professor Christopher Conselice of the University of Nottingham in the U.K.

Full Story: http://mcdonaldobservatory.org/news/releases/2012/JanAAS.html

First Low-Mass Star Detected in Globular Cluster

December 22, 2011 Leave a comment

Until now, it was merely assumed that low-mass and therefore extremely faint stars must exist. However, in view of the vast distances and weak luminosity of low-mass stars, even the most modern telescopes fail. Together with a Polish-Chilean team of researchers, Swiss astrophysicist Philippe Jetzer from the University of Zurich has now detected the first low-mass star in the globular cluster M22 indirectly. As their recent article accepted for publication in Astrophysical Journal Letters reveals, it involves a dwarf star that has less than a fifth of the mass of our sun and is 3.2 kiloparsecs from it (one kiloparsec corresponding to 3,210 light years).

The evidence, which enables the mass to be determined highly accurately, is based upon so-called gravitational microlensing and requires the highest technical standards available. The measurements were carried out on the ESO VLT 8-meter telescope with adaptive optics at the Paranal Observatory in Chile.

Full Story: http://www.mnf.uzh.ch/en/news/detailview/archive/2011/12/article/erstmals-massearmer-stern-in-kugelsternhaufen-nach.html