domingo, 13 de noviembre de 2011

Astronomy - Stars Discovered Forming in Galaxies' "Forbidden Zones"


"We’re finding stars in extreme galactic environments where star formation isn't supposed to happen," explains NASA GALEX project scientist Susan Neff of the Goddard Space Flight Center. “This is a very surprising development."

The image above shows long octopus-like arms of star formation stretching far away from the main disk of spiral galaxy M83. Like our own Milky Way Galaxy. M83, is a prominent member of a group of galaxies that includes Centaurus A and NGC 5253, all of which lie about 15 million light years distant. To date, six supernova explosions have been recorded in M83. An intriguing double circumnuclear ring has been discovered at the center of M83.
GALEX, which stands for “Galaxy Evolution Explorer,” is an ultraviolet space telescope with a special ability: It is super-sensitive to the kind of UV rays emitted by the youngest stars.  This means the observatory can detect stars being born at very great distances from Earth, more than halfway across the Universe.  The observatory was launched in 2003 on a mission to study how galaxies change and evolve as new stars coalesce inside them.
"In some GALEX images, we see stars forming outside of galaxiesin places where we thought the gas density would be too low for star birth to occur," says GALEX team member Don Neil of Caltech.
Stars are born when interstellar clouds of gas collapse and contract under the pull of their own gravity.  If a cloud gets dense and hot enough as it collapses, nuclear fusion will kick in and—voila!--a star is born.
The spiral arms of the Milky Way are a "goldilocks zone" for this process.  "Here in the Milky Way we have plenty of gas.  It’s a cozy place for stars to form," says Neil.
But when GALEX looks at other more distant spiral galaxies, it sees stars forming far outside the gassy spiral disk. 
"I was dumbfounded," he says. "These stars are truly 'living on the edge. '"
The observatory has also found stars being born:
--in elliptical and irregular galaxies thought to be gas-poor (e.g., 1, 2)
--in the gaseous debris of colliding galaxies (1, 2)
--in vast "comet-like" tails that trail behind some fast-moving galaxies (1, 2)
--in cold primordial gas clouds, which are small and barely massive enough to hang together
According to GALEX, stellar extremophiles populate just about every nook and cranny of the cosmos where a wisp of gas can get together to make a new sun.
“This could be telling us something profound about the star-forming process,” says Neff.  “There could be ways to make stars in extreme environments that we haven’t even thought of yet.”

Image credits:

Source: The Daily Galaxy - Science@NASA

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