"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 is Hubble’s close-up view of the myriad stars near the core of Galaxy M83, the bright whitish region at far right. 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.
"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. "I was dumbfounded. These stars are truly 'living on the edge."
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.
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.”
The Daily Galaxy via Science@NASA
Image credits:FORS Team, 8.2-meter VLT, ESO
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