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Boo-tiful Ring Galaxies

Boo-tiful Ring Galaxies

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A ghoulish secret lurks within each of these
gorgeous galaxies. Their rings are dotted with stellar graveyards!

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These objects are called ring galaxies, and
scientists think most of them form in monster-sized crashes. Not just any
galaxy collision will do the trick, though. To produce the treat of
a ring, a smaller galaxy needs to ram through the center of a larger galaxy at
just the perfect angle.

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The collision causes ripples that disturb both
galaxies. The gravitational shock causes dust, gas, and stars in the larger
galaxy’s disk to rush outward. As this ring of material plows out from the
galaxy’s center, gas clouds collide and trigger the birth of new stars.

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In visible light, the blue areas in the
galaxies’ rings show us where young, hot stars are growing up. Faint, pink
regions around the ring mark stellar nurseries where even younger stars set
hydrogen gas aglow.

The newborn stars come in a mix of sizes, from
smaller ones like our Sun all the way up to huge stars with tens of times the
Sun’s mass. And those massive stars live large!

While a star like our Sun will last many
billions of years before running out of fuel, larger stars burn much brighter and
faster. After just a few million years, the largest stars explode as supernovae. When
massive stars die, they leave behind a stellar corpse, either a neutron star or
black hole.

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When we turn our X-ray telescopes to these ring galaxies, we
see telltale signs of stellar remnants dotted throughout
their ghostly circles. The purple dots in the X-ray image above are
neutron stars or black holes that are siphoning off gas from a companion star,
like a vampire. The gas reinvigorates stellar corpses, which heat up and emit
X-rays. These gas-thirsty remains are beacons lighting the way to stellar
graveyards.

Spiral galaxies — like our home galaxy, the Milky Way — have curved
arms that appear to sweep out around a bright center. The dust and gas in those
spiral arms press together, causing cycles of star formation that result in a
more even mix of new stars and stellar corpses scattered throughout our galaxy.
No creepy ring of stellar corpses here!  

To visit some other eerie places in the
universe, check out the latest additions to the Galaxy of Horrors poster series and follow NASA Universe on Twitter
and Facebook
for news about black holes, neutron stars, galaxies, and all the amazing
objects outside our solar system.

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