Scientists have finally identified the mysterious source of X-ray emissions at the center of our galaxy's youngest supernova: Inside the remains of Cassiopeia A sits a baby neutron star surrounded by a thin layer of carbon.

Twenty times heavier than our sun and 11,000 light years away, Cassiopeia A was a dense star whose explosion was observed from Earth roughly 330 years ago. The supernova left behind a dense central core 12.5 miles wide that was first spotted in 1999 by NASA's Chandra X-ray Observatory. But until now, astronomers hadn't come up with a model to explain the object's confusing X-ray emission spectrum. Previous attempts had come up with a stellar radius too small to be a neutron star, or a non-uniform surface temperature, which didn't make sense.

Now, combining data from two prior studies, researchers have discovered that Cassiopeia's X-ray emission pattern can be explained by the presence of a very young neutron star with a low magnetic field and an unusually thin carbon atmosphere.

Published Wednesday in Nature, the findings make Cassiopeia's core the youngest neutron star scientists have ever encountered.

"This discovery helps us understand how neutron stars are born in violent supernova explosions," astrophysicist Craig Heinke of the University of Alberta said in a press release. "This neutron star was born so hot that nuclear fusion happened on its surface, producing a carbon atmosphere just 10 centimeters thick."

Images: 1) A Chandra X-ray Observatory image of the supernova remnant Cassiopeia A, NASA/CXC/Southampton/W.Ho. 2) A close-up of the same image, with an artist's rendering of the neutron star at the center of the remnant, NASA/CXC/M.Weiss.

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