Cassiopeia A appears in this photo, with the neutron star at its center highlighted in the right-hand corner.
Chandra image: NASA/CXC/Southampton/W.Ho; Illustration: NASA/CXC/M.Weiss
Astronomers have just solved a decade-old mystery that explains the unusual behavior of a neutron star -- the dense, hot corpse left behind after a massive stellar explosion -- at the center of the Cassiopeia A supernova remnant.
It wasn't the X-rays streaming from the center of the supernova remnant that astronomers found puzzling. It's why the beams weren't pulsating as expected. Now the scientists know why: The neutron star is covered with a thin atmosphere of carbon, which acts like a giant bulb to smooth light in all directions.
The findings help to illustrate the extreme nature of these entities.
"The carbon is unique," Wynn Ho, a researcher with the University of Southampton in the United Kingdom, told Discovery News. "The neutron stars that have been detected with atmosphere have evolved with hydrogen, and that's what we'd expect because hydrogen is the most abundant element in the universe."
Scientists believe the neutron star in Cassiopeia A is so young and hot that in addition to fusing hydrogen to form helium, the surface of the star is fusing helium into carbon.
Computer models show the carbon veil to be extremely thin -- up to just four inches thick -- due to the immense gravitational pull of the neutron star, which is about one billion times stronger than Earth's gravity.
Though the shroud is as dense as diamonds, the star's 3.6 million-degree Fahrenheit temperature would keep the atmosphere gaseous.
"It's incredibly hot, so it's still a gas," said Peter Edmonds, with the Chandra X-ray Center at the Harvard-Smithsonian Center for Astrophysics.
Direct observations of the neutron star's atmosphere are not possible with today's technology, given its distance and other factors, but scientists are on the lookout for other young neutron stars that may also sport carbon shells.
Being based on computer models, the finding isn't ironclad, added Edmonds, "but it's a strong case."
Cassiopeia A's neutron star also serves as proverbial lab rat for physicists wondering what sort of exotic matter exists inside.
"We're using it to study the neutron star interior to determine whether its interior is made of superconducting material or quark matter. You can determine this based on its temperature and its age," Ho said. "Any exotic matter will determine how rapidly it cools over time."
Ho's work appears in this week's Nature.
COMMENTS (0)