There are thought to be millions of neutron stars in the Milky Way galaxy. Astronomers believe they may have found the Earth’s closest neutron star ever known, located in the constellation Ursa Minor just 250 light years from Earth. It has been nicknamed Calvera, after the villain in the movie "The Magnificent Seven."
The star is the exotic remnant of a supernova that was too small to form a black hole. Instead, the leftover gas and dust compacted into a glowing, incredibly dense body only a few miles wide and consisting almost entirely of neutrons. It is so incredibly dense that just a single teaspoon of its material would weigh 100 million metric tons.
"The seven previously known isolated neutron stars are known collectively as 'The Magnificent Seven' within the community and so the name Calvera is a bit of an inside joke on our part," said co-discoverer Derek Fox of Penn State.
Once the new finding is confirmed, it would be only the eighth "isolated neutron star" known to science and it may even be an entirely new type of neutron star altogether.
First author Robert Rutledge of McGill University in Montreal, Quebec says he is confident that their discovery will be confirmed because there are no other widely accepted alternatives for objects like Calvera that are bright in X-rays but faint in visible light. But exactly which type of neutron star it is remains a mystery for now.
"Either Calvera is an unusual example of a known type of neutron star, or it is some new type of neutron star, the first of its kind," says Rutledge.
Calvera's location high above the plane of the Milky Way Galaxy is part of its mystery. In all likelihood, the neutron star is the remnant of a star that lived in our galaxy's starry disk before exploding as a supernova. In order to reach its current position, it had to wander some distance out of the disk. It was found using NASA’s Swift satellite’s X-ray telescope.
"The best guess is that it is still close to its birthplace and, therefore, close to Earth," said Rutledge. He says that means Calvera could be just 250 light years away—the closest of any Neutron star.
"Because it is so bright and probably close to Earth, it is a promising target for many types of observations," said Fox.
Posted by Rebecca Sato
*A paper describing this research will be published in the Astrophysical Journal.
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