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.

The new one, spotted with NASA's Chandra X-Ray Observatory, is the aftermath of a supernova observed in 1979, when a star roughly 20 times the mass of the sun collapsed in on itself.

In 2004, astronomers spotted a spectacular gamma-ray explosion bursting off a neutron star in the Sagittarius constellation, 50,000 light years from Earth.