NASA scientists have discovered a special kind of neutron star for the first time outside of the Milky Way galaxy, and released a stunning image of the stellar body located 200,000 light years from Earth.
Neutron stars are the ultra-dense cores of massive stars that collapse and undergo a supernova explosion.
The newly identified neutron star, discovered using data from NASA’s Chandra X-ray Observatory and the European Southern Observatory’s Very Large Telescope (VLT) in Chile, is a rare variety that has both a low magnetic field and no stellar companion. The neutron star is located within the remains of a supernova – known as 1E 0102.2-7219 (E0102) – in the Small Magellanic Cloud, located 200,000 light years from Earth. A new composite image of E0102 allows astronomers to learn new details about this object that was discovered more than three decades ago.
Oxygen-rich supernova remnants like E0102 are important for understanding how massive stars fuse lighter elements into heavier ones before they explode. Seen up to a few thousand years after the original explosion, oxygen-rich remnants contain the debris ejected from the dead star’s interior. This debris is observed today hurtling through space after being expelled at millions of miles per hour.
Chandra observations of E0102 show that the supernova remnant is dominated by a large ring-shaped structure in X-rays, associated with the blast wave of the supernova.
The new MUSE data revealed a smaller ring of gas that is expanding more slowly than the blast wave. At the centre of this ring is a blue point-like source of X-rays. Together, the small ring and point source act like a celestial bull’s eye. The combined Chandra and MUSE data suggest that this source is an isolated neutron star, created in the supernova explosion about two millennia ago. The X-ray energy signature, or ‘spectrum’, of this source is very similar to that of the neutron stars located at the center of two other famous oxygen-rich supernova remnants: Cassiopeia A (Cas A) and Puppis A. These two neutron stars also do not have companion stars.
The lack of evidence for extended radio emission or pulsed X-ray radiation, typically associated with rapidly rotating highly-magnetised neutron stars, indicates that the astronomers have detected the X-radiation from the hot surface of an isolated neutron star with low magnetic fields. About ten such objects have been detected in the Milky Way galaxy, but this is the first one detected outside our galaxy. Future observations of E0102 at X-ray, optical, and radio wavelengths should help astronomers understand how the neutron star ended up in its current position, seemingly offset from the centre of the circular shell of X-ray emission produced by the blast wave of the supernova.