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‘Lonely’ Neutron Star 200,000 Light-Years From Earth Is The First Of Its Kind Spotted Outside The Milky Way

By Alexandra Lozovschi
Published on: 20:30 PST, May 29, 2018

About 2,000 years ago, a supernova dubbed 1E 0102.2-7219 (E0102 for short) exploded in the Small Magellanic Cloud, a dwarf galaxy near the Milky Way. In the aftermath, a rare type of neutron star was born, the likes of which has never before been encountered outside the borders of our galaxy.

What makes this neutron star so unusual is that, unlike many other neutron stars (ultra dense and massive stars formed from the collapsed cores of supernovae), it has a very low magnetic field and it lacks a white dwarf companion, NASA reports.

Referred to as a “lonely” neutron star, this cosmic oddity could help shed more light into how supernovae form heavy elements, such as oxygen and carbon, notes the space agency.

Because the E0102 remnant exists independently of a binary star system and doesn’t emit pulsed X-ray radiation like most fast-spinning and highly-magnetized X-ray pulsars, it falls into a special category of neutron stars, of which only a handful have been ever spotted inside the Milky Way.

Such examples include the oxygen-rich neutron stars residing in the center of the Cassiopeia A supernova remnant, some 11,000 light-years away from our planet, and the Puppis A supernova remnant, located about 7,000 light-years from Earth.

But this particular neutron star lies a lot further from our planet than the similar neutron stars left behind by the explosions of the Cassiopeia A and Puppis A supernovae.

Discovered more than 30 years ago, the E0102 remnant is located 200,000 light-years away from Earth and is, in fact, the first neutron star of this kind ever found outside our own galaxy.

Recent examinations with NASA’s Chandra X-ray Telescope and the European Southern Observatory’s Very Large Telescope (VLT) in Chile revealed that the neutron star is enveloped in two separate ring-shaped structures of leftover material from E0102’s explosion two millennia ago.

In the photo below, a composite derived from X-ray and optical observations with the two telescopes, the neutron star is imaged as a blue point that seeps out X-rays.

The star is encased in a large outer blue ring of X-ray emissions produced by the blast wave of the supernova explosion (X-ray view from Chandra). Inside the outer ring lies another ring-shaped structure, a smaller circle of gas pictured in bright-red (optical view from the VLT).

A composite image of the E0102 remnant, made up of X-ray observations from Chandra (blue and purple), visible light data from VLT’s MUSE instrument (bright red), and additional data from Hubble (dark red and green).

As NASA explains, the green filament-like structure floating around inside the outer ring is debris from the E0102 supernova, material from the original star ejected after its massive explosion that got propelled into space at speeds of millions of miles per hour.

Such material, captured in the composite image above by the Hubble Space Telescope, got trapped inside the E0102 remnant as the neutron star was formed, revealed the latest observations.

Moreover, data from the VLT’s Multi Unit Spectroscopic Explorer (MUSE) instrument uncovered that the neutron star’s X-ray spectrum (or its X-ray energy signature) is very similar to that of the Cassiopeia A and Puppis A remnants, which builds a good case that the E0102 remnant is also rich in oxygen.

This finding is important in terms of understanding how heavy elements are created from supernovae explosions, as these massive stars run out of fuel and collapse into neutron stars.

“Oxygen-rich supernova remnants like E0102 are important for understanding how massive stars fuse lighter elements into heavier ones before they explode.”

The agency plans to conduct radio observations of the neutron star as well in an attempt to decipher another one of the “lonely” star’s puzzles, namely why it’s located off-center from the blue circle of X-ray emissions.

One theory suggests that the E0102 supernova exploded near the middle of its remnant, kicking the neutron star away from the explosion site at incredible speeds of about 2 million mph.

Another explanation sets the supernova explosion site somewhere near the current location of the neutron star, which would imply that the star is moving very slowly and that the gas ring imaged in the optical red circle could actually come from the E0102 remnant as much as from the supernova itself.

The results of the research are published in Nature Astronomy.

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