New images from the MUSE instrument on ESO’s Very Large Telescope in Chile have revealed a ring-shaped structure in the young supernova remnant 1E 0102.2-7219 (1E 0102 for short), expanding slowly within the depths of fast-moving filaments left behind after the supernova explosion. This discovery allowed ESO astronomer Frédéric Vogt and co-authors to track down the first ever isolated neutron star with low magnetic field located beyond the Milky Way Galaxy.

Dr. Vogt and his colleagues from ESO, the University of New South Wales, Australian National University, Towson University and the University of Georgia noticed that the ring of gas in the 1E 0102 system was centered on an X-ray source that had been noted years before and designated p1.

The nature of this source had remained a mystery. In particular, it was not clear whether 1E 0102 p1 actually lies inside the remnant or behind it.

It was only when the ring of gas — which includes both neon and oxygen — was observed with MUSE that the astronomers noticed it perfectly circled 1E 0102 p1.

The coincidence was too great, and they realized that 1E 0102 p1 must lie within the supernova remnant itself.

Once 1E 0102 p1’s location was known, the team used existing X-ray observations of this target from NASA’s Chandra X-ray Observatory to determine that it must be an isolated neutron star, with a low magnetic field.

“If you look for a point source, it doesn’t get much better than when the Universe quite literally draws a circle around it to show you where to look,” Dr. Vogt said.

When massive stars explode as supernovae, they leave behind a curdled web of hot gas and dust, known as a supernova remnant.

These turbulent structures are key to the redistribution of the heavier elements into the interstellar medium, where they eventually form new stars and planets.

Typically barely 10 km across, yet weighing more than our Sun, isolated neutron stars with low magnetic fields are thought to be abundant across the Universe, but they are very hard to find because they only shine at X-ray wavelengths.

The fact that the confirmation of 1E 0102 p1 as an isolated neutron star was enabled by optical observations is thus particularly exciting.

“This is the first object of its kind to be confirmed beyond the Milky Way, made possible using MUSE as a guidance tool,” said team member Dr. Liz Bartlett, also from ESO.

“We think that this could open up new channels of discovery and study for these elusive stellar remains.”

The team’s results were published online this week in the journal Nature Astronomy (arXiv.org preprint).

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Frédéric P.A. Vogt et al. Identification of the central compact object in the young supernova remnant 1E 0102.2–7219. Nature Astronomy, published online April 2, 2018; doi: 10.1038/s41550-018-0433-0