A star exploded in a part of the galaxy where it shouldn't have: meet Calvera

X-ray image of the neutron star Calvera, marked by the yellow circle, and of the diffuse emission region studied in this article, identified by the white ellipse. The material responsible for the observed emission has a temperature between 1 and 10 million degrees Celsius. Credits: E. Greco, INAF

Astronomers have spotted the remains of a massive star explosion exactly in a place where, by all expectations, it should not happen. The neutron star dubbed Calvera seems to be connected to a supernova remnant located over 6,500 light-years above the galactic plane, far outside of the dense mid-plane of the Milky Way where the majority of massive stars are born and die.

In a new peer-reviewed publication led by Italy's National Institute for Astrophysics (INAF) and the University of Palermo, researchers combined X-ray, gamma, and radio observations to draw together this unusual event. Instruments that were available to them including the LOFAR radio telescope, ESA’s XMM-Newton, NASA’s Fermi space telescope, and the Galileo National Telescope confirming that Calvera was somehow connected to the surrounding shell of superheated gas.

The remnant likely is 10,000–20,000 years of age, and the pulsar is currently blasting away at approximately 78 milliarcseconds per year, a genuine runaway. Its gas is member of the supernova remnant at temperatures of around 10 million degrees Celsius, and yet the region is surprisingly sparse.

The researchers believe the star was likely born nearer to the plane of the Milky Way galaxy and was somehow cast out to the outer halo before it exploded. This contradicts a long-held assumption that only in dense environments of a galaxy can we witness these high-energy stellar deaths.

As Emanuele Greco, the lead author puts it: "We have shown that even empty parts of the Milky Way galaxy contain powerful, high-energy processes. It causes us to rethink how and ultimately where stars are born and die."

References:

https://www.aanda.org/articles/aa/full_html/2025/09/aa55640-25/aa55640-25.html

https://www.aanda.org/articles/aa/pdf/2025/09/aa55640-25.pdf

https://www.media.inaf.it/2025/08/29/calvera-esplosione-pulsar-vialattea/