Astronomers spot ‘forbidden’ pulsar Calvera fleeing supernova through Milky Way outskirts

Photos show Calvera, a rare system with a runaway pulsar and supernova remnant. (Image: E. Greco/ INAF.)

Astronomers have spotted a pulsar racing away from a supernova. The system, named Calvera, sits in an unlikely galactic region. Its presence could reshape how scientists understand star formation.

Where was Calvera found?
Calvera lies around 6,500 light-years above the Milky Way’s plane. This region holds very few stars of massive size. Stars here rarely form heavy enough to trigger supernovas. Yet, Calvera emerged after one such star exploded. The name recalls a Western villain living outside the norm.

In 2022, LOFAR radio telescopes spotted an unusual shape. It appeared as a near-perfect circle of extended emission. That suggested the wreckage of a long-ago stellar explosion. Pulsars are neutron stars left after massive stars collapse violently. Astronomers had earlier noted Calvera as a strong X-ray source. Tracing its path showed it fleeing from the supernova’s centre.

When did this supernova explosion happen?
X-ray data from ESA’s XMM-Newton spacecraft revealed more clues. Astronomers combined this with telescope data across other wavelengths. They found the blast erupted 10,000 to 20,000 years ago. The pulsar now sits 13,000 to 16,500 light-years away. Both the expanding shell and runaway pulsar link to one origin.

Supernovas usually occur in the Milky Way’s dense plane. These regions hold the gas needed for massive stars. Calvera, however, formed in a sparse and quiet zone. The system shows gamma-ray emissions can occur in low densities. This challenges earlier thinking about supernova processes in empty regions.

What do scientists say about Calvera?
Team leader Emanuele Greco said massive stars rarely form here. His group studied Calvera’s hot gas and shock interactions. They believe the blast met small clumps, igniting plasma emission. Such conditions revealed secrets of the progenitor star’s evolution. Greco said even empty regions can hide extreme cosmic activity.

The research proves supernovas can still shine far from the plane. It also urges astronomers to study galactic peripheries more closely. Calvera’s story shows that emptiness may still hold surprises. The findings were published on 29 August in Astronomy & Astrophysics.