Newly Exploded Star Solves Old Riddles Surrounding Neutron Stars, Creates New Ones

Sifting through the wreckage of a newly exploded star, researchers from the University of Wisconsin, Madison uncovered a glowing nebula created when the star detonated.

The nebula is a novelty, the researchers write in The Astrophysical Journal. Inside it is a neutron star, the collapsed core of the exploded star. Dubbed Circinus X-1, it is the only such system ever discovered in the galaxy.

"This particular remnant is only about 2,500 years old, which makes the system the youngest known X-ray binary," Sebastian Heinz, an astronomy professor and team leader, explained.

If it were a human, it would be only a handful of days old, according to co-author Paul Sell, a former UW-Madison graduate student.

Located in the plane of the Milky Way roughly 24,000-30,000 light years away, the system, known as an X-ray binary, offers a perfect lab to test theories regarding stellar evolution, and in particular the period shortly following a star's fiery end.

In an X-ray binary system, an evolving star and either a black hole or neutron star orbit one another closely, producing X-rays as the denser companion absorbs material from the evolving star.

Most X-ray binaries are old, their supernova remnant long gone. For this reason, the discovery of the ionized gas shell marking the supernova blast that led to the system's creation is especially rare and exciting, the researchers explain.

"It basically creates the historical record of that explosion," Heinz said. "They don't last very long, so they are quite accurate clocks for finding things that are recent."

Having it there served as a key component to many of the researcher's findings.

"Our observations solve a number of puzzles both about this object and the way that neutron stars evolve after they are born," Heinz said. "For example, the unusual elliptical orbit on which these two stars swing around each other is exactly what you would expect for a very young X-ray binary."

Like most studies, the report poses new questions even as it provides answers to old ones.

"General theory holds neutron stars are born with a large magnetic field," Heinz said. "This newly minted neutron star has a field much smaller than expected."