Magnetars are an unusual variant of a neutron star that have a extraordinarily powerful magnetic pull, despite their tiny size. It has long been a mystery how our galaxy's only magnetar ever came to be, as conventional wisdom said that it should have formed a black hole. Now, scientists believe they have discovered the answer.
A team of researchers who have long been investigating the astral phenomenon of magnitars report that they have found the "runaway star" that caused the Milk Way Galaxy's only magnitar to form.
"In our earlier work we showed that the magnetar ... must have been born in the explosive death of a star about 40 times as massive as the Sun." Lead author of a recent study said in a news release. "But this presents its own problem, since stars this massive are expected to collapse to form black holes after their deaths, not neutron stars. We did not understand how it could have become a magnetar."
Clarke has been studying the magnetar simply known as CXOU J164710.2-455216 for years, and published his first assessment of the unusual neutron star in 2010. Now, four years later, his second study of the star has been published in the journal Astronomy and Astrophysics, detailing how Clarke has identified " Cl-Westerlund 1 W 5," a "runaway" star that was likely involved in the process that created the magnetar.
According to the study, data and observations suggest that the Milky Way magnetar did not become a black hole because it was not initially alone prior to going supernova.
Clarke and his team found evidence that indicates that a highly magnetic magnetar forms after the larger of two closely orbiting stars (no farther than the Earth orbits the Sun) begins to die. As it dies, the larger star transfers its outer layers to the smaller star, escalating the rotational force of the second star in the process. This second start soon becomes so massive that it too sheds its mass - most of which is dispersed, but some of which is transferred back to the first star, essentially rekindling it.
The massive second star, having grown too large, then collapses in upon itself. The resulting supernova hurtles the first star away, but the high rotational forces of the dual-star process cause the supernovaed star to become a magnetar rather than a black hole.
When his team first found Cl-Westerlund 1 W 5, Clarke knew his theory was right.
"Not only does this star have the high velocity expected if it is recoiling from a supernova explosion, but the combination of its low mass, high luminosity and carbon-rich composition appear impossible to replicate in a single star - a smoking gun that shows it must have originally formed with a binary companion," Ben Ritchie a co-author to the study, said in a recent press release.
The study was published in Astronomy and Astrophysics on May 12.