Astronomers’ long-standing mystery regarding the identify of a star has finally been solved.
A fading Wolf-Rayet star called HD 45166 is located around 3,000 light-years distant. It has a companion and is helium-rich like the majority of stars in its class.
However, HD 45166 also exhibits certain unexpected traits not observed in other Wolf-Rayet stars, including a higher than anticipated loss of mass and an odd pattern in the direction of its winds.
Now, a group headed by astronomer Tomer Shenar from the University of Amsterdam in the Netherlands has found that this strange beast has one tremendously potent magnetic field, indicating that when it eventually pops its star blockages it will turn into something known as a magnetar.
The discovery resolves earlier issues with the binary, identifies HD 45166 as the first magnetic Wolf-Rayet star, and closes certain knowledge gaps regarding how massive stars become the most magnetic objects in the universe.
Wolf-Rayet stars are uncommon, but when they do exist, they can be among the Milky Way’s most dazzling stars since they have used up all of the atomic fuel that powers their core fusion. They contain relatively little hydrogen, are extremely hot and luminous, but are abundant in carbon and nitrogen.
They also rapidly lose mass due to stellar winds and are doomed to explode as supernovae in a relatively little period of cosmic time. Their cores swiftly collapse into neutron stars, an ultradense entity with a diameter of just 20 kilometers and a mass of up to 2.4 times that of the Sun, after expelling their outer material into space.
A form of neutron star called a magnetar has magnetic fields that are 1,000 times stronger than those of a typical neutron star and a quadrillion times stronger than those of Earth.
It is unclear how they became that way, but models indicate that one possibility is that the magnetic field existed before the star went supernova and its core collapsed. The issue with this is that no detections of a dying star with a strong enough magnetic field had been made.
We now return to HD 45166. Previous analyses of the binary revealed that the Wolf-Rayet star was helium-rich, about four times as massive as the Sun, and orbited a B-type star in a close, 1.6-day orbit. These characteristics, however, are inconsistent with what is known about the development of binaries and the origin of stellar winds.
Shenar claims, “This star kind of became an obsession of mine.” While reading the literature, “What if the star is magnetic?” came to my mind.
Shenar and his associates made a fresh set of studies of the star in order to search for signs of a magnetic field. Along with it, they also discovered a fresh set of measures that virtually entirely recharacterized the binary.
First of all, HD 45166 possesses the strongest magnetic field ever measured in a massive star, measuring 43,000 gauss.
Second, the star is only around two times as massive as the Sun, which is much less than we had anticipated.
Last but not least, the binary’s orbital period is a much bigger 8,200 days, give or take. The B-type companion star’s internal oscillations are the cause of the 1.6-day periodicity that was previously discovered.
The Wolf-Rayet star’s origin is unknown, but the research team speculates that it may have arisen from the union of two smaller stars. There are probably additional magnetar evolution pathways because that seems to be a fairly particular and maybe uncommon occurrence.
As for where it’s going, HD 45166 is predicted to undergo a supernova in a matter of million years. A magnetar with a magnetic field strength of approximately 100 trillion gauss will occur from the magnetic field being concentrated by the collapsing core as it contracts around it.
Even though we might not live to witness it, the discovery provides us with a new tool for understanding magnetar development and a starting point for searching for other systems like it in the universe.
Finding a new class of celestial object is exciting, adds Shenar, “especially when it has been hiding in plain sight the entire time.”
The research has been published in Science.
