It had eluded astronomers for more than half a century, but researchers have finally laid eyes on the first pulsar-like white dwarf. Dubbed AR Sco, it is the first discovery of its kind in the known Universe.
So far, the thousands of pulsars discovered to date have all formed in the same way: when a massive star reaches the end of its life, it explodes as a supernova. The outer envelope of the star volatilizes, its core collapses under the effect of gravitation and gives birth to a neutron star, a small very massive object composed essentially of a « mash » of neutrons. This neutron star rotates very rapidly (several times per second) and projects a beam of very intense radiation around it in space, much like the light from a lighthouse on the seashore. where the name « pulsar ». But this new object discovered 380 light years away is different and has eluded astronomers for more than fifty years.
The difference between neutron stars and white dwarfs essentially lies in the way they form. Both stars burn up all their fuel, but unlike neutron stars resulting from the collapse of very massive stars, white dwarfs are the result of low-mass stars. Due to the difference in their initial mass, neutron stars have much higher temperatures, spin faster, and have stronger magnetic fields than white dwarfs.
In contrast, in the 1960s, researchers suggested the existence of a dwarf version of a pulsar. Today, a study published in the journal Nature Astronomy confirms its existence. This white dwarf pulsar is associated with a red dwarf star. Nicknamed AR Sco (AR Scorpii), you will find the star in the constellation of Scorpius located 380 light years from Earth. About the size of the earth, it has a mass 200,000 times greater and orbits every 3.6 hours around its colder companion star, which is about a third of the mass of the sun. Its magnetic field is also 100 million times stronger than Earth’s.
In (very) rapid rotation, the pulsar produces a flux of particles and radiation that whips its companion star. According to the researchers, it is a kind of gigantic dynamo, a magnet the size of the Earth with a magnetic field 10,000 times more powerful than anything that can be produced in the laboratory which turns on itself every two minutes « . This powerful flux accelerates the electrons in the atmosphere of the red dwarf to a speed close to that of the speed of light and because of this, the red dwarf is powered by the kinetic energy of its neighbor. This process generates a gigantic electric current on its companion star which produces the variations of light that we detect. The distance between the two stars is only 1.4 million kilometers.