Astronomers from the University of Warwick have discovered a rare type of pulsar white dwarf star system, of which there is only one other recorded precedent in 2016.
White dwarfs are small, dense stars, typically about the size of a planet. They form when a low-mass star has burned all its fuel, losing its outer layers. Sometimes called “stellar fossils”, they offer information about different aspects of stellar formation and evolution. The new find includes a rapidly spinning, burnt-out stellar remnant called a white dwarf, which pummels its neighbor, a red dwarf, with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically at regular intervals. This is due to strong magnetic fields, but scientists aren’t sure what causes it. A key theory explaining strong magnetic fields is the “dynamo model”: white dwarfs have dynamos (electrical generators) at their core, just like the Earth, but much more powerful. But to test this theory, the scientists needed to search for other white dwarf pulsars to see if their predictions were true.
Published in Nature Astronomy, the scientists describe the newly detected white dwarf pulsar, J191213.72-441045.1. It is only the second time such a star system has been found, following the discovery of AR Scorpii (AR Sco) in 2016. At 773 light-years from Earth and spinning 300 times faster than our planet, the white dwarf pulsar is similar in size to Earth, but at least as massive in mass as the Sun. This means that a teaspoon of matter from white dwarf would weigh about 15 tons. White dwarfs begin life at extremely high temperatures before cooling off over billions of years, and the low temperature of J1912-4410 points to old age. Dr Ingrid Pelisoli, STFC Ernest Rutherford Research Fellow in the Department of Physics at the University of Warwick, said in a statement: “The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true. for white dwarf stars Fields in white dwarf stars can be more than a million times stronger than the Sun’s magnetic field, and the dynamo model helps explain why The discovery of J1912-4410 was a fundamental step in this field”.
“We used data from a few different surveys to find candidates, focusing on systems that had similar characteristics to AR Sco. We followed the candidates with ULTRACAM, which detects the very fast light variations expected of white dwarf pulsars. After observing a Out of a couple dozen candidates, we found one that showed light variations very similar to AR Sco. Our follow-up campaign with other telescopes revealed that every five minutes or so, this system was sending a radio signal and X-rays in our direction.” “This confirmed that there are more white dwarf pulsars, as previous models predicted. The dynamo model made other predictions, which were confirmed by the discovery of J1912-4410.”
source: https://www.nature.com/articles/s41550-023-01995-x