2023-06-19 16:36:44
The discovery of a rare type of white dwarf star system provides a new understanding of stellar evolution.
White dwarfs are small, dense stars usually the size of a planet. They form when a low-mass star has burned up all of its fuel, losing its outer layers. Sometimes called “stellar fossils”, they offer insight into different aspects of star formation and evolution.
A rare type of white dwarf pulsar has been discovered for only the second time, in research led by the University of Warwick. The white dwarf pulsars include a rapidly rotating scorched stellar remnant called a white dwarf, which lashed its neighbor – a red dwarf – with powerful beams of electrical particles and radiation, causing the entire system to lighten and fade to regular intervals. . This is caused by strong magnetic fields, but scientists don’t know what causes them.
A key theory that explains strong magnetic fields is the “dynamo model” – according to which white dwarfs have dynamos (electrical generators) in their core, just like Earth, but much more powerful. But for this theory to be tested, scientists had to search for other white dwarf pulsars to see if their predictions were true.
Published today in natural astronomy, scientists funded by the UK Science and Technology Facilities Council (STFC) describe the newly detected white dwarf pulsar, J191213.72-441045.1 (J1912-4410 for short). This is only the second time such a star system has been discovered, following the discovery of AR Scorpii (AR Sco) in 2016.
At 773 light-years from Earth and rotating 300 times faster than our planet, the white dwarf pulsar is similar in size to Earth, but at least as large in mass as the Sun. This means that a teaspoon of white dwarf matter would weigh about 15 tons. White dwarfs begin life at extremely hot temperatures before cooling for billions of years, and the low temperature of J1912−4410 indicates advanced age.
Dr Ingrid Pelisoli, from the University of Warwick’s Department of Physics, said: “The origin of magnetic fields is a big open question in many areas of astronomy, and this is particularly true for white dwarf stars. . Magnetic fields in white dwarfs 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 breakthrough in this area.
“We used data from a few different surveys to find candidates, focusing on systems that had similar features to AR Sco. We tracked all candidates with ULTRACAM, which detects the very fast light variations expected from white dwarf pulsars. After observing a few dozen candidates, we found one that exhibited light variations very similar to AR Sco. Our follow-up campaign with other telescopes revealed that every five minutes or so this system sent a radio and X-ray signal in our direction.
“This confirmed that there are more white dwarf pulsars out there, as predicted by previous models. There were other predictions made by the dynamo model, which were confirmed by the discovery of J1912−4410. the pulsar system should be cold. Their companions should be close enough that the gravitational pull of the white dwarf would in the past be strong enough to capture the mass of the companion, causing them to spin rapidly. All these predictions are valid for the discovery of a new pulsar: the white dwarf is colder than 13,000 K, rotates on its axis once every five minutes and the gravitational pull of the white dwarf has a strong effect on the fellow.
“This research is a great demonstration that science works – we can make predictions and test them, and that’s how all science progresses.”
Dr Pelisoli is among the first group of researchers and PhD students to be supported by a £3.5million private philanthropic donation from a Warwick alumnus. One of the most important donations for the study of astronomy and astrophysics in the UK, this donation enables the next generation of astronomers to explore the far reaches of our universe.
Axel Schwope, of the Leibniz Institute for Astrophysics in Potsdam (AIP), who is leading a complementary study published as a letter in Astronomy and Astrophysics, added: “We are delighted to have independently found the object in the All-sky X-ray survey with SRG/eROSITA Follow-up survey with ESA’s XMM-Newton satellite revealed pulsations in the high-energy X-ray regime, confirming the unusual nature of the new object and firmly establishing white dwarf pulsars as a new class. “
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