New white dwarf pulsar discovered, provides new insights into stellar evolution

Researchers from the University of Warwick have made a significant discovery regarding a rare type of white dwarf star system, shedding new light on stellar evolution. White dwarfs, which are compact stars about the size of a planet, are formed when low-mass stars burn out all their fuel and shed their outer layers. These stellar remnants, often referred to as “stellar fossils,” provide valuable insights into various aspects of star formation and evolution.

The recent breakthrough involves the identification of a rare type of white dwarf pulsar, a phenomenon that has been observed only twice before. In this particular system, a rapidly rotating white dwarf, a burnt-out remnant, emits intense beams of electrical particles and radiation towards its companion star, a red dwarf. This interaction causes the entire system to undergo dramatic brightness fluctuations at regular intervals. The origin of these strong magnetic fields, which are responsible for the pulsar behavior, remains unclear to scientists.

One prominent theory explaining the source of these magnetic fields is the “dynamo model,” which suggests that white dwarfs possess highly powerful electrical generators, or dynamos, in their cores, similar to Earth but on a much larger scale. To test this theory, scientists needed to search for additional white dwarf pulsars and observe if the dynamo model’s predictions held true.

The findings, published in Nature Astronomy, present the discovery of a new white dwarf pulsar known as J191213.72-441045.1, or J1912-4410 for short. This star system, located approximately 773 light years away from Earth, spins around 300 times faster than our planet and has a size comparable to Earth but a mass at least as large as the Sun. A mere teaspoon of white dwarf material would weigh approximately 15 tons. The relatively low temperature of J1912-4410 suggests that it is quite old, as white dwarfs cool down over billions of years.

Dr. Ingrid Pelisoli, an STFC Ernest Rutherford Research Fellow at the University of Warwick’s Department of Physics, emphasized the significance of the discovery, stating, “The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true for white dwarf stars. The magnetic fields in white dwarfs can be more than a million times stronger than the magnetic field of the Sun, and the dynamo model helps to explain why. The discovery of J1912-4410 provided a critical step forward in this field.”

To identify candidates for white dwarf pulsars, the researchers analyzed data from various surveys, focusing on systems exhibiting similar characteristics to the previously discovered AR Scorpii (AR Sco) in 2016. After observing several potential candidates using the ULTRACAM instrument, which detects rapid light variations expected from white dwarf pulsars, they identified one system that displayed comparable light patterns to AR Sco. Subsequent observations with different telescopes confirmed that this system emitted radio and X-ray signals towards Earth approximately every five minutes.

This discovery validates the existence of more white dwarf pulsars, as predicted by previous models, and confirms additional predictions made by the dynamo model. The white dwarfs in pulsar systems are expected to be cool due to their advanced age, and their companions should have been close enough for the white dwarf’s gravitational pull to capture mass from them, leading to their rapid rotation. The newly found pulsar, J1912-4410, aligns with these predictions: the white dwarf has a temperature cooler than 13,000K, completes a full rotation every five minutes, and exerts a strong gravitational influence on its companion.

Axel Schwope from the Leibniz Institute for Astrophysics Potsdam (AIP), who led a complementary study published in Astronomy and Astrophysics, expressed excitement about independently discovering the object in the X-ray all-sky survey conducted with SRG/eROSITA. Further investigation using the ESA satellite XMM-Newton confirmed the pulsations in the high-energy X-ray range, solidifying the unique nature of the new object and establishing white dwarf pulsars as a distinct class of celestial objects.

This remarkable research showcases the progress of scientific inquiry, where predictions can be formulated and subsequently tested to advance our understanding of the universe. The discovery of white dwarf pulsars like J1912-4410 and the confirmation of their properties aligning with theoretical predictions provide valuable insights into the formation and behavior of these enigmatic stellar remnants. The study of white dwarf pulsars contributes to our broader knowledge of stellar evolution and magnetic field dynamics, bringing us closer to unraveling the mysteries of the cosmos.

Source: University of Warwick

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