The rotation is so fast that the white dwarf must have an above average mass just to stay together and not be torn apart. Lead author Dr Ingrid Pelisoli of the University of Warwick Department of Physics said: “J0240+1952 will have completed several rotations in the short amount of time that people take to read about it, it is really incredible. It gathers in bright spots on the surface of the star and as these rotate in and out of view they cause pulsations in the light that the astronomers observe from Earth, which they then used to measure the rotation of the entire star. The remainder will flow towards the star’s magnetic poles. The magnetic field acts a protective barrier, causing most of the falling plasma to be propelled away from the white dwarf. However, at some point in its evolutionary history J0240+1952 developed a strong magnetic field.
That’s almost 20% faster than the confirmed white dwarf with the most comparable spin rate, which completes a rotation in just over 29 seconds. Put into context, one rotation of the planet Earth takes 24 hours, while the equivalent on J0240+1952 is a mere 25 seconds. In the past, this plasma was falling onto the white dwarf’s equator at high speed, providing the energy that has given it this dizzyingly fast spin. It is part of a binary star system and its immense gravity is pulling material from its larger companion star in the form of plasma. The star that the Warwick team observed, named LAMOST J024048.51+195226.9 - or J0240+1952 for short, is the size of the Earth but is thought to be at least 200,000 times more massive. The study was led by the University of Warwick with the University of Sheffield, and funded by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation, and the Leverhulme Trust.Ī white dwarf is a star that has burnt up all of its fuel and shed its outer layers, now undergoing a process of shrinking and cooling over millions of years. Reported today (22 November) in the journal Monthly Notices of the Royal Astronomical Society: Letters, it is only the second magnetic propeller white dwarf to have been identified in over seventy years thanks to a combination of powerful and sensitive instruments that allowed scientists to catch a glimpse of the speeding star.