The first white dwarf pulsar

Tuesday 17th January, 2017

Our speaker was Professor Tom Marsh from the Department of Physics at Warwick University and he came to talk to us about "The First White Dwarf Pulsar". He mentioned that it was 13 years ago that he had started the astrophysics group at the University and now they have around 40 people in the department studying things such as exoplanets, black holes and white dwarf stars.

The object of his talk, the first white dwarf pulsar, was actually discovered by amateur astronomers in May 2015 who then alerted professional astronomers to its strange behaviour. The amateurs had looked at how the light from the star varied and plotted its change in brightness over time. Past observations in the 1970s had concluded that it was a type of variable star called a "Delta Scuti" but the amateur observations recorded changes in light levels that did not match this type of star. In fact the scientific paper that came out last year about this strange astronomical object actually cited a number of amateur astronomers in the list of authors due to the quality of their observations.

Prof Marsh explained that this unusual object is actually one of a pair of stars that orbit around each other in the constellation of Scorpius (the Scorpion) and its official designation is AR Scorpii which is often abbreviated to AR Sco. One of the stars is a rapidly rotating star called a white dwarf that is roughly the size of the Earth but with a mass 200,000 times that of Earth. The other star is known as a red dwarf which has about a third of the mass of our Sun and they orbit around each other in only 3.6 hours.

He then said that the white dwarf is spinning so rapidly that it is sending out radiation in concentrated beams just like a lighthouse does over the sea. These beams hit the red dwarf star, which in turn makes the whole system pulse every 1.97 minutes, and these pulses of radiation are seen in all the different wavelengths of light from the ultraviolet to radio waves.