Frame dragging seen in a pulsar-white dwarf binary

A prediction of Einstein’s general theory of relativity is that a body that is spinning  has the capacity to “drag” space-time around with it.

A pair of stars known as PSR J1141-6545, consisting of a pulsar and a white dwarf, have been observed for several decades at the Parkes Radio telescope by a team lead by Prof Matthew Bailes. Molonglo has been observing the system for the last three years as well.

Artist’s view of a white dwarf (central blue object) and a pulsar (purple, with beams of radiation being emitted). The pulsar has a 4.8 hour orbit. Very accurate timing of the pulsar’s pulses with the Parkes Radio Telescope, and for the last three years with Molonglo, have shown that the white dwarf is dragging space time around with it, as predicted by General Relativity. Credit Mark Myers / Swinburne University of Technology

PhD student at Swinburne University of Technology, Vivek Venkatraman Krishnan has processed these data for his PhD thesis. Now a postdoctoral fellow at the Max Planck Institute for Radio Astronomy in Bonn, Vivek published his ground-breaking results in Science magazine this week.

Vivek has been able to show that frame-dragging by the white dwarf is affecting the orbit of the two stars around each other, by using the amazingly accurate clock in the system provided by the pulsar.

Timing residuals — or the accuracy of the match between a physical model for the binary system and the observational data — shown for Parkes (red, orange, purple and blue symbols, for different instruments used on the telescope) and Molonglo (green symbols) over the last few decades.

“Vivek achieved extraordinary things during his PhD at Swinburne University of Technology. He was part of the team that refurbished the Molonglo telescope back to full operations, and wrote a highly configurable software application that converted Molonglo to a fully-automated robotic system, so that we could observe this pulsar, and hundreds more besides, on a near daily basis. And what a remarkable use he has put all this hard work to, by detecting a very rare phenomenon via observations of this binary system” says Dr. Chris Flynn, who was one of Vivek’s supervisors.

Another of Vivek’s supervisors, Dr Evan Keane of the SKA organisation says : “Pulsars are super clocks in space. Super clocks in strong gravitational fields are Einstein’s dream laboratories. We have been studying one of the most unusual of these in this binary star system. Treating the periodic pulses of light from the pulsar like the ticks of a clock we can see and disentangle many gravitational effects as they change the orbital configuration, and the arrival time of the clock-tick pulses. In this case we have seen Lens-Thirring precession, a prediction of General Relativity, for the first time in any stellar system.”

Artist’s depiction of a neutron star orbiting a rapidly-spinning white dwarf. The white dwarf’s spin drags the very fabric of space-time around with it, causing the orbit to tumble in space. Credit: Mark Myers, OzGrav ARC Centre of Excellence/Swinburne University of Technology

Read more about this remarkable source at the Conversation in an article by Matthew Bailes and Vivek Venkatraman Krishnan.

Read the Science article “Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system“, by Venkatraman Krishnan et alia 2020