We’ve Observed A Spinning Star That Drags The Very Fabric Of Space And Time

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A white dward (centre) and its companion pulsar make for an excellent natural gravitational laboratory. Mark Myers/OzGrav

One of the predictions of Einstein’s general theory of relativity is that any spinning body drags the very fabric of space-time in its vicinity around with it. This is known as “frame-dragging”.

In everyday life, frame-dragging is both undetectable and inconsequential, as the effect is so ridiculously tiny. Detecting the frame-dragging caused by the entire Earth’s spin requires satellites such as the US$750 million Gravity Probe B, and the detection of angular changes in gyroscopes equivalent to just one degree every 100,000 years or so.

Luckily for us, the Universe contains many naturally occurring gravitational laboratories where physicists can observe Einstein’s predictions at work in exquisite detail. Our team’s research, published today in Science, reveals evidence of frame-dragging on a much more noticeable scale, using a radio telescope and a unique pair of compact stars whizzing around each other at dizzying speeds.

The motion of these stars would have perplexed astronomers in Newton’s time, as they clearly move in a warped space-time, and require Einstein’s general theory of relativity to explain their trajectories.

The white dwarf-pulsar binary system PSR J1141-6545 discovered by the CSIRO’s Parkes radio telescope. The pulsar orbits its white dwarf companion every 4.8 hours. The white dwarf’s rapid rotation drags space-time around it, causing the entire orbit to tumble in space. Mark Myers/ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

General relativity is the foundation of modern gravitational theory. It explains the precise motion of the stars, planets and satellites, and even the flow of time. One of its lesser-known predictions is that spinning bodies drag space-time around with them. The faster an object spins and the more massive it is, the more powerful the drag.

One type of object for which this is very relevant is called a white dwarf. These are the leftover cores from dead stars that were once several times the mass of our Sun, but have since exhausted their hydrogen fuel. What remains is similar in size to Earth but hundreds of thousands of times more massive. White dwarfs can also spin very quickly, rotating every minute or two, rather than every 24 hours like Earth does.

The frame-dragging caused by such a white dwarf would be roughly 100 million times as powerful as Earth’s.

That is all well and good, but we can’t fly to a white dwarf and launch satellites around it. Fortunately, however, nature is kind to astronomers and has its own way of letting us observe them, via orbiting stars called pulsars.