The pulsar was discovered in 2004 with the Arecibo Observatory, the world’s most sensitive radio telescope due to its large, 305-meter dish. From that moment on, the team monitored the pulsar almost daily with the 5 largest radio telescopes on Earth: the Arecibo Telescope (USA), the Green Bank Telescope (USA), Nançay Telescope (France), the Lovell Telescope (UK) and the Westerbork Synthesis Radio Telescope (The Netherlands). Over 5 years, that campaign kept exact score of all rotations of the pulsar — an astounding one billion in total.
“By precisely tracking the motion of the pulsar, we were able to measure the gravitational interaction between the two highly compact stars with extreme accuracy,” notes co-author Ingrid Stairs, professor of physics and astronomy at The University of British Columbia, Canada. “These two stars each weigh more than the Sun, but are still over 100 times closer together than the Earth is to the Sun. The resulting extreme gravity causes many remarkable effects.”
One of these is geodetic precession. When you start a spinning top, it doesn’t only rotate – it also wobbles. According to general relativity, neutron stars, too, should start to wobble as they move through the gravitational well of a massive, nearby companion star. Orbit after orbit the pulsar travels through a space-time that is curved, which leaves an imprint on the spin axis.
The team now measured this geodetic precession in J1906. Because of the curved space time, 1 part in about a million of the pulsar’s orbit is “missing”, compared to a flat space time. Over the course of an Earth year of observations, this adds up to a change of 2.2 degrees in the orientation of the pulsar rotation axis.
“Through the effects of the immense mutual gravitational pull, the spin axis of the pulsar has now wobbled so much that the beams no longer hit Earth,” said van Leeuwen. “The pulsar is now all but invisible to even the largest telescopes on Earth. This is the first time such a young pulsar has disappeared through precession. Fortunately this cosmic spinning top is expected to wobble back into view .. but it might take as long as 160 years.”