11th January 2015

Neutron star hidden by warp in space-time

Astronomers have observed and measured a neutron star slipping out of view because of the warp in space-time its orbit creates. The star is expected to reappear in about 160 years.

	Illustration of one orbit of pulsar J1906 (on the right, with radio beams) around its companion (centred). In the space-time curvature caused by the companion (blue), the pulsar rotation axis slants throughout the orbit. For illustration the effect is exaggerated 1 million times here. Videos and image credit: Joeri van Leeuwen / ASTRON / University of British Columbia (CC BY-SA 4.0)

In an interstellar race against time, astronomers have measured the space-time warp in the gravity of a binary star system and determined the mass of a neutron star – just before it vanished from view.

The team, including University of British Columbia astronomer Ingrid Stairs, measured the masses of both stars in a binary pulsar system called J1906, which lies in a globular cluster known as Terzan 5, about 25,000 light years away. The pulsar spins and emits a lighthouse-like beam of radio waves every 144 milliseconds and orbits its companion star in under four hours.

"By precisely tracking the motion of the pulsar, we were able to measure the gravitational interaction between the two highly compact stars with extreme precision," says Stairs, a professor of physics and astronomy. "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."

According to general relativity, neutron stars wobble like a spinning top 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 impacts the star's spin 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," explains Joeri van Leeuwen, an astrophysicist at the Netherlands Institute for Radio Astronomy, and University of Amsterdam, who led the study.

"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."

Only a handful of double neutron stars have had their mass calculated, with J1906 being the youngest. The results were published on Thursday in the Astrophysical Journal and presented at the American Astronomical Society meeting.

Comments »