Astronomers use vanishing neutron star to measure space-time warp

January 8, 2015, University of British Columbia
One orbit of pulsar J1906 (on the right, with radio beams) around its companion (centered), with space-time curvature (blue grid). Credit: Joeri van Leeuwen

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

The international team, including University of British Columbia astronomer Ingrid Stairs, measured the masses of both stars in binary pulsar system J1906. The pulsar spins and emits a lighthouse-like beam of radio waves every 144 milliseconds. It orbits its in a little 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, professor of physics and astronomy at UBC.

"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 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.

Effect of geodetic precession in the observer pulsar. Two neutron stars orbit one another. The star visible as a pulsar shows rotating beams. The companion is frozen at the frame center. Credit: Joeri van Leeuwen

"The pulsar is now all but invisible to even the largest telescopes on Earth. This is the first time such a young 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."

The mass of only a handful of double have ever been measured, with J1906 being the youngest. It is located about 25,000 light years from Earth.The results were published in the Astrophysical Journal and presented at the American Astronomical Society meeting in Seattle on January 8.

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bruce36b
not rated yet Jan 09, 2015
Did anyone see the difference between theorizing curved space and a simple two masses falling towards each other in vectors that made it so when one star fell, it was already on the other side of the other star, hence an orbit?
antialias_physorg
5 / 5 (2) Jan 09, 2015
"These two stars each weigh more than the Sun, but are still over 100 times closer together than the Earth is to the Sun

I don't really like formulations like this (x times smaller/lighter/closer, etc. ) they sound nonsensical.
AlienOverlord
4.5 / 5 (2) Jan 09, 2015
Ant, I think the person who made that statement was lacking in communication skills at that moment because they were distracted by the fact that these two stars were so close together; with huge gravitational forces; yet were still not crashing into each other. A: These two stars each weigh more than the Sun. B: They are 100 times closer together than the earth is to the Sun. C: Why are they still separate? ..Or maybe they live in Denver...
AlienOverlord
not rated yet Jan 09, 2015
Bruce, but doesn't the orbiting body "sense" that it is traveling in a straight line?
lomed
5 / 5 (2) Jan 10, 2015
The article is at http://iopscience...98/2/118 . While they did use the rate of precession to determine the masses of the stars, it seems that there are other compact systems that yield better tests of General Relativity (as they state in the concluding section).

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