National Radio Astronomy Observatory | 2015 Aug 06
[img3="A 21-year study of a pair of ancient stars -- one a pulsar and the other a white dwarf -- helps astronomers understand how gravity works across the cosmos. The study was conducted with the NSF's Green Bank Telescope and the Arecibo Observatory.Gravity, one of the four fundamental forces of nature, appears reassuringly constant across the Universe, according to a decades-long study of a distant pulsar. This research helps to answer a long-standing question in cosmology: Is the force of gravity the same everywhere and at all times? The answer, so far, appears to be yes.
(Credit: B. Saxton (NRAO/AUI/NSF))"]https://public.nrao.edu/images/non-gall ... f_nrao.jpg[/img3][hr][/hr]
Astronomers using the National Science Foundation’s (NSF) Green Bank Telescope (GBT) in West Virginia and its Arecibo Observatory in Puerto Rico conducted a 21-year study to precisely measure the steady "tick-tick-tick" of a pulsar known as PSR J1713+0747. This painstaking research produced the best constraint ever of the gravitational constant measured outside of our Solar System.
Pulsars are the rapidly spinning, superdense remains of massive stars that detonated as supernovas. They are detected from Earth by the beams of radio waves that emanate from their magnetic poles and sweep across space as the pulsar rotates. Since they are phenomenally dense and massive, yet comparatively small – a mere 20–25 kilometers across – some pulsars are able to maintain their rate of spin with a consistency that rivals the best atomic clocks on Earth. This makes pulsars exceptional cosmic laboratories to study the fundamental nature of space, time, and gravity.
This particular pulsar is approximately 3,750 light-years from Earth. It orbits a companion white dwarf star and is one of the brightest, most stable pulsars known. Previous studies show that it takes about 68 days for the pulsar to orbit its white dwarf companion, meaning they share an uncommonly wide orbit. This separation is essential for the study of gravity because the effect of gravitational radiation – the steady conversion of orbital velocity to gravitational waves as predicted by Einstein – is incredibly small and would have negligible impact on the orbit of the pulsar. A more pronounced orbital change would confound the accuracy of the pulsar timing experiment. ...
Testing Theories of Gravitation Using 21-Year Timing of Pulsar Binary J1713+0747 - W. W. Zhu et al
- arXiv.org > astro-ph > arXiv:1504.00662 > 02 Apr 2015