Second, it is relatively nearby-at a distance of about 2000 light years from Earth. First, it has the advantage that it is the only binary where both components are visible as pulsars (Fig. In terms of studying gravitational effects, the double pulsar PSR J0737–3039A/B-detected in 2003-is, in many ways, superior to its binary rivals. For example, observations of the Hulse-Taylor pulsar, the first known stellar binary containing a pulsar, revealed a shrinking in the orbital radius and an acceleration in the revolution rate-evidence that orbital energy was being lost to gravitational-wave radiation. Precise measurements of these arrival times over the course of years to decades allow tiny changes in the orbital motion to be detected. When a pulsar is located in a binary, the arrival times of pulses at radio telescopes are modified by the binary’s orbital motion in a characteristic way. Certain alternative gravity theories predict that neutron-star clocks could display large deviations from general relativity predictions. On top of that, neutron stars are almost as compact as black holes, meaning that their precise ticking occurs in a highly curved spacetime. Because of angular momentum conservation, neutron-star rotation is remarkably stable, which means the ticks of a pulsar clock have a long-term consistency comparable to that of the best atomic clocks on Earth. The most relevant superproperty for gravity tests is that pulsars are superprecise clocks. Einstein’s general relativity passes all these challenges with flying colors.Īstrophysicists refer to neutron stars as superstars because of their superdense matter, superconducting/superfluid interiors, superfast rotation, and superstrong gravity and magnetism. The new extended dataset does not disappoint: It not only improves the precision of previous gravity tests by orders of magnitude, but it also enables a few new ones. The gravity community has long awaited this update, as an earlier study-based on just 2.5 years of data-showed that the pulsar pair is an excellent testbed for strong-field gravity. The team has now released 16 years’ worth of their data. For nearly two decades, Michael Kramer from the Max Planck Institute for Radio Astronomy, Germany, and his collaborators have monitored the double pulsar PSR J0737–3039A/B, a unique system composed of two pulsars in orbit around each other.
By recording the flashes from these so-called pulsars, giant radio telescopes can infer physical properties of neutron stars. But unlike black holes, some neutron stars emit beams of radiation out of their magnetic poles, producing a “lighthouse” effect as they rotate.
Neutron stars are the densest celestial objects after black holes. This loss matches what Einstein’s general relativity predicts to a level of one part in 10,000. By monitoring changes in the timing of the flashes, researchers have measured the amount of energy taken away by gravitational waves. As the two pulsars revolve around each other, gravitational waves are emitted (represented by “ripples” in the underlying spacetime fabric). On Earth, we see these beams as flashes at regular intervals.
The light beams from each pulsar (yellow) are shown exiting through a donut-shaped magnetic field (blue). Kramer/ Max Planck Institute for Radio Astronomy Figure 1: The double pulsar is a pair of rotating neutron stars, both of which are pulsars.
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