Shift in orbit in one year

Shift in orbit in one year

Binary pulsar orbit. (a) The radial velocity as a function of time within a period, expressed as a fraction of the period. (b) The shift in the orbit over a one year period. [Joseph Taylor, Princeton University]

sar. Also, as long as there is mass transfer, the rotation rate can be kept very high, explaining why the slowdown of millisecond pulsars is very small.

While discussing neutron stars in binary systems, we should mention one other interesting object. This is a radio pulsar discovered in 1974 by Joseph Taylor and Russel Hulse, then of the University of Massachusetts. This pulsar has a period of 0.059 s but the period varies periodically, suggesting that the pulsar is in a binary system. The variation in the period is like a Doppler shift (Fig. 12.8), with the period appearing longer when the pulsar is moving away from us and shorter when it is coming towards us. This system provides us with an interesting test of a prediction of general relativity-gravitational radiation. For their studies of this binary pulsar, Taylor and Hulse were awarded the Nobel Prize in physics in 1993.

Since the gravitational radiation carries away energy, the total energy of the orbit should be decreasing. In hopes of seeing this, Taylor and his co-workers have monitored this binary pulsar for several years. Some results are shown in Fig. 12.9. They have found that the orbital period is changing by —2.3 X 10—12 s/s. The change in energy of the orbit corresponds to the energy that would be given off by gravitational radiation from the orbiting bodies. This may provide us with the first indirect observational confirmation of gravitational radiation.

Orbit phase shift -1

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