Hulse-Taylor Binary [PSR B1913+16]

The Hulse-Taylor Binary is a pair of neutron stars in the region of the Aquila constellation as viewed from Earth. Even though the neutron stars of the Hulse-Taylor Binary orbit one another at a distance about 30% greater than the Earth-Sun distance (about 2 million km) they complete an orbit in a mere 7 hours.

They are traveling very fast.

The Hulse-Taylor Binary neutron stars are of the pulsar class. They are millisecond pulsars, meaning that they rotate very quickly (~59 ms per rotation) emitting radio waves out of each of their magnetic poles. These radio waves are beamed through space, enabling us to observe them with radio telescopes as pulses of radio waves. Each pulse is in time with their rotation, when their beam of radio waves is directed towards the Earth.

The Hulse-Taylor Binary Pulsar was the first pulsar binary ever to be discovered. It was discovered by Russell Hulse and Joseph Taylor with the Aricebo 305 m radio dish in 1974, earning them the 1993 Nobel Prize in physics. [1]

They found that the object they classified as a pulsar pulsed 17 times per second, meaning that it rotates once every 59 ms. Yet on further investigation they found another trend in the data. They found that the pulses arrived either 3 seconds earlier or 3 seconds later than expected over a regular period of about 7.8 h.

The explanation for this observation is that the neutron star was in orbit with another neutron star, henceforth called the Hulse-Taylor Binary Pulsars. The 3 second delay or advance in the radio signal tells us the radius of their orbit, which is 3 light seconds across. We have only detected radio pulses from one of the neutron stars of the Hulse-Taylor Binary.

Testing For Gravitational Waves

The orbital radius between these two neutron stars is gradually decaying, because energy is released as gravitational waves according to Einstein’s theory of relativity. This orbital decay causes them to reach periastron early each year, by about 4.2° per year in longitude, moving as far in a day as Mercury’s moves in a century. [1]

The observed orbital decay agrees almost perfectly with the energy loss that Einstein’s theory of general relativity predicted, in the form of gravitational waves. The discovery of the Hulse-Taylor Binary is actually powerful evidence that proves Einstein’s General Relativity. The ratio of observed to predicted rate of orbital decay is calculated to 0.997±0.002. [1]

Notes

References

1. Wikipedia Contributors. Hulse-Taylor binary. Wikipedia. <>.