Double Pulsar Tests General Relativity

Double Pulsar Tests General Relativity

My graduate research focused on detecting extremely energetic gamma rays from astronomical objects. Using an arbitrary set of units, if the light from a standard incandescent bulb has the energy of one, then the X-rays in a doctor’s office have energy around 10,000. The gamma rays I searched for had energies 100 million times larger than the doctor’s X- rays. Astronomical objects capable of producing such high-energy radiation must exhibit some of the most extreme environments in the universe.

Detected in 1988, the first discovered high-energy gamma-ray emitting object is the Crab Nebula. In the middle of this nebula resides a star with a mass about 1.5 times the mass of the sun. However, this star is only 15 to 20 miles across and spins around 30 times a second! Objects like this—known as neutron stars—often emit opposing beams of radio emission. If the radio beam(s) pass across Earth as the neutron star rotates, astronomers call them pulsars.

Beyond emitting gamma rays, the large masses and small sizes of neutron stars also generate huge gravitational fields that astronomers use to test the validity of general relativity. One particular object, with the functional but boring name of PSR J0737—3039A/B, consists of two pulsars orbiting one another every 2.45 hours. Additionally, the magnetic field surrounding one of the pulsars (the blue region in the image below) eclipses the radio emission of the other for roughly 30 seconds each orbit.

In the past, this object has provided four independent timing tests of general relativity. As described in a recent Science article (see the article in Science Daily also), an international team of astronomers and physicists took advantage of the eclipsing nature of the binary pulsar PSR J0737-3039A/B to perform a different test. If general relativity accurately describes how gravity operates, the axis around which a pulsar spins should change direction like the gyroscope below (called precession) with a specific rate.

The team was able to determine the precession rate of pulsar A using precision measurements of its pulsations as the magnetic field of pulsar B eclipsed its radio beam. The measured precession matched the value predicted by general relativity. These results provide another confirmation of general relativity in a regime where it most likely would break down—in the presence of strong gravitational fields.

RTB’s creation model assumes that general relativity gives an accurate description of the development of the universe. Consequently, this new test further strengthens the model and gives support to its central premise that the God of the Bible created the universe with humanity in mind.