The relative calm of physics and astronomy departments everywhere was toppled over last month with the announcement of the discovery of gravity waves from a colliding pair of neutron stars.
The detection was made by two gravitational wave observatories collectively called LIGO, and by the Virgo observatory as well. In the middle of all the well-rewarded hoopla over the discovery, including the announcement the month before of a Nobel Prize in Physics, it turns out that there is another potential route to discover gravity waves that does not involve any of these three observatories.
The idea is to make use of ultra-fast rotating neutron stars in space, or millisecond pulsars. These pulsars rotate at nearly 1000 times per second, speed so high for being able to drag more than one solar mass of material into fast circles that up until 1983 it was thought not to be possible for such objects even to exist.
These pulsars send radio beams of light in the direction of Earth with such regularity as to make for excellent, if not perfect, clocks. This is because occasionally tiny ‘glitches’ render these clocks a bit less accurate at times than the best atomic clocks on Earth. Speaking in favor of the pulsars, they are expected to lose only a few milliseconds over the course of billions of years, a specification that any clock on Earth would be hard-pressed to match in a warranty.
The pulses from these rapidly rotating objects must pass through spacetime en route to us. Just as seismographs register vibrations traveling across the Earth as a result of an earthquake, the idea is that the pulsars can register disturbances in spacetime, as would be caused by say, a colliding pair of neutron stars.
In such an event, the colliding neutron stars would produce extra ripples in spacetime that would induce a delay in the receipt of the pulses on Earth. As another way to look at it, it is as if Earth is bobbing up and down on a very very big lake and bobs with higher amplitude when it receives the wake from a speedboat on the other side of the lake which can be detected by the millisecond pulsars.
To date gravitational waves have only been detected by LIGO and Virgo observatories, but is it possible that millisecond pulsars can make a sort of natural “observatory” in space already set up to help us to detect gravitational waves here on Earth?
