Since existing gravitational observatories
can only detect the strongest waves created
in collisions of massive black holes and neutron stars,
future detectors are being made with ever increasing
sensitivities to find more subtle changes in the fabric of spacetime.
One concept being developed is called a Pulsar Timing Array,
which would allow scientists to probe Einstein's general theory of relativity
and the effects of gravitational waves over thousands of light years.
Since a pulsar is a rotating neutron star which emits a jet of radiation,
if the beam of the jet points towards Earth,
we detect a short radio burst.
Those radio bursts arrive at regular intervals,
sweeping across the earth for every rotation of the pulsar.
The fastest spinning pulsar,
PSR J1748-2446AD, which lives within the globular cluster of Terzan 5,
1,800 thousand light years from earth,
rotates 716 times per second,
which would sound like an F5 tone if the radio pulses were converted to sound.
A spinning pulsar is of great interest,
because some pulsar's rotation rates are incredibly stable.
So much so, that they can arrival the precision of atomic clocks.
So, PSR J1748, the fastest spinning pulsar has been measured to rotate exactly
once every 0.01395952482 seconds,
with an error of less than 600 femtoseconds.
This incredibly precise timing,
is one of the most accurately measured observables in all of astrophysics.
By the way, this pulsar was discovered by Dr. Jason Hustle's,
who graduated with a Bachelor of Science in
Honors Physics from the University of Alberta.
The precision of a pulsars rotation rate is very much
like a clock ticking at regular intervals.
Just like the effects of gravitational Doppler shift
that redshift photons as they escape from a gravity well,
gravitational waves alter the timing of pulses from pulsars.
In order to actually do anything useful though,
you need several pulsars in an array.
Now, you know why they're called pulsar timing arrays.
It may be easier to imagine pulsar timing arrays as similar to
the technology that underpins the Global Positioning System, or GPS.
The GPS sensors in smartphones and navigation devices work by listening
carefully for radio signals from GPS satellites high in orbit above Earth.
By comparing the arrival time of the pulses from each GPS satellite,
your device can triangulate your position on the surface of the earth.
NASA's Nicer-sextant X-ray telescope,
which is on the International Space Station is observing a collection of X-ray pulsars to
test out the feasibility of using pulsar arrays as future navigational aids.
By listening to the regular pulses from several nearby pulsars,
you could triangulate your position anywhere in interstellar space around those pulsars.
This map, created by
the Jet Propulsion Laboratory was affixed to the Pioneer 10 spacecraft,
which after completing a survey of Jupiter became
the first satellite with sufficient escape velocity to leave the solar system.
The image shows the relative positions of pulsars near
Earth with their particular timings encoded on the line that joins them.
If this map were discovered,
the position of Earth could be deduced.
But our civilization hasn't reached the point of navigating with pulsar timing arrays.
Instead, we're patiently listening to them for evidence of
large scale gravitational waves passing in between Earth and the pulsars.