The ancient Polynesian seafarers could count and time the rolls and pitches of their canoes and feel the wave patterns generated by weather systems thousands of miles away. This allowed them to steer a straight course even when the sky was overcast. They could detect the presence of land, its distance and direction, by sensing the diffraction of wave trains around islands far over the horizon. It is said they avoided the continents because of the confused and distorted reflections of the seas near large land masses. They sensed that was too close to the edges of their known universe, an infinite sea dotted with scattered archipelagoes.

And their radar was passive, there was no need to give away their presence.

Artwork by Fritz Seegers.

But in reality its a lot more complicated (and not my field)
http://arxiv.org/pdf/1304.1775v4.pdf

http://arxiv.org/pdf/1309.5731v1.pdf

THAT is what it took to give us an unambiguous signal.

Events that cataclysmic pretty much have to be one-offs… 3 solar masses don’t grow on trees…

And when 3 solar masses get turned into energy there isn’t likely to be much left in the region for a repeat performance.

All the detections so far have been the final moments of 2 MASSIVE black holes spiraling into each other, and the resulting single black hole ‘ringing down’ shedding energy in the form of gravitational waves…

When two bodies orbit each other they radiate gravity waves with a luminosity proportional to the (mass*orbital frequency)^(10/3) – in the case of our solar system the masses are so small, and the orbital frequency is so low (earth orbits the sun once per year) the radiated gravitational wave energy is negligible.

In the case of two massive black holes orbiting each other its a different story – they will (slowly at first) lose orbital energy to these gravitational waves, as a result the will orbit each other closer which means the orbital frequency increases. Since the power of the radiated gravity waves depends on the orbital frequency to the 10/3 power the rate of energy loss increases with time.

The two black holes spiral in towards each other until they are moving at significant fractions of the speed of light- the gravity wave power increasing very rapidly until in that final moment it becomes powerful enough for our detectors at this distance can detect them.

These are guaranteed to be one time events.

In the future we may detect other sources- such as asymmetric supernovae, or maybe fast rotating neutron stars that have a small 10 cm high ‘mountain’ on them.

(spherically symmetric bodies or events cannot radiate gravity waves)

LIGOs next run will maybe have 1.2 times the sensitivity of the last run, meaning that the distance at which we can detect a given event increases by a factor of 1.2, so the potential volume we can see that even increases by nearly a factor of 2. We could expect nearly double the rate of LIGO discoveries.

And if we get the Space based gravity wave detector (LISA) put up we will have far greater sensitivity and be able to detect different types of events happening at different time scales- lower frequencies.

As they said- this is just the beginning of a whole new era of astronomy.

The gravity waves travel at the speed of light, so LIGO will see the event just once, but a detector a light year further away could see it a year later….

Hmmmmm that last sentence got me thinking… gravitational lensing can allow us to see light from the same event more than once- I wonder if gravitational waves can be gravitationally lensed … it seems like they should be, but I will have to look into that… that could be very interesting….

To put it another way, can I set up my own detector and listen to these two gravity waves, or do I have to sit and wait for another cosmic catastrophe to generate one?