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eLisa - Evolved Laser Interferometer Space Antenna.

A LISA-like mission is designed to directly observe gravitational waves, which are distortions of space-time travelling at the speed of light. Passing gravitational waves alternately squeeze and stretch objects by a tiny amount. Gravitational waves are caused by energetic events in the universe and, unlike any other radiation, can pass unhindered by intervening mass. Launching eLISA will add a new sense to scientists' perception of the universe and enable them to listen to a world that is invisible in normal light.

The "duh" answer to my question is "Gravity waves, of course."

Obviously this is not what I'm asking.

So, we've deployed eLISA and we spotted a gravitational wave passing. Well, there went the wave. What data do we extract from it? What discoveries, observations will we acquire? What else can we discover with it than "there was a gravity wave, and it came from this direction"?

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The first observation is whether gravitation radiation exists as predicted by General Relativity. Evidence from observations of binary neutron stars says it does, but it remains a major unknown.

Now Gravitational waves have been discovered, and the predictions of GR have been confirmed

Gravitational astronomy will be more like listening than looking. Right now I can hear my kids playing upstairs. I can learn a lot about what they are doing just by noting that sound waves are passing, from a particular direction.

Since the first detection of gravitational waves, we have observed several black hole merges, of different sizes. We have also observed neutron star collisions and subsequently observed these at gamma ray and visible wavelengths. This confirms these events as a potential source of many heavy elements.

We would expect extreme gravitational events to produce particular wave forms, for example black hole mergers should make a "tone" that rises in pitch as the two event horizons merge at faster rates. Again we have lots of theory on this but if we can "hear" these events we can check if GR does correctly model gravity in these situation, or if there is something missing.

Most interesting would be if we do hear Black hole mergers, but they don't sound like what we have expected. That would mean that there is more to gravity than we understand, and would lead to new science.

Now after several observations, it is the combination of gravitational observations combined with light observations that are producing the most science. E-Lisa will allow much smaller to be detected.

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