Not everything in the universe can be measured with a telescope. Black holes merging, for example, do not emit light but they do send out gravitational wave radiation. Other cosmic events generate those waves, like distant supernovas. LISA is designed to "hear" those waves: much like listening in a pitch-black forest, you can't see the wildlife but know it's there, ESA official Fabio Favata said in today'spress briefing.

To do this, LISA has two gold-platinum alloy cubes inside it. Once the spacecraft successfully positioned itself at L1, a static point between the gravity of Earth and Sun, those cubes float in near-perfect freefall. Without other forces acting on them, scientists can use the cubes like a microphone to track the only force left: gravitational waves.

Scientists first successfully measured gravitational waves at an observatory on Earth's surface last September, proving their long-theorized existence. Tracking them provides further support for Einstein's theory of relativity, which posited that colossal events like two black holes colliding cause ripples in space-time reaching outward -- which are the waves. Scientists launched LISA for further research with less terrestrial interference as a proof-of-concept for a much larger space observatory that scientists hope to put in space by 2034.