Environment & Science

The hunt for gravitational waves is moving to space

Artist's impression of LISA Pathfinder, ESA's mission to test technology for future gravitational-wave observatories in space.
Artist's impression of LISA Pathfinder, ESA's mission to test technology for future gravitational-wave observatories in space.

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It’s been about a month since scientists using Earth-based sensors announced the first detection of gravitational waves from the merger of two distant black holes a billion years ago.

This week, a new instrument started testing equipment to one day help find more of these waves — this time from space.

It’s a device called LISA Pathfinder. LISA stands for Laser Interferometer Space Antenna, and it's called Pathfinder because this is a proof-of-concept mission. While it won't detect gravitational waves itself, it will help researchers design a tool that can.

The European Space Agency led the effort and launched the spacecraft in December. It's currently orbiting a million miles from Earth.

LISA Pathfinder contains two identical two-kilogram gold and platinum cubes, and it carefully measures the distance between them using lasers.

In theory, a passing gravitational wave would change the distance between them ever so slightly, disturbing the lasers and allowing scientists to measure the distortion. However, in this iteration of the tool, the cubes are too close to measure any waves.

Inside LISA Pathfinder

The European Space Agency is testing this device to see if it can suspend those cubes in near-perfect stillness, so they'd be sensitive enough accurately measure subtle gravitational waves.

You’d think stillness would be easy in space, but even the sun can mess with something this delicate, said Charles Dunn, from NASA’s Jet Propulsion Laboratory.

Dunn said the force of solar radiation on LISA Pathfinder is equivalent to the force of a mosquito landing on the machine.

"But then what is even more difficult is that the sun is a very hot, turbulent body," he said. "So the sunlight itself varies a little bit as if the mosquito were walking around or dancing on the spacecraft."

To counteract these subtle forces, Dunn's team developed tiny micro thrusters that balance out any disturbances and, it is hoped, will keep the cubes perfectly still.

If the thrusters and other components work out, a more advanced LISA project will eventually be launched, but not until 2034.

That one is expected to have components separated by 1 million kilometers beaming lasers back and forth. In theory, it should be able to pick up gravitational waves in a much lower range than the ones the Earthbound detectors have recorded.

Dunn said once complete, the LISA system may one day pick up signals from the Big Bang itself.