When scientists directly detected a gravitational wave—a ripple in the fabric of the cosmos—for the first time back in September 2015, it marked the advent of a new field of astronomy.
Long reliant on bright objects like stars or galaxies for observational data about the universe, astronomers can now "hear" and study these extremely subtle waves, which are created by major upheavals, like the merging of black holes or the deaths of massive stars, and travel at the speed of light. Gravitational waves are essentially the cosmos's drum-and-bass track, and they can now be tapped into with facilities like the Laser Interferometer Gravitational-Wave Observatory (LIGO) based in Louisiana and Washington State.
Scientists are taking the search for gravitational waves into outer space. Just a few months after LIGO's landmark detection, the European Space Agency (ESA) launched LISA Pathfinder, a spacecraft designed to roadtest the technologies needed to build an epic gravitational wave observatory that would trail Earth in its orbit around the Sun. This future project is called the Laser Interferometer Space Antenna (LISA), and is currently slated for launch in 2034.
After exceeding expectations over its 16-month mission lifespan, LISA Pathfinder was switched off on Tuesday at 2PM ET, and retired from service.
Paul McNamara, the project scientist for the LISA Pathfinder spacecraft, sums up his team's successes in proving that "the dark side of the universe" can be explored from space, in this newly released ESA explainer.
The proof-of-concept involved two gold platinum cubes, which were suspended in free-fall about 38 centimeters apart within the spacecraft, where only gravity could influence them. The trick was to see if they could maintain a stable orientation with enough precision to perform laser interferometry, a method of bouncing lasers between locations to create a tripwire tuned to the spectral signatures of passing gravitational waves. The longer the laser-wire, the greater its sensitivity to these cosmic ripples, which is why LIGO's ground-based laser pathways are each four kilometers long.
LISA, the future successor to LISA Pathfinder, will scale this detection technique up to astronomical proportions, allowing it to tune into the lower frequency band of the gravitational wave spectrum, where some of the most cataclysmic ruptures in the universe are written in gravitational ink.
Consisting of three spacecraft flying 2.5 million kilometers distant from one another, the constellation will be able to pick up the rippled fallout of galaxy collisions, supermassive black hole mergers, and perhaps even the primordial waves created in the wake of the Big Bang.
"When galaxies merge together, eventually black holes collide, and when that happens, it rips the universe apart," McNamara explains in the ESA short. "We can observe these things which there's no other way to see."
This dazzling vision of a sprawling space-based gravitational wave observatory would not have been possible without LISA's prototype, LISA Pathfinder, which is now safely parked in an orbit around the Sun.
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