Humanity’s first space-based gravitational wave detector has been approved.
Consisting of three spacecraft that together form a single gravitational wave detector, the Laser Interferometer Space Antenna (LISA) mission is a collaboration between NASA and the European Space Agency (ESA). It is planned to be released in the mid-2030s.
The adoption of LISA was announced by ESA on 25 January, with the mission concept and associated technology deemed sufficiently advanced. Getting the green light means scientists can start building the spacecraft and its necessary instruments; Work will begin in January 2025 after a European industrial contractor has been selected for construction.
LISA’s three spacecraft will follow Earth, forming an equilateral triangle in space as our planet orbits the sun. Each side of this triangle will be a staggering 1.6 million miles (2.6 kilometers) long. The LISA craft will fire laser beams down these edges, and these beams will experience minute-long changes as gravitational waves pass over them, crushing and compressing the fabric of space.
“LISA is an effort that has never been attempted before,” Nora Lützgendorf, LISA’s lead project scientist, said in a statement. “Ground-based devices using laser beams over distances of several kilometers can detect gravitational waves from events involving star-sized objects, such as supernova explosions or mergers of extremely dense stars and stellar-mass black holes. To expand the frontier, we must go into space for Gravitational research.”
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Gravitational waves were first predicted by Albert Einstein in 1915, based on his theory of gravity: general relativity.
This revolutionary theory proposed that gravity arose as a result of massive objects bending the fabric of space and time, essentially merging into a single entity called spacetime. The greater the mass of an object, the greater the curvature caused by the object and therefore the greater the gravitational effect. General relativity therefore explains why, for example, stars have a stronger gravity than planets, but black holes have a stronger gravity than stars.
In addition, general relativity says that when an object in space accelerates, this motion creates ripples in space-time that propagate outward. These gravitational waves are unimportant unless the accelerating objects are huge compact objects (like black holes or neutron stars) that orbit each other and eventually collide. The collapse of massive stars, which also trigger supernova explosions, can send out some significant waves.
But even in the most extreme cases, Einstein believed that gravitational waves would be too weak to be detected from Earth. He was wrong about this.
Fortunately, in September 2015, the Laser Interferometer Gravitational Wave Observatory (LIGO) in the USA and the Virgo interferometer in Italy did indeed detect ripples in space-time. These waves were formed by the collision and merger of two black holes, 29 and 36 times the mass of the Sun, located 1 billion light years away.
And. Since then, gravitational wave astronomers have detected signals from numerous events, including more black hole mergers, neutron star collisions, and even mixed mergers between a black hole and a neutron star.
LISA is poised to take this success even further as a space-based interferometer with the sensitivity to “hear” gravitational waves resulting from the mergers of black holes, neutron stars, and supernovae at much greater distances than are possible for Earth-based detectors. This also means it can look for waves originating from events further back in time.
“Thanks to the large distance traveled by the laser signals at LISA and the excellent stability of its instrumentation, we will investigate gravitational waves at frequencies lower than are possible on Earth and reveal events on different scales. It is time,” said Lützgendorf.
In addition to detecting gravitational waves from more distant sources, LISA should also provide astronomers with the sensitivity to investigate closer, less extreme events, such as mergers of compact white stars born when smaller stars like the Sun die.
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“For centuries, we have been studying our Universe by capturing light. Combining this with the detection of gravitational waves brings a completely new dimension to our perception of the Universe,” LISA project scientist Oliver Jennrich said in a statement. said. “If we imagine that we have been viewing the cosmos like a silent movie in our astrophysics missions so far, capturing the ripples of space-time with LISA will be a real game changer, just like when sound is added to motion pictures.”