Putting a gravitational wave detector on the Moon could find new physics
It’s tricky business detecting gravitational waves – these ripples in the very fabric of spacetime are often drowned out by background vibrations from earthquakes, traffic and other human activity. Now a pair of astrophysicists has proposed a new location that would be far quieter – the Moon.
Gravitational waves are produced by some of the most energetic events in the universe, such as collisions between black holes and neutron stars. But these cataclysms occur hundreds of millions of light-years away, so by the time the waves wash over Earth, they’re distorting reality by tiny amounts – as little as a thousandth of the width of a proton.
Detecting them requires extremely sensitive instruments, such as LIGO and Virgo. These facilities beam lasers down 4-km-long (2.5-mile) tunnels, bounce them off mirrors and measure how the light reflects to sensors. When a gravitational wave passes by, that laser beam wobbles ever so slightly, and scientists can learn a surprising amount of information from that.
The problem is, Earth is a busy place. Even when these facilities are located deep underground, they’re still susceptible to noise and vibrations from the environment around them. Is that a ripple in reality, or just a truck driving past overhead?
Now, a pair of astrophysicists has made the case for a gravitational wave facility on the Moon. Karan Jani of Vanderbilt University and Avi Loeb of Harvard say that the lunar surface naturally has several useful properties that are hard to replicate here on Earth.
Named the Gravitational-wave Lunar Observatory for Cosmology (GLOC), the facility would enjoy an almost total lack of environmental interference. For starters there’s no human activity yet, and even as future crewed missions ramp up there will still be plenty of room to set up a spot away from the hustle and bustle.
There’s far less natural interference too. Lunar quakes are far weaker and less frequent than their earthly counterparts, and being open to the vacuum of space means the experiments won’t need to be done in a vacuum tube like they do here.
Importantly, these factors mean that GLOC could be far more sensitive than any Earth-bound detector. The researchers say a lunar facility like this could potentially pick up gravitational waves from within 70 percent of the observable universe, and detect frequencies in a range that would be almost impossible for facilities on Earth to hear. There’s no telling what space oddities that might reveal.
“The Moon offers an ideal backdrop for the ultimate gravitational wave observatory, since it lacks an atmosphere and noticeable seismic noise, which we must mitigate at great cost for laser interferometers on Earth,” says Loeb. “A lunar observatory would provide unprecedented sensitivity for discovering sources that we do not anticipate and that could inform us of new physics. GLOC could be the jewel in the crown of science on the surface of the Moon.”
Of course, there is the added challenge of getting construction materials and scientific instruments to the Moon in the first place, but there’s renewed focus on missions like this lately. For instance, NASA’s Artemis program plans to return humans to the Moon in 2024, and set up a permanent presence there. GLOC, or something like it, could be a valuable facility to set up once we get there.
The research was published in the Journal of Cosmology and Astroparticle Physics. The team discusses the proposal in the video below.
Source: Vanderbilt University