Notes from the October night sky: Come on, Ligo!

by Kat Troche of the Pacific Astronomical Society

September 2025 has marked ten years since the first direct detection of gravitational waves as provided for by the theory of general relativity of Albert Einstein. These invisible ripples in space were first detected directly by the laser interferometer (LIGO) gravitational waves observatory. By traveling at the speed of light (~ 186,000 miles per second), these waves extend and press the fabric of the space itself, modifying the distance between objects when they pass.

Waves in space

Gravitational waves are created when massive objects accelerate in space, especially in violent events. Ligo detected the first gravitational waves When two black holes, in orbit, finally merged, creating undulations in space-time. But these waves are Not exclusive to black holes. If a star should go supernova, it could have the same effect. Neutron stars can also create these waves for various reasons. Although these waves are invisible to the human eye, this animation of the NASA scientific visualization studio shows the fusion of two black holes and the waves they create in the process.

How does it work

An observatory of gravitational waves, like Ligo, is built with two tunnels, each about 2.5 miles long, arranged in the form of “L”. At the end of each tunnel, a highly polished 40 kg mirror (about 16 inches in diameter) is mounted; This will reflect the laser beam sent by the observatory. A laser beam is sent from the room of the observatory and divided in two, with equal parts descending each tunnel, bouncing on the mirrors at the end. When the beams come back, they are recominated. If the lengths of the arm are perfectly equal, the light waves are canceled in the right way, producing the darkness to the detector. But if a gravitational wave passes, it slightly stretches an arm while tightening the other, so that the return beams no longer cancel perfectly, creating a sparkle of light which reveals the presence of the wave.

The actual detection occurs at the recombination point, when even a tiny stretch of one arm and the compression of others change how long it takes laser beams to return. This difference produces a measurable offset in the interference model. To be certain that the signal is real and not the local noise, the two observatories of Ligo – one in the state of Washington (Ligo Hanford) and the other in Louisiana (Ligo Livingston) – must record the same diagram in a few milliseconds. When they do it, it is the confirmation of a wave gravitational wave across the earth. We do not feel these waves when they cross our planet, but we now have a method to detect them!

Get involved

With the help of two additional observatories with gravitational waves, VIRGIN And Kagrathere was 300 mergers of black hole detected in the past decade; Some of which are confirmed, while others await a more in -depth study.

Although the average person cannot have a laser interferometer hanging out in the backyard, you can help with two projects focused on the detection of gravitational waves and the black holes that contribute to it:

• Black hole hunters: Using data from Tess satelliteYou would study the graphics of how the brightness of the stars changes over time, looking for a effect called gravitational microlensage. This lens effect can indicate that a massive object has passed in front of a star, like a black hole.
• Gravity spy: You can help Ligo scientists with their research on gravitational waves by looking for seeds that can imitate gravitational waves. By sorting the mimics, we can form algorithms on how to detect the real thing.

You can also use gelatin, magnetic marbles and a small mirror for a more practical demonstration on how the gravitational waves move in space-time with JPL Stop with gravitational waves activity!

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