Earlier this week I was lucky enough to meet and see a fascinating talk by Shane L. Larson, astronomer at Chicago's Adler Planetarium. The topic was Black Holes and Gravitational Waves, and the first part of the talk focused on the LIGO project, a pair of massive detectors in Washington and Louisiana that can detect the tiny ripples in space caused by massive gravitational events far in the universe, like stars going supernova or black holes colliding. And on September 14 last year, not long after the detectors were first turned on, that's exactly what they detected: two massive black holes, merging in space.
Here's what that event would look like, if you could position yourself near the merging black holes. This computer simulation was generated using the same software used for the movie Interstellar.)
However, something I learned about LIGO was that while telescopes are more like eyes on the universe, these gravity-wave detectors are more like ears: they can 'hear' the 'sound' from these cataclysmic events as the gravity waves pass through earth, but don't form an image of them directly. We can get a rough idea of the direction of the event because we have two sensors (in much the same way our two ears give us a rough idea of the direction of a loud sound). You can actually convert the sensor readings into audible sound, and this is what the above event sounded like:
The actual sound is just 1 second long; it's played 4 times here, first in its actual frequency, then upsampled to a higher register where it's easier to hear (and then the cycle repeats). The little "chirp" you hear is the final phase of the black hole merger, where they spin super-rapidly before colliding at half the speed of light.
We're in the early days of gravitational wave observation, which literally gives us a new view (or listen?) on the universe to observe events that don't generate light or are obscured by the dust of the galaxy. More sensors are being constructed around the globe, which will give us the ability to detect more events and get a better sense of where they occurred. And there's even a project to build an observatory in space: LISA, the Laser Interferometry Space Antenna. (The original NASA project was sadly not funded, but the European Space Agency has taken up the mantle.) Like the ground-based detectors, LISA uses lasers to detect the minute (smaller than the diameter of a proton!) change in lengths of the detection arms as the gravity waves roll through. A precursor mission, LISA Pathfinder, was launched in December as a proof of concept to make sure accurate space-based detection of distances was possible. The experiment was to float two small masses in space, and use a laser reflecting off the sides to measure the distance. Dr Larson gave me a replica of one of the masses to hold — even though it was made of tungsten and not gold/platinum like the real ones, it was still surprisingly dense!
Thankfully, the LISA Pathfinder mission was a success, and the space-based gravity wave observational platform could be launched as early as 2039.
That's all from us on the blog for this week. See you on Monday, and have a great weekend!
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