A new test mass for the revamped Laser Interferometer Gravitational-Wave Observatory (Image: Caltech/MIT/LIGO Lab)
We are more than ready to hear the plucked strings of space-time. Last Friday, the revamped LIGO took its first observations 鈥� a step towards picking up the ripples that Einstein predicted should come from exotic cosmic collisions.
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During its original run from 2002 to 2010, the Laser Interferometer Gravitational-Wave Observatory listened for gravitational waves in a range that included about 100 galaxies. It didn鈥檛 find any, probably because the main event it was searching for 鈥� the death spiral of two neutron stars 鈥� might only happen in a single galaxy once every 30,000 years.
The new experiment, Advanced LIGO, uses stronger lasers and better mirrors in two detectors 鈥� one in Hanford, Washington, and the other in Livingston, Louisiana. It will hopefully reach a volume of space that includes roughly 300,000 galaxies, and will be able to hear one neutron-star clashes per month, on average.
But it will take some ramping up before Advanced LIGO is that sensitive.
鈥淵ou don鈥檛 turn on these things like a light and have them just work,鈥� says of the Massachusetts Institute of Technology.
Passing waves
The detector works by bouncing laser light between mirrors inside twin perpendicular tunnels, each 4 kilometres long. It then waits for a passing gravitational wave to slightly change the length of one tunnel relative to the other.
But that means it feels the ground鈥檚 every tremor. Delayed aftershocks from Chile鈥檚 recent earthquake have already drowned out parts of the data. However, it looks like Advanced LIGO will hear signals as far away as 230 million light years in this first run. This is the first of three scheduled observation runs that should become progressively more sensitive.
If found, long-awaited gravitational waves could allow us to test Einstein鈥檚 theory of general relativity, pinpoint the sources of gamma-ray bursts, and understand the extreme physics with which black holes merge. But for now we鈥檙e still waiting.
鈥淓very generation has told their grad students: 鈥楬ey, you鈥檙e going to be the ones to detect gravitational waves!'鈥� Evans says. 鈥淲ell, I tell my grad students this, and I think it鈥檚 really true.鈥�
