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LIGO interferometer in Hanford, Washington

The massive LIGO interferometers in Hanford, Washington (above), and Livingston, Louisiana, are back in action after nearly a year of tuning.

Caltech/MIT/LIGO Lab

Slightly more sensitive, LIGO resumes hunt for gravitational waves

Fourteen months after scoring one of the biggest discoveries ever in physics, experimenters are back in the hunt for gravitational waves—ripples in spacetime set off by some of the cosmos's most violent events. On 14 September 2015, physicists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of gigantic instruments in Hanford, Washington, and Livingston, Louisiana, spotted a set of these waves that  emanated from two massive black holes spiraling into each other. LIGO researchers spotted a second black hole merger before ending the observation run on 12 January. This morning, after 11 months of tweaking and tuning, the LIGO interferometers began taking data again.

LIGO's goal, of course, is to see more sources of gravitational waves. To up the observation rate researchers have been striving to improve the sensitivity of each interferometer—a gigantic L-shaped contraption that researchers use to measure the stretching of space itself. The detectors are starting the new run with about 10% better sensitivity than they had during the previous observing run, says Gabriela González, a physicist at Louisiana State University in Baton Rouge, and spokesperson for the 1000-member LIGO Scientific Collaboration. That means they can detect sources 10% farther into space. The plan is to take 6 months of data over the next calendar year, González says. Researchers aim to improve the devices’ sensitivity by a factor of two in the next few years. If they can reach that goal, then, extrapolating from the current observations, LIGO might eventually spot as many as one black hole merger per day.

LIGO should soon have company in the hunt. Researchers in Italy plan to turn on the upgraded VIRGO interferometer near Pisa early next year.