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Prepare for a big wave – a wave of gravitational waves. A mass of predictions from the latest meeting of the American Physical Society in Washington DC is shedding light on what’s next for the massive LIGO collaboration.

With two sets of colliding black holes in its net and in its second run, LIGO, the world’s is finally ready to see the unexpected.

Gravitational waves are created whenever something with mass moves. Like insects on the surface of a pond, masses create ripples in the fabric of space-time. When massive objects like black holes accelerate, as they do when they orbit each other in an ever-tightening spiral before they collide, those ripples are powerful enough that we can detect the contractions in space-time using LIGO’s twin detectors, and .

The detectors use lasers to precisely measure the distance down two perpendicular tunnels. When a gravitational wave goes by, one tunnel shrinks and the other stretches by less than the width of a proton – just enough to be noticed.

Almost exactly a year ago, the team announced its first-ever detection, from a pair of black holes about 30 times the mass of the sun crashing together.

Fantastic beasts

Now, a few months into the detector’s second “advanced” run, team members are scrambling to predict what the signals will look like from even weirder things, so we can recognise what they are coming from when we glimpse them.

“We’re making a big pile of data, which is what astronomers do, and then we’re playing this taxonomy game,” of Northwestern University in Evanston, Illinois, told New Ů��С��Ƶ at at the end of last month. “We go through all the phenomena in space that people have looked at, and we ask ‘Could we get a gravitational wave signal from that? Sure! This is what it might look like. This is what we could learn.’”

LIGO’s second run began on 30 November 2016. On 28 January, the team announced that it had seen two event candidates so far, which matches the expected rate of about one per month.

If they turn out to be real events, they will probably be more gravitational waves from merging black holes. Building up our bank of data on black holes is useful for comparisons and will help test questions like how stars evolve and whether Einstein’s theory of general relativity holds true.

“The only way we’re ever going to answer them is with more detections of the same type,” says Larson.

Unstoppable waves

Light is easy to stop in its tracks – a cloud of dust will do the trick. But nothing should stop gravitational waves, so they offer access to the inside of astronomical objects that were shrouded in dust or gas before.

“Our eyes are a big sensory input, so in some sense a telescope is a natural thing to build. But none of us has a gravitational wave detector in our elbow, so we don’t have an intuitive sense for what we can learn with gravitational waves,” Larson says.

As the LIGO detectors are incrementally improved, we’ll be able to peer inside neutron stars, supernovae and other enormous or catastrophic events in space that we may not have even considered yet.

But this run also holds the possibility of seeing something new.

Homing in

“Now that we’ve seen black hole binary collisions, binaries with neutron stars are the next most promising gravitational wave candidate for Advanced LIGO,” Prayush Kumar of the Canadian Institute for Theoretical Astrophysics said at the APS meeting.

There are about 1 billion neutron stars in the Milky Way, but we’ve only observed 2500 of them. Gravitational waves give us a new way to look for and characterise the many neutron stars that we can’t see with telescopes.

The LIGO team recently published the results of its as they spin. None of the 200 pulsars surveyed was emitting detectable gravitational waves, but it let the researchers place limits on their shapes and magnetic fields, finding that some are extremely round.

Pulsars and other neutron stars are so massive that they should be able to continuously make gravitational waves just by spinning – if they aren’t perfect spheres, any small bump could make waves.

“Some of these are incredibly round objects – far rounder than the Earth or anything humans have ever made,” says team member Evan Goetz of the Max Planck Institute for Gravitational Physics in Hannover, Germany, who presented the results at the APS meeting.

Inside a neutron star

When we do catch waves from neutron stars in binary systems, it will help us learn about their mysterious insides. Their cores are probably superfluid, made of neutrons packed so close together that they start to flow without any viscosity or friction. Within this superfluid, neutrons would be able to drift freely.

The movement of that fluid is driven by the star’s orbit around a companion: the closer the star gets to its partner, the faster its interior tides come and go.

This motion can cause standing waves that we would never be able to observe with visible light – but we could get a look at them with LIGO. They lie right in LIGO’s detection “sweet spot,” said , a member of MIT’s LIGO Laboratory. Improving the detector’s sensitivity could bring these waves into view.

Even things that we can see with ordinary telescopes hold mysteries. The mechanisms behind supernovae are difficult to study observationally because dust and the chaos of such a huge explosion can stop you getting a clear picture.

In the Milky Way, supernovae occur every 50 years or so. But core collapse supernovae, which are the most energetic explosions we’ve seen in the universe, should produce gravitational waves right in LIGO’s current detection range.

The hope is that those waves will let us look deep inside supernovae, watching the cores of stars fold under the force of gravity and the shock waves, explosions and baby neutron stars that result.

“We are now able to predict gravitational wave signals from core collapse supernovae models, but this is just the beginning,” said from the Oak Ridge National Laboratory in Tennessee.