Scientists Catch Another Gravitational Wave, And They Know Where It Came From

By Eric Betz | September 27, 2017 11:44 am

VRIGO (Credit: Wikimedia Commons)

Last year, physicists made history by observing the first-ever gravitational wave. Their discovery confirmed Albert Einstein’s century-old theory of gravity and capped decades of effort to build an instrument sensitive enough to catch these ripples in spacetime.

Since then, researchers working at the government-funded Laser Interferometer Gravitational Wave Observatory (LIGO) — twin detectors in Louisiana and Washington State — have caught several more gravitational waves.

At a press conference Wednesday in Italy, the team announced a fourth detection from two colliding black holes, each dozens of times more massive than our sun.

And for the first time, they had the benefit of three gravitational wave detectors. Italy’s version of LIGO — called Virgo — came online Aug. 1 following massive upgrades. And it took just two weeks for the Italian gravitational wave detector to prove its worth. The research was published online in the journal Physical Review Letters.

Three’s a Charm

On Aug. 14, a gravitational wave passed over Earth at the speed of light, reaching Washington, then Louisiana and finally, Italy.

Compared to the other fundamental forces, gravity is actually very weak, so only extreme events like colliding black holes produce detectable waves. Those waves warp the very fabric of space, but are so tiny that they’d alter the distance between Earth and the sun by just the width of a hydrogen atom.

So scientists were somewhat surprised that Virgo, which was still being commissioned, was already sensitive enough to detect gravitational waves. But having a third detector let the team use the time difference between the gravitational wave’s arrival at each site to figure out exactly where the signal came from. This signal emerged from the constellation Eridanus.

They could already tell how far away the collision happened, but LIGOs twin detectors could only narrow the direction of origin down to a vast ring in Earth’s sky — they couldn’t tell where the signal was coming from.

“That’s very important to us,” says LIGO physicist Jolien Creighton of the University of Wisconsin-Milwaukee.

It allows the LIGO collaboration to loop in more traditional telescopes so they can turn their instruments in that direction and search for a corresponding light signal.

“The great advantage that having Virgo brings is it has now three different times, which allows you to triangulate to a point on the sky,” Creighton says. “That brought the area it could have been from about 1,000 square degrees in the sky down to about 60 square degrees.”

For perspective, the moon covers less than one square degree of Earth’s sky.

With this latest gravitational wave, computers picked up on the signal less than a minute after it arrived at Earth. And 25 telescopes — everything from gamma and x-ray telescopes to neutrino observatories — then looked to see if they could see any light from these colliding black holes.

Theory suggests that kind of collision wouldn’t put out any light, but if it did it could tell us something new about the cosmos.

Another advantage of Virgo’s triangulation is that physicists were able to deduce how the gravitational wave was polarized. Einstein’s general relativity theory only allows for two types of gravitational wave polarization, but other theories imply as many as six different polarizations. The gravitational wave’s polarization last month was one of the two that meshes with general relativity, providing yet another sign that Einstein got it right a century ago.

CATEGORIZED UNDER: Space & Physics, top posts
  • DocOct

    If you need help visualizing how the gravitational wave passed over the Earth, here are the coordinates for the three interferometer locations. On a side note, if I had to work at one I’d go with Virgo because Hanford looks like its on Mars and I know Livingston is going to be mosquito city, haha!

    Virgo 43° 37′ 52.68″ N, 10° 30′ 16.2″ E
    LIGO Hanford 46°27’18.5″N 119°24’27.6″W
    LIGO Livingston 30°33’46.4″N 90°46’27.3″W

    • Uncle Al

      Trilateration requires a fourth interferometer deep in the Southern hemisphere – South Africa (politically unstable), southernmost Argentina or Chile (tectonically unstable), Southern Australia (quiet flat desert, -31.362316, 125.660629 to -30.855212, 130.008863 ) or Tasmania (kinda lumpy, but -41.584636, 147.301115)

  • Uncle Al

    All four black hole mergers are disturbing versus Official Truth.

    …1) Gravitational binding energy release, [merged mass]/[summed merging masses],was always less than 4.8%. Gravitational binding energy for a mere neutron star is 15% – 20%.
    …2) Numerical general relativity perfectly describes orbital decay (good), merger (not so good), and post-merger ring down (disaster), There were no quantum gravitation and merging singularities’ (angular momentum!) perturbations.

    Consider two soap bubbles touching, merging, then popping into one larger soap bubble.

    …1) Black holes are (2D + ϵ)-dimensional bubbles. There is no
    inside (filled with quantum gravitation). There is no singularity.
    …2) Binding energy emission is mostly decreasing surface curvature.
    …3) The event horizon contains all black hole observables because there is nothing but event horizon.

    • Greg Prichard


  • OWilson

    OK, so we proved Einstein was right again.

    We found there are gravitational waves, so let’s shut down this very expensive facility and do something more useful with the borrowed money from the National Debt! :)

    Oh, I see. “More study needed!” :)

    • emsr

      You maybe paid $1 or so for this. But now we have a better tool to tell the MANY other optical telescopes you paid for where to point.

      • OWilson

        That’s the attitude that runs up impossible National Debt to be kicked down the road to generations unborn, long after the spenders have left office and retired on their fat pensions!

        I can tell you it didn’t cost ($1.00 or so) :)

      • Mike Richardson

        And radio telescopes as well. We really don’t know yet what we may directly gain from these observations, but they are providing a more complete view of the universe, and how gravity can behave in extreme circumstances. But unfortunately, some folks seem to know the cost of everything and the value of nothing.

    • Don Haywood

      Why is it so hard for people who seem to understand some science that the national debt is nothing like credit card debt??? The national debt is money owed to the US by the US. The US could pay off the debt tomorrow. The US owns the currency that the debt is in. For your credit card, if you made the currency then you could pay off that debt anytime, too. So – this whole bogus thing about the national debt being so huge and unmanageable is mostly smoke screen. The downside is that if the US paid off the debt there would be inflation because the dollar would be worth much less. That won’t happen because China and the rest of the debt holders would go broke if the dollar became worth so much less.

      • Sean

        Don stick to science. You know nothing….i mean nothing about economics and debt

        • Don Haywood

          I guess my friends at the Fed are wrong. Tell me what you know about economics. Would you like to discuss micro or macro?

        • StanChaz

          If that idiot Trump can play President then Mr. Haywood can most certainly dabble in anything he wants to without your blessings or approval.
          Too many so-called “experts” in too many fields have gotten us in far too many messes too many times…..


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