3rd Gravitational Wave Detection Is About Much More Than Black Holes

By Eric Betz | June 1, 2017 10:00 am
More than a year after detecting the first confirmed gravitational waves, researchers were busy at the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, La., upgrading the massive instrument. (LIGO Lab)

More than a year after detecting the first confirmed gravitational waves, researchers were busy at the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, La., upgrading the massive instrument. (LIGO lab)

Our sun was still dim. Waves crashed on martian beaches. Life was emerging on Earth.

That’s when the ghosts of two dead stars — black holes dozens of times more massive than our sun — merged in a far-off corner of the universe. In their final moments, these binary black holes were circling each other hundreds of times per second, as each one spun at 10 times that rate.

The rumbles of distant thunder from that collision reached Earth on Jan. 4 of this year, passing through the detector at the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Hanford, Washington. Then, traveling at the speed of light, this wrinkle in space-time passed through LIGO’s second detector in Livingston, Louisiana, just a fraction of a second later.

The results were published Thursday in the journal Physical Review Letters.

Cosmic Forces

Gravity is the weakest among nature’s four fundamental forces. So only extreme cosmic events like supernovas, neutron stars and merging black holes can make detectable gravitational waves. The waves are so weak that they’d warp the distance between Earth and sun by just the width of a hydrogen atom. But as these waves pass through LIGO’s twin detectors, its enormous lasers can pick up on the truly tiny stretches and squeezes of space-time. You can think of it like a seismometer for measuring mini quakes in the cosmos’ gravitational fabric.

When LIGO gets a hit, the gravitational wave makes a characteristic signal that scientists’ call a “chirp” because of the sound it makes once translated into a format human ears can hear.

This was the third such detection since Albert Einstein first predicted gravitational waves a century ago as part of his general theory of relativity, or theory of gravity. Taken together, these observations form the first samples of a black hole census with far-reaching implications.

Before colliding, the binary black holes spotted earlier this year weighed in at 19 and 31 times our sun’s mass. After merging, the pair created a single black hole 49 times more massive than the sun. Einstein’s equations tell us that energy and mass are interchangeable. And so the missing solar mass worth of energy was radiated out across the universe as gravitational waves.

And with this detection, scientists for the first time think the two black holes might have been spinning in opposite directions. That could reveal clues about the lives of the stars that formed them. It’s possible that the two stars lived in a dense stellar cluster.

Before LIGO, astronomers didn’t know that so-called solar mass black holes, which form when stars die, could reach such extreme sizes.

This census can also help explain an enduring mystery in astronomy. Scientists have seen supermassive black holes that dominate entire galaxies, as well as small black holes that form after stars die. We even now know about so-called intermediate mass black holes weighing as much as thousands of suns. But how do these all form? Do many small black holes combine intro larger and larger behemoths? LIGO is just starting to piece together this puzzle.

Astrophysicist Stuart Aston monitors external vibrations on the LIGO test mass mirrors during an engineering run in November 2016. (Ernie Mastroianni/Discover)

Astrophysicist Stuart Aston monitors external vibrations on the LIGO test mass mirrors during an engineering run in November 2016. (Ernie Mastroianni/Discover)

More Than Black Holes

The latest signal took nearly 3 billion light years to reach Earth — twice as far off as the other detections. And because the gravitational wave arrived undiminished, it provides yet another proof of one of Einstein’s theories, showing that gravity travels at light speed.

“LIGO is going to be about a lot more than black holes,” says University of Wisconsin-Milwaukee (UWM) physicist Jolien Creighton, a veteran member of the detection team.

The observatory has forced open a new window on the universe, allowing scientists to hear from distant cosmic reaches — places where conventional telescopes come up empty. LIGO will bring new insights into everything from the heaviest elements on Earth to the nature of gravity itself.

LIGO’s next big breakthrough is expected to come from detecting collisions of binary neutron stars — the corpses of dead stars that pack a sun’s worth of mass into a city-sized sphere. These mergers happen at similar wavelengths to the black hole collisions LIGO’s already seen, and scientists once expected to see neutron stars first.

“This paper only reports on a few weeks worth of data, and we plan to run until August,” says Chad Hanna, a LIGO scientist from Pennsylvania State University. “We might still detect more events.”

So it’s possible that a binary neutron star merger could still be seen this year, or after the LIGO collaboration upgrades its instruments over the coming years. An upgrade over last summer didn’t increase the instrument’s sensitivity quite as much as scientists’ hoped.

“A lot of the elements we see on Earth were not formed in exploding stars but formed in the collision of binary neutron stars,” Creighton says. Humans are mostly made of typical star stuff like carbon and hydrogen, but other earthly elements with high atomic numbers, like gold, are suspected to have come from these more exotic events.

“Most of the gold we see in the solar system might have come from a binary neutron star collision that produced something like a Jupiter mass of gold and dispersed it in all directions,” Creighton says.

LIGO will detect neutron star mergers and send out an alert to the larger astronomy community, telling researchers to all point their telescopes to that region of sky and catch the event. The observations will let scientists test theories under conditions that could never be recreated in a lab.

Astrophysicist Stuart Aston monitors external vibrations on the LIGO test mass mirrors during an engineering run in November 2016. (Ernie Mastroianni/Discover)

Inside a stainless steel chamber, LIGO technicians examine the surface of one of the test mass mirrors that will reflect infrared laser light to measure the effect of gravity waves. After installation, all air was vacuumed from this chamber. (Mike Fyffe/LIGO lab)

Physicists also hope that more observations from LIGO will reveal new insights into gravity itself, as well as the theorized force-carrying particle called the graviton. It is to gravity what the photon is to light. Like the photon, scientists suspect it too has no mass. And this third LIGO gravitational wave detection helped constrain how big the graviton could possibly be. But new tests are on the horizon as well.

“I’m really excited about testing general relativity,” says UWM physicist Sarah Caudill, who works with the computer clusters that make LIGO detections possible. She suspects LIGO could reveal Einstein’s theory needs some small corrections.

“I think most people would be surprised if general relativity was 100 percent correct, but there’s no evidence that it’s not yet. Einstein created this theory 100 years ago and with no ability to observe gravitational waves, so for him to be 100 percent correct would be quite a feat.”

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  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    Phys. Rev. Lett. 118(22), 221101 (2017)
    …” In all cases, we find that GW170104 is consistent with general relativity”
    DOI:10.1103/PhysRevLett.118.221101

    50 years of non-classical gravitation theories – literal hectares of peer-reviewed published papers by regiments of the most powerful minds on Earth – the Emperor is naked

  • Ted Wilson

    How close to this event would one have to be to feel the effect. Or is it not possible to feel it?

    • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

      If you were close enough to feel it, associated events would instantly rend you into atoms or smaller. You would be distracted.

  • Erik Bosma

    So mere days after installing this expensive machine they magically get a ‘hit’. One would think that black hole collisions would be a fairly common occurrence. Especially from these results but also from the sheer magnitude of attracting black holes especially when the U was young and dense. But we wait and wait. Finally another blip but now it’s time for an upgrade. Excuse me, another upgrade. Job security at work in your local “corner” of the Universe. Maybe I’m a dolt (well, OK I am) but how can we measure a fraction of the diameter of an atomic nucleus when big trucks and planes and whatever else are out there? They just don’t explain that to my liking or level of understanding. However, I think they should be able to.
    One little question: if Albert E said that gravity was caused by curves in space-time why do we need particles? Uncle Al? (English please)

    • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

      LIGO atoms thermally vibrate. Squeezing thermal noise outside net signal is difficult. Solutions require recursion because the world is dirty materials not clean equations.

      LIGO measurement is not absolute (a gallon of milk, ten volts) but relative (it’s an interferometer, re a Wheatstone bridge). The fun is in the footnotes,

      www(dot)ligo(dot)caltech(dot)edu(slash)page(slash)ligos-ifo

      A beam of light horizontally traverses (a foot/nanosecond) an elevator accelerating upward. It’s exit point is not opposite its entry point. During the traversal interval the elevator moves upward. Bit by bit, light’s path appears to be curved downward versus the elevator. Acceleration and gravitation are indistinguishable – the Equivalence Principle.

      General relativity’s spacetime curvature can be traded for Einstein-Cartan spacetime torsion, arXiv:1609.09275, DOI:10.1103/PhysRevD.95.104007. The Equivalence Principle can then be violated on a bench top, What fun!

      www(dot)mazepath(dot)com(slash)uncleal(slash)
      EquivPrinFail(dot)pdf

      Reality is quantized. Nobody knows how to so render classical gravitation – that works perfectly while ignoring it, arXiv:1512.04654, doi:10.3847/2041-8205/819/1/L8

      • Erik Bosma

        Thanks Unc… I’ll check out those URLs. Stay anonymous BTW…

        • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

          journals(dot)aps(dot)org(slash)prl(slash)pdf(slash)10(dot)1103(slash)PhysRevLett(dot)118(dot)221101

          Latest LIGO black hole merger, then challenging general relativity to all other classes of gravitation theory versus observation. Cage match! Lots go in, only one comes out.

          • Erik Bosma

            Well, I went there and waded through the tech-speak. They certainly have their butts covered don’t they? Perhaps I’ll mull it over…..

    • nrrd

      They did not “magically” get a hit. A physical process (black hole merger) caused it. They were indeed very lucky to see a signal so soon after finishing construction, but LIGO in some form or another has been active since 2002, so it was hardly suspicious. Let’s ignore your bizarre and insulting insinuation that they’re lying.

      LIGO can factor out environmental noise (a truck driving by is an excellent example) partly because it consists of two detectors: one in Hannaford and one in Livingston, AL. The same disturbance must be detected at the same time at both installations to be considered valid. There’s a lot more sophisticated noise reduction that happens, too, but I would refer you to technical articles to explain those.

      • Erik Bosma

        I am becoming more of a skeptic in my upcoming old age. I’m not a conspiracy theorist by any stretch of the imagination but we’ve seen everything now so doubt keeps growing. And that is my right and my duty. Say hello to Piltdown Man. By the way, both locations are on the same plate…

  • Ted Wilson

    How far away from the collision event would I need to be for the gravitational force to be noticeable but not strong enough to overcome the electric force holding the atoms in my body together?

  • OWilson

    So much excitement and promise, confirming Einstein, even discovering the true nature of gravity itself. Who could be against that?

    No, not LIGO, I’m talking about that other 20 billion project, the LHC in Europe. Likewise started off with the promise of the answer to everything “the “GOD PARTICLE”. a permanent staff of some 10,000, and high annual upgrade and maintenance costs. Runs on fossil fuel, of course! Why no windmills and solar panels? It is Europe, after all! :)

    But this LIGO new kid in town is now where the action, and the money, is!

    One just hopes that this latest money pit it will deliver more than hope for the annual expenditures, staffing and constant upgrades.

    I’m not against research, I love my quartz watch, but I wonder if governments are spending the money wisely.

    NASA used to be the big player in town, but are now reduced to sending Radio Shack robots to Mars for the last 50 years, and cadging a ride from KGB Satan Putin for our astronauts to the Space Station.

    While it’s budget grows.

    But they have found a much easier gig. Our weather forecast, a hundred years from now!

    As a wise man once said, “Who makes these deals? Anybody home?”

    Maybe it’s time to de-Nationalize. The private sector always seems to get a bigger bang for their own buck!

    • Erik Bosma

      You see, doubters??!!! This guy says what I think. We may disagree on Climate games but definitely agree on most of the above. Oh, by the way OW, It’s its, not it’s.(4 paragraphs from bottom) And, I believe the “God particle” was inferred, not seen. I may be totally wrong but, “I’m a dancing fool…..”

      • OWilson

        Thanks.

        I don’t cut and paste this stuff, I dash it off anywhere I am, at lunch, even in my car on the way to work.

        When I get home or to work I check it out for grammar and spelling. I will edit it even more, if nobody has responded yet, to make it say more like what I meant to say.

    • Adam Farson

      CERN buys electrical power from EDF (Electricité de France) which is mostly nuclear, and from the Swiss electric utilities which are mostly hydro.

      • OWilson

        I stand corrected!

        Hooray for ‘mostly” Nuclear! and hydro!

  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    After installation, all air was vacuumed from this chamber. ” That is not how it is done in the real world – not a Dyson to be found. Turbomolecular pumps, titanium sublimation pumps, adsorbtive baffles cooled to 4 kelvins. Hydrogen is a pisser, helium is Hell itself.

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