A More Perfect Union

In Gravity by Brian Koberlein6 Comments

On 26 December 2015 the LIGO observatory saw another merger of two black holes. This time the black holes were smaller, with masses of about 8 and 14 Suns. As a result, we captured the inspiraling of the black holes for a longer time. Gravitational wave astronomy is now fully under way. 

The cleaned up observation of the black hole merger. Credit: LIGO

The cleaned up observation of the black hole merger. Credit: LIGO

Because of the size and distance of this merger (about 1.4 billion light years) this particular merger is fainter than the first. It was seen a periodic fluctuation buried within the LIGO noise, so the data has to be matched to computer simulations to really determine its properties. It’s statistical validity dances around the usual five sigma range, so there is no doubt the signal is real.

More than the first merger, this is a textbook example of a merger. We captured nearly thirty orbits of the two black holes as they danced ever closer to each other. We can see not only the steady gravitational waves of their orbits, we can also see how their orbital periods get shorter, orbiting ever faster as they approach the merger. This is textbook behavior. It is exactly the type of event we expected to see. The merging of stellar-mass binaries.

Overall this new observation is further confirmation not only of general relativity, but of central aspects of astrophysics. Black holes are real, they occasionally merge just as we predicted, and we can now start using gravitational waves as an astronomical tool.

Paper: B. P. Abbott et al. GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence. Phys. Rev. Lett. 116, 241103 (2016)  DOI: 10.1103/PhysRevLett.116.241103


  1. If I understand it right, there is mass and distance information about these binary black hole mergers, but not much accuracy about direction.

    1. Author

      Yeah, knowing the masses you can compare the gravitational wave luminosity to determine the distance. Direction is a bit more difficult.

  2. This is great news!

    A single detection is surely interesting, but not really enough to do any decent astronomy. Two new, which strongly suggests many more are likely this year. And when Advanced Virgo comes online, greatly shrinking the location (on the sky) of the events, even more astronomy awaits!

  3. Very exciting stuff!

    Brian, I’ve been reading where this second result might bolster the idea of “primordial black holes” and possibly shed light on the dark matter puzzle. I don’t know if this is worth addressing in another of your excellent posts, but personally I found the connection interesting.

    I also found it very encouraging that the second result from LIGO followed so quickly after the first – I imagine this has lots of people excited! Looks like they are going to take it offline to upgrade to 1.5 – 2x sensitivity (wow) and by then the Italy facility will also be online, allowing for triangulation of locating the events in the night sky. Amazing.

  4. The distortions of space which we now measure and which are the result of gravitational waves are miniscule. Is this just because of the vast distance of the events which generated the waves? What would be the amplitude of distortions measured up close and caused by, for example, the merger of two 10 s.m. black holes?

  5. I’m lucky enough to live within about 40 minutes of the Livingston, La LIGO facility, and I remember the discussions around the area when it was announced and being built. (Well, for those who had any understanding of what it actually is, anyhow. There were also plenty who had no concept of the science behind it or the implications of what it could discover and many just thought it was a huge waste of time and money.) The announcement of the first successful detection after the last upgrade was thrilling news. But one thing I have always wondered is, besides proving yet another facet of Einstein’s most famous work and apparently confirming the ‘fabric’-like nature of spacetime, what is the information from these waves actually telling us that we don’t already have a reasonable theory of?
    As you stated, the second detection was of a ‘textbook’ merger, which means we already have an obviously competent idea of the physics involved. So other than confirming that the propagation of gravity is also bound by C, what new information do these wave detections present?
    Please understand, I am not in any way trying to diminish the importance of the discoveries or the science behind the detectors. I just honestly would like to know what new information we have gleaned from them, other than coming closer to confirming that Einstein was correct about Relativity in pretty much every implication. (Though I still think that seeing a pattern in the Planck CMB data that resembles the letters ‘S H’ tells us all we need to know about physics in the macro scale. The Good Professor signed his work…)

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