LIGO detects a second merger of black holes

There’s additional news from LIGO (the Laser Interferometry Gravitational Observatory) about gravitational waves today. What was a giant discovery just a few months ago will soon become almost routine… but for now it is still very exciting…

LIGO got a Christmas (US) present: Dec 25th/26th 2015, two more black holes were detected coalescing 1.4 billion light years away — changing the length of LIGO’s arms by 300 parts in a trillion trillion, even less than the first merger observed in September. The black holes had 14 solar masses and 8 solar masses, and merged into a black hole with 21 solar masses, emitting 1 solar mass of energy in gravitational waves. In contrast to the September event, which was short and showed just a few orbits before the merger, in this event nearly 30 orbits over a full second are observed, making more information available to scientists about the black holes, the merger, and general relativity.  (Apparently one of the incoming black holes was spinning with at least 20% of the maximum possible rotation rate for a black hole.)

The signal is not so “bright” as the first one, so it cannot be seen by eye if you just look at the data; to find it, some clever mathematical techniques are needed. But the signal, after signal processing, is very clear. (Signal-to-noise ratio is 13; it was 24 for the September detection.) For such a clear signal to occur due to random noise is 5 standard deviations — officially a detection. The corresponding “chirp” is nowhere near so obvious, but there is a faint trace.

This gives two detections of black hole mergers over about 48 days of 2015 quality data. There’s also a third “candidate”, not so clear — signal-to-noise of just under 10. If it is really due to gravitational waves, it would be merging black holes again… midway in size between the September and December events… but it is borderline, and might just be a statistical fluke.

It is interesting that we already have two, maybe three, mergers of large black holes… and no mergers of neutron stars with black holes or with each other, which are harder to observe. It seems there really are a lot of big black holes in binary pairs out there in the universe. Incidentally, the question of whether they might form the dark matter of the universe has been raised; it’s still a long-shot idea, since there are arguments against it for black holes of this size, but seeing these merger rates one has to reconsider those arguments carefully and keep an open mind about the evidence.

Let’s remember also that advanced-LIGO is still not running at full capacity. When LIGO starts its next run, six months long starting in September, the improvements over last year’s run will probably give a 50% to 100% increase in the rate for observed mergers.   In the longer run, the possibility of one merger per week is possible.

Meanwhile, VIRGO in Italy will come on line soon too, early in 2017. Japan and India are getting into the game too over the coming years. More detectors will allow scientists to know where on the sky the merger took place, which then can allow normal telescopes to look for flashes of light (or other forms of electromagnetic radiation) that might occur simultaneously with the merger… as is expected for neutron star mergers but not widely expected for black hole mergers.  The era of gravitational wave astronomy is underway.

32 responses to “LIGO detects a second merger of black holes

  1. Why did Ligo stop observations in last Janiuary ? When will it resume observations ?

    • Because LIGO began another, minor upgrade in which the sensitivity (smallest detectable “delta L / L”) will increase by a factor of 1.15-1.25. Because that amplitude is predicted to be inversely proportional to the distance of the source and because the volume grows with the distance cubed, it means that LIGO effectively sees further and to a volume greater by a factor of 1.5-2, thus (almost) doubling the rate at which events will be heard by LIGO after this modest upgrade.

  2. Thanks for the update. We live in interesting times.

    sean s.

  3. Alain,
    To perform the upgrades necessary to reach the improved sensitivity Prof. Strassler mentions that LIGO will have starting in September.

  4. More so, I’ve got my hopes trained on LISA, an interferometer in the proof of concept stage that would have arms several million miles long. Interesting times indeed!

  5. thank you for update.

  6. Matt,

    Thanks for “staying in the game” and continuing to post your comments about physics.

  7. David Strehlow

    Hi Matt – Will next week’s gravity wave talks be videoed and posted online? – David 

    Sent via the Samsung Galaxy S® 6, an AT&T 4G LTE smartphone

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  9. Robert L. Oldershaw

    Right on cue a second gravitational wave event has been reported.
    Blurb from Nature piece: “this second event suggests that there is a large population of black hole pairs out there …”.

    Other astrophysicists have proposed that primordial black holes are the dark matter, which is also what Discrete Scale Relativity has predicted since 1985.

    This is getting interesting and I anxiously await news this summer from the new Kepler mission looking toward the Galactic center for microlensing events.

    RLO 🙂 Fractal Cosmology/Discrete Scale Relativity

  10. As I understand it black hole dark matter is supposed to be primordial. Does the high spin of one of these black holes argue against it being primordial?

    • No; we don’t have a particularly clear or favorite idea as to how primordial black holes would form. [Primordial: not formed in the collapse of a star, and instead formed through some early-universe process before there were stars.]

  11. This is so damn exciting that I don’t know whether to scream, cry, run in circles or just stand with my mouth agape. The full awesomeness – all meanings of the word – of the universe and our ability to understand it will never cease to provide me with overpowering emotions.

    Thank you so much for curating such key events!

  12. What is the form of the force carrier particle wave and does it promulgate at the speed of light like a photon and massless? Are the physicists calling it a graviton or something else? Maybe I am to lazy or just can’t find what it is that allows the disturbance to travel through space to the instrument, but I find little discussion about what the carrier wave is. I very much enjoy your science and objectivity Doctor Strassler!

    • The force carrier might be the graviton. However we don’t know enough about how gravity works to be sure it requires a particle-based explanation. In relativity the waves are just waves in spacetime and avoid particles entirely.

  13. jacksanders7777

    Primordial black holes formed via compaction of Subtle Space and Subtle Energy as a one dimensional singularity as time/space where time began in universe for the most first time where such compaction could become no more compressed, rebounding from the infinitesimal (most finite) and closing the Space of the real infinite Nothing off like a drop of water and allowing universe to begin to evolve. The space of time/space mass/energy existing as potentiality (Dark Matter) in singularity were lines of force pulled away from the bottom of compaction Dr. Susskind refers to as Strings which formed into three separate tetrahedrons in two dimensions with perfectly mirrored surfaces which began to orbit the infinitesimal singularity in all manner of directions and spin, near or at the sped of light, causing the formation of space/time energy/mass to form at Big Bang due to higher energy states seeking to return to lower energy states as absolute vacuum thus setting up the repulsive force and the attraction force which is the source and causation of gravitation as the atom within the atom formed from 276 forms of subtle gases finally forming hydrogen by transmutation of energy at Big Bang at trillions of degrees Celsius from particles, Quarks and Leptons and Bosons, from the Strings orbiting the singularity and the three generations of matter as one, two and three dimensional evolutions from the rebounding of time/space into the one dimensional singularity in each and every atom condensed and precipitated where the finite resides within the infinite by definition and everything is separate and/or opposite but the same: ad infinitum squared as the triple tetrahedral triangle, ellipsoidal cubical sphere, double spiral void. Posited. Sorry, was just answering the question above. As an adjunct, Dark Energy is the result of the generations of massive stars and binaries which implode/explode into Black Holes where space/time matter is burned up in stars and radiated away as heavy particles as Cosmic Rays(gamma, X-rays, etc.) and striped photons accelerated at singularity to the speed of light squared creating neutrinos and leaving the repulsive force of Dark Matter time/space potentiality to expand the space of space/time as an inflationary event gathering momentum due to the increasing numbers of Black Hole Bodies without the attraction of matter attracting back to absolute vacuum and balancing the singularity of each newly formed Black Hole, forcing the universe of persistent space/time to appear to be expanding at inflationary (Dr. Alan Guth) rates back to the real infinite Nothing of Subtle Space, Unified Feld Theory (Dr. Einstein). Sorry, went off again.

    • Cosmic Inflation Was Invented By The Chinese Communists!!!

      I don’t know what in Ragnarok you’re going on about, but striped photons do sound pretty.

  14. kashyap vasavada

    Matt, glad to see you back on the blog. Apart from total amount of energy radiated, what are the other factors which make gravitational waves detectable. Since the energy involved (radiated?) in the big bang would be orders of magnitude larger than in the case of merger of black holes, I would think that one of these days they will detect gravitational waves from the big bang. What do you think?

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  16. Gravitational waves are always their, but only the sensitivity of the instrument is increased to detect it. ?
    Gauge invariance is like constant distance between parallel lines. Lorentz invariance is like a straight line – both arise classically from quantum chaos ??

    The “flip” in electromagnetism – the Gauge connection curvature unite various photons as straight line light. But in this process “flip” right to left. The curvature is the turning point. Due to fractal universe “c^2” – causing magnetism – magnetic monopole will prevent this c^2 ?
    Space is not elastic, but fractal. The cosmological constant is less where matter presents – more and expands where low density is.
    Gauge invariance is there due to almost static cosmoligical constant in our section of fractal.
    But overall it is an “almost non-repeating pattern”.
    So the mirror image is not you ?

    The curvature of 4 dimensional spacetime with time behaving just like space.
    In GR theory one starts from Einstein-Hilbert Lagrangian that’s not gauge invariant but is diffeomorphism invariant. This Lagrangian includes the effect of all the mass-energy via energy-momentum tensor.
    It is like diffeomorphism of straight line to appear like parallel lines – connecting like penrose stairs.
    The mathematical measuring insteuments makes this penrose stairs connection ?

    But the violation of Gauge invariance occur from “new physics”, indeed makes “the mirror image and you the same” !?

    In the case of QED where a large collection of U(1) gauge bosons (photons) at low energy leads to the observed classical light.
    The classical Mass arise from Stokes-Raman effect from other fractal ?
    W and Z bosons get massive due to anti-Stokes Raman scattering (~ radio activity) ?

    • In radioactivity, mass => Energy. Violation of gauge invariance is actually break the “Shear” of Isomorphic gauge invariance – making Energy => Space (more cosmological constant) – turning metastable to stable vacuum.
      But the Diffeomorphism (due to goldstone bosons ?) – makes infinity to finity – by spontaneous symmetry breaking – as Lorentz invariance or momentum.
      If according to quantum theory, nothing but quantum information exists in the world – the Blackholes are just the “Shear (surface information)” and the Gravitational waves are blackhole evoporation (decrease of entropy) ?

  17. I’ll feel happier when Virgo and other detectors “allow scientists to know where on the sky the merger took place”, whereupon we can use normal telescopes to look for light and radio signals.

  18. Blackholes cannot merge because – the surface information is the maximum Entropy. It can only exhibit diffeomorphism (gauge invariance) at Shear.
    The Lorentz invariance which obeys Newtonian laws is the limit of mathematics. Relativity connects them like penrose stairs.
    Classical mass arise from “new physics” – from decrease of entropy at shear – an isomorphic gauge invariance ???

  19. I am following

  20. W against T, reference required. #conspiracyofscience

  21. Thanks for the nice post. Always great to see your informative expository work.

    I have what I am sure is a dumb question, but what the heck: As you note 14 and 8 solar mass black holes merged to form a 21 solar mass black hole, converting the remainder to energy in the form of gravitational waves. This looks superficially like the original black holes “lost mass” through the process of merging, which would be impossible (at this rate, at least) in other circumstances. How does the merger process allow all that mass to “get out”? It doesn’t appear that some binding energy of the binary system is what’s being converted to gravitational wave energy; it’s the mass of the two original black holes themselves. This seems to be contradictory to the notion that nothing can get out of a black hole except via the incredibly slow process of Hawking radiation.

    Thanks for your time!

    • Edwin Steiner

      I do not think the question is dumb. I rather think it is based on a somewhat oversimplified view of black holes as “containers of energy”. As far as I know there is no way to exactly localize the energy stored in a gravitational field like for example that of a black hole. You cannot pinpoint where a certain amount of energy “actually is” at a given moment. So in particular one cannot make the statement that all the energy is behind the event horizon. Therefore there is also no contradiction in the energy being radiated from the merger. Also the precise location of the event horizon during a merger is a complicated question. The event horizon is not a surface that can be defined in an instant. It is rather defined by looking at the whole history (including the merger in this case) “backwards” from the far future. (I think “event horizon” is actually one of the rare cases where physicists actually picked a good name for something. 😉 Like the horizon in normal language use it is something that is only well-defined for an observer who is looking from far away. If you actually would “walk to the horizon”, you would not find any special “horizon line” there.)

      • That actually makes a lot of sense to me, and you are exactly right: I’m imagining a sharp demarcation of the mass-energy of the black hole at the horizon, when in fact that’s not really so. Ergo, there’s no paradox. Thanks!

        • Edwin Steiner

          I’m glad it helped. I cannot offer a more detailed explanation, as I’m still weak in general relativity. The localization of energy in the gravitational field is a confusing topic, and it is so even to physicists. So confusing, in deed, that there were long debates among physicists about whether gravitational waves actually can transport energy.

          Feynman finally ended this debate in his characteristic manner by proposing a (thought) experiment with two sticky beads on a stick (google “Sticky bead argument”). The argument clearly showed that a gravitational wave would make the beads oscillate and rub against the stick, passing energy to it. In a way LIGO is an insanely advanced high-tech realization of Feynman’s sticky bead antenna. — Of course, it uses laser interference instead of friction to detect the wave.

  22. What do we know about these waves? Are they sinusoidal? Do they reflect? Refract? Diffract? How about harmonics?

  23. “Gravity is important for keeping the universe out of thermal equilibrium. Gravitationally bound systems have negative specific heat – decrease of entropy or blackhole evoporation, through Stokes Raman scattering ?
    —that is, the velocities of their components increase when energy is removed – variation of entropy at shear – or involution ?

    So Higgs field is not Tachyonic at critical temperature – but Diffeomorphic (isomorphic) ??