A grand cosmological event: the collision of two neutron stars pumps up the physics community

Well, this astronomy/physics news is just in, and of course it’s above my pay grade, but at least I can refer you to articles in both the New York Times and CNN about a new discovery: the collision of two neutron stars, emitting both electromagnetic and gravity waves. The collision was detected in August, but was announced today.

What, you ask, is a neutron star? CNN says this:

Neutron stars are the smallest in the universe, with a diameter comparable to the size of a city like Chicago or Atlanta. They are the leftover remnants of supernovae. But they are incredibly dense, with masses bigger than that of our sun. So think of the sun, compressed into a major city. Now, think of two of them violently crashing into each other.

“This is more energy than has been released by the sun during its entire life, and this was released during just tens of seconds as the neutron stars (spiraled) together,” Piro said.

The New York Times notes that a teaspoon of neutron star weighs as much as Mount Everest! Can you imagine?

Now, why is this important? CNN again:

The collision [on August 17]created the first observed instance of a single source emitting ripples in space-time, known as gravitational waves, as well as light, which was released in the form of a two-second gamma ray burst. The collision also created heavy elements such as gold, platinum and lead, scattering them across the universe in a kilonova — similar to a supernova — after the initial fireball.

It is being hailed as the first known instance of multi-messenger astrophysics: one source in the universe emitting two kinds of waves, gravitational and electromagnetic.

News conferences were held around the world and a multitude of research papers were published Monday to detail the discovery, which was captured by space and Earth-based telescopes on August 17. These papers and conferences include representatives for the thousands of scientists, 70 observatories and gravitational wave detectors LIGO and Virgo that participated in one of the most-observed and -studied astronomical events of our time. One paper includes thousands of authors making up 35% of the global astronomy community.

And the NYT:

For the LIGO researchers, this is in some ways an even bigger bonanza than the original discovery. This is the first time they have discovered anything that regular astronomers could see and study. All of LIGO’s previous discoveries have involved colliding black holes, which are composed of empty tortured space-time — there is nothing for the eye or the telescope to see.

But neutron stars are full of stuff, matter packed at the density of Mount Everest in a teaspoon. When neutron stars slam together, all kinds of things burst out: gamma rays, X-rays, radio waves. Something for everyone who has a window on the sky.

“Joy for all,” said David Shoemaker, a physicist at the Massachusetts Institute of Technology who is the spokesman for the LIGO Scientific Collaboration.


  1. Posted October 16, 2017 at 1:46 pm | Permalink

    I’ve been reading about this. Fascinating.

  2. Posted October 16, 2017 at 1:55 pm | Permalink

    There is an excellent explanation of this on our official physicist’s site.

    • Randy schenck
      Posted October 16, 2017 at 2:23 pm | Permalink

      Yes, the post shows this, at the end.

    • Chris Swart
      Posted October 16, 2017 at 5:43 pm | Permalink

      Thanks for posting this. Very illuminating on why everybody is going bananas. You don’t find an independent measuring tool every day, and this one has lots of potential.

  3. loren russell
    Posted October 16, 2017 at 2:06 pm | Permalink

    Is the collision of 4500 professional astronomers in a single paper energetic enough to be detected across the universe?

  4. Joseph Stans
    Posted October 16, 2017 at 2:09 pm | Permalink

    It is2017if someone does not know waht Neutron Star is, they are Trump supporters and would not know what to do with the i9nformation if they had it.

    • biz
      Posted October 17, 2017 at 9:24 am | Permalink

      Was the irony in that comment intentional or unintentional? I can’t tell.

  5. Dave
    Posted October 16, 2017 at 2:13 pm | Permalink

    Does this herald the birth of the Antichrist?

    • gravelinspector-Aidan
      Posted October 17, 2017 at 2:03 pm | Permalink

      No, that event is heralded by the presence of Tabasco in a kitchen where I’m cooking.

  6. Posted October 16, 2017 at 2:17 pm | Permalink

    Think about this for a moment: the gravitational field around a neutron star is so strong that it bends light so that you can see ‘behind’ it.

    If it is small enough you can see the entire surface, front and back, from a single point in space.

    • David Harper
      Posted October 16, 2017 at 2:54 pm | Permalink

      “Small enough” being just 1.5 times the Schwarzschild (black hole) radius for the given mass.

    • Posted October 17, 2017 at 11:35 am | Permalink

      Correct me if I am wrong, but that’s an extreme case of “gravitational lensing”, no?

  7. Randy schenck
    Posted October 16, 2017 at 3:08 pm | Permalink

    Do I understand correctly that LIGO is the only way something like this was detected for further observation and study? Amazing as it is incomprehensible.

    • Posted October 16, 2017 at 4:23 pm | Permalink

      That is correct. ESA has a testbed for LISA (which is LIGO in space): lower frequency and greater sensitivity.

      I imagine there will be more LIGOs and/or upgrades to LIGO and VIRGO.

    • gravelinspector-Aidan
      Posted October 17, 2017 at 3:41 pm | Permalink

      Well, sort of. The GWs are what shows very clearly the masses and sizes of the participants (and thus their densities, and thus their identities ). However, coincident with the GW ‘chirp’ (find the file – it’s all over the Internet ; fascinating) there was a GRB (Gamma Ray Burst) of a few seconds duratioin. GRBs of this class (as opposed to “long” GRBs) have been recognised for some 30+ years and were *theorised* to be the result of NS-NS mergers, but the complexity of the GRB events obscures the precursor “in-spiral” phase which the “chirp” so clearly demonstrates. The theory of NS-NS merger → has thereby been confirmed. (Where was I? Interrupted.)
      You could think of the LIGO telescope as more like a microscope which sees events of a few tens of km scale, but extremely high energy, and can see “through” obscuring dirt, gas clouds and other low-energy interference. By seeing through the debris that our 50 year old GR telescopes couldn’t see, the real details of the origin events become clear. Or clearer – once they have a corpus of a few dozen of these events, they’ll start to see some that are average, and some that are different … and a new window will open. (With the GR telescopes it took a few hundred recorded GRBs – aound 10 years work – before people noticed that there were two populations – short GRBs versus long GRBs ; one of those has now been explained as being NS-NS mergers by the LIGO result.
      Incidentally, though LIGO saw GW170817, and it was strong enough to be seen by VIRGO (the European GW telescope), it was not seen. This immediately told people – a matter of minutes – where in the sky to look for any optical counterpart. And since telescopes were already slewing into position to observe the GRB in the middle of the target zone … I bet that was a fun few minutes in control rooms over half the globe. Slewing to get ‘first light’ of an optical counterpart of a GRB is a well-established race, driven by a communications pipeline from the Fermi GR telescope (predecessors BATSE and Compton GRO). I forget what the current record is – it’s either 9 seconds from satellite triggering to telescope starting imaging or 14 seconds. And it’s not a new record.
      Other new pipelines are in work – from neutrino telescopes 1km under Antarctica and 2km below the Mediterranean – which will plug into this transient-observing network. The telescopes will have to have strict isolation and lock-out procedures to avoid taking the fingers (or heads) off of technicians working on the slewing drives, gears and bearings. Don’t want blood spurting across that mirror surface, because that’ll mean a re-silvering operation.

  8. Posted October 16, 2017 at 3:10 pm | Permalink

    That CNN article is a little irritating:

    “This detection was like experiencing a storm in a room with windows, changing everything scientists thought they knew.”

    Dr. Coyne, you’re a scientist. Did this change everything you thought you knew? 😉

    And I’m not sure what this is supposed to mean:

    “People tend to think that all of the elements on the periodic table form in nature, such as at the centers of stars, but it isn’t true, Kalogera said. That occurs only up to the level of iron. Anything heavier than that can’t be formed naturally; it results from violent collisions of dense stars or explosions during the collapse of massive stars.”

    • darrelle
      Posted October 16, 2017 at 4:26 pm | Permalink

      FFS, that is fricking awful.

    • Posted October 16, 2017 at 4:29 pm | Permalink

      “changing everything scientists thought they knew”. Shame on the media.

      It verifies, again, that general relativity has incredibly useful predictive capability for making astronomical observations using precision interferometry. We have learned, from what I have read, that about half the high Z elements (>~70) in the universe might be made through such collisions. From what I have read, this is the most fundamental change. There is some suggestion such neutron stars were not meant to be that heavy (possibly). Hardly everything known to scientists.

    • infiniteimprobabilit
      Posted October 18, 2017 at 3:16 am | Permalink

      “Anything heavier than that can’t be formed naturally by fusion in ordinary stars

      There, ftfy.

      Okay, it depends on what you call ‘naturally’, of course.


  9. stuartcoyle
    Posted October 16, 2017 at 3:11 pm | Permalink

    It’s impressive that this dual event allows us to validate that the speed of gravitational waves is exactly the speed of light as Einstein predicted a hundred years ago.

    The measurement is accurate to one part in 10^15 or so. I don’t know of any other branch of science able to get such accuracy.

    • Posted October 16, 2017 at 6:21 pm | Permalink

      One or two of the predictions of QED are in the same ballpark.

      Almost the most fascinating things is that, in spite of the unbelievable accuracy of the predictions, physicists mostly think General Relativity is (ever so slightly) wrong because it is not unified with quantum mechanics.

  10. Mark Reaume
    Posted October 16, 2017 at 3:24 pm | Permalink

    Does anyone know what the result is when two Neutron stars collide? One larger Neutron star or a black hole? I suppose it depends on how large the bodies are.

    • Posted October 16, 2017 at 3:31 pm | Permalink

      The articles I’ve read about this collision say it formed a black hole. I don’t know if that is a usual outcome of two neutron stars colliding.

    • Gregory Kusnick
      Posted October 16, 2017 at 8:52 pm | Permalink

      Neutron stars have a fairly narrow range of possible masses: too light and they stop at white dwarfs, too heavy and they go straight to black holes. So for two neutron stars to merge and still remain below the black hole threshold is fairly unlikely.

    • Torbjörn Larsson
      Posted October 17, 2017 at 1:22 pm | Permalink

      That is the most open question that is irritatingly out of reach in this first detection; that part of the signal was drowned in noise and must await the next upgrade. (The LIGO science meeting implies that a new type of laser will enable lowering noise with a factor tow, which should be sufficient.)

      The end result of this merger ended up a little above two solar masses, in the “mass gap” of 2-5 solar masses between the most massive neutron stars observed and the least massive black holes observed. Any data on either class from the gap is apparently hotly searched for!

  11. Vaal
    Posted October 16, 2017 at 3:37 pm | Permalink

    Well, I’m first going to have to do a hierarchical inventory of the privileges of these scientists, to see if I ought to accept their narrative.

    But if it passes the purity test…wow that sounds cool!


    • Paul S
      Posted October 16, 2017 at 3:57 pm | Permalink

      Both stars were gender neutron, so I guess they’re safe.

  12. Frank Bath
    Posted October 16, 2017 at 3:51 pm | Permalink

    A tremendous achievement. Over here in the UK TV and radio are playing the released ‘sound’ of the explosion. Oh dear, bathetic.

  13. Posted October 16, 2017 at 4:08 pm | Permalink

    Wonderful stuff. But for some reason it burns my marshmallows that there are papers with with hundreds or thousands of authors. Its a way of doing science where there are ‘authors’ that do nothing. Or am I wrong?

    • darrelle
      Posted October 16, 2017 at 4:39 pm | Permalink

      I’ve no doubt that authors that do nothing happens, but in this case it may be reasonably legit. Many observatories observed this event and it involved several disciplines. Between instrumentalists using many observatories and many theorists using the data to investigate the parts of this event that they specialize in it seems like that could add up to quite a few people for a paper that, for example, sought to give an overview of the event.

      But I’m just guessing!

      • Posted October 16, 2017 at 7:08 pm | Permalink

        I think that I have to just accept that some disciplines have a different science culture than what i am used to. I should not lose sight that they are getting results, and that their research questions operate on a magnitude far greater than a genome or ecosystem.

      • Gregory Kusnick
        Posted October 16, 2017 at 8:47 pm | Permalink

        Also, in astronomy and high-energy physics, there are scientists who spend their entire careers building instruments and detectors for use by other scientists. Those instrument-builders get listed as co-authors of any discoveries made using their instruments, because that’s the only sort of publication credit available to them.

      • Posted October 17, 2017 at 11:36 am | Permalink

        I am not a physicist, but I got the impression that it is a perhaps semi-overreaction to the previous habit of omitting people who helped, like the grad student who did a calculation or three, the lab techs who ran various equipment or computers, etc.

  14. aljones909
    Posted October 16, 2017 at 6:13 pm | Permalink

    My favourite stat. Ligo’s sensitivity:
    “equivalent to measuring the distance to the nearest star to an accuracy smaller than the width of a human hair”

  15. Steve Gerrard
    Posted October 16, 2017 at 7:47 pm | Permalink

    Another good post from a physicist:


    “almost everything that was observed by all these different experiments was predicted in advance…Apparently our understanding of gravity, of neutron stars, and of their mergers, and of all sorts of sources of electromagnetic radiation that are produced in those merges, is even better than we might have thought. But fortunately there are a few new puzzles. The X-rays were late; the gamma rays were dim…”

  16. JonLynnHarvey
    Posted October 16, 2017 at 11:37 pm | Permalink

    In the future, historians of computer science will always know roughly when this happened (after the mid-2000s) from the use of the phrase “multi-messenger”.

  17. andrewnwest
    Posted October 17, 2017 at 1:13 am | Permalink

    I’m not sure I like the NYT saying black holes colliding ’empty space-time’ and contrasting them to neutron stars which are ‘full of stuff’. Black holes have mass, and that mass came from matter.

    Also, 1/3 of all professional astronomers is interesting. Does this mean we can’t realistically do anything bigger than this?

    • Posted October 17, 2017 at 5:15 am | Permalink

      Must suck to be in the other 2/3 right now.

    • Posted October 17, 2017 at 11:37 am | Permalink

      They aren’t empty – they contain gravitational fields (presumably).

      • Gregory Kusnick
        Posted October 17, 2017 at 12:36 pm | Permalink

        I don’t think so. You can talk about curved spacetime (Einstein), or you can talk about gravitational fields (Newton), but you can’t have it both ways and say that a black hole’s curved spacetime contains a gravitational field.

        • Posted October 18, 2017 at 11:45 am | Permalink

          I’m no expert on GR, but I was under the impression one could do it the way one does classical E&M: with a field which has the appropriate spatiotemporal relations. (Rather than Newton’s “space as a stuff” notion.)

  18. gravelinspector-Aidan
    Posted October 17, 2017 at 6:46 pm | Permalink

    The New York Times notes that a teaspoon of neutron star weighs as much as Mount Everest! Can you imagine?

    A different write-up I saw (Beeb? not sure; doesn’t matter) said that a teaspoon full of neutronium (neutron star matter) weighed as much as the whole human species.
    Without getting into sidelines about whether we’re talking about metric teaspoons (5ml, I think), Imperial Everests (what other sort could there be? Pink, too!), or avoirdupois whales, isn’t this a fine statement of the inconsequentiality of the human species that we don’t even outweigh a mountain that isn’t even the locally tallest, just the one furthest from the Plimsoll line.
    Is it still true that you could kill almost the entire human species by piling them into Loch Ness without having to crush or drown (m)any in neighbouring Loch Oich?
    If you’re at an astrophysics conference and you find blood splatter on the walls, it’s probably nothing important – just two neutron star physicists settling a disagreement over the “equation of state” of neutronium. The first rule of Neutronium EOS Fight Club is you don’t talk … (fill in the trope).

  19. Posted October 17, 2017 at 7:37 pm | Permalink

    This is most fascinating. Thanks!
    Not sure what I saw at the end of the video provided by the NYT. There seemed to be *two* flashes (more like bright dots) that appeared one after another. This is supposed to be the explosion, according to the various articles and the post here.

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