Ask Ethan: Why Did Light Arrive 1.7 Seconds After Gravitational Waves In The Neutron Star Merger? (Synopsis)

Ask Ethan: Why Did Light Arrive 1.7 Seconds After Gravitational Waves In The Neutron Star Merger? (Synopsis)

“Delay is the deadliest form of denial.” -C. Northcote Parkinson

Every massless particle and wave travels at the speed of light when it moves through a vacuum. Over a distance of 130 million light years, the gamma rays and gravitational waves emitted by merging neutron stars arrived offset by a mere 1.7 seconds, an incredible result! Yet if the light was emitted at the same time as the merger, that 1.7 second delay shouldn’t be there, unless something funny is afoot.

In the final moments of merging, two neutron stars don’t merely emit gravitational waves, but a catastrophic explosion that echoes across the electromagnetic spectrum. The arrival time difference between light and gravitational waves enables us to learn a lot about the Universe. Image credit: University of Warwick / Mark Garlick.

While your instinct might be to attribute an exotic cause to this, it’s important to take a look at “mundane” astrophysics first, such as the environment surrounding the neutron star merger, the mechanism that produces the gamma rays, and the thickness of the matter shell that the gamma rays need to travel through. After all, matter is transparent to gravitational waves, but it interacts with light all the time! 30 years ago, neutrinos arrived four hours before the light did in a supernova; could this 1.7 second difference be an ultra-sped-up version of the same effect?

The remnant of supernova 1987a, located in the Large Magellanic Cloud some 165,000 light years away. The fact that neutrinos arrived hours before the first light signal taught us more about the duration it takes light to propagate through the star’s layers of a supernova than it did about the speed neutrinos travel at, which was indistinguishable from the speed of light. Image credit: Noel Carboni & the ESA/ESO/NASA Photoshop FITS Liberator.

There’s no doubt that the first gamma rays from this neutron star-neutron star merger arrived after the gravitational waves did. But why? Find out on this week’s Ask Ethan!

19 thoughts on “Ask Ethan: Why Did Light Arrive 1.7 Seconds After Gravitational Waves In The Neutron Star Merger? (Synopsis)”

  1. I would imagine the neutrino signal ought to be comparable to that from a core collapse SN. What does the theory say? And how close would the event need to be (SN1987 was only a couple hundred thousand LY.) for detection.

  2. General comment on this blog:

    “In with Bang!… out with a whimper.”

    Really?! As your blog dies (I know you like the language), you go out quibbling about that 1.7 second difference!

  3. #3
    You quibble incessantly about something infinitely small when you say 0.999,,,,, isn’t the same a 1. 🙂

  4. On reading about LIGO, a text said that when the black holes merged, ‘they radiated 100 times more energy than all the stars in the universe combined’.
    Is that right? Thats mind blowing.

    Also I asked if making the chirp ‘audible’ was misleading – I assumed they must have shifted down. But it seems the frequency is in the audible range so maybe its not so bad. They compare the chirps from different objects to an orchestra, LIGO will only detect ‘violins and violas’ and new devices are underway to hear more. The Europeans are building and underground version of LIGO with arms twice as long.

  5. And then there is the space detector with satellites a million miles apart. Fun time to be alive!!

    Thanks Ethan for a great blog. Tell me where to go to follow your discourse.

  6. @dean #5: “Nothing you write is remotely close to factual.”

    Fact: The dimensions of physical objects and distances between them does not depend on how they are differently observed and measured, contrary to special relativity. The cosmos exists independently of all observation. the job of science is to accurately describe the world as it is, not to create an infinite variety of versions of it via differing observations, as relativity does.

    Fact: There is no evidence for an actual entity/medium “spacetime” which is curved by mass and guides the motion of masses, contrary to general relativity. Yet GR claims the above as fact, beyond criticism.

    Fact: There is no evidence for “Hawking radiation” by which black holes “evaporate,” contrary to the beliefs of all Hawking followers (including Ethan.)

    Fact: Nobody knows how old the universe is, because an eternally oscillating, “Bang/ Crunch” cosmos has not been ruled out, and no other model explains cosmic origin.
    Related fact: “Everything manifesting out of nothing” is a blind stupid appeal to magic. It did not all pop out of a Cosmic Magic Hat.

    Fact: personal attacks are not science.

  7. @Steve Blackband #6
    First, I didn’t bring it up. Second, numbers are meaningless without referents in the world. Third, a very very very large and ever increasing PART of anything is still not the whole thing (represented by 1.)
    Ability to think and reason clearly is at least as important as a high degree of expertise in crunching numbers.

  8. #3 sounds like a personal attack to me.

    #10, “The cosmos exists independently of all observation.”

    How can you call that a fact when you cannot prove it i.e. cannot show it true unless you observe it?

    #11. I was winding you up – hence the smiley face. I thought it was funny 🙂

    Not not being funny: then again, tell me what is between 0.999… and 1 if they are different.

    I think we’ve done this to death. Signing off from this blog.
    It has been fun and informative.
    May the Bang be with you!!!!!

  9. SB (even in your absence),
    My #3 was not science. Ethan’s focus on trivia ignores all major serious criticism, like my #10.

    If you believe that things cease to exist when not being observed you are in serious need of a reality check. Even if the universe were only 13.7 billion years old, it existed for quite awhile before being observed. But that is too philosophical/ reasonable for you.
    You seem to have ignored my answer in #11 to the stupid shit about a part being the same as the whole. Yes, it was done to death… until you resurrected it yet again.

  10. “Fact: personal attacks are not science.”

    That was not a personal attack – it was a statement of, well, fact. You continually object to things that experience and experiment support, and to theoretical conjectures of what might be, not because you have the ability to counter the physics with your own research or calculations, but because of your imagined offense to your third rate “philosophy of knowing” crap.

    “Second, numbers are meaningless without referents in the world.”
    Mathematicians from the past and the present are laughing at you.

    “Third, a very very very large and ever increasing PART of anything is still not the whole thing (represented by 1.)”

    And they are boggled by your inability to understand even the simplest of concepts.

  11. Ah well.
    Its weird I think but I will actually miss MM.
    #14, I dont have beliefs, thank you. You do, without evidence, You think that by just thinking you know what happened before.
    I DONT.
    we have theories that we test and until shown otherwise….
    Crap. We don’t even know what 96% of the universe is made of.
    But by sitting around an jabber walking you can figure it all out.

    Sorry dude. Not gonna happen.

    You’re a 0.999,,,, thats for sure.

    Common now MM, THATS funny 🙂

    Have a good life my man. Its been a pleasure, for real.

  12. numbers are meaningless without referents in the world

    Those “referents” are usually called “observers.” Anyway, does the Poincare group get to be sad here?

  13. @SB #16: “#14, I dont have beliefs, thank you. You do, without evidence, You think that by just thinking you know what happened before.
    I DONT.”

    Are you sure you don’t BELIEVE that “philosophy is bullshit,” to quote a famous physicist? You avoided any dialogue on philosophy of science that I presented. You have no clue that epistemology is the bedrock foundation of science. (Just more mystical philosophy to you.)

    I do think (make that ‘know’) that the world must exist before it can be observed. Is that too philosophical?

    I know that the whole observable universe didn’t just pop into existence out of nothingness. That is religion, (“Let there be light!”) not science. The oscillating universe is the only alternative to such nonsense.
    The last word is yours if you want it.

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