Why is the discovery of merging neutron stars important?

  • I'm fairly certain people here will have heard about it, already, but apparently, two supernova leftovers clashed some 130 million years ago and some billion billion kilometres away ...



    What I haven't heard yet, however, is why we should care.



    I mean sure, it's an interesting phenomenon and measuring it can't have been easy.



    But now that we've heard it ... what changes?



    I'll admit it, I don't know particularly much about astronomy, but I'm curious:



    What's the significance of having achieved this? Why does it matter whether or not we know?


    From Veritasium's First Ever Light & Gravitational Wave Cosmic Event! I would say: the way the discovery went shows human ingenuity.

    Reminds me that we can't build a Doomsday Machine without research. People tried to sue the LHC to stop it wiping us all out (rejected by court). But really it was true - we just want to destroy the universe. :-)

    Gamma ray bursts *are* a plausible extinction event - learning everything we can about them is the first step in understanding the mechanism and eventually predicting them. Any plausible protection is unfortunately still in the sci-fi domain.

    When Einstein published general relativity theory in 1915 possibly many contemporaries wondered "what's the deal? Can't we just use Newtonian physics?". Fast forward 2017, everyone takes for granted having in pockets devices that tell exact location wherever on globe, technology made possible by Einstein discovery.

    Among other things, it explains where heavy metals like gold and platinum come from.

    You should work some of your comment to @RobJeffries' answer into your question, because some of the other answers also take the tone that you were downplaying the event's significance. So clarification in the question itself is a good idea.

    Your question sounds like "Why should the average person care?" But your positive response to Rob Jeffries' answer makes it seem like your question should have been "Why do scientists care?" or "Why should those interested in astronomy or astrophysics care?"

    "Why does it matter whether or not we know?" That one is easy to answer even without the context in a general way only: It always matters. Knowing things is the only way to advance scientifically and technologically. Experience tells us that knowing things leads to a better/wiser/more comfortable life eventually.

    I just wanted to add that now we know we have a way to "filter" these gamma ray burst events. We have been detecting a relatively large number of these with current observation methods and we can't do intensive study of all of them. The LIGO "observation" told us to aim our telescopes (including Hubble) at this this one.

  • ProfRob

    ProfRob Correct answer

    4 years ago

    Reasons why this is important:



    It is the first simultaneous detection of a gravitational wave and electromagnetic signal, and the strongest GW signal yet in terms of signal to noise (Abbott et al. 2017a). It spectacularly corroborates the reality of the GW detection technology and analysis. The progenitor has been unambiguously located in a (relatively) nearby galaxy (Soares-Santos et al. 2017), allowing a host of other telescopes to obtain detailed measurements.



    It shows that GWs travel at the speed of light, a further verification of Einstein's General Relativity (Abbott et al. 2017b).



    It shows that most of the very heavy elements such as gold, platinum, osmium etc. are plausibly produced by merging neutron stars and constrains the rate of such mergers in the local universe (e.g. Chornock et al. 2017; Tanvir et al. 2017).



    It shows that short gamma ray bursts — some of the most energetic explosions in the universe — can be caused by neutron star mergers (e.g. Savchenko et al. 2017; Goldstein et al. 2017).



    It is the closest detected short gamma ray burst (with a known distance). That the progenitor has also been characterised allows a closer investigation of the interesting physics underlying the ejection and jet mechanisms thought to be responsible for the gamma rays and later X-ray and radio emission (e.g. Margutti et al. 2017; Alexander et al. 2017).



    It provides observational constraints on how matter behaves at extremely high densities, testing our understanding of fundamental physics to its limits — for example, the details of the gravitational wave signal moments before merger are diagnostic of the interior conditions of neutron stars at densities of $\sim 10^{18}$ kg/m$^3$ (Hinderer et al. 2010; Postnikov et al. 2010).



    It provides an independent way of measuring the expansion of the universe. Merging binary gravitational wave sources are known as "standard sirens", because the distance to the GW source pops straight out of the analysis and can be compared with the redshift of the identified host galaxy (Abbott et al. 2017c). The result agrees with measurements made using the cosmic microwave background and the distance-redshift relation calibrated by other means, verifying our estimation of distances, at least in the local universe.



    Finally, this event will turn out to be important because it was lucky; in the sense that the source was detected well-inside the sensitivity horizon of LIGO (Abbott et al. 2017a). The detection itself, was not unexpected given the rates predicted based on studying the neutron star binary systems in our own Galaxy (e.g. Kim et al. 2015), but the fact that it was so close —
    within the closest 5% of the sensitive survey volume where it could have been detected — is fortunate.



    In the end, if someone thinks none of the above is interesting or important, then nothing I can write will convince them otherwise. The vast majority of people I speak to are curious and fascinated to find out about our cosmic origins and how the universe works.


    Now that's the kind of answer I was hoping for. Thank you. For the record, I wasn't saying it's not interesting, just that the media telling us little more than "scientists heard explosion from the past, yay", doesn't immediately impress on your average Joe why anybody would care.

    @User1291 I did assume (incorrectly). Small edit made.

    One question: does this show that all short GRBs are caused by neutron star mergers, or only some of them?

    @jamesqf It shows that merging neutron stars can produce a sGRB. So, at least some are caused by merging neutron stars.

    @jamesqf You need to be careful not to make a corellation fallacy here. A short GRB was observed. It neither mean that all sGRBs are caused by neutron star mergers nor that all neutron star mergers will cause a sGRB. It however does show that a sGRB can be generated and probably might be generated by such an event regularly considering the energy released, but we won't know with reasonable certainty until we've observed more such events.

    It might be worth to point out that GPS only works with GR (at least with the accuracy we expect), and that verification of GR thus makes us more confident in such technologies.

    @Polygnome Tests like observing the orbit of Mercury have already shown GR to be good enough for GPS. Nothing about this detection was going to change that.

    @Adwaenyth: Yes, that's what I thought. I just wasn't clear on what the answer was saying.

    Another point to add to that impressive list is; It also suggests that merging neutron stars may be more common in the universe than is currently thought. Given the general ideas around this phenomenon the chances of observing this event is minuscule. The fact that one has been observed at all suggests that either the scientists we're **incredibly** lucky or this type of event is much more prevalent than first though.

    @Liam Actually it doesn't suggest that. The revised rate for these events in the local universe pretty much agrees (with large uncertainties) with previous ideas about the rate as judged from our own galactic double neutron star systems. e.g. Kim et al. (2015) https://arxiv.org/abs/1308.4676 predicted aLIGO neutron star merger detection rates in the range 3-18 per year. What *was* lucky is that this event was well inside the sensitivity horizon (40 vs 200 Mpc) and so was very "bright".

    I'm pretty much repeating what I heard one of the scientists who worked on the project said when it was announced. not an expert TBH

    @Adwaenyth "*probably might*" LOL

    Matt Strassler has an explanation of the distance measurement and other aspects.

    Any idea why the process which produced the gravitational waves from more massive systems didn't produce accompanying photon-signals ??

    @PERFESSERCREEK-WATER Because they were merging black holes. No matter to emit light.

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Content dated before 7/24/2021 11:53 AM