I have read about and heard about the theory that most of the heavy elements we have here on Earth came from colliding neutron stars rather than by way of supernovae.

I'm not sure how strong this theory is, but I wonder if a LIGO (and backup observational/ gamma ray) detection would help answer this question in any way.

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    $\begingroup$ Could you give references for that theory? $\endgroup$
    – Grimaldi
    Commented Sep 19, 2017 at 4:35
  • 1
    $\begingroup$ Like Grimaldi said: Please always provide references for theories or discoveries $\endgroup$ Commented Sep 19, 2017 at 11:50
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    $\begingroup$ Neutron star collision is now becoming the predominant model for the production of heavy r-process elements. $\endgroup$
    – ProfRob
    Commented Sep 20, 2017 at 10:12
  • $\begingroup$ There you go, my reference is the comment above. $\endgroup$ Commented Sep 21, 2017 at 2:21

2 Answers 2


I just found out the answer to my question from a live press release on You Tube that has been covered by blogs like this: http://news.nationalgeographic.com/2017/10/gravitational-waves-discovered-neutron-stars-pictures-science/

What LIGO does is tell you what is causing the gamma ray burst that can be studied different ways. The highly anticipated announcement I just watched explained that LIGO observed the neutron star merger (they're calling the event a kilonova). With the help of VIRGO, the area of the sky could be narrowed down better than previous LIGO detections. LIGO told us the masses of the bodies, the distance to the objects, how much mass was ejected and thus what the end product of the collision is expected to be.

We have observed many gamma ray bursts and this one was not particularly bright, but LIGO told astronomers to check this one out and so it was being observed within a few hours.

The electromagnetic spectrum of this event was collected and very broad lines were detected which are believed to be caused by heavy elements being ejected at near light speeds.

By our knowledge of how often these "kilonovae" should happen and the volume of elements heavier than iron thought now to have been emitted (16 Earth masses was the number mentioned in the press release), it can be said that a majority of many of the heavy elements we see around us may have come from these events.

  • $\begingroup$ You shouldn't believe everything in press releases., Especially if you've seen one that says kilonova events produce all the elements beyond iron (which is patently untrue).. Elements beyond iron are produced in a number of ways. Merging neutron stars may be a significant contributor to the r-process component. $\endgroup$
    – ProfRob
    Commented Oct 16, 2017 at 18:26
  • $\begingroup$ Sorry, I misrepresented what was said. I think it would be more accurate to say that the evidence supports that kilonovae produce a majority of certain elements heavier than iron (ie. gold). $\endgroup$ Commented Oct 22, 2017 at 17:33
  • $\begingroup$ That might be more accurate, though given that the "yield" from this event is only known to a factor of 3 and the Galactic rate of NS mergers is only known to a factor of 3, then the production rate of some elements heavier than iron is only known to an order of magnitude. In any case, the relevant sentence in your answer is still incorrect. $\endgroup$
    – ProfRob
    Commented Oct 22, 2017 at 20:27
  • $\begingroup$ @Rob Jeffries I've edited my "answer". Hopefully, this will be better. I also urge anybody reading this to checkout your answer to the question of "why is this important?". $\endgroup$ Commented Oct 23, 2017 at 21:09

It seems very likely that merging neutron stars are a major contributor to some of the (heavier) elements in the universe. These elements are made by rapid neutron capture onto pre-existing seed nuclei - known as the r-process. The process could work well in the hot ejecta created by the merger of two neutron stars.

Whether this mechanism dominates the creation of these elements is still uncertain. Firstly, there are other possible r-process sites - most obviously, supernovae, that may also be important. Secondly, in order to compare the production rates in neutron star mergers with the abundances of heavy elements in say the Solar System, we need to know what the rate of these neutron star mergers is, as a function of cosmic time, and we need to know how much of what chemical elements are produced in the merger.

What the new LIGO gravitational wave observations give us, is some very approximate idea of the rate at which these mergers are happening. But it is still order-of-magnitude stuff. The second important thing is that via the identification of an optical/infrared counterpart to one of these mergers one is able to study the chemical composition of the ejecta in some detail. These observations are broadly consistent with the idea that the ejecta contain a lot of material that is produced in the r-process, though don't really give much information on the abundances of individual chemical elements.

I would conclude that the one detection of GW170817 has moved us from an upper limit on the merger rate to an order-of-magnitude estimate, and the identification of the signatures of r-process elements in the ejecta tells us that mergers can produced heavy elements in some quantity. This is consistent with the notion that most of some specific heavy elements are produced in this way, but the detailed quantitative evidence for that is still some way off.

  • $\begingroup$ Would Ligo get a good enough picture of what happens to add a lot of info??, and that's assuming it observes a collision at all. I would think collisions like that are quite rare if limited to the Milky way. $\endgroup$
    – userLTK
    Commented Sep 20, 2017 at 0:29

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