<p>Because its awesome (<a href="http://www.smbc-comics.com/index.php?id=2088#comic" rel="noreferrer">SMBC</a>)</p>

<p>So this guy called Copernicus suggested that the Earth orbits the Sun (not the other way round) - What changes?</p>

<p>This guy Newton had a theory for how a mass responds to force, and how gravity works - So what?</p>

<p>Another guy called Maxwell had this idea of how light could actually be waves of electromagnetic fields - does this matter?</p>

<p>A guy called Monet decided to paint some pictures of some waterlilies. Who cares?</p>

<p>Last February, some guys from Denver carried a ball over a line more often than some guys from Carolina carried the ball over another line. So what?</p>

<p>It is worth finding things out because it means finding things out. It is worth understanding our world because it is there to be understood. Discovery is its own reward. It is not measured in by £ or $. </p>

<p>The observations of GW170817 show that heavy elements are created by the merger of neutron stars. Heavy elements like gold, platinum on Earth were likely created in a neutron star merger in The Milky Way, billions of years ago, that enriched the interstellar dust. </p>

<p>If it doesn't matter to you that's fine. If Monet's Waterlilies or the Superbowl leave you cold, that's no problem either. But not everything of value is of use.</p>

CC BY-SA 3.0
2017-10-17T04:18:19.683Z
`Last February, some guys from Denver carried a ball over a line more often than some guys from Carolina carried the ball over another line. So what?`  I'm totally asking that one on Sports SE...
Michael
CC BY-SA 3.0
2017-10-21T23:35:13.150Z
"*Discovery is its own reward*" but not when there's a limited amount of money, and lots of hands trying to grab at it.
RonJohn
CC BY-SA 3.0
2017-10-16T18:06:04.730Z
2017-10-16T18:06:04.730Z
James K
<p>Reasons why this is important:</p>

<p>It is the <em>first</em> simultaneous detection of a gravitational wave and electromagnetic signal, and the strongest GW signal yet in terms of signal to noise (<a href="http://www.google.com/calendar/render" rel="noreferrer">Abbott et al. 2017a</a>). It spectacularly corroborates the reality of the GW detection technology and analysis. The progenitor has been unambiguously located in a (relatively) nearby galaxy (<a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa9059/meta" rel="noreferrer">Soares-Santos et al. 2017</a>), allowing a host of other telescopes to obtain detailed measurements.</p>

<p>It shows that GWs travel at the speed of light, a further verification of Einstein's General Relativity (<a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa920c" rel="noreferrer">Abbott et al. 2017b</a>).</p>

<p>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. <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa905c/meta" rel="noreferrer">Chornock et al. 2017</a>; <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa90b6/meta" rel="noreferrer">Tanvir et al. 2017</a>).</p>

<p>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. <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa8f94/meta" rel="noreferrer">Savchenko et al. 2017</a>; <a href="https://mail.google.com/mail/?hl=en&amp;shva=1#inbox" rel="noreferrer">Goldstein et al. 2017</a>).</p>

<p>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. <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa9057/meta" rel="noreferrer">Margutti et al. 2017</a>; <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa905d/meta" rel="noreferrer">Alexander et al. 2017</a>).</p>

<p>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$^3$ (<a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.123016" rel="noreferrer">Hinderer et al. 2010</a>; <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.82.024016" rel="noreferrer">Postnikov et al. 2010</a>).</p>

<p>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 (<a href="http://www.nature.com/nature/journal/vaap/ncurrent/full/nature24471.html" rel="noreferrer">Abbott et al. 2017c</a>). 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.</p>

<p>Finally, this event will turn out to be important because it was <em>lucky</em>; in the sense that the source was detected well-inside the sensitivity horizon of LIGO (<a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161101" rel="noreferrer">Abbott et al. 2017a</a>). The detection itself, was not unexpected given the rates predicted based on studying the neutron star binary systems in our own Galaxy (e.g. <a href="https://arxiv.org/abs/1308.4676" rel="noreferrer">Kim et al. 2015</a>), 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.</p>

<p>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.</p>

CC BY-SA 3.0
2017-10-16T21:55:41.097Z
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
CC BY-SA 3.0
2017-10-16T22:38:21.127Z
@User1291 I did assume (incorrectly). Small edit made.
ProfRob
CC BY-SA 3.0
2017-10-17T03:51:10.943Z
One question: does this show that all short GRBs are caused by neutron star mergers, or only some of them?
jamesqf
CC BY-SA 3.0
2017-10-17T05:50:46.457Z
@jamesqf It shows that merging neutron stars can produce a sGRB. So, at least some are caused by merging neutron stars.
ProfRob
CC BY-SA 3.0
2017-10-17T07:24:15.000Z
@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.
Adwaenyth
CC BY-SA 3.0
2017-10-17T14:17:56.980Z
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
CC BY-SA 3.0
2017-10-17T14:19:26.217Z
@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.
ProfRob
CC BY-SA 3.0
2017-10-17T17:18:08.110Z
@Adwaenyth: Yes, that's what I thought.  I just wasn't clear on what the answer was saying.
jamesqf
CC BY-SA 3.0
2017-10-20T09:36:41.097Z
@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".
ProfRob
CC BY-SA 3.0
2017-10-20T11:48:22.287Z
@Liam You misheard, or they were careless. See also http://adsabs.harvard.edu/abs/2012MNRAS.425.2668C and https://arxiv.org/abs/1003.2480
ProfRob
CC BY-SA 3.0
2017-10-21T23:32:56.000Z
@Adwaenyth "*probably might*" LOL
RonJohn
CC BY-SA 3.0
2017-10-23T00:48:31.167Z
Matt Strassler has an explanation of the [distance measurement](https://profmattstrassler.com/2017/10/17/the-significance-of-yesterdays-gravitational-wave-announcement-an-faq/) and other aspects.
Keith McClary
CC BY-SA 4.0
2019-01-09T12:35:56.260Z
Any idea why the process which produced the gravitational waves from more massive systems didn't produce accompanying photon-signals ??
PERFESSER CREEK-WATER
CC BY-SA 4.0
2020-04-13T09:19:05.117Z
@PERFESSERCREEK-WATER Because they were merging black holes. No matter to emit light.
ProfRob
CC BY-SA 3.0
2017-10-16T18:44:49.387Z
2017-10-23T07:02:05.017Z
2017-10-23T07:02:05.017Z
ProfRob
<p>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 ...</p>

<p>What I <em>haven't</em> heard yet, however, is <em>why</em> we should care.</p>

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

<p>But now that we've heard it ... what changes?</p>

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

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

CC BY-SA 3.0
2017-10-17T01:18:39.453Z
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](https://www.computerhope.com/forum/index.php?topic=64969.0) (rejected by court).  But really it was true - we just want to destroy the universe. :-)
StephenG - Help Ukraine
CC BY-SA 3.0
2017-10-17T07:11:52.350Z
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.
Radovan Garabík
CC BY-SA 3.0
2017-10-17T10:51:40.047Z
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.
el.pescado - нет войне
CC BY-SA 3.0
2017-10-17T13:43:46.063Z
Related: [Is there any practical use for astronomy?](https://astronomy.stackexchange.com/questions/10341/is-there-any-practical-use-for-astronomy)
David Hammen
CC BY-SA 3.0
2017-10-18T15:18:31.817Z
Among other things, it explains where heavy metals like gold and platinum come from.
Robert Harvey
CC BY-SA 3.0
2017-10-21T15:20:15.800Z
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.
Spencer
CC BY-SA 3.0
2017-10-21T17:14:59.910Z
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?"
Shawn V. Wilson
CC BY-SA 3.0
2017-10-23T10:33:48.740Z
"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.
NoDataDumpNoContribution
CC BY-SA 3.0
2017-10-23T18:17:37.523Z
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.
Jack R. Woods
<gravitational-waves><neutron-star>
Why is the discovery of merging neutron stars important?
User1291
# Why is the discovery of merging neutron stars important?

(Asked by: username_0 on 2017-10-16)

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?

**Tags:** gravitational-waves, neutron-star

> **Comments:**
> **username_1**: 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](https://www.computerhope.com/forum/index.php?topic=64969.0) (rejected by court).  But really it was true - we just want to destroy the universe. :-)  
> **username_2**: 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.  
> **username_3**: 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.  
> **username_4**: Related: [Is there any practical use for astronomy?](https://astronomy.stackexchange.com/questions/10341/is-there-any-practical-use-for-astronomy)  
> **username_5**: Among other things, it explains where heavy metals like gold and platinum come from.  
> **username_6**: 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.  
> **username_7**: 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?"  
> **username_8**: "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.  
> **username_9**: 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.  

---

## 2 answers

### Answer by username_13 on 2017-10-16. Score: 177 | Accepted answer

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](http://www.google.com/calendar/render)). 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](http://iopscience.iop.org/article/10.3847/2041-8213/aa9059/meta)), 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](http://iopscience.iop.org/article/10.3847/2041-8213/aa920c)).

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](http://iopscience.iop.org/article/10.3847/2041-8213/aa905c/meta); [Tanvir et al. 2017](http://iopscience.iop.org/article/10.3847/2041-8213/aa90b6/meta)).

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](http://iopscience.iop.org/article/10.3847/2041-8213/aa8f94/meta); [Goldstein et al. 2017](https://mail.google.com/mail/?hl=en&shva=1#inbox)).

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](http://iopscience.iop.org/article/10.3847/2041-8213/aa9057/meta); [Alexander et al. 2017](http://iopscience.iop.org/article/10.3847/2041-8213/aa905d/meta)).

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](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.123016); [Postnikov et al. 2010](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.82.024016)).

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](http://www.nature.com/nature/journal/vaap/ncurrent/full/nature24471.html)). 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](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161101)). 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](https://arxiv.org/abs/1308.4676)), 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.

> **Comments:**
> **username_0**: 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.  
> **username_13**: @username_0 I did assume (incorrectly). Small edit made.  
> **username_14**: One question: does this show that all short GRBs are caused by neutron star mergers, or only some of them?  
> **username_13**: @username_14 It shows that merging neutron stars can produce a sGRB. So, at least some are caused by merging neutron stars.  
> **username_15**: @username_14 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.  
> **username_16**: 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.  
> **username_13**: @username_16 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.  
> **username_14**: @username_15: Yes, that's what I thought.  I just wasn't clear on what the answer was saying.  
> **username_13**: @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".  
> **username_13**: @Liam You misheard, or they were careless. See also http://adsabs.harvard.edu/abs/2012MNRAS.425.2668C and https://arxiv.org/abs/1003.2480  
> **username_12**: @username_15 "*probably might*" LOL  
> **username_17**: Matt Strassler has an explanation of the [distance measurement](https://profmattstrassler.com/2017/10/17/the-significance-of-yesterdays-gravitational-wave-announcement-an-faq/) and other aspects.  
> **username_18**: Any idea why the process which produced the gravitational waves from more massive systems didn't produce accompanying photon-signals ??  
> **username_13**: @PERFESSERCREEK-WATER Because they were merging black holes. No matter to emit light.  

---

### Answer by username_10 on 2017-10-16. Score: 46

Because its awesome ([SMBC](http://www.smbc-comics.com/index.php?id=2088#comic))

So this guy called Copernicus suggested that the Earth orbits the Sun (not the other way round) - What changes?

This guy Newton had a theory for how a mass responds to force, and how gravity works - So what?

Another guy called Maxwell had this idea of how light could actually be waves of electromagnetic fields - does this matter?

A guy called Monet decided to paint some pictures of some waterlilies. Who cares?

Last February, some guys from Denver carried a ball over a line more often than some guys from Carolina carried the ball over another line. So what?

It is worth finding things out because it means finding things out. It is worth understanding our world because it is there to be understood. Discovery is its own reward. It is not measured in by £ or $.

The observations of GW170817 show that heavy elements are created by the merger of neutron stars. Heavy elements like gold, platinum on Earth were likely created in a neutron star merger in The Milky Way, billions of years ago, that enriched the interstellar dust.

If it doesn't matter to you that's fine. If Monet's Waterlilies or the Superbowl leave you cold, that's no problem either. But not everything of value is of use.

> **Comments:**
> **username_11**: `Last February, some guys from Denver carried a ball over a line more often than some guys from Carolina carried the ball over another line. So what?`  I'm totally asking that one on Sports SE...  
> **username_12**: "*Discovery is its own reward*" but not when there's a limited amount of money, and lots of hands trying to grab at it.  

---

