Merging Neutron Stars: What We Know So Far

In summary, rumors are circulating that LIGO/VIRGO has detected a signal of merging neutron stars, accompanied by an optical counterpart. These rumors were sparked by the sudden pointing of multiple telescopes at the same patch of sky. While the science behind the rumors cannot be discussed pre-publication, it is reasonable to use this as an opportunity to discuss the science behind merging neutron stars. The leading hypothesis for the origin of short gamma ray bursts is that they are caused by neutron star mergers, so if LIGO has truly detected such an event, we can expect a gamma ray counterpart as well. The gravitational wave signal from such an event would be very informative, as it would help refine models of neutron stars. However, it is uncertain if
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  • #37
From the panel:

* Vicky Kalogera is an expert for binary neutron stars and white dwarfs.
* Andy Howell and Ryan Foley use supernovae to study dark energy and work on quick optical follow-up observations for the supernovae.
* Marcelle Soares-Santos studies dark energy and cosmological gravitational waves
* David Sand is another supernova expert
* Nial Tanvir studies gamma ray bursts, and found evidence that short GRBs are caused by binary mergers
* Edo Berger studies GRBs and other supernovae
* Eleonora Troja studies GRBs
* Alessandra Corsi studies GRBs
* Various LIGO/Virgo people, of course.

We get a very consistent picture here. I predict that LIGO and Virgo measured a binary neutron star or neutron star black hole merger, which was also seen as short-duration gamma ray burst.
 
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  • #38
It's difficult to keep secrets with so many people involved. A Google search already finds a two web pages containing abstracts of papers about this event from the electromagnetic point of view (X-ray and optical); the pages themselves have been removed, but Google has cached them!

Also, Francis Villatoro "emulenews" has tweeted a brief summary at https://twitter.com/emulenews/status/917302944990728193 as follows:

Non-official GW170817 = time coincidence with short GRB170817A (Fermi GBM, INTEGRAL); optical counterpart localization in NGC4993 (40 Mpc)
Official press-conference LIGO/Virgo on Oct 16 – keep tuned!
 
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  • #39
ESO announced a press conference "to present groundbreaking observations of an astronomical phenomenon that has never been witnessed before" at the same time as the LIGO press conference. Is this the same conference, or do they announce the same thing in separate conferences, or is this unrelated? The timing is very suspicious.

16:00 CEST, 14:00 UTC, 10:00 EDT, or 11:20 after this post.
 
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  • #40
16th October, day of two important announcements: one astronomical and the other related to WiFi security (google KRACK).
 
  • #42
ESO spoiled it - yes , two neutron stars merging. About 70 telescopes looked at it in a giant observation campaign.
 
  • #44
It's been confirmed!
 
  • #45
Lots of very neat results. GW170817 was detected for more than 30 seconds in this case, gradually building up to the merger of two neutron stars (probably to form a combined neutron star). Then Fermi and Integral both saw a short GRB within the next couple of seconds, so everyone pointed their telescopes in the general direction to try to spot anything. A few hours afterwards a bright new electromagnetic source was identified in NGC 4993 which matched the expected characteristics of a kilonova, and provided a lot of interesting spectral features as it died away over a few days. Detected in just about everything except neutrinos!
 
  • #47
It looks like there is a new standard candle source.
 
  • #48
Some of the published papers (reportedly there are 40 in all):

B. P. Abbott et al. GW170817: Observation of gravitational waves from a binary neutron star inspiral. Physical Review Letters. Published online October 16, 2017. doi: 10.1103/PhysRevLett.119.161101.

B. P. Abbott et al. Multi-messenger observations of a binary neutron star merger. Astrophysical Journal Letters. Published online October 16, 2017. doi: 10.3847/2041-8213/aa91c9.

I. Arcavi et al. Optical follow-up of gravitational-wave events with Las Cumbres Observatory. Astrophysical Journal Letters. Published online October 16, 2017. doi: 10.3847/2041-8213/aa910f.

J. Hjorth et al. The distance to NGC 4993: The host galaxy of the gravitational-wave event GW170817. Astrophysical Journal Letters. Published online October 16, 2017. doi: 10.3847/2041-8213/aa9110.

M.C. Diaz et al. Observations of the first electromagnetic counterpart to a gravitational-wave source by the TOROS collaboration. Astrophysical Journal Letters. Published online October 16, 2017. doi: 10.3847/2041-8213/aa9060.

B. P. Abbott et al. Gravitational waves and gamma-rays from a binary neutron star merger: GW170817 and GRB 170817A. Astrophysical Journal Letters. Published online October 16, 2017. doi: 10.3847/2041-8213/aa920c.

E. Troja et al. The X-ray counterpart to the gravitational-wave event GW170817. Nature. Published online October 16, 2017. doi: 10.1038/nature24290.

I. Arcavi et al. Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger. Nature. Published online October 16, 2017. doi: 10.1038/nature24291.

The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration. A gravitational-wave standard siren measurement of the Hubble constant. Nature. Published online October 16, 2017. doi: 10.1038/nature24471.

D. Kasen et al. Origin of the heavy elements in binary neutron star mergers from a gravitational wave event. Nature. Published online October 16, 2017. doi:1038/nature24453.

S.J. Smartt et al. A kilonova as the electromagnetic counterpart to a gravitational wave source. Nature. Published online October 16, 2017. doi: 10.1038/nature24303.

E. Pian et al. Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger. Nature. Published online October 16, 2017. doi: 10.1038/nature24298.

S. Covino et al. The unpolarized macronova associated with the gravitational wave event GW 170817. Nature Astronomy. Published online October 16, 2017. doi:10.1038/s41550-017-0285-z.

M.M. Kasliwal et al. Illuminating gravitational waves: A concordant picture of photons from a neutron star merger. Science. Published online October 16, 2017. doi: 10.1126/science.aap9455.

P.A. Evans et al. Swift and NuSTAR observations of GW170817: Detection of a blue kilonova. Science. Published online October 16. doi: 10.1126/science.aap9580.

G. Hallinan et al. A radio counterpart to a neutron star merger. Science. Published online October 16, 2017. doi: 10.1126/science.aap9855.

D.A. Coulter et al. Swope Supernova Survey 2017a (SSS17a), the optical counterpart to a gravitational wave source. Science. Published online October 16, 2017. doi: 10.1126/science.aap9811.

M.R. Drout et al. Light curves of the neutron star merger GW170817/SSS17a: Implications for r-process nucleosynthesis. Science Published online October 16, 2017. doi: 10.1126/science.aaq0049.

B.J. Shappee et al. Early spectra of the gravitational wave source GW170817: Evolution of a neutron star merger. Science. Published online October 16, 2017. doi: 10.1126/science.aaq0186.

C.D. Kilpatrick et al. Electromagnetic evidence that SSS17a is the result of a binary neutron star merger. Science. Published online October 16, 2017. doi: 10.1126/science.aaq0073.
 
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  • #49
And now comes the confusing and perhaps non-meaningful mainstream reportage of this event.

This AM, this was breathlessly reported on NPR news, with some extremely confusing comments. I am abundantly cognizant that an NPR radio newsbrief is hardly a source that once can hang a hat on, however there were some strangely specific comments that I hope somebody here can help me make some sense (or nonsense as the case may be) of.

The matter of the observed collision was noted, followed by the comments (unsourced) that this resulted in the production of a large quantity of gold and platinum, and that consequently we now have a clear idea where heavy metals come from.

Again, please note, this was radio news reporting, which I tend to assume is both incomplete, misleading and confused.

I have some general knowledge of supernova based nucleosynthesis ... but this just left me 'alone in the dark' so to speak. Superficially, it sounds like an outrageously general and conclusive statement. I mean, I am sure that there may have been some observation of relevant spectral lines (my guess... I am sure someone can shed some light on this) but the general conclusion sounds like... well... mainstream science journalism overreach or over-summerization... I don't know which, if either. Either way, before I go semi-randomly punching up web pages, perhaps someone could offer some clarity, guidance and maybe a direction on some more meaningful sources online to at least get some more meaningful (albeit informed-layman digestible) information.

Is the wiki article a reasonable place to start?

diogenesNY

Edit: Okay, read the wiki page ... and the kilonova reference and the kilonova wiki page. Very cool and interesting. Would like to read more about this
 
  • #50
The Science News article is the best place to start before trying to dive into any of the scientific papers, many of which are closed access. https://www.sciencenews.org/article/neutron-star-collision-gravitational-waves?tgt=nr I'd recommend reading the abstracts to the papers next. The wiki article is too short to really tell the whole story or even a meaningful enough part of it and only cites to secondary sources so far.
 
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  • #51
@ohwilleke --

Thank you. I am on it, with great enthusiasm!

diogenesNY

Edit: Read the sciencenews article. This is very very cool. Looks like I have a bunch of reading ahead of me. :)

Damn, this is cool!
 
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  • #52
Haelfix said:
It looks like there is a new standard candle source.

Yup. Although the margin of error on the Hubble measurement is big: 70 +12/-8, even though the mean value is right in the middle of the range of existing values and this measurement has the virtue of being completely independent of other methodologies and, almost, model independent.

The 1.7 second gap between the gravity wave detection and the first detection of an EM source (which could have happened slightly later or could have been detected midway through the first gamma ray arrival) at a distance of 130 million light years is also great direct proof that the speed of gravitational waves and the speed of light are the same. Another experimental test of GR checked off the list.
 
  • #53
ohwilleke said:
Yup. Although the margin of error on the Hubble measurement is big: 70 +12/-8, even though the mean value is right in the middle of the range of existing values and this measurement has the virtue of being completely independent of other methodologies and, almost, model independent.

The 1.7 second gap between the gravity wave detection and the first detection of an EM source (which could have happened slightly later or could have been detected midway through the first gamma ray arrival) at a distance of 130 million light years is also great direct proof that the speed of gravitational waves and the speed of light are the same. Another experimental test of GR checked off the list.

I agree that this independent measurement is significant. Unfortunately, the sigma is too large to resolve the tension between Planck and the Riess,et.al. measurement.
 
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  • #54
5 minute video by Veritasium (Derek Muller) on the event:

 
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  • #55
The red shift is roughly z=0.0098, quite a precise measurement (admittedly with a 20% MOE in terms of absolute distance).

The confirmation of the speed of gravity relative to the speed is light is exact to roughly one part per 1015. Prior to this test, it was confirmed only to roughly one part per 103 per the Particle Data Group.

Lubos Motl has a play by play account of the press conference for people who don't have the luxury of playing You Tube videos at work. https://motls.blogspot.com/2017/10/ligo-virgo-detects-neutron-stars.html#more

Professor Matt Strassler also provides commentary, notably observing that almost everything that was seen was just as it was predicted to be. Not as exciting as new physics, but a sign that the discipline is very mature and reality-based to get so much right about phenomena that have never been observed until now. https://profmattstrassler.com/2017/...ning-gravitational-and-electromagnetic-waves/
 
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  • #56
Here's a mainstream news article about it:

https://www.washingtonpost.com/news...-new-era-in-astronomy/?utm_term=.1fd43124d34a

"Some 130 million years ago, in a galaxy far away, the smoldering cores of two collapsed stars smashed into each other. The resulting explosion sent a burst of gamma rays streaming through space and rippled the very fabric of the universe.

"On Aug. 17, those signals reached Earth — and sparked an astronomy revolution."​
 
  • #57
Thinking about what we can do as we get more of this kind of data over a decade or so.

At some point the instruments used here will make it possible to determine with quite a bit of precision the density of neutron star collisions and black hole collisions at various scales in the universe (and also probably black hole-star collisions). I wonder how much precision you can get, given that there seem to be events observed every 2-3ish months, over say, ten years. Surely, those ca. 50 or so events (with pretty rich data sets for each individual event) have to greatly improve the present set of knowledge and will create parameters that can be used in conjunction with observations such as Planck, WMAP and BAO data to constrain a lot of cosmology theories. On the other hand, the statistical margins of error for 50 events spread over several categories of observations aren't going to be really low either. Pretty much, we're going to get order of magnitude estimates, tops, although I suppose other constraints can further bound the LIGO/VIRGO estimates. Maybe you could do better if you knew you were fitting, say, a power law or Poisson distribution, so you could apply all or most of the data points to single one parameter to fit.

Neutron star-neutron star event density, that we may be lucky to get 6-10 data points like this one on over a decade could be particularly valuable because that could be tied into other measurement of post-Big Bang Nucleosynthesis and corroborated with metallicity data from star spectral data to figure out the relative importance of this v. other processes for creating heavy elements and for the life cycle and evolution of stars, galaxies and the universe in general. The proportion of heavy element formation that comes from neutron star-neutron star events v. other means is probably one of the least constrained factors in the entire model of heavy element formation in the universe so pinning it down even a little could be a huge gain in the precision of how we model heavy element formation which in turn could be use to more tightly constrain cosmology simulations generally.

The statistical power on testing the extent to which the frequencies are the same, in all spherical directions, or per galaxy within range, or per galaxy within range adjusted for galaxy age, to test homogeneity and uniformity of physical laws is going to be even worse. On each 360 degree axis you'll have 50 data points, with an average of 7.2 degrees per event on average before adjusting for blind spots, basically you'd do some sort of Chi-square analysis, but you'd have to have a very skewed distribution to disprove a null hypothesis of directional neutrality with a sample that small.

On the other hand, while event density accuracy might be only order of magnitude, the kind of independent Hubble constant value determination made here, assuming similar margins of error in individual future measurements, might improve a lot if you got, say 6-10 of these kinds of measurements and pooled the results appropriately. This might get competitive with our means of measuring that parameter by other means.

Similarly, the signature signal of particular types of events (e.g. neutron star collisions or medium sized black hole mergers) could also be very tightly constrained (probably to the sub-percent level) with fairly modest data sets because there is a very exacting theoretical prediction and each event has very rich data on something like that. These tight constraints could shed a lot of data on the complex processes that go on in strong gravitational fields such a neutron stars where we are quite long on detailed models and short on empirical confirmation so far. The gains in nuclear physics could easily exceed those for astronomy or fundamental physics.

I suppose another globally valuable thing you get with say 10 years of operation is a 95% confidence interval of the maximum density of a multitude of phenomena that aren't observed in that time period which, once you work out the formulas for calculating them once, can be updated as a matter of course every year, bounding all sorts of theories about all sorts of astronomy phenomena that would generate gravitational waves but would be hard to observe otherwise. Basically, for each calculation you'd need to know how far away you have sufficient sensitivity to pick up an event of a particular type, figure out what kind of luminous matter and lensed matter is present in that sphere, and then figure out what number would have to be in the bin per time and per volume/relevant mass to have a 95% chance of seeing nothing.
 
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  • #58
ohwilleke said:
Yup. Although the margin of error on the Hubble measurement is big: 70 +12/-8, even though the mean value is right in the middle of the range of existing values and this measurement has the virtue of being completely independent of other methodologies and, almost, model independent.

The 1.7 second gap between the gravity wave detection and the first detection of an EM source (which could have happened slightly later or could have been detected midway through the first gamma ray arrival) at a distance of 130 million light years is also great direct proof that the speed of gravitational waves and the speed of light are the same. Another experimental test of GR checked off the list.

It seems strange that this observation that light and gravity are behaving so similarly (forming waves that propogate at the same speed) can't somehow be used to show that gravitons belong in the standard model like photons. There has got to be a way.
 
  • #59
Sophrosyne said:
It seems strange that this observation that light and gravity are behaving so similarly (forming waves that propogate at the same speed) can't somehow be used to show that gravitons belong in the standard model like photons. There has got to be a way.

Gravitational waves in GR propagate at the speed of light and so do EM waves in Maxwell's classical EM equations. The speed of propagation is something that the classical theories and quantum ones have in common, not a distinction.
 
  • #60
ohwilleke said:
The speed of propagation is something that the classical theories and quantum ones have in common, not a distinction.
Well the quantum ones have some "commuting" variable that circumvents the whole speed limit problem...
On another note, at least we are getting to the point that we (to drift off in some Star Trek type speculation) have long range sensors on-line.
 
  • #61
Sophrosyne said:
It seems strange that this observation that light and gravity are behaving so similarly (forming waves that propogate at the same speed) can't somehow be used to show that gravitons belong in the standard model like photons. There has got to be a way.
The SM, by definition, doesn't include gravity. And just because both photons and hypothetical gravitons are massless doesn't mean the phenomena would be similar in any way. We know they are not, otherwise we would have a consistent theory of quantum gravity by now.

@ohwilleke: You underestimate the number of events we will get. Let's say conservatively 1 NS event in 1 year of running, ignoring that the sensitivity improved over time. In a year, with twice the sensitivity, we would expect 8 events per year. In ~3 years, with the full sensitivity, we might get something like 20-30 per year. Add KAGRA and the number will get even larger. Add INDIGO and we might get more than 100 events per year. And then we can build the Einstein telescope which will see these events routinely.
Of course we might have been extremely lucky with this NS event, but that is unlikely. For binary black hole mergers the situation is even better, with 4 events observed already we can be quite sure they are not extremely uncommon.

diogenesNY said:
The matter of the observed collision was noted, followed by the comments (unsourced) that this resulted in the production of a large quantity of gold and platinum, and that consequently we now have a clear idea where heavy metals come from.
That was said by the scientists during the press conference.
 
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  • #62
So apparently the GW signal was too weak to get any information on the ring-down phase. At least I haven't seen it mentioned anywhere. Did I just miss it? Has anyone seen any information on a ring-down phase?
 
  • #63
ohwilleke said:
Gravitational waves in GR propagate at the speed of light and so do EM waves in Maxwell's classical EM equations. The speed of propagation is something that the classical theories and quantum ones have in common, not a distinction.

Sure. But currently we have a quantum theory of light, but not gravitation. Isn't there anything in these findings of observed gravitational waves that we can use to try to confirm or rule out some of the current proposals for a quantum theory of gravity, whether strings or quantum loop or whatever?
 
  • #64
Sophrosyne said:
Isn't there anything in these findings of observed gravitational waves that we can use to try to confirm or rule out some of the current proposals for a quantum theory of gravity, whether strings or quantum loop or whatever?

No.
 
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  • #65
phyzguy said:
So apparently the GW signal was too weak to get any information on the ring-down phase. At least I haven't seen it mentioned anywhere. Did I just miss it? Has anyone seen any information on a ring-down phase?

As the inspiral progressed, the frequency of the gravitational waves increases to higher than the frequency range the detectors are sensitive to. I think the merger and ringdown were missed because of this.
 
  • #66
You underestimate the number of events we will get. Let's say conservatively 1 NS event in 1 year of running, ignoring that the sensitivity improved over time. In a year, with twice the sensitivity, we would expect 8 events per year. In ~3 years, with the full sensitivity, we might get something like 20-30 per year. Add KAGRA and the number will get even larger. Add INDIGO and we might get more than 100 events per year. And then we can build the Einstein telescope which will see these events routinely.
Of course we might have been extremely lucky with this NS event, but that is unlikely. For binary black hole mergers the situation is even better, with 4 events observed already we can be quite sure they are not extremely uncommon.

This is very encouraging. I knew there would be some improvement in sensitivity and the number of detectors over time, but I had no idea that it would be so dramatic.
 
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  • #67
How long after merger did visual spectrum start to show lines (whether emission or absorption)?
 
  • #68
snorkack said:
How long after merger did visual spectrum start to show lines (whether emission or absorption)?
I believe physzguy kind of answered that in Borek's "splinter" thread:

phyzguy said:
It took about 11 hours for the optical telescopes to start looking, mostly because they were waiting for it to get dark. As soon as they started looking, the optical radiation was there, but it shifted to longer wavelengths as the ejecta cooled off over time.

ps. I've been thinking of starting a "splinter" thread myself, after a bunch of people on the internet started whining that; "Those aren't real pictures!" to NASA, et. al.
My very bad maths told me yesterday that it would take a telescope that is 3 light years in diameter to get a clear visual image of the event.
I googled feverishly to get confirmation that my maths was wrong, and found a web site* that said an optical telescope of that size would be so massive, it would collapse into a black hole.

[edit] *found it in my browsing history: http://quarksandcoffee.com/index.php/2015/07/08/aliens-and-dinosaurs/
 
  • #69
The optical pictures you see are not resolved images of the merger. They just capture the total light emitted. Optical photos of distant stars are never resolved. The stars are just points of light.
 
  • #70
phyzguy said:
The optical pictures you see are not resolved images of the merger. They just capture the total light emitted. Optical photos of distant stars are never resolved. The stars are just points of light.

I know that. But how do you explain to someone who might find out that all of the data comes from a pin point, how the [FAKE!] pictures are created?

ps. I really wish that Goddard had put in time stamps for their little movie.

​


I like watching it at 1/4 speed, at max resolution.
 

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