We run a network of 20 telescopes that are triggered remotely (mostly via API). Because of our ability to schedule observations quickly, we were the only ones able to observe the peak luminosity of the kilonova.
Random internet browsing! I have a previous interest in astronomy and I stumbled upon our website, which had a jobs page. They were looking for someone with Django experience.
The field has an increasingly large demand for people with software engineering experience due to the complexity of modern observatories, instrumentation and data analysis. It's only going to grow from here. The problem is competing with SV, which tends to be a black hole for talented software engineers.
I think the meaning implied is in terms of quality of work. Even the best Silicon Valley company you might join, the big ones that pay well, will largely have you parsing xmls or other mundane programming ritual done and demonstrated to death.
Controlling telescopes, photographing once in a billion year astronomical events obviously has its coolness factor associated with it.
It tracts most of them. We can't really compete on the salary, benefits or programmer community/culture that is available in the bay area. You also are unlike to get rich in an industry that relies mostly on grants. What we do offer is meaningful work. The upside is we attract more motivated, idealistic people that tend to produce amazing work.
I work for the NRAO and concur with WD-42: there are more positions than software developers. The main problem is finding people who can withstand our sadistic hiring process and then not laugh when we tell them the salary and where you will live. :)
Given that GRBs have been detected for a long time and thought to have been a result of neutron star mergers, has a GRB detection ever led to an optical light detection of such a merger before? Is the news here that gravitational wave detection allowed us to see neutron star mergers optically or that they simply coincided with detections of the previously seen optical and gamma ray events?
Yes, there have been optical counterparts to GRBs before. What is news here is the first optical counterpart to a gravitational wave detection, along with a GRB, which gives us the strongest evidence yet that these are neutron star mergers.
Is there any new information gained from the optical observations in this particular instance? Did the initial gravitational wave detection allow us to capture the optical counterpart at an earlier stage than normal and therefore get more information as a result?
Yes, absolutely. This wasn't a very large gamma ray burst - as far as I know it may have not been followed up at all. GRBs are hard to localize - but the detection of the gravitational wave made it possible to search for the source quickly in a much smaller area of the sky. This got a lot of people looking, and a lot of good data collected.
My read is that the news here is that this is the first visual counterpart to a gravitational wave detection. (It's also very strong supporting evidence for the leading theory that neutron stars merging are sources of those gravitational waves.)
Hi! I've been working on a project that's similar to what LCO does, but uses existing amateur telescopes rather than deploying its own. My goal is to reap similar network benefits, and make astronomy more affordable and accessible for everyone.
Would you be open to talking about this project? I'd love to hear an insider's perspective on things, and poke at how my project could be most helpful/useful to astronomers.
Thanks for your work! I live in Santa Barbara and love the Astronomy On Tap events you guys put together. It's very cool what you have enabled astronomers across the world to do, and it's even better that you give back to the community and get people excited about space. Keep it up!
A team from UC Santa Cruz used the data from the Swope telescope in Chile to locate the source of the gravitation waves and observe the light from the event. The data provides evidence of how gold and other heavy elements formed in the universe.
It's a field in which international collaboration is forced - no amount of intelligence or money will let a nothern-hemisphere observatory get a shot of southern-hemisphere stars, for example.
That's a nice feel-good position to express, but is there any empirical evidence for it? There are plenty of very smart people (in academia) who are narcissistic, paranoid of potential rivals, and generally the opposite of cooperative and collaborative.
Narcissistic, paranoid are not traits what I call smart people. Humility on the other hand is. I guess studying and observing the universe makes people humble. The great physicians Einstein, Bohr and co of the beginning of 20 century worked together a lot for example. But anyway according the first fundamental of human stupidity there is fixed ratio of stupid poeple in any group of people. I think we can agree those you are referring to can be called stupid.
May not be admirable qualities, but they are often qualities of genius. The paranoia of Goedel was about as debilitating as it comes. And if you read a good Einstein biography, I think you'll discover more about him than you were expecting.
It might be more of a question of field. Based on my hopelessly incomplete view from the outside, in cosmology and closely-related subjects, it's impossible to work independently and accomplish much of anything. You need observations from many different sources.
Apologies, I'm not one of the researchers involved in the discovery. I'm just the web developer who built the announcement site for UCSC. Ryan Foley will participate in a Reddit AMA tomorrow (Tuesday, 10/17). I imagine your questions might get answered there.
This paper by one of the team members has more detail about the process used to narrow down the search field to a list of galaxies and identify possible locations of the event:
Not involved in this, I'm guessing this is how it goes: there are algorithms that automatically register the image that was just taken, diff it with a reference image of the sky from before, and if there's a significant difference that passes some false positive tests, then there's some notification for human intervention.
Indeed there could be events we are missing right now. Astronomers are building instruments that have larger fields of view (e.g., LSST), so that they can scan the sky ever few days.
Yes, but we observe more gold and other heavy elements than can be attributed to supernovae alone. Events like neutron star mergers might help explain where the rest comes from.
is that really significant? There are about 10 supernovas in the universe per second; neutron star mergers must to be at least 2 orders of magnitude rarer, estimating based on the percentage of stars that wind up becoming neutron stars
Since the first hominids looked up at the stars, till literally yesterday, mankind had only one fundamental force to observe the universe with: electromagnetic waves, be it light, radio waves or infrared. From today, we have two. The other two remaining fundamental forces do not operate at astronomical scales.
Of course, we had LIGO before yesterday, but for me, the confirmation through electromagnetic wave observations is key. This is an historic day!
We've also been observing the universe using neutrinos (generated by the weak force). In fact, there have even been one neutrino event linked to a possible astrophysical source[1], but with less certainty than this gravitational wave/EM detection.
This is so cool because we used our ears (the LIGO detectors) to hear/feel the gravitational wave hit then used our eyes (electromagnetic radiation telescopes) to focus in on where we thought we felt the ripple. And what's more, machines all over the planet were involved. Just awe-inspiring.
Wonderfully summed up. Thank you. By the way I thought gravitational waves have only been a theory. How can they be detected and is there such a thing as a gravitational quantum ?
Gravitational wave detectors like LIGO (https://www.ligo.caltech.edu/page/what-is-ligo) are very precise laser range finders used as rulers. They can measure extremely small expansions and contractions of space itself.
Discovering a quantized theory of gravity is possibly _the_ major open question in physics atm. We presume there's a 'graviton' of some sort, but have not observed it yet.
If I'm remembering the analogy in the livestream correctly, if you applied the laser's precision to astronomical scales, it would be the equivalent of measuring the distance to the moon with a tolerance the width of a human hair. And in the scales they deal with, a tolerance one-tenth the diameter of a proton.
These are completely classical waves, exactly like a pressure wave from a detonation, expanding in a sphere outwards from a neutron star merger. While a pressure wave is a rapidly moving but small change in gas density, a gravitational wave is a veery rapidly moving but veeery small change in the "density" of spacetime itself.
These gravitational waves are predicted by (completely non-quantum) general relativity. Einstein predicted their existence in 1916, but thought we would never have good enough detectors to measure them.
These waves travel at the speed of light, right? How is light itself affected by gravitational waves? I guess also changed, if they're using lasers to detect them, yea?
The waves do travel at the speed of light, since that's the upper speed limit in GR.
The light is affected only because the distance it has to travel changes when spacetime compresses and expands. So the time it takes from A to B changes, but also the wavelength of the light.
What is used in Ligo etc. is interference. They shoot two perpendicular laser beams that collide in a point. Ordinarily, the lasers interfere at this point and everything is aligned so they cancel each other out almost perfectly. But when a gravitational wave changes the length in one of the arms, the interference isn't perfect anymore and you can detect the laser signal.
To a very very good approximation, a gravitational wave front hitting Earth is a flat plane. This means the detectors cannot see waves that hit the arms at close to 45°, as well as waves that hit the Earth's surface close to vertically at the detector location.
Jesus, I can't imagine the type of resolution necessary to make those detectors work!
So the indication that "gravity wave happened" is wavelength change? Freaky stuff, I really have a hard time wrapping my head around all this, even after reading layman intros.
No, it's not wavelength change, it's the number of wavelengths that fit in each "arm" of the detector. With 4 km arms and 1000 nanometer laser wavelength (actual numbers), you will have 4 000 000 000.00 wavelengths that fit in each arm. When a gravitational wave passes, one arm will have 4 000 000 000.10 wavelengths and the other is unchanges. Since we're working with interference, this parts-per-billion change is converted into a large change in light.
Mechanical analogy: there are two very long very fine pitch helical gears that are both suspended from one end and mesh perfectly at the other end. When the gravitational wave makes one gear undetectably longer, we can easily see that the gears no longer mesh.
How do they distinguish between 4 000 000 000.10 and 4 000 000 001.10 wavelengths? Do they simply count how often they cross a full-phase change and keep track of the direction of that change?
Your statement is true, but it is important to emphasise that they travel at the speed of light in vacuum, this is important because the universe is only almost empty and electro-magnetic radiation actually travels slower than the speed of light in vacuum in this medium. This means that one would expect for light to arrive a few seconds after the detection of the gravitational wave.
The statement is also only true for perturbations with respect to a fixed background metric. In principle it is possible for space-time to expand much faster than the speed of light (this is believed to have happened just after the big-bang).
These kind of waves do, but not all gravitational waves do. (You can think of the class these are as "normal", smooth waves.)
Sufficiently "foamy" ones should act like waves passing through material and cause interference based losses while sufficiently strange waves will travel faster than light, a la the hypothetical warp drive using negative mass.
It's worth mentioning that there is a very common confusion around what is meant by a theory. It isn't the same as a guess. It has to be well supported. We've had good reason to think gravitational waves existed based on the well supported math of gravity.
Last year we got the first expirmental confirmation of this.
The correct term of an idea that hasn't been tested yet is a hypothesis. A `theory' is a full featured explanation. Generally, one requires a theory to be 'accepted as true' by the majority of the scientific community.
The nomenclature here really sucks, because colloquially theory and hypothesis are essentially synonyms. However, it makes no sense to talk about the hypothesis of gravity. This discussion comes up most often around claims like "The theory of evolution is just a theory".
But the work on the gravitational wave detectors started much earlier, some fundamental calculations to support the current project were made already in the 1967, 50 years ago! That scientist (Rainer Weiss) got a half of the Nobel Prize in Physics this year for that:
Richard Feynman contributed his (valid) argument in support of the energy actually carried by the gravitational waves at the first American conference on general relativity, GR1, in 1957, 60 years ago:
Regarding the false understanding of the term "scientific theory" by the non-scientific public:
"A scientific theory is an explanation of some aspect of the natural world that has been substantiated through repeated experiments or testing [emphasis mine]. But to the average Jane or Joe, a theory is [wrongly] just an idea that lives in someone's head, rather than an explanation rooted in experiment and testing [the actual scientific meaning]."
The gravitational waves are the consequence of the General Relativity, the theory introduced in 1915 by Einstein (102 years ago), but which was also based on the centuries of the previous observations and calculations i.e. all the discoveries of the gravitation (Newton 1687, 330 years ago), electricity, magnetism, electromagnetic waves (more than 200 years ago), etc.
"Though these words [like "theory"] may be routinely misunderstood, the real problem, scientists say, is that people don't get rigorous science education in middle school and high school. As a result, the public doesn't understand how scientific explanations are formed, tested and accepted."
That I have to write all this is a kind of confirmation of that statement.
Just the same, the science of global warming is also based on the scientific observations and valid theories since 1824 (almost 200 years ago):
People misunderstand this stuff in part because of the failure to make a distinction between a theory (which is often a mathematical description of a system, though this depends on the discipline) and an interpretation (which really is an idea in someone’s head, though often one we have good reason to believe). Scientists mostly work with the former day-to-day, but the general public is mostly interested in the latter.
Usually this distinction isn’t really a big deal, but in some cases - quantum mechanics, for example - there’s a big difference between the two, with multiple interesting interpretations to consider.
When we don’t make this distinction it creates an opening for people with poor understanding (or, occasionally, bad motives) to nitpick extremely well-established theories on the basis of quibbling about interpretation. I worry about this with respect to climate change specifically: deniers come up with a million reasons that climate change may be partially natural, or that this or that industry may be unfairly maligned, but we can’t get sucked into those debates so much that we forget the big picture painted by the data and models we have.
I don't know about the quantums but to detect the waves you basically split a laser beam using mirrors and redirect each split to a detector. When the wave hits it stretches each split in the beam slightly which causes an interference pattern. That pattern, as it evolves over time as the wave hits, can be converted into sound which is that "chirp" that everyone talks about.
The Gravitational wave was detected 2 seconds before the Gamma Ray Burst. I wonder why it is faster?
> On 17 August 2017 the NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.
The gravitational waves here were measured for about 100 seconds (as opposed to the much shorter 'chirp' from the first gravitational wave detection made in 2016) so the whole event took some time to unfold.
The 2 second delay was due to the fact that gamma rays were generated by matter slowing down after it was ejected from the system and which collided with galactic gas. That matter was ejected from the black hole's axis of rotation and the black hole formed some time after the gravity waves were detected.
"As this material was sucked into the black hole, a fast-moving jet of material blasted outward along the black hole's axis of rotation. When this jet collided with gas in the galaxy, it started slowing down and the lost kinetic energy was broadcast as gamma rays"
IANAAstronomer but my a-little-bit educated guess is gravity waves are emited during the "very close dance" phase of the merger and the GRB is the explosion that happens right after that.
I would assume it's for a similar reason to why neutrinos from a supernova arrive before the photons. Photons won't be traveling at the speed of light (in a vacuum) until the're actually in a vacuum. Neutrinos and the propagation of gravitational waves wouldn't be slowed down as much by the matter between the center of the event and open space.
That's the fun science bit where we say "Oh that's odd" :)
Is there some matter along the path that interacts with the gamma ray burst and slows it by two seconds? Why is it two seconds? Does it tell us something about the source?
Yeah my first thought was that space isn't quite a vacuum, which maybe adds up over 130M light years to something measurable. Meanwhile, the gravitational wave is a fluctuation in space itself, so always moves at SoL?
The sibling comment about one simply happening after another also seems very plausible though.
Gravitational wave is caused by the abrupt change of movement of massive object through spacetime. I would imagine the two neutron stars are traveling to each other in way slower speed than the speed of light. When the edges of the two neutron stars first touched, their movement was abruptly stopped and the gravitational wave propagated out. The light only went out after the merging of the two objects, the compression, and the ignition of the kilonova, which took some time.
My guess would be resolution. Gravitational waves are not only caused by the actual merger but also from the two masses losing energy while spinning closer and closer to each other. The GRB happens when they finally merge.
I wonder if the gravitation waves stretches the Space-time in such a way that it takes 2 seconds longer for the photons of GRB to travel "on top of it" and reach earth.
By davidhydes comment [1] it is because the gamma burst actually happens after the merger. It is caused by the ejected mass slowing down due to friction.
My layman's interpretation is that this is cherenkov radiation on an astronomical scale, though that suggests it is caused by charged particles, which neutrons aren't.
It appears this was the discovery, they're talking about it on stream now: http://www.eso.org/public/news/eso1733/ (ESO Telescopes Observe First Light from Gravitational Wave Source)
Taking a while to load. The summary suggests that GRBs are caused by neutron star mergers:
"ESO’s fleet of telescopes in Chile have detected the first visible counterpart to a gravitational wave source. These historic observations suggest that this unique object is the result of the merger of two neutron stars. The cataclysmic aftermaths of this kind of merger — long-predicted events called kilonovae — disperse heavy elements such as gold and platinum throughout the Universe. This discovery, published in several papers in the journal Nature and elsewhere, also provides the strongest evidence yet that short-duration gamma-ray bursts are caused by mergers of neutron stars."
I disagree, the Veritasium video has way more information than the two videos you linked. It shows how the gamma ray telescopes and gravitational wave detectors worked together to narrow the source in the sky of event. What a gravitational wave signal looks like, what a gamma ray signal looks like. The fact that the optical signal was made 11 hours after that. Etc. There is a lot more info on top of that which makes the video worth watching.
It probably reflects my personal tastes, I understand he's a kind a Youtube star or something, but I find the Veritasium presenter too attention-grabbing distracting, so much that I can't even concentrate to what he is talking about. There is no visible presenter in the Science Mag video, ad I like that, and there is another presenter appearing in the Georgia Tech video (Laura Cadonati, a professor), but there I definitely don't have that "WTH the presenter is demanding more attention than the topic" effect, even if she has an accent.
I surely in this case react just like a "mom" from this comment: "Showed this video with amazing science discoveries about the universe to my mom and all she said was : "this guy likes orange decorations"." I also just see the guy, his appearance, his body movements and his room decorations etc and I just have this "look at me" impression. I can imagine that helps his personal popularity on that medium, and I guess he optimizes for that, but it obscures the actual content, at least to me.
So I don't have energy to analyze it further, but I have had an impression that the videos I've suggested contain some information that doesn't exist in the Veritasium's video, and that the level of the information is better suited for those who need short summary. Maybe there is a target group which, like I, better responds to the videos I've suggested.
For those who are really interested in the details, I think there's no substitute to reading the main scientific paper, written by 4600 people(!):
It is much more accessible than you'd imagine, it starts with:
"Over 80 years ago Baade & Zwicky (1934) proposed the idea of neutron stars, and soon after, Oppenheimer & Volkoff (1939) carried out the first calculations of neutron star models..."
(Yes, it's "the" Oppenheimer, who later go to be called "the father of the atomic bomb." Fritz Zwicky was apparently "the first astronomer to propose the existence of dark matter, supernovas, neutron stars, galactic cosmic rays, gravitational lensing by galaxies, and galaxy clusters.")
Reading the original sources further, the first map of the potential area on the sky and the first trigger that set everything in motion is:
"On 2017 August 17 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM; Meegan et al. 2009) onboard flight software triggered on, classified, and localized a GRB." My understanding is that it was therefore never technically necessary for Virgo to reject the second (lower) LIGO area on this image:
BTW, this is also the basis of a story by Greg Egan. Diaspora. (Aside: I highly recommend Greg Egan's work, especially Diaspora)
The claim he makes in the fiction novel, is that a neutron star-neutron star collision event would be enough energy to sterilize 100 light year radius around the event. The one in the novel happens closer than 100ly.
As a fan of the Astro-sciences I am so glad to be alive. I have all the confidence that within my lifetime hopefully (next 50 years hopefully) we will see great things maybe even a unification relativity and quantum mechanics.
Can some astronomer or physicist actually make an image where the source is marked? All I see is some stars and a galaxy which is basically and some textual explanation where I should look for it.
That one is only an announcement of the press event, posted cca 7 minutes before the start of the event, not what was discovered, which was officially published exactly at the start of the hour, as the news conferences started.
Anyway, at the moment there are still live streams, like
There's also Reddit "AskScience AMA Series: European Southern Observatory announcement concerning groundbreaking observations" unlocked now, starting at 18:30 CEST / 12:30 ET:
After observers found the source of the collision the scientist at the Chile observatory claims to have spent 45 minutes to locate it in the sky. Do they not have some sort of coordinate system they could use to pinpoint it?
So, was there a telescope monitoring the light location already, or was the light only found after the Gr detection... I.e. Was it not truly concurrent?
Is it just me, or does anyone else think that its strange that an observatory press release on the specific subject of the "observed light" can only lead it with what I assume is an artists'impression? I'm sure that there is oodles of data to go through, but after 3 months, surely a representation of the actual data imaged could be presented?
The actual images are also on the very same page where you only see an artist impression: PR Image eso1733b, PR Image eso1733c, PR Image eso1733d, PR Image eso1733e, PR Image eso1733h, PR Image eso1733k, PR Image eso1733m.
There also are actual pictures in the scientific papers, for example:
Also see the actual main paper, written by 4600 scientists together: there were many more observations and images than these two, but unfortunately they aren't "sexy" for the general public: a dot which appears and then disappears later. But the astronomers know how to even detect the presence of gold in that dot! Note: the chemical element helium, which today is even used to fill the balloons for the children, was first discovered on the Sun(!), using that kind of observations and analysis, and only later at our Earth.
There is also a video, directly linked from the page you criticize, and part of the press release, which was made from the real images taken at different times, where the changes in time are visible:
Also, there are a lot of papers that are published, most observers will publish or have published their observations.
The galaxy where the kilonova happened is some 130 million light years away, or 8 billion times more distant than the Sun is away from us, and what's observed (in different spectrums) is a source of a lot of light (or electromagnetic radiation) at the edge of that galaxy, and also the gravitational waves. To compare the sizes, there could be 1000 of our own galaxies placed one after another to fill the distance to that kilonova. There are around 400 billion stars just in our own galaxy.
Cool, but i want more. All we have so far is confirmations of rather well-understood interactions. I want "we see these massive waves, but have no idea what is causing them." If they are being seen, such results aren't published.
> All we have so far is confirmations of rather well-understood interactions.
Confirmations of commonly assumed interactions. This is vital, as numbers of other hypothesise/theories/other rely on that understanding. Without results like these all that work is on shaky ground, now it looks far more solid.
Confirming current understanding isn't as sexy as discovering new physics, but just as important, possibly more so.
That depends. I'd bet money that LIGO was not pitched on the idea that it would only confirm the existence of waves. New instruments are pitched on the expectation of novel measurements. the "new physics". The parallels to the LHC and other massively-expensive instruments are striking. They confirm something that has already been widely accepted, generate the expected prize and raft of phds, but when it is all over the universe hasn't changed. I worry that those greenlighting these projects are being too conservative, only investing in projects that have clear pathways. This trend matters. Physics needs these giant instruments to generate something truly new otherwise the billions will drift towards other disciplines.
You are wrong. The LHC was absolutely prepared to observe new "unexpected" (for the "Standard model") particles. It just didn't happen. A lot of theorists who had developed the theoretical extensions of the "Standard model" are disappointed about that, but that's what is observed.
Regarding the gravitational waves, you're also wrong, as the theory and the observations matched even without the gravitational waves being directly observed, the science is simply so good that completely unexpected results (in the sense you talk) are outside of the resulting limits of the previous measurements and calculations.
The level of the science we have now is really stunning. The only sad part of the story is that all investments in the science are really minute compared to all the money spent on armies and weapons (e.g. just as the order of magnitude one year of the US military budget is at least 30 times bigger than the NASA's).
There's immense amount of the new information that can be obtained by the repeated observations. But the expectation of anything to disprove too much of what we know up to now is simply not realistic.
LIGO is a new telescope. Everyone is hoping that, like every other form of telescope ever built, it will 'see' things that we didn't know were out there. There are lists of unexplained phenomena that telescopes see very regularly. Trying to explain such observations is the forefront of astronomy and physics (see dark matter/energy). But this telescope has yet to add to the lists.
This is a huge observation, and many more insights are to come, and that this one or the previous three didn't add to that list you'd wish to be added to doesn't in any way diminish the achievement.
You're misunderstanding the purpose of LIGO. LIGO is partly a physics experiment to confirm general relativity, like Gravity Probe B, but mostly an astronomical observatory. All astronomy before was based on electromagnetic waves (light, then radio, UV, IR, Xray, gamma). This is a completely separate information source about the behavior of stars and will have a huge impact on astrophysics.
LIGO may or may not turn up "new physics," but I for one think it's already plenty exciting to (i) confirm the predictions of GR (not a given), and (ii) be able to "see" the state of the universe through this new instrument -- there's more to (astro)physics than just the relevant physical laws.
This is awesome! We should be able to find more gravitational wave sources and it will give us a better picture of the cosmos. Also, that we have more sources with better correlation and more information.
The best part is that gravitational waves stand out in a way that events in the visible spectrum do not, so these gravitational wave observatories will be helping find events and get them observed in every portion of the electromagnetic spectrum that we can observe. That means we'll be observing many more of these kilonovae now. This truly is a new era, as we'll now be able to use all these observatories at the same time to observe the same events, and this will yield the highest possible resolution imaging of these events, as far-flung telescopes are able to function as one really, really big, virtual one.
Quite possibly I think. This is both confirmation that neutron star mergers do indeed exist and create kilonova, and the first detection of an astronomical event with both gravitational waves and light. Nobel prize is only limited to three people though, so it's unclear who they would give it to, given there are thousands of people that contributed to this.
awesome discovery. Can't wait to see the pictures. So much closer than the other detections of black holes - I assume the detection range of neutron starts is much smaller.
For 130 million light years the difference between gravitational wave signal and gamma burst is 2s. That constrains the speed difference to 1.6e-18 m/s. This is fascinating number especially given that speed of light is 3e8.
> For 130 million light years the difference between gravitational wave signal and gamma burst is 2s. That constrains the speed difference to 1.6e-18 m/s.
This assumes that the production of gravitational waves and the gamma rays occurred at the same time.
Newbie question: While this is a very small fractional difference, could it be theoretically significant? What is the explanation of this difference? My best guess is that this difference must also be there in when the waves _started_.
It reminds me of a point from non-Euclidean geometry. In Euclidean geometry a triangle has 180 degrees, but in hyperbolic or elliptic geometry it has more or less (I forget which way). So you could start measuring triangles to find out whether our universe is Euclidean or not. But since every measurement has an error interval, e.g. 180 +/- 0.000001 degrees, you may some day prove the universe is non-Euclidean, but you could never prove it is Euclidean! It may be "skewed", but just less skewed than your instruments can measure.
As neutron stars are small, like 20 kilometers, while the light travels 600 000 km within 2 seconds and one can roughly assume that speed of processes that generates the gamma burst during the stars collisions matches the speed of light the delay may need some explanations. It could be just scattering of gamma rays by intergalactic medium that does not affect the gravitational waves, but what ever it is, I suppose it matches models or this delay will be in the news.
Simplest explanation I can think of: there's no reason to model this event as if all of its energy is emitted from a point source. As the NYT article put it, the size of the explosion is comparable to the orbit of Neptune. Meanwhile, two seconds at the speed of light is less than the orbit of Earth's moon.
So, if the gravitational effects originate from the center of mass of the explosion, and the gamma rays originate from some kind of Big Bang-like recombination phenomenon happening a few hundred million km away from the center of the expanding shell, that would easily account for the difference.
I'm not a physicist, but I did do the 101 course a long time ago. I read "That constrains the speed difference to 1.6e-18 m/s" as "we measured as accurately as we could, and if they do differ, they must differ by this amount or less, which could just be the tolerances of our experiment"
In other words, there's always a confidence interval, the trick is to measure it and minimise it: The speeds could be identical numbers, but what was measured was an either no or a very small difference. Larger differences have been ruled out. Identical numbers are _suggested_.
What is observed is the delay between the two signals. Fractional speed difference is calculated from it. As I understand, there is little chance that the 2 second delta isn't real.
OK, but there are other possible explanations besides fundamental physics: either the order of events at the source, or the effects of the interstellar medium along the way.
Basically, yes: The speed of both gravity waves and light waves is limited by c, the speed of light in vacuum.
But actually, no, because the light is not in a vacuum - it's ricocheting out from the center of a star, and bouncing through the interstellar medium (which is incredibly sparse; very nearly a vacuum: but there's an awful lot of it between these events and us).
This is also the mechanism behind neutrino detectors. When a star's core goes supernova, it releases a cataclysm of neutrinos which pass through the upper layers of the star almost unaffected. The light and radio waves are still bouncing around trying to get to the surface of the star, and the blast wave is still physically propagating much slower than the speed of light, but the neutrinos are long gone. That gives scientists a short time period to point their telescopes in the right direction!
Yes and this is different in as much as LIGO / gravitational waves gave us the 'tip off' that the light was incoming, we fortunately had a satellite that captured that.
It's a whole other information stream we are just learning how to use, basically with using gravitational waves we are at the stage Galileo was at with light. Very early, very low res but enough to give us massive new discoveries.
http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...
http://iopscience.iop.org/article/10.3847/2041-8213/aa910f/m...
We run a network of 20 telescopes that are triggered remotely (mostly via API). Because of our ability to schedule observations quickly, we were the only ones able to observe the peak luminosity of the kilonova.
Disclosure: I am a software engineer at LCO.