Fermi telescope poised to pin down gravitational wave sources

April 18, 2016 by Francis Reddy, NASA's Goddard Space Flight Center
This image, taken in May 2008 as the Fermi Gamma-ray Space Telescope was being readied for launch, highlights the detectors of its Gamma-ray Burst Monitor (GBM). The GBM is an array of 14 crystal detectors. Credit: NASA/Jim Grossmann

On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because are expected to merge "cleanly," without producing any sort of light.

"This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we'll need to see more bursts associated with gravitational waves from black hole mergers," said Valerie Connaughton, a GBM team member at the National Space, Science and Technology Center in Huntsville, Alabama, and lead author of a paper on the burst now under review by The Astrophysical Journal.

Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi's GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun's mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its "ringdown" phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA's Ames Research Center. Credit: Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC)

With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves.

"With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB," said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. "There is an incredible synergy between the two observations, with gamma rays revealing details about the source's energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event." He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.

Fermi's GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections. Credit: NASA's Goddard Space Flight Center
"That's a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that's what our instrument is designed to do," said Eric Burns, a GBM team member at the University of Alabama in Huntsville. "A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack."

Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst's likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst's position.

The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi's view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM's detectors, or one bright enough to be seen by Fermi's Large Area Telescope, even greater improvements are possible.

The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

Albert Einstein predicted the existence of in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

Explore further: Did a gamma ray burst accompany LIGO's gravity wave detection?

More information: "Fermi GBM Observations of LIGO Gravitational Wave Event GW150914," V. Connaughton et al., 2016, submitted to the Astrophysical Journal: arxiv.org/abs/1602.03920

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tblakely1357
5 / 5 (4) Apr 18, 2016
Anyone else curious on how they came up with a '0.2%' figure? I could have gone with an 'extremely unlikely coincidence' declaration but '0.2%' is a pretty precise number.
Captain Stumpy
4.1 / 5 (17) Apr 18, 2016
Anyone else curious on how they came up with a '0.2%' figure? I could have gone with an 'extremely unlikely coincidence' declaration but '0.2%' is a pretty precise number.
@tblakely

start with here
The rate of detection of short hard transients in the GBM data
http://arxiv.org/...20v3.pdf

cantdrive85
1.5 / 5 (23) Apr 18, 2016
I was unaware Fermi was capable of seeing unicorns, fancy that! Look at that, the pseudoscientists have peers, and they decided to write a paper about their mumbo jumbo.
marcush
3.9 / 5 (29) Apr 18, 2016
cantdrive85 If you don't want to read about science why go to this site?
cantdrive85
1.7 / 5 (17) Apr 18, 2016
I enjoy real science thoroughly and why I'm here, sadly this pseudoscientific mumbo jumbo is what is offered up.
Mike_Massen
2.7 / 5 (24) Apr 18, 2016
One sentence cantdrive85 says
I enjoy real science thoroughly and why I'm here
1. Ok, I'll bite, give us your top 3 examples of what you define and have seen here as "real science" ?

2. Tell us also about your interpretation of the "Scientific Method" in context of 1 ?

3. Tell us also about the "Balance of Probabilities" & Math upon which 1 & 2 are based ?

cantdrive85 says
, sadly this pseudoscientific mumbo jumbo is what is offered up
4. Tell us please how you discriminate "pseudoscientific" from "real science" assuming you have or can find tangible foundation for your beliefs as related to 2 & 3 ?

One liners cantdrive85; doesn't help your case, doesn't lend you credibility, muttering from the sidelines without examples, math, logic or even some worthy rationalisation just waste's everyone's time & obfuscates achievements which have made the "Scientific Method" a very useful basis for Engineering offering immense tangible benefits.
Andrew Palfreyman
2.6 / 5 (10) Apr 19, 2016
The time delay between the two receptions is interesting. Both set of waves (grav, gamma) are going to traverse the same path, so it's a true delay at the source location. Perhaps the gammas are emitted as a result of some sort of "knock-on" effect. Recall the monumental power output of that black hole merger. It isn't a big stretch to imagine that this could act as a trigger for some sort of gamma event in the vicinity.
obama_socks
2 / 5 (8) Apr 19, 2016
I'm gonna wait for the next ones to hit and be detected by the new toys before I put much faith in all the hullabaloo and back slapping going on. How long until the next one? Was only ONE wave and ONE GRB generated, or can we expect more?
And what if it IS only ONE and any subsequent GW and GRB will be traveling from another location of the Universe from yet another pair of Black Holes that LIGO can't detect because of the angle or it has been intercepted by another body?
Sheeesh it's enough to drive a man to drink.
Mike_Massen
2.1 / 5 (18) Apr 19, 2016
obama_socks (OS) says
.. before I put much faith in all the hullabaloo and back slapping ..
Surely not about faith its the core of Science re material properties (detectors) in conjunction with Math (probability) ie Not just another event but, balance of probabilities combination of both instruments configuration didn't detect anything else.

Given energy changes offer wavelike properties emission/absorbance at *all* scales, its therefore very likely, given large number of massive objects observed, there will be more.

OS asks
.. expect more?
Obviously can't say when but, balance of probabilities indicate there will be many & over very long periods too.

OS oddly
.. intercepted by another body?
Beg pardon - are you implying a GW will be attenuated sufficiently well ie 'absorbed' thus energy too low for detection ?

Clearly helpful we have more LIGOs & at diverse orientations/locations

OS
..drive a man to drink
Deducing your ideas ;-)
antialias_physorg
5 / 5 (6) Apr 19, 2016
Just shooting the breeze here: Maybe we are we seeing energy densities large enough for particle/antiparticle creations (and annihilation...i.e. a burst of Hawking radaition)? Anyone have a source for the energy densities involved?
Mike_Massen
1.9 / 5 (17) Apr 19, 2016
antialias_physorg offers
.. Maybe we are we seeing energy densities large enough for particle/antiparticle creations ..
Hmm, reminds me of thought when I first heard the GW news, what effect might be as GW's ostensibly from different but massive sources interfere whilst passing through a stars core & the effect it might have (some time later) re sun spots, solar flares etc... Also how it might affect accretion disk of another black hole - could inspire even more search criteria permutations through masses of data already from radio astronomy & more when SKA fully operational ?

antialias_physorg asked
Anyone have a source for the energy densities involved?
Me too please ?

Normally take a stab myself on google scholar but, way too busy & tedious anyway as so many false leads, might ask on quora.com, a smarter nicely moderated site unlike here with idle prejudice/nastiness dragging tone down, more Physics please

Cheers; merlot, jarlsberg, ginger & almonds
antialias_physorg
5 / 5 (6) Apr 19, 2016
Hmm, reminds me of thought when I first heard the GW news, what effect might be as GW's ostensibly from different but massive sources interfere whilst passing through a stars core & the effect it might have (some time later) re sun spots, solar flares etc

For that the affected star would have to be very close

Quick "back-of-the-envelope" calculation:

Effect at roughly 10^9 ly distance was 10^(-18)m (roughly 1 thousandth of a proton width)
Effect is inversely proportional to distance squared.

So at 1 ly distance it would cause a displacement of 1 meter. Which would be uncool for anything living at that distance, but not much of an issue for a star.

A minute, temporary phase shift in the star's output as seen from Earth (no energy shift, though) *might* be observable. But that would be very hard to detect as stars don't produce phase-coherent radiation.
Mike_Massen
1.8 / 5 (16) Apr 19, 2016
antialias_physorg offers
Effect at roughly 10^9 ly distance was 10^(-18)m (roughly 1 thousandth of a proton width)
Effect is inversely..
Too true of course but, I'm focused on key effect on Sol's core & potential delay recognising effects subsequently. Core only generates ~275 W/m^3 (despite density ~ 150g/cm^3) multi-path nuclear fusion via probabilistic tunneling - ie less power than human body's mere chemistry.

I say interfering GW from 2 large sources interfering waves pass through core shift power equilibria probabilistic base, one can arrange math to work out how far away for possible 0.1-0.2% power shift, because that will, perhaps cause variant perturbation patterns re neutrinos (Hmm recent GW correlation ?) & millennia later; sunspots & chaotically to solar flare inflections

antialias_physorg says
A minute, temporary phase shift in the star's output as seen from Earth (no energy shift, though)
I'd expect shift but with correlation woes...
antialias_physorg
5 / 5 (7) Apr 19, 2016
More back-of-the-envelope stuff:

The gravitational wave observed lasted 20ms and travels at c. Which makes for a disturbance on the order of 6000km. Again, seemingly large but really not much compared to the size of a star (Roughly on the order of 1% of the most common stellar diameter).

The heat/radiation generated in the core also isn't immediately visible on the outside. That may take a lot of time to reach the surface. Depending on what textbook you look at this ranges from thousands to a million years (due to the very short mean free path of photons inside the sun). That's plenty of time to average out any 'kinks' in energy production during those few seconds the gravitational wave travels through a sun
Mike_Massen
1.8 / 5 (16) Apr 19, 2016
antialias_physorg (AP) says
.. disturbance on the order of 6000km. Again, seemingly large but really not much compared to the size of a star..
Sorry not relevant re perspective of my point starting at other end re possible 0.1-0.2% core power shift

Anyway disturbance still passes through *whole* core (?) or do you imply it peters out at short range 6000Km ie attenuated so it's effect 'rolls off', if so then why should it ?

AP
.. isn't immediately visible on the outside
Sure, ie millennia as I said but, review my point please

AP
.. average out any 'kinks' in energy production during those few seconds the gravitational wave travels..
Of course, ie why I'm curious re neutrino detection correlation as neutrinos negligibly delayed, core to corona, hence is there any info re neutrino detectors that might offer further perspective re core, even seconds after core density wave reflections, all core dynamics, consequences, so called 'Freak wave'/QM etc ?
antialias_physorg
5 / 5 (7) Apr 19, 2016
Hmmm..thinking a bit more on this: from this one could actually get an energy density

According to the paper on the gravitational wave about 3 solar masses in energy were radiated away.
3 solar masses represent roughly 2 x 10^47 Joules (vie E = mc^2)

If we take the 20ms as the duration of the wave then that would equal a sphere of 6000km radius (the volume of the merged black hole at the center is neglected since this is tiny by comparison at roughly 10km radius) - so we get a volume of about 10^21 m^3

Which gives us an energy density of a whopping 2 x 10^26 J/ m^3 (if I didn't mangle a few decimal points along the way)..and that is with an uniform distribution. The peak energy density may be quite a bit larger than that with a non-uniform distribution.

Now this is assuming a flat spacetime, which is most definitely NOT what we are dealing with at this point, but still...wow...that's one hell of a lot of energy in one small space.

Mike_Massen
1.5 / 5 (15) Apr 19, 2016
antialias_physorg (AP) replies
If we take the 20ms as the duration of the wave then that would equal a sphere of 6000km radius
Sorry disagree, not spherical as BH very distant & energy radiates (expanding) spherically (inv sq) so passage through Sol's core would be a simple cone albeit both radii almost identical as ~1GLyr

AP adds
.. an energy density of a whopping 2 x 10^26 J/ m^3
Okie, will trust your calcs for mo, many tabs :/

AP
..but still...wow...that's one hell of a lot of energy in one small space
Getting bang onto my point, that energy passes through Sol's whole core& rapidly, given probabilistic nature of multi-path nuclear fusion tunneling & its 'normal' meta-stable high inertia equilibria - you then add huge burst of gravitational energy increasing perturbation QM effects resulting in heaps of (comparatively minor at first) shifts in fusion rate summing chaotic core density wave interference therefore Δ neutrinos detection relevant
Mike_Massen
1.5 / 5 (15) Apr 19, 2016
@antialias_physorg (AP)
To clarify, BH event being ~1GLyr away means energy fluctuation as far as Sol's core sees it is a cone thats far more like a rod ie circular diameter with length appropriate to the 20mS passage but, it will pass through all volumes whether core through to full Sol's diameter & beyond

AP did say
.. assuming a flat spacetime, which is most definitely NOT what we are dealing with at this point, but still...wow...that's one hell of a lot of energy..
Brings up another issue.

Won't the higher gravitational field of Sol's core further constrain or rather compress that fluctuation cross section as it approaches core from corona down as a funneling effect thus, having even more perturbation effects upon core's equilibria ?

Is one more reason why neutrino rates of keen interest either way, ie If no change then not enough Δ energy to influence core fusion rate (needs to be over >> 20mS) but, if is a change, then what Δ fusion rate + or -
antialias_physorg
5 / 5 (5) Apr 19, 2016
Getting bang onto my point, that energy passes through Sol's whole core

As noted the actual energy that a star that is 1ly away (much less 1.3 bn ly away, like our sun) experiences would be minute. There's no 'huge bursts' of gravitational energy, here. energy density goes with 1 / distance squared.

At 1 ly distance we're already talking energy densities on the order of 0.01 milliJoule per cubic meter energy density in the gravitational wave. For 2 seconds while it travels through the star. That isn't going to phaze a star. (actually none of this energy is deposited in the star at all since gravity isn't attenuated by mass)
Protoplasmix
5 / 5 (11) Apr 19, 2016
Sorry disagree, not spherical as BH very distant & energy radiates (expanding) spherically (inv sq) so passage through Sol's core would be a simple cone albeit both radii almost identical as ~1GLyr
I think you misunderstood what he's saying. 3 solar masses of energy in the form of gravitational wave radiation propagates outward from the merger. If the event lasted 20 ms (or all that energy was emitted during the last 20 ms prior to merging) then it would have propagated outward to a distance (equals rate times time) of (300,000 km/s)(0.020 s) = 6000 km. Your point about 'not spherical' 'expanding spherically' passing through the sun 'as simple cone' hurts my brain, but I'll get over it.
Mike_Massen
1.8 / 5 (16) Apr 19, 2016
antialias_physorg (AP) says
There's no 'huge bursts' of gravitational energy, here. energy density goes with 1 / distance squared
O course already stated inv sq, sigh...

I used 'huge' qualitatively upon base Δ fusion tunneling, its *why* indication of neutrino rates is relevant/interesting as points to confirmation within standard model or otherwise, I like to see if there is *any* correlation statistically meaningful but, with timing issues ?

AP says
..none of this energy is deposited in the star..
No Eg deposited in LIGO & Sol much more massive (Eg feynman test)

Didnt make myself clear, QM probabilistic tunneling influenced by Δ energy local to N.reactions even mere p+ dia - eg comparatively dense core & large volume already is subject to summed perturbation chaotic effects Eg density wave reflections, thus all contributory effects summed must be through QM, neutrinos are an effective instrument of Δ fusion rate, data then of keen interest, cheers
antialias_physorg
5 / 5 (9) Apr 19, 2016
O course already stated inv sq, sigh...

Well, your posts are hard to read 'cause t'r fl of abbv & stf u kno?
I'm sure you know what you want to write - but everyone else just has to guess.

It would add no end of quality to your posts if you were to use english (and proper sentence structure.)

E.g. this:
QM probabilistic tunneling influenced by Δ energy local to N.reactions even mere p+ dia - eg comparatively dense core & large volume already is subject to summed perturbation chaotic effects Eg density wave reflections, thus all contributory effects summed must be through QM, neutrinos are an effective instrument of Δ fusion rate, data then of keen interest,

...is just a total garble of semi-scientific terms. No idea what you're actually trying to say. It's a waste of time for you to type because no one can read/understand it..
Mike_Massen
1.8 / 5 (16) Apr 19, 2016
Protoplasmix offers
I think you misunderstood what he's saying
I see your point, it did trouble me a tad, I see he just encompassed it to give weight to sense of scale. I'm focused on the QM overall effect Δ energy on core fusion re neutrinos.

Protoplasmix said :-) Your point about 'not spherical' 'expanding spherically' passing through the sun 'as simple cone' hurts my brain, but I'll get over it. lol, glad you will get over it, artistic license has its joys.

Of course (more so for peripheral onlookers other than us), distribution expands spherically re inv square law with an expanding 20mS as if a 'shell' but, by time energy sees Sol's core it can only see it as a cone both radii almost equal so more like a rod as far as transference to the cores cross section integrated over that 20mS.

Anyway, I'm curious where the data might be collated/brought to account re neutrino flux at that time & for much longer than the 20mS re any secondary effects.
Mike_Massen
1.5 / 5 (15) Apr 19, 2016
antialias_physorg asks
QM probabilistic tunneling influenced by Δ energy local to N.reactions even mere p+ dia - eg comparatively dense core & large volume already is subject to summed perturbation chaotic effects Eg density wave reflections, thus all contributory effects summed must be through QM, neutrinos are an effective instrument of Δ fusion rate ..
Apologies, keen to fit 1 post, thought you're into nucleonics so short hand

- QM Quantum mechanics
- Interactions subject to QM probability key factors
- Sol's fusion by tunneling processes ie QM
- Difference in energy (passing GW) may affect base fusion reaction rate
- p+ proton diameter
- Sol's core large but subject to many perturbation effects with chaotic potentials thus shift up or down to different equilibria ultimately affecting overall output
- Densities waves propagate, reflect off different layers from core out
- All summed through QM
- Neutrinos indicator of fusion rate as an instrument

Cheers
antialias_physorg
5 / 5 (5) Apr 19, 2016
Sorry. I still have no idea what you are trying to say. I'll drop out of this.

Proto: Thanks for clearing my posts up. Yes, that was exactly what I was trying to say.
Protoplasmix
5 / 5 (9) Apr 19, 2016
Sorry. I still have no idea what you are trying to say. I'll drop out of this.
He seems to be suggesting gravitational waves can affect things at the atomic scale. @Mike – you need a quantum theory of gravity to properly frame such questions, and there are a few, like loop quantum gravity – did you have a specific one in mind? If not, how do your questions compare to them?
Proto: Thanks for clearing my posts up. Yes, that was exactly what I was trying to say.
I thought you said it pretty clearly. It's certainly a phenomenal amount of energy in a small volume as it begins radiating outwards.
antialias_physorg
5 / 5 (3) Apr 19, 2016
It's certainly a phenomenal amount of energy in a small volume as it begins radiating outwards.

I wonder how one could calculate the actual volume as we're talking a about a gravitational wave which is stretched/compressed space(time). But if I'm not mistaken then the integral over all the stretching in the wave is zero, right?
So it might turn out that the average energy density calculated above is roughly correct.

Anyone know what the energy densities in a collider are for comparison?
Mike_Massen
1.5 / 5 (15) Apr 19, 2016
Protoplasmix offers
.. suggesting gravitational waves can affect things at the atomic scale
Not needed at all, key is Feynman's gravity wave thought experiment
1 https://en.wikipe...argument

Protoplasmix says
... need a quantum theory of gravity to properly frame such questions..
Not needed (yet), please review above in conjunction with this example of a macro (variance) wave phenomena, which also applies at QM scale
2 https://en.wikipe...ckground

@antialias_physorg
Factor in tunneling is Σ energy influencing equilibria. To explore it & upon an evidentiary base to craft a hypothesis, useful to obtain as much neutrino data at highest resolutions correlated with time (& shortly thereafter) of LIGO detection.

As to reason for interest, investigating a potential finer aspect of variance driving change impacting fusion tunneling rates ie by combining 1 & 2 probabilistically at QM scales

Cheers :-)
Mike_Massen
1.5 / 5 (16) Apr 19, 2016
antialias_physorg (AP) says
.. gravitational wave which is stretched/compressed space(time)
Understand your view but, observed effects in respect of reference frames doesn't mean space being stretched/compressed is proven, only energy variance observed.

Eg. Two magnets & appropriate sensor all equidistant, suddenly move one magnet far away, sensor would only register energy disturbance, LIGO paradigm same.

ie. See context of feynman thought experiment, there's definitely compression/tension of matter appearing to imply space is stretched/compressed but, not proven ie careful re tautology...

AP asks
... the integral over all the stretching in the wave is zero, right?
I expect so

AP .. average energy density calculated above is roughly correct Maybe, would need to review how energy at source determined.

AP
.. energy densities in a collider are for comparison?
But, what basis would you proportion them re scale for effective comparison ?
Protoplasmix
5 / 5 (8) Apr 19, 2016
@Mike – how much mass does that stick need to have, or be fixed to, or attached to, in order to prevent the stick from moving together with the bead as the wave passes by? If you drop the stick (and whatever it's attached to) and the bead from the same height at the same time, which hits the ground first? It seems to me the energy that's imparted into the gravitational field stays in the gravitational field – nothing absorbs it or reflects or scatters it. Maybe I'm not thinking about it properly.

The rogue wave link is cool. The very first science runs of LIGO (back in '05 iirc) put strong constraints on the gravitational wave stochastic background.
Protoplasmix
5 / 5 (7) Apr 20, 2016
Late edit – if the length of the stick is much greater than the wavelength you could say both ends keep the middle fixed while the bead moves. I shouldn't have questioned Feynman. There's obviously an interaction between GW radiation and the matter in it (or LIGO wouldn't work), but I think you need quantum gravity and numerical relativity using something like ADM mass to produce a realistic picture of how it might affect subatomic processes. Does any particle ever follow a path other than a geodesic?
Mike_Massen
1.6 / 5 (14) Apr 20, 2016
Protoplasmix (Px) says
.. if the length of the stick is much greater than the wavelength you could say both ends keep the middle fixed while the bead moves
You imply there's some tuned effect, like an antenna dipole etc ?

If so No. Evidence LIGO hasn't any tuned aspect, long tunnels etc as economically practical within best physics constraints re structure size to manage bulk noise influences eg crust/strata shifts at inopportune times etc

Px adds
.. obviously an interaction between GW radiation and the matter in it (or LIGO wouldn't work)
Indeed, GW perturbs all relative positions, lasers :-)

Px says
.. you need quantum gravity..
Only if viewing GW as space/time compression alone.

I don't, instead see it as delta gravity per se' summing to matter encountered as it passes through (gravity has 'mass') ie adds/subtracts local gravitational potential between masses as it passes, its why affects LIGO therefore Sol's fusion rate too

analogy continued
Mike_Massen
1.6 / 5 (14) Apr 20, 2016
@Protoplasmix
First pre-requisite, so I'm not accused of contextual short hand, sorry don't know you...
Observe:-
"Mass generates gravity & gravity [definitely] influences mass"
is accepted at core level of all gravitational phenomena.

Therefore this can (and I deduce it) does also mean - in preparatory philosophical terms

"Mass creates gravity which therefore means (Δ) gravity results in (Δ) mass"
however, we don't see a mass created only a change (really as weight), we see the equivalent effect (by simple addition) & thus best restated more appropriately as:-
"Mass creates gravitational potential so gravity creates a change in mass-effect as weight"

Instead of an acoustic analogy, think it best I pursue a thought experiment which I expect can be rationalised independently

Unbound free space; 2 equal masses m1, m2, distance d apart, radiative transfer repulsion balanced by gravitation ie static; nil orbit, nil angular momenta, gravity wave approaches m1.

cont
Protoplasmix
5 / 5 (10) Apr 20, 2016
You imply there's some tuned effect, like an antenna dipole etc ?
Um, no. I wasn't thinking about it properly, in several ways. The wavelength can be very short, as in a "chirp," and the stick can be made arbitrarily long enough to suffice for the point that Feynman was making, which is that gravitational waves are real, they have energy, and they can impart energy to matter.

But do they affect stellar fusion? A strong field would tear apart a star, but in the weak field it would require a major undertaking just to detect any waves. As with aLIGO.

And neutrinos are incredibly hard to detect even when you aim a beam of them directly at a detector. How many additional ones might be produced as a wave passes through a stellar core, and how many stars did GW150914 pass through on the way here?
compose
Apr 20, 2016
This comment has been removed by a moderator.
Protoplasmix
4.7 / 5 (15) Apr 20, 2016
Those aren't problems, Zeph, and you know it. They're typical crackpot complaints just like the ones we see here all the time. Are you getting lazy? Old? What?
Mike_Massen
1.6 / 5 (14) Apr 20, 2016
Protoplasmix (Px)asked
But do they affect stellar fusion?
When I finish m1,m2 point to conclusion hope it will be clear. It adds equivalent mass effect (weight) to each particle, in any case summed over immense volume cyah tomorrow, busy.

Tunneling is probabilistic & activation potentials depends on flux, may not need much energy to shift..

Px says
As with aLIGO
Well 4Km's minimal probabilism low density vs millions of cubic kms with high probabilism & very high density ie high mass therefore large summing (integration) potential, my first guess is shifts fusion equilibria ~ 0.1-0.2% overall including secondary effects

Px adds
. neutrinos are incredibly hard to detect even when you aim a beam of them directly at a detector
Not many from a beam, as I said need more info & with more resolution in progress long term

Px asked
... how many stars did GW150914 pass through on the way here?
Huh, you mean in line of sight exactly dead-on chirp ?
eachus
5 / 5 (2) Apr 20, 2016
The time delay between the two receptions is interesting. Both set of waves (grav, gamma) are going to traverse the same path, so it's a true delay at the source location.


Not true. Gravitational waves travel at the speed of light in a vacuum. Gamma rays travel at the speed of light. But there almost certainly is a lot of (interstellar and intergalactic) gas and dust between Earth and the gamma ray source. Assuming they are from the same source, we need much more data to decide whether or not the gamma burst preceded or followed the merger at the end of the gravitational wave event. Maybe next time, especially if the Italian aVIRGO observatory is operational. (Four detectors is even better, it cuts the possible source position to one. In addition to aVIRGO, detectors are now funded in Japan and India. GEO600 in Germany is operational, but is not as sensitive.)
Da Schneib
4.5 / 5 (8) Apr 20, 2016
QM probabilistic tunneling influenced by Δ energy local to N.reactions even mere p+ dia - eg comparatively dense core & large volume already is subject to summed perturbation chaotic effects Eg density wave reflections, thus all contributory effects summed must be through QM, neutrinos are an effective instrument of Δ fusion rate, data then of keen interest,
No idea what you're actually trying to say.
Errr,

QM probabilistic tunneling is influenced by delta-energy (i.e. change in energy) local to neutron reactions and even merely by the proton diameter. For example, in the comparatively dense core & large volume in the Sun, these already are subject to summed perturbation leading to chaotic effects within the core, for example density wave reflections. Thus, all contributory effects must be summed through QM; neutrinos are an effective instrument of delta in the fusion rate, and neutrino data are then of keen interest.

Did that help?
Mike_Massen
2.1 / 5 (16) Apr 20, 2016
Da Schneib with kind translation
QM probabilistic tunneling is influenced by delta-energy (i.e. change in energy) local to neutron reactions and even merely by the proton diameter..
Did that help?
Indeed tah, you've probably noticed one can either get accused of over-simplifying or talking over the top, to manage this I address the person according to my perception of their understanding, I infer antialias_physorg had more pressing matters...

Will be adding more of the m1, m2 thought experiment later & to follow from "neutron reactions", it should be noted the activation energy for proton to neutron fusion is by far the lowest in Sol's core - this is where the 'weight' fluctuation via passing gravity wave (GW) might be enough to shift equilibria by the ~ 0.1-0.2% I imagine, of course other than neutrino's as best indicator we won't know about it for many millennia, shurg

Suggests, could Sol's lower output recently be due to less average GW influence long ago
Enthusiastic Fool
2.6 / 5 (10) Apr 22, 2016
So I took AA's numbers and found an inverse sq calculator because I'm lazy and "worked" it out to 16m of displacement at a quarter of a light year. I moved on down to 8/525600(minutes in a year) to figure out what fraction of a lightyear 1 AU was. That got me 4.33e9 meters of displacement at 1AU if I did it correctly. With Earth having a diameter of ~12.7 million meters that would put Earth beside itself with sadness at that distance.
Mike_Massen
1.5 / 5 (15) Apr 22, 2016
Enthusiastic Fool (EF) has me intrigued & I like it :-)
.. took AA's numbers .. and "worked" it out to 16m of displacement at a quarter of a light year. I moved on down to 8/525600(minutes in a year) to figure out what fraction of a lightyear 1 AU
Um, which numbers initial input:-

1. Solar masses equiv 2 x 10^47 J ?
or
2. energy density 2 x 10^26 J/m^3 ?

EF adds
.. got me 4.33e9 meters of displacement at 1AU if I did it correctly. With Earth having a diameter of ~12.7 million meters that would put Earth beside itself ..
Maybe um but, what overall transfer function/algebra (& assumptions) you relied upon to translate; energy J OR cubic density J/m^3 ( from source as sphere or effective point ?) to displacement in meters - which I expect has to be in relation to event origin only not re Sol ?

Will peek after formulating next part of my post, hmm, my brain in odd stall mode

Wow & yes suggests massive destructive acceleration over a tiny 20ms chirp !
Enthusiastic Fool
3.4 / 5 (10) Apr 22, 2016
@MM, neither the energy density nor the solar masses. I just extrapolated off his first post with this bit:
Quick "back-of-the-envelope" calculation:
Effect at roughly 10^9 ly distance was 10^(-18)m (roughly 1 thousandth of a proton width)
Effect is inversely proportional to distance squared.
So at 1 ly distance it would cause a displacement of 1 meter. Which would be uncool for anything living at that distance, but not much of an issue for a star.
Mike_Massen
1.6 / 5 (14) Apr 23, 2016
Enthusiastic Fool (EF) replied
@MM, neither the energy density nor the solar masses. I just extrapolated off his first post..
Ok I see approach fair enough, I was imaging provenance first principles re
https://en.wikipe..._gravity

ie Event simplified to mass held in field & energy calculated as = mgd & with Gauss' equivalent point ref

Where EF used antialias_physorg's (AP) Back of Envelope (BoE)
Effect at roughly 10^9 ly distance was 10^(-18)
Which I expect gleaned from LIGO calcs

Minor problem is the 20mS, I can't see a LIGO correction re smear, ie Maybe began shorter or longer (GR), lengthened by path gravitational attenuation from other (massive) bodies.

Also given huge disparity between Earth & pair BH mass + and huge distance you'd need to factor in Netwon's formula & factor Lorentz Δ t stretch at source BH, hmm tricky, need BoE too

:-) EF's BoE based on AP's BoE & likely fairly close
retrosurf
3 / 5 (4) Apr 24, 2016
And neutrinos are incredibly hard to detect even when you aim a beam of them directly at a detector.


Yeah, that's what I'm here to say. I think it's long shots all the way, just from an experimental standpoint.

Even the very best detectors work at a little over a single qualified event per hour. I don't think a real-time perturbation in neutrino production of the order you describe is possible with current detectors, not even by a long shot.

Perturbation of equilibrium of the solar core's steady-station neutrino production is a tough one, too. I don't know if earth has enough detectors operating continuously to detect that under any circumstances. We might detect something gross, like a stellar core shutdown, but a small change in neutrino production would likely sail right through our heads.
Mike_Massen
1 / 5 (12) Apr 30, 2016
retrosurf confirmed
I don't know if earth has enough detectors operating continuously to detect that under any circumstances
Indeed this is one reason of many its worth adding to that instrumentation base.

retrosurf added
We might detect something gross, like a stellar core shutdown, but a small change in neutrino production would likely sail right through our heads
This is one issue I have addressed elsewhere, it may not be that small "as a burst" and has overtones as secondary bursts in respect of shock wave reflections from disparate density boundary layers, yet one more reason we can use more neutrino detectors at higher resolution with far less latency.

ie. Being able to correlate various solar events adds to information base re data from the LIGO series, which I also read is expanding.

From what I have seen on recent micro-electronics on another forum, it might just be possible to build 100's of LIGO like detectors all in the size of a car...

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