• LIGO sensitivity compared with the human eye

    From Jos Bergervoet@21:1/5 to All on Sat Jan 12 11:01:48 2019
    Recently in another newsgroup (nl.wetenschap) the question
    came up of LIGO's sensitivity compared to the human eye.

    a) LIGO can (easily) see a source at one billion light years
    distance which emits the energy of 3 solar masses in 1 second
    (like the black hole mergers!)

    b) The eye can (also quite easily) see a source at 10 lightyears
    distance emitting the energy of 0.1 solar mass in 10 billion
    years (like some of the sun-like nearby stars, burning 10% mass
    in their entire lifetime).

    Comparing the energy flux received:
    - In case a) source power (energy per second) is 1e19 x higher.
    - 1/r^2 attenuation with distance is 1e16 x larger for a).

    So it seems that LIGO receives 1000 times stronger energy flux
    and therefore the eye is 1000 times more sensitive than LIGO.

    Still, since we are playing with many orders of magnitude here,
    the difference is remarkably small. Also the cases compared are
    not the absolute sensitivity levels of the two systems, both
    LIGO and the eye can see somewhat weaker signals. So the simple
    estimate here might not completely settle it. Should anything
    be adjusted in the comparison above?

    (And if not, when will LIGO's successors surpass the eye?)

    --
    Jos

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  • From Michael Asherman@21:1/5 to All on Sat Jan 12 23:57:23 2019
    [Moderator's note: Quoted text moved to top, and trimmed. -P.H.]

    a) LIGO can (easily) see a source at one billion light years
    distance which emits the energy of 3 solar masses in 1 second
    (like the black hole mergers!)

    Does the figure of 3 solar masses include only gravitational energy, or is
    it total energy including electromagnetic?

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  • From Thomas 'PointedEars' Lahn@21:1/5 to Michael Asherman on Sun Jan 13 16:35:48 2019
    Michael Asherman wrote:
    [Moderator's note: Quoted text moved to top, and trimmed. -P.H.]
    a) LIGO can (easily) see a source at one billion light years
    distance which emits the energy of 3 solar masses in 1 second
    (like the black hole mergers!)

    Does the figure of 3 solar masses include only gravitational energy, or is
    it total energy including electromagnetic?

    By contrast to the merger of neutron stars (e.g. GW170817), there is no electromagnetic (EM) energy coming from the merger of black holes (BHs).

    *That* they do NOT emit EM radiation is why they are called *black* holes.

    The result of such a merger is also a BH whose mass is necessarily
    larger than each of the progenitor masses; therefore its Schwarzschild
    radius is larger, too (r=9B = 2 G M/c²), and any EM radiation produced
    in the merger is then already beyond the event horizon of the resulting
    BH.

    The number of 3 M probably refers to the first event detected by
    Advanced LIGO, GW150914, where two BHs of masses 29 M_sun and 36 M_sun
    merged to form a BH of 62 M_sun (instead of 65 M_sun), emitting the *equivalent* of 3 M_sun (this is a *mass*, NOT an energy) in gravitational energy (the energy is E = 3 M_sun c instead). But that was NOT emitted
    in 1 s, but in \_a fraction of a second_/, precisely 20 ms = 0.02 s.

    <https://www.ligo.caltech.edu/page/press-release-gw150914> <https://arxiv.org/abs/1602.03837>

    <https://www.ligo.caltech.edu/page/press-release-gw170817>

    --
    PointedEars

    Twitter: @PointedEars2
    Please do not cc me. / Bitte keine Kopien per E-Mail.

    [Moderator's note: Some 8-bit characters converted to more friendly
    7-bit printable ASCII form. -P.H.]

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  • From jacobnavia@21:1/5 to All on Sun Jan 13 15:45:50 2019
    Le 12/01/2019 =C3=A0 12:01, Jos Bergervoet a =C3=A9crit=C2=A0:

    The human eye can detect a SINGLE PHOTON...

    See:

    Direct detection of a single photon by humans https://www.nature.com/articles/ncomms12172

    That is the absolute minimum I would say.

    Now, what is the quantum particle of gravity???

    Well, better leave that question open isn't it?

    :-)

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  • From Steve Willner@21:1/5 to Jos Bergervoet on Tue Feb 5 10:50:26 2019
    In article <5c39c814$0$22346$e4fe514c@news.xs4all.nl>,
    Jos Bergervoet <bergervo@iae.nl> writes:
    Recently in another newsgroup (nl.wetenschap) the question
    came up of LIGO's sensitivity compared to the human eye.

    This is a hard comparison to make. Not the least of the problems is
    that LIGO measures "strain," which falls off only linearly with
    distance, not with distance squared. That means improving LIGO
    sensitivity by a factor of 2 increases the volume surveyed by a
    factor of 8.

    I suppose one could pick some distance and ask what energy release is
    needed to produce a detectable signal in each case. However,
    efficiency of energy conversion is also relevant. When black holes
    merge, all the energy that doesn't end up in the final object goes
    into gravitational waves. By contrast, a supernova emits only a tiny
    fraction (about 10^-4 from unreliable memory) of its energy in
    visible light.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

    [[Mod. note -- Another very important difference in comparing LIGO/Virgo sensitivity with that of any optical detector (e.g., the human eye) is
    that the optical detector absorbs the indident photons, whereas LIGO/Virgo
    is 99.9999...% transparent to gravitational waves. That is, only a very
    tiny fraction of an incident gravitational wave's energy is transferred
    to LIGO/Virgo -- the vast majority (much more than 99.999999%) passes
    right through LIGO/Virgo (and right through the Earth).

    One analogy I've read is that building a gravitational-wave detector
    like LIGO/Virgo is like building a radio antenna out of wood. So it's
    only by incredibly sophisticated optical and mechanical engineering that LIGO/Virgo can detect gravitational waves at all.
    -- jt]]

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