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Posted by Ken S. Tucker on March 13, 2007, 2:54 am
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On Mar 12, 4:24 pm, h...@spsystems.net (Henry Spencer) wrote:
>
> >> In fact, it's not just stars that they can detect that way -- if you check
> >> out <http://www.nd.edu/~srhie/MPS/97-BLG-41/97blg41.html>, you'll see the
> >> light curve of a microlensing event where the passing object seems to be a
> >> binary star *with a Jovian-sized planet*...
>
> >Thanks for the refs. That the gravitation of a Jovian
> >can operate as a poorly focused lense with a long
> >focal length is reasonable, but I'm uncertain to it's relevancy.
>
> It's not particularly relevant, except as a comment on the sensitivity of
> the technique -- far from being unable to detect transiting stars (which
> was your claim, remember), it can detect planets accompanying the stars as
> well, in favorable cases.
Ok, Sirius with Sirius B, is an interesting case,
have you read about that?
> I don't believe it can spot Jovians *by themselves*. They're detectable
> because the light curve of their parent star's microlensing event is quite
> sensitive to smaller masses if they're in just the right place.
>
> >Perhaps you're suggesting we should observe n-stars
> >orbiting apparent stars...
>
> No, microlensing works just fine to spot neutron stars -- or even black
> holes -- by themselves. They bend light just as much as an ordinary star
> of the same mass.
>
> That's why people *started* looking for microlensing in the first place:
> as a way to estimate the abundance of non-luminous stellar-mass objects.
> (Using it for extrasolar-planet discovery came later.) And to bring this
> back to the original topic, they simply didn't find nearly enough of them
> to supply any significant fraction of the galactic dark mass. A decade
> of microlensing searches has given us pretty solid statistics on that.
My goodness, the probability of a telescope,
star and an n-star event in a 4D alignment is
infinitesmal. Put an n-star (10 mile diameter)
in every cubic light-year, use the area of a side
of that cube.
Roughly, 3e7 secs in a year, c=2e5 miles/sec,
LY=6e12, said area = 4E25.
Max out the detected event using n-star effective
diameter at 10^5 miles, (Area= 10^10) and we have
the ratio 4E25 / 10E10 = 4e15.
I'll ask, what's the nature of the "dust" that obsures
SgrA* and the center of the galaxy in general?
> >Excuse me, the fact that these brightness blips
> >do occur (anomalous micro-lensing) is evidence
> >for an n-star population. The odds of a diffraction
> >event due to the gravitation of an n-star and an
> >apparent star are extraordinary small, but they
> >have been reported.
>
> Excuse me, it's *NOT* diffraction.
That's a semantic. In Quantum Field Theory
I accept the term "diffraction".
> It's gravitational lensing.
Lensing is a poor choice of words. The "deflection"
of light in a g-field is proportional to 4GM/r, that's
a pretty poorly focused "lense", diffraction is as
good or better, it's less pop-sci.
>(You do know the difference, don't you?
Sure do.
>If not, please learn before sounding off about it.)
Agreed. Did you know that Einstein in his original
GR1916 paper used "Huyghens principle" to calculate
the deflection of light? I think that falls under the
idea of diffraction, I recommend tolerance.
> And again, *numbers matter*. This isn't a case of a few isolated events.
> There are enough observations now to put good statistical bounds on the
> density of neutron stars and such along the major lines of sight used for
> microlensing searches. They're not high.
I did the "stat's" above and proved you and your
friends wrong. That 4e15 ratio is inescapable, do
you know what it means?
Let me put it into perspective, in a 100 miles x
100 miles area throw in a penny randomly.
Now throw in a another penny, how much
will it cost before you toss enough pennies
so that two are touching?
Well 1000x(Bill Gates) going broke get's ball-park.
> > Compare that to how apparent stars diffract,
> >well it's nil. The proper motion of stars, relative
> >to Earth should at some time bring two visible
> >stars into apparent visual coincident positions,
> >and then the apparent position of the rear star
> >would be offset by the forward star. If that ever
> >is observed it's extremely rare.
>
> Please actually *follow* some of those references and learn something
> about microlensing before you pontificate about it. The radius at which
> most of it takes place is large enough that it works just fine for
> ordinary stars. (In that Jovian-planet event I supplied a pointer to, for
> example, the parent star is believed to be a red-dwarf pair.)
Henry, you're sliding into a domain that is clearly
unknown to you, theoretics, do the calculations
yourself and let's try to stay relevent, I've provided
a demo on that.
Regards
Ken
> --
> spsystems.net is temporarily off the air; | Henry Spencer
> mail to henry at zoo.utoronto.ca instead. | h...@spsystems.net
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