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Posted by Ken S. Tucker on March 12, 2007, 3:55 am
Please log in for more thread options On Mar 11, 8:41 pm, h...@spsystems.net (Henry Spencer) wrote:
>
> >> For example, the MACHO searches -- monitoring brightness of background
> >> stars for long periods of time, looking for brief gravitational-lensing
> >> effects caused by objects (Massive Compact Halo Objects, MACHOs) passing
> >> in front of them -- did not come up entirely empty-handed, but their
> >> object counts were much too low...
>
> >...with each n-star ~ 10 miles in diameter, that sums
> >to an object that blocks light to be ~ 100 miles in
> >diameter, equivalent to one tiny moon...
>
> They were looking for gravitational lensing, not occultation. Not only is
> that much less sensitive to the size of the actual object, but it also
> doesn't require the object to pass exactly in front of the star -- the
> effect from a near miss is weaker but still detectable. A neutron star
> actually makes a better gravitational lens than a normal star of the same
> mass, precisely *because* it's smaller and doesn't get in the way of the
> light as much.
>
> >The transit effect of such of an object - even including GR light
> >deflection - is next to impossible to detect, that's
> >plain old common sense.
>
> Common sense is no substitute for arithmetic. The MACHO searches took
> some development effort, and good detectors -- and they monitored huge
> numbers of background stars simultaneously, not just one at a time -- but
> yes, they *could* detect such objects. As soon as people made a serious
> effort to look, they did indeed start finding such "microlensing" events.
>
> 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*. See <http://planet.iap.fr/> for
> one of the current efforts which is looking for (and finding) extrasolar
> planets via microlensing.
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.
Perhaps you're suggesting we should observe n-stars
orbiting apparent stars, but stellar evolution and
orbital dynamics would make that a rare occurance.
> >I recommend you re-visit
> >your data source, you sound mis-informed, perhaps
> >site an online reference for us all.
>
> This isn't some obscure mystery that nobody has heard of; anybody who
> doesn't know about it simply hasn't been paying attention to the astronomy
> news for the last decade or so. Google on "microlensing" "planet" for
> starters.
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.
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.
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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