[meteorite-list] OT: New Smallest, Possibly Earth-like, Extra-Solar Plane...

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Wed Jun 15 22:42:17 2005
Message-ID: <42B0E6E4.BC39B4CF_at_bhil.com>

Hi, Jerry,

    Because of their low temperatures, these stars are brighter in the infrared
than visible light. That is how they were discovered by 2MASS. The problem is
determining their distance. Is this or that super-faint object near or far?

    Many conventional means of estimating distance from optical properties fail
in the case of the super dim star. Their stellar atmospheres are actually
dusty! We can't get good spectra because their visible light emissions are
dimmer than what the biggest optical telescopes can pick up.

    These are very difficult objects to observe. The surveys we're talking
about here were undertaken with the biggest telescopes at the very limit of
their light-gathering power. Distances are the hardest piece of information to
come up with for these stars. We could have already discovered a nearby one and
not even know it's nearby!

    A nearby star could be in any direction, so it means looking at the entire
sky, everywhere. There is another way to measure the distance to a star, the
oldest method of all. Chart everything, wait six months until we're on the
other side of the Earth's orbit, chart everything again, and see if anybody has
moved!

    This is the parallax method. Back in 1838 a German astromer named Bessel
noticed that a double star, 61 Cygni, made a little loop in its sky position,
one loop every year, and was able to measure the distance to the star.
<www.noao.edu/outreach/nop/nophigh/steve9.html>

    Turns out 61 Cygni's the 11th nearest star at 11.1 light years. In
1989-1993, the Hipparchos satellite did this same thing with an eccentric orbit
of its own for 118,000 visible light stars but nobody's done it in infrared, at
least, I don't think so.

    Then, there's proper motion studies. Because stars close together are all
moving at slightly different speeds in slightly different directions and will in
time change their sky positions as seen by their neighbors, not in little annual
loops, but in a constant continuing drift across the sky, called proper motion.

    The amount of proper motion doesn't correspond perfectly to the distance.
The star with the greatest proper motion, dim little Barnard's Star, is the 2nd
nearest star, but the nearest star, alpha Centauri, only has the 15th greatest
proper motion, because we and it are moving in similar directtions and speeds.
Actually, we're getting slowly closer to each other (but it's too long to wait
-- build the starship!).

    And if a star was, by chance, moving more or less directly towards us, it
would appear to have no proper motion (side to side) at all! Sneaky!

    In the nineteen century, astromers were always invoking a "passing star" as
a cause of things they couldn't explain, so in this last century, the notion of
nearby stars getting close to us fell into disfavor. However, since the
computer and all that number crunching power, it turns out that other nearby
stars do intrude on our little Solar neighborhood all the time.

    7,000,000 years ago, the giant star Algol made a pass of the Sun that
probably stirred up our Oort Cloud of comets. In less than 1,000,000 years from
now, Gliese 710 is going to plow right through our Oort Cloud, passing the Sun
at only 69,000 AU (about a lightyear) away.

    Right now, the "nearest star" is little dim Proxima Centauri, a companion of
Alpha Centauri A and B, but in 33,000 years, Ross 248 will have drifted closer.
Over the next 45,000 years, six other neighboring stars will be passing closer
than Proxima, each taking their turn as the "nearest" star. Not to worry, not
real close, just closer than Proxima.

    In fact, Alpha Centauri A and B is getting closer all the time, and only
about 50,000 AU separate the edge of its comet cloud from our comet cloud.
Eventually, they will merge. (If you were a good comet jumper, you could get to
the next star this way. Take a long time, though...)

    I found a paper out there by a guy that claims that alpha Centauri A & B is
already influencing our comet cloud, based on the orientation of new comets. The
Hipparcos data suggest we have about 2.5 encounters with other stars every
million years!

    Not to be completely Sun-centered, somebody did a paper, calculating close
encounters for other big stars in our neightbor, like Vega, and found they all
have close passes with their local small stars, just as we do, never closer than
a comet ruffler in 10,000,000 years.

    Of course, a big infall of comets is no joke. Just ask the dinosaurs.

    Then, there's the recent discovery of the Kuiper Belt Object named Sedna,
It has a very eccentric orbit and attempts to model how it could have been
perturbed into that orbit by Neptune, and so forth, have all come up with no
good answer. Maybe a passing star kicked it around.

    With 2.5 passes per million years (that's 2500 passes per billion years),
one might have come close enough to boot Sedna into a high eccentricity orbit.
Turns out there's another KBO, 2000 CR105, with an equally high eccentricity
orbit.

    Whoops! Someboday already thought of that. See:
<http://www.spaceref.com/news/viewpr.html?pid=15588>

    All the good ideas get taken quick... I got to get faster!

    This is what happens, off topic. We just jump from one interesting thing to
the next!


Sterling K. Webb
-------------------------------------------------------------------------------
Gerald Flaherty wrote:

> But trying to find a nearby "invisible" star is a truly daunting technical
> problem
> concerning which no light bulbs have turned on in my brain... It's as dim
> in there as
> the L dwarves themselves!
>
> Sterling K. Webb

--------------------------------------

>
> infared won't detect the L's??? Jerry Flaherty
>
Received on Wed 15 Jun 2005 10:41:40 PM PDT