[extropy-chat] cosmic dust!

Amara Graps amara at amara.com
Sat Apr 2 09:11:00 UTC 2005

From: "spike" <spike66 at comcast.net>, Thu, 31 Mar 2005

>I thank Amara for showing how interesting is cosmic dust.

You're very welcome, Spike. Sometime soon, I'll have my next set of
simulation results to add to these

Colored Spaghetti
Cloud of the Jovian Dust Streams
Trails of the Jovian Dust Streams

My colleagues have discovered *Saturn* dust streams as well; there
are Nature and Science publications that are imminently in print
(if they have not be published already).

>She managed to write a doctoral thesis on the topic and
>make it compelling enough to make me read every word.

well... a thesis is pretty thick reading. If anyone is
interested look here:

I'm practicing and improving my popular science skills. I will
have a Sky and Telescope article sometime (this summer, I hope)
about how Earth got its water. And after early May, when I complete
the semester teaching astronomy to liberal art majors, I will have
completed ~70 hours of general astronomy lectures. I've learned
alot in the last year about  how to present these topics to
nonscience majors.

>Like dust bunnies that lurk in corners and under beds, surprisingly
>complex loops and blobs of cosmic dust lie hidden in the giant
>elliptical galaxy NGC 1316. This image made from data obtained with the
>NASA Hubble Space Telescope reveals the dust lanes and star clusters of
>this giant galaxy that give evidence that it was formed from a past
>merger of two gas-rich galaxies.
>   http://spaceflightnow.com/news/n0503/31hubble/

Well no one here wondered why we hear so often in the astronomy
news of galaxies colliding. It seems strange, no? Here is the

Why Galaxies Collide and Stars Rarely Do

Stars are extremely small compared to the distances between them -

For example; Our sun is ~1.5 x 10^6 km wide but it is separated from
the closest other star by about 4 light years = 38 trillion
(=10^{12}) km. So the Sun is 27 million (=10^6) of its own diameters
from its nearest neighbor. This is typical of stars are not inthe
nuclear bulge of a galaxy, or inside of of star clusters.

Now contrasting stars with the separation of galaxies using our own
Milky Way galaxy as an example.

The visible disk of the Milky Way is 100,000 light years in
diameter. We have three satellite galaxies that are just one or two
Milky Way diameters from us (in the Milky Way), which will
eventually collide with us. The closest major spiral galaxy is M31,
about 2.4 million light years away.

Therefore the nearest large galaxy neighbor is ~24 of our Galaxy's
diameters from us. And that does not consider that both galaxies
have a much larger corona of dark matter.

Galaxies in rich clusters are even closer together than the members
of our poor Local Group. Thus the chances of galaxies colliding are
far greater than the chances of stars in the disk of a galaxy


Amara Graps, PhD          email: amara at amara.com
Computational Physics     vita:  ftp://ftp.amara.com/pub/resume.txt
Multiplex Answers         URL:   http://www.amara.com/
"Whenever I see an adult on a bicycle, I do not despair for the
future of the human race."   -- H. G. Wells

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