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G=EMC^2 Glazier
July 4th 03, 06:15 AM
I find it interesting that galaxies come in different shapes. I'm
thinking they should all be spiral Just looking at a spiral galaxy you
know its rotation that gave it its shape. I can't vision an elliptical
galaxy rotating. I can't see its stars being in lock step ether. I read
that if two spiral galaxies merged they would form an elliptical
galaxy(I don't like that theory) Can't see how an elliptical galaxy
would have a central blackhole?? Then we have irregular
galaxies,and I have no thoughts regarding them. Like to think "Spin is
in" Our Milky Way has spin,and I like that. I see the universe as a
big spiral galaxy rotating at 93% of the speed of light. From the
outside looking into the universe I see the galaxies,as we see stars in
our Milky Way. Bert

David Knisely
July 5th 03, 06:34 AM
Bert posted:

> I'm thinking they should all be spiral

Nope, there is no reason they should all be spiral. In the area around
our local group of galaxies and other nearby galaxy clusters less than
30 million light years away, about 33 percent of the galaxies observed
within that volume are spirals, 13 percent are ellipticals, and 54% are
irregulars (often faint dwarf irregulars). Out beyond this distance,
the small irregulars get very difficult to detect, so the big bright
spirals tend to dominate and the balance of *observed* galaxies shifts a
bit in favor of the spirals (even though faint irregular galaxies
probably are there too but are too faint to see at the larger
distances). However, there is no overriding reason why all galaxies
should be spirals.

> I can't vision an elliptical
> galaxy rotating. I can't see its stars being in lock step ether.

Elliptical galaxies *do* rotate, as is easily seen by looking at the
doppler shifts of different portions of them. The stars aren't
necessarily "in lock step" with each other, but orbit the center of the
galaxy in a wide variety of orbits with all sorts of inclinations and
eccentricities. This is why they are the shape that they are.

> I read
> that if two spiral galaxies merged they would form an elliptical
> galaxy(I don't like that theory)

Well, its too bad you don't like that theory because there is clear
evidence that this happens, mostly with the very large ellipticals which
often sit near the center of large clusters of galaxies. Faint halos,
rings, and streamers are often seen around these big elliptical galaxies
in very long exposure photographs of them, remnants of their original
galaxy components after mergers. Computer simulations of colliding
spiral galaxies often show them eventually settling down after billions
of years into the form of a giant elliptical galaxy. Not all
ellipticals form this way, but there is evidence that many of them have
formed from galactic mergers.

> Can't see how an elliptical galaxy would have a central blackhole??

Why would it need one? There are galaxies with central black holes and
galaxies without them. Its not a requirement that any galaxy have a
black hole at the center. Spiral galaxies show spiral arms not because
there is a black hole in the middle, but because of density waves
(possibly with the help of magnetic fields) propagating around the disk
of the galaxy triggering star formation in the spiral arms. The arms in
a spiral galaxy are *not* spiraling-in towards the center of the galaxy,
but are rotating around the galaxy just like the stars in them do.

> Then we have irregular
> galaxies,and I have no thoughts regarding them.

Well, better start thinking about them, because there are a *lot* of
them in our universe.


--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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Joseph Edinger
July 5th 03, 11:14 PM
I don't mean this as an attack, but have you ever heard the expression
"How boring life would be if we were all the same." I feel that hold's
true to the universe.......It wouldn't be full of wonder and
suprise.........
My 2 cent's.

Joe

G=EMC^2 Glazier
July 6th 03, 04:45 AM
Hi Joe Just having a little fun. Don't take the universe to seriously
Bert