A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Others » Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Question on Gravity/black holes/galaxies.



 
 
Thread Tools Display Modes
  #1  
Old April 11th 04, 08:47 PM
XeNO
external usenet poster
 
Posts: n/a
Default Question on Gravity/black holes/galaxies.

Okay I understand that current thinking leans towards hidden matter in the
spiral arms of our galaxy. And that a black hole is at the center of the
galaxy. Couldn't the problem of the spiral arms not "flying off" be due to
the possibility that they are in the Event Horizon of the galactic center?
Would we still need hidden matter even then? It just seems kind of "extra"
and not fitting quite right with Occam's Razor to me.


--
--XeNO
"Order of the Eigth Digit"
www.digitalmessiahmusic.net
(no the band is not religously themed.)
AA# 1901
"In Hoc Signo Vinces"
----------- . -----------
\ | /
\ /
/ \
/ | \
----------- . -----------


  #2  
Old April 11th 04, 09:34 PM
Greg Neill
external usenet poster
 
Posts: n/a
Default

"XeNO" wrote in message news:mhhec.951$fS6.831@okepread01...
Okay I understand that current thinking leans towards hidden matter in the
spiral arms of our galaxy. And that a black hole is at the center of the
galaxy. Couldn't the problem of the spiral arms not "flying off" be due to
the possibility that they are in the Event Horizon of the galactic center?
Would we still need hidden matter even then? It just seems kind of "extra"
and not fitting quite right with Occam's Razor to me.


There are a few problems with this hypotheses.

First, a black hole with a Schwarzschild radius
(event horizon) large enough to encompass the
spiral arms of the galaxy would need to have a
truly prodigious mass.

The Schwarzschild radius Rs for a mass M is:

Rs = 2*M*G/c^2

If the galaxy disk has a radius of about 50,000 LY,
then the mass of the galaxy would have to be on the
order of 1.6x10^17 solar masses. Estimates for the
number of stars in the galaxy have an upper limit of
about 2x10^11 stars. No one would credit an amount
of dark matter some 10^5 times that of ordinary
matter.

Next, inside an event horizon, all matter must follow
trajectories that end in the central singularity.
That means that there would be no stable spiral arms
(they would collapse into the center), and no stars
could follow a path that leads it outwards from the
center. Yet we observe stars within our galaxy with
velocities that take them outwards.

Further, the "problem" of flattened velocity curves
exists for other galaxies as well. Since we can
observe their stars, they can't be hidden behind an
event horizon.



 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Another rotation question BigKhat Astronomy Misc 4 June 19th 04 12:12 PM
Double Star Question Lisa Amateur Astronomy 7 September 26th 03 10:14 PM
Question about alignment & pointing north, level Mike Amateur Astronomy 8 September 7th 03 12:04 AM
Rookie question. How dark is MY sky? justbeats Amateur Astronomy 4 August 3rd 03 12:08 PM


All times are GMT +1. The time now is 04:18 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.