non-expansion of galaxies

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PSB

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<p>As far as I understand the Universe is expanding outward due to something called dark energy, however, the galaxies themselves are not expanding although the space between them is.&nbsp; Is this because the combination of gravity and dark matter (which I understand&nbsp;could be either&nbsp;exotic particles, MACHO's&nbsp;or something new to science) plus the mass of the galaxy,&nbsp;is&nbsp;still exerting a greater&nbsp;force than that of the dark energy, or is there a totally different reason?&nbsp; </p> <div class="Discussion_UserSignature"> </div>
 
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MeteorWayne

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>As far as I understand the Universe is expanding outward due to something called dark energy, however, the galaxies themselves are not expanding although the space between them is.&nbsp; Is this because the combination of gravity and dark matter (which I understand&nbsp;could be either&nbsp;exotic particles, MACHO's&nbsp;or something new to science) plus the mass of the galaxy,&nbsp;is&nbsp;still exerting a greater&nbsp;force than that of the dark energy, or is there a totally different reason?&nbsp; <br />Posted by PSB</DIV><br /><br />You've pretty much got it right. The gravitational contraction is greater (much) than the expansion of space at galactic scales. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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PSB

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You've pretty much got it right. The gravitational contraction is greater (much) than the expansion of space at galactic scales. <br />Posted by MeteorWayne</DIV><br /><br />Thank you for that.&nbsp; It's nice to know that some of my late-night reading is&nbsp;sinking in and beginning to make sense, even if it is only one small item&nbsp; :) <div class="Discussion_UserSignature"> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>As far as I understand the Universe is expanding outward due to something called dark energy, however, the galaxies themselves are not expanding although the space between them is.&nbsp; Is this because the combination of gravity and dark matter (which I understand&nbsp;could be either&nbsp;exotic particles, MACHO's&nbsp;or something new to science) plus the mass of the galaxy,&nbsp;is&nbsp;still exerting a greater&nbsp;force than that of the dark energy, or is there a totally different reason?&nbsp; <br /> Posted by PSB</DIV></p><p>Actually, dark energy isn't the reason for the expansion.&nbsp; Dark energy is put in place to explain the <strong><em>accelerated</em></strong> expansion through recent observation of Type 1a supernovae.</p><p>The actual expansion of the universe is referred to as Hubble's Constant.&nbsp; If I'm not mistaken, the constant is simply the residual expansion left over from the initial big bang.&nbsp; What caused this expansion is anyone's guess.</p><p>If you remove dark energy from the equations, you can still have expansion depending on the critical density of the universe.&nbsp;</p><p>I should also note that the Hubble constant isn't observed on the galactic scale, rather it is observed between clusters and superclusters.&nbsp;&nbsp; The Hubble constant is about 70 km per second per megaparsec (about 3.2 million light years distance).&nbsp; This expansion speed is really difficult to measure between galaxies within a cluster due to the gravitational influences between said galaxies.&nbsp; More often than not, galaxies within a cluster will be less redshifted than what should be measure using Hubble's constant... meaning they are gravitationally bound to each other.</p><p>Often, galactic collisions take place.&nbsp; The Milky Way and the Andromeda Galaxy will merge in a few billion years.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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PSB

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Actually, dark energy isn't the reason for the expansion.&nbsp; Dark energy is put in place to explain the accelerated expansion through recent observation of Type 1a supernovae.The actual expansion of the universe is referred to as Hubble's Constant.&nbsp; If I'm not mistaken, the constant is simply the residual expansion left over from the initial big bang.&nbsp; What caused this expansion is anyone's guess.If you remove dark energy from the equations, you can still have expansion depending on the critical density of the universe.&nbsp;I should also note that the Hubble constant isn't observed on the galactic scale, rather it is observed between clusters and superclusters.&nbsp;&nbsp; The Hubble constant is about 70 km per second per megaparsec (about 3.2 million light years distance).&nbsp; This expansion speed is really difficult to measure between galaxies within a cluster due to the gravitational influences between said galaxies.&nbsp; More often than not, galaxies within a cluster will be less redshifted than what should be measure using Hubble's constant... meaning they are gravitationally bound to each other.Often, galactic collisions take place.&nbsp; The Milky Way and the Andromeda Galaxy will merge in a few billion years.&nbsp; <br />Posted by derekmcd</DIV><br /><br />Yes of course, you're right.&nbsp; I&nbsp;am aware that dark energy is thought to be the cause of the accelerated expansion, and not expansion itself,&nbsp;and just did not fully engage brain&nbsp;on this part of the question.&nbsp; <div class="Discussion_UserSignature"> </div>
 
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weeman

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Yes of course, you're right.&nbsp; I&nbsp;am aware that dark energy is thought to be the cause of the accelerated expansion, and not expansion itself,&nbsp;and just did not fully engage brain&nbsp;on this part of the question.&nbsp; <br />Posted by PSB</DIV><br /><br />derek's explaination probably makes the most sense. All dark energy really is right now is a name, we really don't know what it is or what's causing it to happen. For all we know, using the term 'energy' is probably completely misleading for what is actually taking place! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
 
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