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NubiWan
Skeptic Friend
USA
424 Posts |
 Posted - 06/16/2003 : 11:04:20 [Permalink]
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At this point in time, to hold that galatic collisions are the exception, rather than the rule, remains a 'valid' position IMO. However so too, is the veiw that such collisions may well be a fundamental step in the evolution of large galaxies such as the Milky Way and Andromeda galaxies. Tend to accept such a model myself, as an explaination for their growth, thou as yet unconfirmed. The evidence is currently still being collected. One such effort is the RAdial Velocity Experiment.
http://www.spaceflightnow.com/news/n0306/03rave/
Edited to welcome uvastronomer 
And one more time with feeling, to add related story link;
http://www.space.com/scienceastronomy/goods_survey_030619.html |
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| Edited by - NubiWan on 01/08/2004 11:51:05 |
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uvastronomer
New Member
USA
4 Posts |
Posted - 06/17/2003 : 10:09:21 [Permalink]
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I thought I'd bring up the recent result from the WMAP(Wilkinson Microwave Anisotropy Probe) satellite, which discovered miniscule fluctuations in the structure of the early universe.
http://map.gsfc.nasa.gov/m_mm.html
The result of these fluctuations in temperature is an uneven distribution of mass and the formation of an uneven distribution of galaxies (ie clusters of galaxies). Galactic distance scales sound enormous, but just about all galaxies are part of a cluster, by the very nature of the early universe. Thus the distance between galaxies in a cluster is much smaller than the distance between two clusters, making collisions more likely (and I say "likely" with the same caveats as "common"). |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 06/17/2003 : 15:10:47 [Permalink]
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quote:
Originally posted by Randy
The Hubble Deep Field pushed the estimated total number of galaxies to upwards of 50 billion now. No doubt quite a far cry from the several hundred colliding galaxies found so far, as mentioned above.
Of all those 50 billion galaxies (which is an estimate not an actual count), most of them are too far for us to determine wether or not they are in the process of colliding. The few hundreds of colliding galaxies we know of comes from a list of maybe a million photographed galaxies, probably much less. It's not like we have image-recognition programs that identifies these collisions because there are too many scenarios to keep track of, so potential collisions has to be recognized by human eye.
We all recognize the effort of examining pics of galaxies. If I take a look at one pic per second, how many man-hours does it take to examine the first million?
The next million?
How far out is our equipment able to correctly, by measurment, verify colliding galaxies? Millions of lightyears: yes. Billions of lightyears: no.
My guess is that we might verify collisions within a sphere with a radius of perhaps a percent of the known universe. That constitute a miniscule fraction of the 50 billion galaxies we started out with. |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 06/17/2003 : 19:49:54 [Permalink]
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Dr. Mabuse wrote:quote:
We all recognize the effort of examining pics of galaxies. If I take a look at one pic per second, how many man-hours does it take to examine the first million?
278.quote:
The next million?
Another 278.
I'm sorry, were those rhetorical questions? 
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- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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Darwin Storm
Skeptic Friend
87 Posts |
Posted - 06/17/2003 : 21:03:53 [Permalink]
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| Since the further away we look is essentially looking further back in time, I would be most curious to see if collisions are more common in the distant past then now. Perhaps collisions were more common when galaxies were just forming, as opposed to the modern evolution of galaxies. |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 06/19/2003 : 12:20:41 [Permalink]
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Just released from the Hubble Space Telscope site....
http://hubble.stsci.edu/newscenter/archive/2003/18/image/a
>snip
"NASA's Hubble Space Telescope reached back to nearly the beginning of time to sample thousands of infant galaxies. This image, taken with Hubble's Advanced Camera for Surveys, shows several thousand galaxies, many of which appear to be interacting or in the process of forming. Some of these galaxies existed when the cosmos was less than about 2 billion years old. The foreground galaxies, however, are much closer to Earth. Two of them [the white, elongated galaxies, left of center] appear to be colliding."
Here's a 1.25 meg jpeg link. It's just transplendid!....
http://imgsrc.hubblesite.org/hu/db/2003/18/images/a/formats/full_jpg.jpg |
"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 06/19/2003 : 12:33:23 [Permalink]
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http://hubble.stsci.edu/newscenter/archive/2003/18/text
Here's the full press release... |
"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 06/19/2003 : 13:24:20 [Permalink]
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quote:
<blockquote id="quote"><font size="1" face="Verdana,Arial,Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Darwin Storm
Since the further away we look is essentially looking further back in time, I would be most curious to see if collisions are more common in the distant past then now. Perhaps collisions were more common when galaxies were just forming, as opposed to the modern evolution of galaxies.
I'm afraid it will be hard verify. There are two relatively exact ways to measure the distance to two galaxies that seems to collide: magnitude measurment of Cepheids (a unique kind of variable star), and magnitude measurements of supernovas. Both offer good reliability, Cepheids for shorter distances and supernovas for larger distances. But the measurement requires that the camera in the telescope is able to single out the star within the galaxy. Background light from the galaxy reduces the signal/noise ratio as distance grows. Beyond 3 to 5 billion lightyears away it's virtually impossible to use other methods than red-shift, and unfortunalty, it's not accurate enough to tell colliding Gs from just neighbours in that local cluster.
That stretches our vision to 5 billion years into the past, one third to half the age of the universe.
Edit: spelling, and formatting error
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Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
Collateralmurder. |
| Edited by - Dr. Mabuse on 06/23/2003 09:24:58 |
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uvastronomer
New Member
USA
4 Posts |
Posted - 06/19/2003 : 21:00:27 [Permalink]
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I thought you all might like to see this good case of galactic scale collision. A common way to determine two (or sometimes more) galaxies are colliding is using their emission in the radio, namely 21 cm emission from the neutral hydrogen(HI). A good example is the colliding galaxies near M81:
http://www.people.virginia.edu/~jpk5z/m81.jpg
In the optical the galaxies appear to have nothing to do with each other, but the gas interactions are clearly visible when looking in the radio. |
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NubiWan
Skeptic Friend
USA
424 Posts |
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Computer Org
Skeptic Friend
392 Posts |
Posted - 09/12/2003 : 06:30:32 [Permalink]
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quote:
Originally posted by Dr. Mabuse
Given that Milkyway is roughly 160000 Ly in diameter, and the distance to Andromeda is 2,9 million Ly, the distance between the two galaxies are no more than 18 times the size of our Milkyway. By comparison, the distance between Earth to Moon is roughly 30 earth diameters. Vast distances - yes, but put in this perspective, "unlikely" does not mean "impossible". There are millions of galaxies out there, all neatly collected in small clusters of 10 to 100 galaxies that orbit around each other in irregular patterns, crashes are bound to happen sooner or later.
Calculating orbits is a bitch when galaxies' movements are hard to measure, but there are some very nice pictures taken by telescopes on colliding galaxies.
http://www.cloudbait.com/gallery/ccd/ngc4038.html
http://apod.gsfc.nasa.gov/apod/ap971022.html
And then consider that elliptical galaxies are rarely born elliptical, they become that way by collisions and near passes disrupting the stellar orbits around its center. When gases contracted to create galaxies once upon a time, they were subject to the same type of mechanics as when the solar system formed. The differences were the larger scale, and that there were only hydrogen and helium present. An accretion-disk is a natural formation, and in a galactic perspective we get a spiral- or a barred spiral- galaxy.
(Elliptical galaxies are more or less spherical in shape, with no spiral tendencies. Stellar orbits are irregular, and stars are not orbiting in the same general direction, like in spirals, or planets in a solar system.)
I (reluctantly) concede, Dr. Mabuse.
Thanks for your time and effort. |
Do thou amend thy face, and I'll amend my life. --Falstaff |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 09/12/2003 : 14:02:46 [Permalink]
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quote:
Originally posted by Computer Org
Thanks for your time and effort.
You're welcome. |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
Collateralmurder. |
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furshur
SFN Regular
USA
1536 Posts |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 10/04/2003 : 15:15:19 [Permalink]
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Ditto that!
http://www.space.com/scienceastronomy/galaxy_gobble_030924.html |
"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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NubiWan
Skeptic Friend
USA
424 Posts |
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Topic Locked
