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Computer Org
Skeptic Friend
392 Posts |
 Posted - 05/22/2003 : 07:33:00
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Last week's issue of Science News contained an article about inter-galactic collisions. ( http://www.sciencenews.org/20030510/fob1.asp )
Because of the VAST distances involved, I don't see how it is even possible for two galaxies to collide. Yet astrophysicists talk about it as if it were routine; that both we and Great Andromeda have been involved in several collisions in the [distant] past.
I am highly skeptical of any galaxy-collisions except as utter anomaly.
Anyone else think that the notion of inter-galactic collision is silly from the viewpoint of Newtonian mechanics.  (asks a non-astronomer  )
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Do thou amend thy face, and I'll amend my life. --Falstaff |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
 Posted - 05/22/2003 : 17:15:14 [Permalink]
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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.) |
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NubiWan
Skeptic Friend
USA
424 Posts |
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Computer Org
Skeptic Friend
392 Posts |
Posted - 06/03/2003 : 07:13:38 [Permalink]
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Thanks, Dr. Mabuse. You make some good points; particularily that Great Andromeda is a mere 18 MWD's away. (MWD = Milky Way diameters  )
I've been thinking hard but am still not convinced. |
Do thou amend thy face, and I'll amend my life. --Falstaff |
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Darwin Storm
Skeptic Friend
87 Posts |
Posted - 06/03/2003 : 10:28:18 [Permalink]
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I have actually seen some astronomical studies that say that andromeda is not only NOT moving away from us, but towards us. If true, our galaxy and adromeda may collide in about 3 to 4 billion years. Of course, in the distant past, galaxies were much closer, and collisions would be much more common. Its akin to the early solar system, where cataclysmic collisions were common place, but as time goes on, the frequence decreases because the solor system has stabilized quite a bit more, and alot of the dangerous moving bodies have already collided or been thrown out of the system. Still,even today, crashes occur. Take Chanra-Levy9 that crashed into jupiter ( or was it saturn, not sure on that one.) Anyway, a rare occurance. However, they do occur. By the way, if that comet had impacted earth, we wouldn't be here talking.
Most of the data for colliding galaxies likewise occurs in the distant past , though collisions can be found closer to our own time, though less frequent. |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 06/06/2003 : 07:37:13 [Permalink]
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quote:
Originally posted by Darwin Storm
I have actually seen some astronomical studies that say that andromeda is not only NOT moving away from us, but towards us. If true, our galaxy and adromeda may collide in about 3 to 4 billion years.
Given the problems of calculating trajectories in such vastness that is intergalactic space, it's hard to say when it will happen. I've read 2 billion years, I've read 5 billion years. And trajectories vary from direct hit through grazing passage to "regular fly-by".
quote:
Of course, in the distant past, galaxies were much closer, and collisions would be much more common.
This is on the border of misconception... The average distance between galaxies within a galaxy-cluster is fairly constant, it's the galaxy-clusters themselves that were closer before, and the space between them are expanding.
quote:
Its akin to the early solar system, where cataclysmic collisions were common place, but as time goes on, the frequence decreases because the solor system has stabilized quite a bit more, and alot of the dangerous moving bodies have already collided or been thrown out of the system. Still,even today, crashes occur. Take Chanra-Levy9 that crashed into jupiter ( or was it saturn, not sure on that one.) Anyway, a rare occurance. However, they do occur. By the way, if that comet had impacted earth, we wouldn't be here talking.
The comet was Shoemaker-Levy 9 and the planet was Jupiter. And yeah, the impact was quite the blast.
quote:
Most of the data for colliding galaxies likewise occurs in the distant past , though collisions can be found closer to our own time, though less frequent.
My point is that we can now observe several galaxy-collisions through telescope. The distance to both galaxies has been verified to be the same, and stars are having the same disperse-pattern as simulations predict them to be.
As time goes by, the disrupted galaxies may or may not merge, but in either way, their spiral structure will not last. Even a near fly-by will affect stellar orbits, and eventually the galaxy evolve into what astronomers call "elliptical' galaxy (looking more or less spherical, not spiral).
When two galaxies collide, no collition does actually occur like with Shoemaker-Levy 9 and Jupiter with high-yield impact, though given the number of stars in a galaxy, two starts may hit eachother. Rather, most of the effect is stars orbits around the galaxy-core are disrupted and trajectories changed due to gravitational pull. The effect galaxies have on eachother is directly corresponding to the inverse square of the distance. There is no Hit-or-Miss, only gradual effects. That's why it's virtually impossible to tell if an elliptical galaxy was changed by several pass-bys or a single direct hit. Maybe it rear-ended another galaxy...
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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
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Slater
SFN Regular
USA
1668 Posts |
Posted - 06/06/2003 : 17:43:51 [Permalink]
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| You do know, don't you that the Milky Way and M31 in Andromeda are heading straight for one another an will crash too |
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I learned something ... I learned that Jehovah's Witnesses do not celebrate Halloween. I guess they don't like strangers going up to their door and annoying them.
-Bruce Clark
There's No Toilet Paper...on the Road Less Traveled |
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ljbrs
SFN Regular
USA
842 Posts |
Posted - 06/07/2003 : 17:26:54 [Permalink]
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Our own Milky Way is currently devouring several smaller galaxies, the largest being the Magellanic Clouds (Large and Small). There are visible streamers connecting these galaxies to the Milky Way. Gravity is what causes galaxies to collide. However, stars are far apart and usually do not collide with each other, although gravitation causes distortions. Then again, the mass in the universe is thought to consist of about 4 percent of the matter as we know it, the rest of the mass consisting of Dark Matter, thought to be remnants of the particles formed in the Big Bang (which was neither big nor a bang), and the greater part being Dark Energy, a/k/a Lambda, thought to be "virtual particles" (particles and their anti-particles) which have been seen in particle accelerators to come into and out of existence in a tiny fraction of a second, immediately annilihating each other (therefore not breaking any rules of physics).
However, not to worry. It will be a few billion years before Andromeda collides with the Milky Way. It will not occur until our Sun has already gone into its giant phase (eventually to become a white dwarf star).
It is a great bedtime story. Sweet dreams!
ljbrs |
"Innumerable suns exist; innumerable earths revolve about these suns in a manner similar to the way the seven planets revolve around our sun. Living beings inhabit these worlds."
Giordano Bruno
(Burned at the stake by the Roman Catholic Church Inquisition in 1600) |
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filthy
SFN Die Hard
USA
14408 Posts |
Posted - 06/07/2003 : 18:38:45 [Permalink]
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This is so fascinating! Keep it going, guys!
Edited to correct a truly amazing version of,'fascinating'. I need to quit drinkin' that home-made stuff.
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"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
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Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist! 
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| Edited by - filthy on 06/07/2003 18:42:15 |
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Computer Org
Skeptic Friend
392 Posts |
Posted - 06/09/2003 : 06:20:30 [Permalink]
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I, for one, am not questioning that somewhere, sometime, galaxies do collide. I'm only questioning the astrophysical suggestion that intergalactic collisions are the norm----if not nearly-ordained.
The gravitational forces are admitedly huge; but the distances are also huge---and the (Newtonian) force-equation uses the inverse square of those distances. Hmmmmm. |
Do thou amend thy face, and I'll amend my life. --Falstaff |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 06/09/2003 : 16:53:01 [Permalink]
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Here's a snippet from the awarding winning site, Ask The Astronomer, and its question archive:
http://itss.raytheon.com/cafe/qadir/q428.html
What happens when galaxies collide?
>snip
"The entire process is very complicated to study but there are hundreds of examples of galaxies in just about every stage of collision, and computer modeling of these encounters has been extremely successful in accounting for many of the common morphologies that we actually see."
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Peering deep into the universe abyss, well beyond our Milky Way and the local group, one can see literally billions of galaxies. And in all forms of developement, age, shapes, and yes, various stages of collision.
Some of those collisons we can see are head-ons, some like two mega frisbees merging, passing thru each other. Others are described as cannabalistic on the smaller. Some may appear to be like a glancing blow.
It's a happenin' place, this universe.
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"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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ljbrs
SFN Regular
USA
842 Posts |
Posted - 06/14/2003 : 15:22:32 [Permalink]
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Randy:
Thank you for the beautiful photographs of the Antennae Galaxy collision. I have seen these before, but it might help the skeptical folks to understand that collisions do happen (frequently, as there are many other such photographs of other galactic encounters showing the distortions of the disruptions encountered in such collisions). Because the galactic groups (and super-groups) are moving away from each other, there are not a great many. You can view galactic collisions in the streaming matter connecting the Large and Small Magellanic Clouds (smaller galaxies viewed in our Southern Hemisphere) with the Milky Way. Sooner or later (mostly later), the Magellanic Clouds will become a part of the Milky Way.
However, those are gorgious photographs! I do not think I would want to experience such a collision first hand. Of course, in about 3 billion years Andromeda and the Milky Way will put on quite a show. By that time, however, the Sun will probably be in a red giant stage and life on Earth will not likely survive such a stellar evolution as our Sun's.
ljbrs |
"Innumerable suns exist; innumerable earths revolve about these suns in a manner similar to the way the seven planets revolve around our sun. Living beings inhabit these worlds."
Giordano Bruno
(Burned at the stake by the Roman Catholic Church Inquisition in 1600) |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 06/14/2003 : 20:18:32 [Permalink]
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Lbjrs, what a ballet, starring our universe, that gravity plays. I just googled "The Great Attractor" and came up with this on the first site. Interesting that the Milky Way/Andromeda galaxy collision course was talked about. Please read on......
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"The Milky Way and Andromeda galaxies are the dominant structures in a galaxy cluster called the Local Group which is, in turn, an outlying member of the Virgo supercluster. Andromeda--about 2.2 million light-years from the Milky Way--is speeding toward our galaxy at 200,000 miles per hour.
This motion can only be accounted for by gravitational attraction, even though the mass that we can observe is not nearly great enough to exert that kind of pull. The only thing that could explain the movement of Andromeda is the gravitational pull of a lot of unseen mass--perhaps the equivalent of 10 Milky Way-size galaxies--lying between the two galaxies.
Furthermore, our entire Local Group is hurtling toward the center of the Virgo cluster at one million miles per hour.
The Virgo cluster lies some 50 million light years from Earth. Only the central region is shown above, containing two giant elliptical galaxies, M84 and M86. The visible part of the cluster is but a small portion of what seems to be out there. Nevertheless, the Virgo Cluster, along with several other large clusters, are in turn speeding towards a gigantic unseen mass named The Great Attractor.
Based on the velocities at these scales, the unseen mass inhabiting the voids between the galaxies and clusters of galaxies amounts to perhaps 10 times more than the visible matter.
Even so, adding this invisible material to luminous matter brings the average mass density of the universe still to within only 10-30 percent of the critical density needed to "close" the universe.
Might the universe be "open" after all? Cosmologists continue to debate this question, just as they are also trying to figure out the nature of the missing mass, or "dark matter."
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I'm a bit out of touch. Can you expand a bit more on this "Great Attractor" or "dark matter" is that has our local group of galaxies hurling towards it?
Thank you for your imput,
Randy
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"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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uvastronomer
New Member
USA
4 Posts |
Posted - 06/15/2003 : 11:03:04 [Permalink]
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| To say that colliding galaxies are "common" is difficult, due to the rather fluid mean of the word "common" when it comes to astronomy. In any direction in the sky, the longer you look, the more galaxies you will see. If anyone remembers the Hubble Deep Field image, in 10 hours the Hubble imaged hundreds of galaxies in a very small portion of the sky. If it had looked longer, more would have become apparent. I think a good way to put it would be, colliding galaxies are not so rare as to be hard to find, but by no means is every galaxy out there colliding with others. |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 06/15/2003 : 17:27:45 [Permalink]
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quote:
Originally posted by uvastronomer
To say that colliding galaxies are "common" is difficult, due to the rather fluid mean of the word "common" when it comes to astronomy. In any direction in the sky, the longer you look, the more galaxies you will see. If anyone remembers the Hubble Deep Field image, in 10 hours the Hubble imaged hundreds of galaxies in a very small portion of the sky. If it had looked longer, more would have become apparent. I think a good way to put it would be, colliding galaxies are not so rare as to be hard to find, but by no means is every galaxy out there colliding with others.
Very good point. I've been thinking along those lines too.
And Welcome to Skeptic Friends!
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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. |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 06/15/2003 : 18:43:12 [Permalink]
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quote:
Originally posted by uvastronomer
To say that colliding galaxies are "common" is difficult, due to the rather fluid mean of the word "common" when it comes to astronomy. In any direction in the sky, the longer you look, the more galaxies you will see. If anyone remembers the Hubble Deep Field image, in 10 hours the Hubble imaged hundreds of galaxies in a very small portion of the sky. If it had looked longer, more would have become apparent. I think a good way to put it would be, colliding galaxies are not so rare as to be hard to find, but by no means is every galaxy out there colliding with others.
Welcome, uvastronomer.
Just a minor correction here, from the below link....
"The image, called the Hubble Deep Field (HDF), was assembled from 342 separate exposures taken with the Wide Field and Planetary Camera 2 (WFPC2) for ten consecutive days between December 18 and 28, 1995."
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.
Go to this link for a interesting visual of the HDF, and other related links to this magnificent Hubble image...
http://hubble.stsci.edu/discoveries/hubble_deep_field/
Another topic but, if we could only force our nations leaders into a "cosmic perspective" class, most, if not all hostilities toward each other would cease on this lonely little planet.
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"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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