View Full Version : Discussion: Our Collision With Andromeda Will ...

2005-Aug-26, 03:54 PM
SUMMARY: In the constellation of Pisces, 100 million light-years from Earth, two galaxies are smashing together in a dramatic demonstration of our far future: when the Milky Way collides with the Andromeda Galaxy. This image of NGC 520 was taken with the Gemini North Telescope on the evening of July 13-14, 2005. It's possible to see dark dust lanes and a long trail of stars thrown out by the cosmic collision.

View full article (http://www.universetoday.com/am/publish/ngc_520_merging_galaxies.html)

What do you think about this story? Post your comments below.

2005-Aug-26, 04:01 PM
here's the right link for the picture

http://www.universetoday.com/am/uploads/ng...c520_gemini.jpg (http://www.universetoday.com/am/uploads/ngc520_gemini.jpg)

2005-Aug-26, 05:02 PM
Watching the zones of brightest color, it almost makes me wonder if the "bar" of "barred" galaxies got their elongation that way--almost. Some of the "bar" galaxy pictures show too much symetry and too little nearby indication of such interference.

Still, with the notion of dark matter, how do we know we don't have some dark hard spot and our snapshot is instead showing a galaxy as a wave splashing about the interstellar equivalent of a rock on a shore? What tells us that the two features, left-center and lower-center are merging together into the one upper-right, instead of separating in a flow the other way? What confirms the direction of flow?

Similarly, with all the talk of the repulsing charateristics of dark matter/dark energy, while we have places that indicate gravitational lensing (gravity bending light), what of this dark matter/energy bending or distorting something like a galaxy. If it can propel a galaxy, can it not bend, crush, or otherwise distort one?

2005-Aug-27, 08:41 PM
Originally posted by lswinford@Aug 26 2005, 05:02 PM
Similarly, with all the talk of the repulsing charateristics of dark matter/dark energy...
Dark Matter isn't hypothesized to have repulsive characteristics, it is simply stuff that adds to the gravity of the galaxy or galaxy cluster without having the ability to interact in a way that could concentrate it into some luminous form.

Dark Energy is too diffuse to make this kind of distortion happen. This image is of two colliding galaxies.

2005-Aug-28, 02:05 AM
I do not understand the references to this event being "scary." As far as I know the distance between stars in each galaxy would allow stars to pass right by each other with few if any collisions. I guess I could concede that the process of the collisoion will stir up dormant dust clouds and generate alot of stars at once. This would yield a period of quite a few supernovas at the same time. But that would not scare me, maybe it would make me a little nervous. If our civilization has survived to the time when the Andromeda collision takes place, we would undoubtedly have colonized a good portion of the galaxy and have evolved our propulsion technology to be able to get out of the way of any impending nearby supernova. Who knows, by then maybe we will be able to skim mass off supergiants and trim them down to a point that they can no longer explode, or move them to a safe corner of the galaxy before they go off.

2005-Aug-29, 05:01 AM
Some questions about this article
1) What scientific calculations are there to say that the Milky Way will collide with Adromeda in about 5 billion years?
2) Where will our sun be in relation to Adromeda at the time of collision? (i.e. our sun is on the outskirts of the Milky Way, so will it be first to collide or last to collide with Adromeda)
3) How long, after the initial radius of collision occurs, will it take for Adromeda to be completly submersed into the Milky Way? (i.e. will it take an additional 5 billion years to be submersed)
4) How fast, in which directions, and what planes are the Milky Way and Adromeda spinning?

I could go on like this, but the point is that there are so many variables in a galactic collision, that you can not possibly claim that the picture of two colliding galaxies will look the same as two other colliding galaxies.

2005-Aug-29, 01:24 PM
Originally posted by Guest_James@Aug 29 2005, 05:01 AM
1) What scientific calculations are there to say that the Milky Way will collide with Adromeda in about 5 billion years?
One important point here is that we DO know from blue-shift that M31 is coming in our general direction, at such a pace that IF it is coming straight at us, it will seriously disturb our galaxy in a few billion years... HOWEVER, we do not know how much it is also moving to the side.

It is very likely that M31 interacted with the Milky Way billions of years ago, and that interaction produced the large and small Magellanic Clouds, and other bound dwarf galaxies. The idea that the two galaxies are headed for a direct merger on this pass is not certain.

2005-Aug-29, 03:16 PM
Antoniseb's note

we DO know from blue-shift that M31 is coming in our general direction

gave me a chuckle. There was a friend, a geophysicist, with which I used to have fun discussions of astronomical things, whose pet line was about how nothing was showing a blue-shift (approaching us), but that it was as if the whole of the universe were flying away (displaying red-shift). I would love to send him that piece of news, if only I knew where he moved to. :D

On my previous note concerning dark matter and repulsion, among other places, there seems to be a pretty fair concensus:

http://www.nasa.gov/missions/deepspace/cha...atter_halo.html (http://www.nasa.gov/missions/deepspace/chandra_dark_matter_halo.html) (discussing NGC 4555, Chandra data on an eliptical galaxy that may have a containing dark matter "halo")

In this discussion (http://map.gsfc.nasa.gov/m_uni/uni_101matter.html), we see a bone thrown to something discussed popularly and in UT:

the mean energy density in the universe is equal to the critical density (within a 2% margin of error). This is equivalent to a mass density of 9.9 x 10-30 g/cm3, which is equivalent to only 5.9 protons per cubic meter. Of this total density, we now know the breakdown to be: 4% Atoms, 23% Cold Dark Matter, 73% Dark Energy. Thus 96% of the energy density in the universe is in a form that has never been directly detected in the laboratory.


The data places new constraints on the Dark Energy. It seems more like a "cosmological constant" than a negative-pressure energy field called "quintessence". But quintessence is not ruled out.

This Berkeley page (http://astron.berkeley.edu/%7emwhite/darkm...kmatter/dm.html (http://astron.berkeley.edu/%7emwhite/darkmatter/dm.html)) uses the term "pressure", so I suppose then that I misspoke.

Thanks for making me look again.