Colliding Spiral Galaxies of Arp 271 (APOD 21 Jul 2008)

[emc]

http://apod.nasa.gov/apod/ap080721.html

Awesome! My first synapse...

Slooowww to develop is my second synapse... Astronomers must be some of the most patient folks around is all I can say! Takes watching paint dry or grass grow to new heights! And to think, we have to wait 3 billion years for our own experience!

My third synapse... (notice how I like to use the word synapse...) uh oh... I had a synapse a moment ago.... I'll have to get back to this when it starts working again...

[ta152h0]

Must be quite a sight for someone sitting on a parallel planet, orbiting a parallel sun in a similar location as us here but over there .........

[apodman]

Awesome!

As long as we're accustomed to counting spiral arms these days, in the upper spiral I see 2 major arms and I see 2 smaller spurs between the arms. In the lower spiral, I see 2 major arms, each with two small outer spurs, sort of.

The structure of the upper spiral appears relatively undistorted, while the arms of the lower spiral are seriously squared off. If they are similar in mass, why is one galaxy more distorted than the other?

---

Don't forget to look at the telescope that took the picture. I'd like to have one just like it, and the location too.

The link from APOD to the Gemini South Telescope in Chile actually takes you to the Gemini North Telescope in Hawaii, and a link from there takes you South.

Link to Gemini North

Link to Gemini South

[emc]

Must be quite a sight for someone sitting on a parallel planet, orbiting a parallel sun in a similar location as us here but over there .........

It is interesting to speculate on other folks on other planets... makes for some keen stories... I suppose they will need a lot of patience also as the scene unfolds before them ever so slowly. And it is interesting how little effect the merging of two galaxies proposes to be based on the incredible separation of objects. That boggles the mind nearly as much as the timeline we perceive in the merger.

[ta152h0]

Very similar to watching New Horizon's treck to Pluto. Pass the beer

[emc]

Speaking of trecks... Astronomers and/or Astrophyisicists, plus, I am sure, some folks in Asterisk... are aware of how fast the galaxies are moving. I wonder if anyone has mapped the relative motions and gravitational forces involved with the merger. What a monumental task that would be!

What I would love to have is a 3D interactive model of the Universe (just the Universe we can see would be fine) such that I could speed up and reverse at will, animations of the motions of the objects... and I would also like detailed surface features for every object... it's OK if the details are only a snapshot of the same instant in time (not like Google Earth where there are different seasons in the same area). It would be icing on the cake if I could run flight simulations with real life gravitational effects at near infinite speed (whatever that is???). I just don't want to wait too long to get from one side of the universe to the other.

[apodman]

What I would love to have is a 3D interactive model of the Universe (just the Universe we can see would be fine) such that I could speed up and reverse at will, animations of the motions of the objects... and I would also like detailed surface features for every object... it's OK if the details are only a snapshot of the same instant in time (not like Google Earth where there are different seasons in the same area). It would be icing on the cake if I could run flight simulations with real life gravitational effects at near infinite speed (whatever that is???). I just don't want to wait too long to get from one side of the universe to the other.

Last year all you asked for was a pony.

[emc]

Last year all you asked for was a pony.

And that turned out to be just a large pile of pony pooh!

[apodman]

just a large pile of pony pooh

Keep digging, the pony is in there.

[Henning Makholm]

The structure of the upper spiral appears relatively undistorted, while the arms of the lower spiral are seriously squared off. If they are similar in mass, why is one galaxy more distorted than the other?

Similar masses does not necessarily mean that the situation is symmetric. It is clear from the image that the discs of the two galaxies are not parallel. So in general, at any time of the encounter the line connecting the two centres will make different angles to the discs.

As an extreme case, suppose that at the point of closes approach, the A-B line lies in the plane of A's disc but is perpendicular to B's disk. Then B's tides will distort A more than A's tides distort B, because B's stars have approximately the same distance to A whereas A's starts have very different distances to A.

[Chris Peterson]

Must be quite a sight for someone sitting on a parallel planet, orbiting a parallel sun in a similar location as us here but over there

Probably not. All they would be likely to see would be something like a pair of Milky Way bands across their sky. It wouldn't be particularly bright or spectacular. Might mess up the development of their cosmology for a while, until they figured out what was going on.

[apodman]

As an extreme case, suppose that at the point of closes approach, the A-B line lies in the plane of A's disc but is perpendicular to B's disk. Then B's tides will distort A more than A's tides distort B, because B's stars have approximately the same distance to A whereas A's starts have very different distances to A.

Right. Nice succinct explanation. If I had known it would be that neat, I would have tried to look at the problem myself instead of asking. So then I looked back at the picture to try to apply the principle to the actual geometry. I couldn't see it, so I thought of projecting the positions (and therefore angles to the A-B line) back in time. Wondering what direction they each came from led me to my next big dumb question:

Eddies move parallel to their own plane of rotation. Same for wheels and little plastic flying saucers. So I'm predisposed to view galaxies the same way - moving in their own plane of rotation. But is this true? Is a spiral galaxy's plane of rotation related to its line of travel at all?

Or have I done it again? In a relativistic universe, is it even valid to ask a question about "line of travel" in terms of fixed coordinates? In any case can my question be posed in terms of one galaxy's local motion with respect to the other?

[BMAONE23]

I would think that if the spiral galaxies direction of travel were oriented in a path other than/opposed to Its galactic plane, that it would tend to loose some of the flat structure due to drag caused by the intergalactic medium.
While this drag wouldn't be enough to rip the structure apart, it could be sufficient to warp the outer edges in the direction of tumble
Kind of like this
http://antwrp.gsfc.nasa.gov/apod/ap030607.html
Or this one
http://antwrp.gsfc.nasa.gov/apod/ap080619.html

[astrolabe]

Hello All,

I'm fairly sure that this line of discussion appeared here somewhere,

http://asterisk.apod.com/vie ... highlight=

Also this is cool:

http://asterisk.apod.com/vie ... ght=#94966

[Henning Makholm]

So then I looked back at the picture to try to apply the principle to the actual geometry. I couldn't see it, so I thought of projecting the positions (and therefore angles to the A-B line) back in time. Wondering what direction they each came from

... not to mention where the actually are. The picture seems to give no clear hints on whether the galaxy to the right is in front of or behind the one to the left, nor whether we're seeing it from the top or from below.

Eddies move parallel to their own plane of rotation. Same for wheels and little plastic flying saucers. So I'm predisposed to view galaxies the same way - moving in their own plane of rotation. But is this true? Is a spiral galaxy's plane of rotation related to its line of travel at all?

I don't see how it could be. Excepting tidal encounters, the disc will keep its orientation, while the galaxy's center-of-mass moves in curved orbits within its local group of galaxies. And galaxy clusters do not appear to have any preferred planar structure.

As a smaller-scale analogy, consider Uranus. Due to its extreme axial tilt, it is currently traveling through the solar system in a direction nearly parallel to its axis of rotation. But when Voyager 2 visited in 1986, it was more like rolling along the ecliptic.

Or have I done it again? In a relativistic universe, is it even valid to ask a question about "line of travel" in terms of fixed coordinates? In any case can my question be posed in terms of one galaxy's local motion with respect to the other?

Measuring thing with respect to the common center-of-mass sounds potentially meaningful. If the galaxies are part of a gravitationally bound group, its center-of-mass would be an even better choice.

In case we're measuring from the center of mass for just the two interacting galaxies, we have a two-body problem, and the galactic centers will stay in the plane traced out by the A-B line and their initial mutual velocity. But their orbits in that plane will be curved, so unless the disc just happens to be aligned with the twobody plane, the angle between velocity and rotation axis will be varying, and most rapidly during the closest encounter.

[Bravo33]

the interacting pair spans about 130,000 light years

Is this correct? I read that the bridge between them alone was over 60,000 light years in length. Or am I misunderstanding the statement?

[emc]

In reference to my wish for a 3D Universe model... guess it will have to wait a while based on the preceding debate regarding the motions of the two galaxies merging. How can anyone build a model without numbers... we need numbers like mass, trajectories, speed, gravitational force, dark matter, dust particles, etc. I don't think I can wait long enough for the merge to develop of its own doing. Have you ever tried to watch grass grow or paint dry? I have and it doesn't work... either some bug or bird distracts you or you simply fall over and loose track.

Speaking of dust particles and dark matter... hey apodman, I reached the bottom of the pony pooh and guess what... no pony! But I did discover a hole... a very dark hole... black in fact... now I am not so sure about the pony pooh... it is very very dark also... matter of fact, it is so dark I can barely see it.

[henk21cm]

In reference to my wish for a 3D Universe model... guess it will have to wait a while based on the preceding debate regarding the motions of the two galaxies merging. How can anyone build a model without numbers... we need numbers like mass, trajectories, speed, gravitational force, dark matter, dust particles, etc. I don't think I can wait long enough for the merge to develop of its own doing.

Art Neufer has send me earlier this year a link to a website, where you can run your own simulations of collisions. Art convinced me that writing a collision program of my own, using a straight forward Newtonian approach, was due to fail, since the orbits of stars around the center of the galaxy don't follow Kepplers 3rd law. The rotational velocity in the spiral arms is more or less constant, when the distance from the center is more than 0.1 R (radius of the galaxy).


Credit: Galaxy Crash

The simulations are nice and reveal what may happen. I ran a lot of them. Figuring out what influences the outcome, tickles the imagination and is certainly not as dull, as watching wallpaper slowly loose its colour or digging for an imaginary pony. Unfortunatedly i did not succeed to copy the result of the mice.

[bystander]

simulations of collisions

URL change: http://burro.astr.cwru.edu/JavaLab/GalC ... /main.html

I had wondered what happened to your galaxy crash program. Decided to not reinvent the wheel?

[henk21cm]

The url has changed: http://burro.astr.cwru.edu/JavaLab/GalC ... /main.html

OK, thanks, the old link still works.

I had wondered what happened to your galaxy crash program. Decided to not reinvent the wheel?

The comparison with a wheel is OK, in the simulations of Galaxy Crash lab the orbits are free, in the simulations i ran, the orbits are fixed like the spokes of a wheel. The results of these simulations are under way. Since a few weeks i can "publish" results on a limited webpage. In the meanwhile i got a replacing power supply for my computer on which i ran the simulations (its power supply stopped rather abruptly). Next step is to "publish" the first results on this forum or in the Asterisk*Cafe: what are the results. Thereafter, if not being completely ridiculized, i can change the distribution of stars in the galaxies, include a tilting angle etc and see what the effects are.

[emc]

[snipped]

The simulations are nice and reveal what may happen. I ran a lot of them. Figuring out what influences the outcome, tickles the imagination and is certainly not as dull, as watching wallpaper slowly loose its colour or digging for an imaginary pony. Unfortunatedly i did not succeed to copy the result of the mice.

Henk, I enjoy your contributions and appreciate your work. You help make my experience here more fun.