APOD: Spiral Galaxies in Collision (2014 Jan 19)

[Chris Peterson]

Of course, there will be many close encounters which change the velocity of both stars, but would any of those close encounters cause the resulting velocity of one or both stars to exceed the escape velocity of the merged galaxy? I suspect not, though quite a few stars will be sent off on long vacations before their new orbits can bring them back.

Many stars toward the outside of galaxies have orbital velocities not much greater than their escape velocities. Stars in some observed tidal tails exceed the escape velocity of the combined galactic mass that created those tails. Certainly, the majority of mass will be retained, but a not insignificant amount is likely to be lost. In galaxy clusters, some of the lost mass may be captured by other galaxies and remain bound to the cluster.

[BDanielMayfield]

We havea personal interest in this. Andromeda and the Milky Way will collide ina few mega-millenia. There are several videos online that purport to show wht will happen. This one happens to be especially smooth and '3D'.

John

One potentially possible outcome selected from an almost infinite number of possible outcomes.

I agree with John's interest, but also with Nitpicker's doubts about the prediction.

So when two galaxies merge, sometimes a spiral is produced, and sometimes an elliptical galaxy is produced. I’ve seen forecasts that predict that Andromeda and the Milky Way are destined to become an elliptical after their merger is complete, and that was what the simulation that John provided ended up with.

What determines the type of galaxy that emerges from these mergers? Is there any chance that our local group heavyweights might end up as a giant spiral instead of an elliptical after everything settles out?

Bruce

[Chris Peterson]

So when two galaxies merge, sometimes a spiral is produced, and sometimes an elliptical galaxy is produced. I’ve seen forecasts that predict that Andromeda and the Milky Way are destined to become an elliptical after their merger is complete, and that was what the simulation that John provided ended up with.

What determines the type of galaxy that emerges from these mergers? Is there any chance that our local group heavyweights might end up as a giant spiral instead of an elliptical after everything settles out?

I think it is very rare for galaxy collisions to produce new spirals. The spiral shape was assumed because of conditions present when galaxies formed... conditions that no longer exist. To maintain a spiral, the result of the collision needs to remain a disc (because there is no strong mechanism to bring a globular structure back into a disc). I'd say that post-collision spirals might happen for two reasons. First, one of the colliding galaxies may be much less massive, and therefore only create limited disruption (not so much creating a new spiral as failing to destroy the original one). Second, the discs of the two galaxies may lie on nearly the same plane, resulting in a collision that doesn't move much mass out of that plane.

[BDanielMayfield]

I think it is very rare for galaxy collisions to produce new spirals. The spiral shape was assumed because of conditions present when galaxies formed... conditions that no longer exist. To maintain a spiral, the result of the collision needs to remain a disc (because there is no strong mechanism to bring a globular structure back into a disc). I'd say that post-collision spirals might happen for two reasons. First, one of the colliding galaxies may be much less massive, and therefore only create limited disruption (not so much creating a new spiral as failing to destroy the original one). Second, the discs of the two galaxies may lie on nearly the same plane, resulting in a collision that doesn't move much mass out of that plane.

That makes perfect sense. Thanks

[ta152h0]

need to crank up HAL to run a simulation of this future event and see if I need to be worried about something smacking us again and make another moon. Pass an icecold one, please