A striking version of Fig 1 of that paper is available here: http://www.noao.edu/outreach/press/pr08/images/M86.jpg

Note the “low-velocity” red streamers of hydrogen gas between M 86 and NGC 4438. The green “high-velocity” streamers seen near NGC 4388 at lower right may actually result from “stripping” by the IGM of the Virgo Cluster, but this is somewhat unclear. Also, the authors of the paper find NGC 4435 an unlikely player, as the galaxy has a higher cluster velocity than NGC 4438 and it shows no obvious signs of gravitational distortions that should be visible in this low-mass galaxy if it was interacting.

http://www.youtube.com/watch?v=GAwO1okR074&playnext=1&list=PL00E6D81DC1EEB9CC

animation on Youtube.

Plus this one :

http://www.youtube.com/watch?v=4m-ZVsLf070&feature=related

As well as :

http://news.nationalgeographic.com/news/2009/03/090304-black-hole-ripples.html

for a text article via National Geo.

.. And if you’re patient ..

And live for near eternity!

Beautiful image.

@1. Diederick asks :

I know that stars won’t collide when their galaxies do, but what about their central black holes? Do they actually attract each other and can they collide, and what happens then?

They merge into one larger supermassive black hole. Or can often do so anyhow. As (#5) dartigan has noted already.

@5. dartigen :

I don’t know what would happen if stars did collide but it probably looks pretty. (At least, to someone not in the immediate vicinity – like so many other things.) Black holes I’d imagine would sort of merge together, although again I don’t know what happens.

Stellar collisions~wise it depends on the mass and type of colliding stars.

Blue stragglers known from globularcluster studies are one result as are FK Comae Berenice variables which, I gather, result from the merger of contact binaries.

The collision – merger – of two white dwarfs is one widely acccepted explanation for type Ia supernovae eruptions.

A white dwarf star passing through a red giant probably strips away its outer atmosphere and produces a white dwarf pairing.

I’ve seen some suggestions that a smaller star can actually orbit inside a red supergiants thin atmosphere. (Betelguese specifically.)

Two neutron stars colliding – merging – probably creates a Black hole as well as being a good test for Relativity in the lead up.

Oh, what an unimaginable night (or even day) sky that would be. I would so love to see that but it’s just “not in the stars”.

I don’t know what would happen if stars did collide but it probably looks pretty. (At least, to someone not in the immediate vicinity – like so many other things.) Black holes I’d imagine would sort of merge together, although again I don’t know what happens. (Does anyone? I’d imagine the odds of two supermassive black holes colliding would be tiny, and the odds of it being observable even smaller, but I’m not trying very hard to find any info.)