Starship Asterisk*

The Slow Dance of Galaxies NGC 5394 and 5395

Explanation: If you like slow dances, then this may be one for you. A single turn in this dance takes several hundred million years. Two galaxies, NGC 5394 and NGC 5395, slowly whirl about each other in a gravitational interaction that sets off a flourish of sparks in the form of new stars. The featured image, taken with the Gemini North 8-meter telescope on Maunakea, Hawaii, USA, combines four different colors. Emission from hydrogen gas, colored red, marks stellar nurseries where new stars drive the evolution of the galaxies. Also visible are dark dust lanes that mark gas that will eventually become stellar nurseries. If you look carefully you will see many more galaxies in the background, some involved in their own slow cosmic dances.

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NGC 5394 and NGC 5395, also known as Arp 84, also known as the Heron Galaxy!





























James D Wray paid special attention to NGC 5395 in his Color Atlas of Galaxies.






Look at the closeup on NGC 5395 at right. Note the bright white "arc" above the galaxy's core.

James D Wray described this feature as a fossil feature. This means that the bright arc was once the site of tremendous star formation, but all the O- and early B-type stars have died. What remains is a dense "soup" of A- and F-type stars (along with fainter and redder stars, obviously). The arc-shape is due to the fact that this feature was once a spiral arm peppered with tremendous clusters. Now the clusters are gone, and only a vast number of intermediate and low-mass stars mark the site of this former wild burst of star formation.





Maybe the fossil arm of NGC 5395 was once like the spiral arm in M83 at left, although probably even more bursting in star formation.

Ann

I now pronounce you Mr. & Mrs Galaxy!

Wondering what the difference in interaction of these two galaxies that appear to be in the same rotational direction vs galaxies that collide coming at each other in opposite rotation.

OB1Kubota wrote: ↑Wed Mar 04, 2020 2:35 pm Wondering what the difference in interaction of these two galaxies that appear to be in the same rotational direction vs galaxies that collide coming at each other in opposite rotation.

Hmmm ... on looking at the image, it was my guess that these two are rotating in nearly opposite directions. Just inferring from the direction of curvature of their spiral arms, that is.

Galaxies are my favorite apods & merging galaxies are even more enjoyable.What I would give to see this sped up( not a simulation).What a truly bizarre Universe.

Would love to see a close up of the jellyfish merge at 3:00.

I often wonder what the night sky would look like if I was on a planet orbiting a star say in the filament that spans the galaxies.

Thanks Mark. Made my observation backwards. But question remains the same.

OB1Kubota wrote: ↑Thu Mar 05, 2020 4:24 am Thanks Mark. Made my observation backwards. But question remains the same.

Yeah, sorry, it's easier to nitpick than to answer a deep question.
I guess I replied because I had been looking at them and thinking of very similar questions.
I'd love to get the software from one of the better galactic collision simulations and do some runs.
If I wasn't lazy, I'd write one, since I don't think it's hard, but the runs probably require supercomputer time.
However, to answer your question could probably be done with models containing just a thousand stars or less.

From what I've seen, when two grand spirals merge, regardless of rotation direction, they are very likely to hugely reduce each other's rotation. If they approach each other edge on, the net rotations are still very cancelling regardless of whether they matched or were opposite before merger. Often you get an elliptical, with low rotation. I think the main counter-example would be two galaxies that approached each other face-on to face-on and were rotating in the same direction.

Anyway, I'd love to hear an answer from someone who's actually done these sims, since I've only seen a modest number of publicized examples.