APOD: M89: Elliptical Galaxy with Outer... (2017 Jun 14)

[BDanielMayfield]

The classifications of spiral, lenticular, and elliptical are morphological, and may not be clearly related to galaxy evolution.

I seem to recall from school days in the sixties and seventies that some astronomers believed that there was a progression from spiral to elliptical over time. I remember seeing illustrations of galaxy types that may have had arrows depicting an assumed evolution over time.

Of course, back in those days, there were no large adaptive optics or orbiting telescopes, nor were there super computers doing massive galactic merger simulations. The view has greatly improved.

As far as the coming merger between our galaxy and Andromeda is concerned, is it certain that "Milkdromeda" must ultimately wind up as an elliptical? Is there a chance that it could become a super large spiral?

Bruce

[Chris Peterson]

The classifications of spiral, lenticular, and elliptical are morphological, and may not be clearly related to galaxy evolution.

I seem to recall from school days in the sixties and seventies that some astronomers believed that there was a progression from spiral to elliptical over time. I remember seeing illustrations of galaxy types that may have had arrows depicting an assumed evolution over time.

And that might be true. Or partly true. Or true in some cases. But most of those diagrams are a bit misleading, since they don't generally represent an evolutionary trend, merely morphological distinctions.

As far as the coming merger between our galaxy and Andromeda is concerned, is it certain that "Milkdromeda" must ultimately wind up as an elliptical? Is there a chance that it could become a super large spiral?

I don't see how. Spirals formed under different conditions, that allowed angular momentum transfer and the formation of a disc. Any disruption now will scatter the inclination of stars. There's no mechanism to restore a disc.

[BDanielMayfield]

As far as the coming merger between our galaxy and Andromeda is concerned, is it certain that "Milkdromeda" must ultimately wind up as an elliptical? Is there a chance that it could become a super large spiral?

I don't see how. Spirals formed under different conditions, that allowed angular momentum transfer and the formation of a disc. Any disruption now will scatter the inclination of stars. There's no mechanism to restore a disc.

Right. In thinking about my question further and with the aid of your points I can only see one pathway that could maybe just possibly result in a bigger spiral from the merger of two of them. If the disks of the two galaxies were in the same plain, if the approach vectors of both of them were also in the same plain, if they are rotating in the same direction, and if the first pass occurred on the correct sides of both galaxies such that the rotations of both sets of spiral arms allow most disk star orbits to receive minimal perturbations ...

We northern hemisphere observers can already see even with our own bare eyes if we have dark skies that Andromeda and the Milky Way are badly misaligned for such a smooth merger. Ah sucks. Should have thought of that myself.

The odds against two big spirals merging to form an even bigger spiral must be ... astronomical. It could happen though, maybe, to a galaxy pair far, far, away.

Bruce

[Chris Peterson]

As far as the coming merger between our galaxy and Andromeda is concerned, is it certain that "Milkdromeda" must ultimately wind up as an elliptical? Is there a chance that it could become a super large spiral?

I don't see how. Spirals formed under different conditions, that allowed angular momentum transfer and the formation of a disc. Any disruption now will scatter the inclination of stars. There's no mechanism to restore a disc.

Right. In thinking about my question further and with the aid of your points I can only see one pathway that could maybe just possibly result in a bigger spiral from the merger of two of them. If the disks of the two galaxies were in the same plain, if the approach vectors of both of them were also in the same plain, if they are rotating in the same direction, and if the first pass occurred on the correct sides of both galaxies such that the rotations of both sets of spiral arms allow most disk star orbits to receive minimal perturbations ...

I wonder if that might not be the most disruptive collision, since the bulges would cross the discs. Maybe the least disruptive collision wouldn't have the galaxies on the same plane, but crossing each other along their common rotation axes with their planes parallel.

[Ann]

Why is it that basically all spiral galaxies are growing a yellow elliptical galaxy in their centers?

It would certainly seem that all spiral galaxies are slowly transforming themselves into ellipticals one way or another.

Why do you think that the bulges of spiral galaxies are evolving or changing or growing? I don't know of anything to suggest that spirals become ellipticals through any process other than tidal disruption by other galaxies.

hubblesite.org wrote:

Click to view full size image

Galaxy Cluster MACS J2129-0741 and Lensed Galaxy MACS2129-1
Science: NASA, ESA, and S. Toft (University of Copenhagen)
Acknowledgment: NASA, ESA, M. Postman (STScI), and the CLASH team

By combining the power of a "natural lens" in space with the capability of NASA's Hubble Space Telescope, astronomers made a surprising discovery—the first example of a compact yet massive, fast-spinning, disk-shaped galaxy that stopped making stars only a few billion years after the big bang.

Finding such a galaxy early in the history of the universe challenges the current understanding of how massive galaxies form and evolve, say researchers.

When Hubble photographed the galaxy, astronomers expected to see a chaotic ball of stars formed through galaxies merging together. Instead, they saw evidence that the stars were born in a pancake-shaped disk.

This is the first direct observational evidence that at least some of the earliest so-called "dead" galaxies — where star formation stopped — somehow evolve from a Milky Way-shaped disk into the giant elliptical galaxies we see today.

http://asterisk.apod.com/viewtopic.php?t=37314

I don't know if this challenges or contradicts your point, Chris. I thought it was interesting.

Ann

[Chris Peterson]

I don't know if this challenges or contradicts your point, Chris. I thought it was interesting.

No, I don't think it does either. Recent observations have made clear that a lot of unusual and unexplained things were going on with galaxies very early in the Universe. That's quite a different environment from what we see in galaxies in the more evolved Universe.

[Happylimpet]

Horrible fake diffraction spikes! Makes one wonder how real this image is. Can't fakery be banned on APOD?

[neufer]

Click to play embedded YouTube video.

The Milky Way is currently colliding with several dwarf galaxies, with streams of stars extending above & below the galactic disk. Evidence of devastation in those areas where the streams intersect with the disk? Uhh, no, but the Milky Way continues into its "good night", 'unperturbed', as it were.

Perhaps what drives such 'sentiments', that of enormous black holes 'tearing up the turf'/wreaking devastation on any that resist them, is the empowerment an 'editor' receives .. when contributing to Wikipedia?