Starship Asterisk*

Rakeera wrote:I noticed what appears to be a foreground star to the lower right of M63 that seems to be affecting the sunflower Galaxy. Could this star be hiding a dwarf galaxy behind it?

Ann wrote:My point is that interactions can both enhance, disrupt and perhaps destroy a galaxy's spiral structure.

Ann wrote:

starsurfer wrote:

Ann wrote:
Okay!

So do you think that the chaotic nature of the spiral pattern of flocculent galaxies as well as their extended tidal shells can be products of mergers and collisions?

Ann

Isn't it generally accepted that the spiral structure in galaxies is a result of density waves? I think collisions would affect density waves and therefore the overall structure. You can easily see this in the visual appearance of interacting and peculiar galaxies.

Click to view full size image

M51, a grand design galaxy with long arms, and companion NGC 5195. Photo: Bill Snyder.

Click to view full size image

NGC 2775, a flocculent galaxy with patchy, broken spiral fragments. Photo: Adam Block.

It is certainly true that interactions can enhance the spiral structure of disk galaxies. M51, the Whirlpool galaxy, is the poster child for this sort of enhanced spiral structure through interactions with another galaxy. Bill Snyder's picture also shows large tidal shells surrounding both M51 and its companion, NGC 5195. These shells are clearly also caused by the mutual interactions.

But take a look at Adam Block's picture of NGC 2775. Go to this page to see a full size image of it. Here you can also see a huge tidal shell surrounding NGC 2775.

NGC 2775 could be considered a poster child for flocculent galaxies. Its spiral structure is extremely broken up and patchy.

But NGC 2775 doesn't have any sort of companion that is in any way comparable to the Whirlpool Galaxy's NGC 5195. Adam Block's full size image shows two small blue galaxies at upper right of NGC 2775; they could be at the same distance as NGC 2775 and possibly be interacting with it, but being small and blue, they are quite clearly not very massive. A small yellowish galaxy is visible in the lower left corner of the full size image. Being yellowish, it is a bit more massive than the small blue ones, but no tidal bridge can be seen between this galaxy and NGC 2775.

I'm wondering if NGC 2775 could have interacted rather violently with another galaxy and perhaps merged with it. That would explain the huge tidal shell. It could also possibly explain NGC 2775's extremely patchy and almost disintegrated spiral structure.

My point is that interactions can both enhance, disrupt and perhaps destroy a galaxy's spiral structure.

Ann

starsurfer wrote:

Ann wrote:

starsurfer wrote: What you describe as haloes in these particular galaxies are actually examples of tidal shells.

Okay!

So do you think that the chaotic nature of the spiral pattern of flocculent galaxies as well as their extended tidal shells can be products of mergers and collisions?

Ann

Isn't it generally accepted that the spiral structure in galaxies is a result of density waves? I think collisions would affect density waves and therefore the overall structure. You can easily see this in the visual appearance of interacting and peculiar galaxies.

Ann wrote:

starsurfer wrote:

Ann wrote:M83 is a so-called flocculent galaxy, one that doesn't have long elegant spiral arms, but rather many short arm segments.

An interesting aspect of today's APOD is that it demonstrates that M63 has an extended halo.

Other flocculent galaxies also have extended halos:

My own guess is that the somewhat chaotic nature of the spiral pattern of flocculent galaxies, as well as their huge extended halos, may be products of mergers and collisions.

Ann

What you describe as haloes in these particular galaxies are actually examples of tidal shells.

Okay!

So do you think that the chaotic nature of the spiral pattern of flocculent galaxies as well as their extended tidal shells can be products of mergers and collisions?

Ann

Ann wrote:

chuckster wrote:Spiral structure in galaxies- from what does it arise? Intuitively, it seems to come from spinning, but that can't be right,
based on all the other flavors of galactic structure. I've read (or heard) that spiral structure is massaged into the galactic disc by gravity waves propagating out from a central black hole.

Black holes don't give galaxies spiral structures.

Check out this list of massive black holes in other galaxies. I haven't bothered trying to identify the galaxies with the fancy designations, but my software easily recognizes the NGC and the Messier galaxies. Most of the NGC and the Messier galaxies in that list are elliptical galaxies, without spiral structure. The spiral galaxies in that list, such as the Andromeda galaxy, the Sombrero galaxy and M81, don't host the most massive black holes.

Ann

Chris Peterson wrote:

chuckster wrote:Spiral structure in galaxies- from what does it arise? Intuitively, it seems to come from spinning, but that can't be right,
based on all the other flavors of galactic structure. I've read (or heard) that spiral structure is massaged into the galactic disc by gravity waves propagating out from a central black hole.

It has nothing to do with gravitational waves. You can read about the more well accepted ideas here.

Ann wrote:
My own guess is that the somewhat chaotic nature of the spiral pattern of flocculent galaxies, as well as their huge extended halos, may be products of mergers and collisions.

https://en.wikipedia.org/wiki/Triangulum_Galaxy wrote:

[b][color=#0000FF][size=135]Triangulum Galaxy taken by VLT Survey Telescope[/size][/color][/b]

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<<In 2004, evidence was announced of a clumpy stream of hydrogen gas linking the Andromeda Galaxy [~1 trillion stars] with Triangulum [~40 billion stars], suggesting that the two may have tidally interacted in the past. This discovery was confirmed in 2011. A distance of less than 300 kiloparsecs between the two supports this hypothesis. A past interaction between these two galaxies took place from 2 to 8 billion years ago, and a more violent encounter will occur 2.5 billion years in the future.>>

http://apod.nasa.gov/apod/ap150926.html
http://apod.nasa.gov/apod/ap121220.html

starsurfer wrote:

Ann wrote:M83 is a so-called flocculent galaxy, one that doesn't have long elegant spiral arms, but rather many short arm segments.

An interesting aspect of today's APOD is that it demonstrates that M63 has an extended halo.

Other flocculent galaxies also have extended halos:

My own guess is that the somewhat chaotic nature of the spiral pattern of flocculent galaxies, as well as their huge extended halos, may be products of mergers and collisions.

Ann

What you describe as haloes in these particular galaxies are actually examples of tidal shells.

Ann wrote:M83 is a so-called flocculent galaxy, one that doesn't have long elegant spiral arms, but rather many short arm segments.

An interesting aspect of today's APOD is that it demonstrates that M63 has an extended halo.

Other flocculent galaxies also have extended halos:

Click to view full size image

NGC 3521. Photo: R Jay GaBany, David Martinez-Delgado et al.

Click to view full size image

NGC 4414. Photo: Adam Block.

My own guess is that the somewhat chaotic nature of the spiral pattern of flocculent galaxies, as well as their huge extended halos, may be products of mergers and collisions.

Ann

chuckster wrote:Spiral structure in galaxies- from what does it arise? Intuitively, it seems to come from spinning, but that can't be right,
based on all the other flavors of galactic structure. I've read (or heard) that spiral structure is massaged into the galactic disc by gravity waves propagating out from a central black hole.

chuckster wrote:Spiral structure in galaxies- from what does it arise? Intuitively, it seems to come from spinning, but that can't be right,
based on all the other flavors of galactic structure. I've read (or heard) that spiral structure is massaged into the galactic disc by gravity waves propagating out from a central black hole.

ShaileshS wrote:
If 2 spiral medium size galaxies collide (e.g. Andromeda and Milky way), then resultant will be eliptical, I heard. Why ? Why not bigger spiral ? And, what happens when 2 elliptical galaxies collide OR when 1 elliptical and 1 spiral collide ?

https://en.wikipedia.org/wiki/Spiral_galaxy#Alignment_of_spin_axis_with_cosmic_voids wrote:
<<Recent results suggest that the orientation of the spin axis of spiral galaxies is not a chance result, but instead they are preferentially aligned along the surface of cosmic voids. That is, spiral galaxies tend to be oriented at a high angle of inclination relative to the large-scale structure of the surroundings. They have been described as lining up like "beads on a string," with their axis of rotation following the filaments around the edges of the voids.>>

https://en.wikipedia.org/wiki/Void_(astronomy) wrote:

[b][color=#0000FF]Matter distribution in a cubic section of the Universe. The blue fiber structures represent the matter (primarily dark matter) and the empty regions in between represent the cosmic voids.[/color][/b]

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<<Cosmic voids are the vast empty spaces between filaments (the largest-scale structures in the Universe), which contain very few or no galaxies. Voids typically have a diameter of 10 to 100 megaparsecs; particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They have less than one-tenth of the average density of matter abundance that is considered typical for the observable Universe.

Voids are believed to have been formed by baryon acoustic oscillations in the Big Bang, collapses of mass followed by implosions of the compressed baryonic matter. Starting from initially small anisotropies from quantum fluctuations in the early Universe, the anisotropies grew larger in scale over time. Regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or “cosmic web” of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe.

Voids appear to correlate with the observed temperature of the cosmic microwave background (CMB) because of the Sachs–Wolfe effect. Colder regions correlate with voids and hotter regions correlate with filaments because of gravitational redshifting. As the Sachs–Wolfe effect is only significant if the Universe is dominated by radiation or dark energy, the existence of voids is significant in providing physical evidence for dark energy.>>

ShaileshS wrote:If spiral galaxy comes in contact with a dwarf galaxy then the resultant will be still spiral (just a bigger version). Right ? If 2 spiral medium size galaxies collide (e.g. Andromeda and Milky way), then resultant will be eliptical, I heard. Why ? Why not bigger spiral ? And, what happens when 2 elliptical galaxies collide OR when 1 elliptical and 1 spiral collide ? Thanks in advance for all the answers and comments.

http://www.nasa.gov/feature/jpl/astrono ... l-galaxies wrote:
A strange new kind of galactic beast has been spotted in the cosmic wilderness. Dubbed "super spirals," these unprecedented galaxies dwarf our own spiral galaxy, the Milky Way, and compete in size and brightness with the largest galaxies in the universe...

In a sample of approximately 800,000 galaxies no more than 3.5 billion light-years from Earth, 53 of the brightest galaxies intriguingly had a spiral, rather than elliptical, shape...

A vital hint about the potential origin of super spirals is that four out of the 53 seen by Ogle and colleagues clearly contain two galactic nuclei, instead of just one as usual. Double nuclei, which look like two egg yolks frying in a pan, are a telltale sign of two galaxies having just merged together. Conventionally, mergers of spiral galaxies are destined to become bloated, elliptical galaxies. Yet Ogle and colleagues speculate that a special merger involving two, gas-rich spiral galaxies could see their pooled gases settle down into a new, larger stellar disk -- presto, a super spiral...

ShaileshS wrote:If spiral galaxy comes in contact with a dwarf galaxy then the resultant will be still spiral (just a bigger version). Right ? If 2 spiral medium size galaxies collide (e.g. Andromeda and Milky way), then resultant will be eliptical, I heard. Why ? Why not bigger spiral ? And, what happens when 2 elliptical galaxies collide OR when 1 elliptical and 1 spiral collide ? Thanks in advance for all the answers and comments.