Barred Spiral Galaxies

[William]

I have been reviewing recent observations and hypotheses concerning the formation and evolution of galaxies. The recent finding that the Milky Way is a barred spiral leads to the question:

Why do barred spiral galaxies form?

(See next comment as to the time evolution in the percentage of barred spirals galaxies.)

http://geology.wcupa.edu/mgagne/ess111/notes/milky.ppt


http://en.wikipedia.org/wiki/Barred_spiral_galaxy

http://www.news.wisc.edu/11405

[William]

Why would there be an increase in the number of barred spiral galaxies?

What is the "bar" in a barred spiral galaxy?


http://www.astronomy.com/asy/default.aspx?c=a&id=7245

A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts...

Bars have been forming steadily over the last 7 billion years, more than tripling in number. "The recently forming bars are not uniformly distributed across galaxy masses, however, and this is a key finding from our investigation," Sheth explains. "They are forming mostly in the small, low-mass galaxies, whereas among the most massive galaxies, the fraction of bars was the same in the past as it is today."

The findings, Sheth continues, have important ramifications for galaxy evolution. "We know that evolution is generally faster for more massive galaxies: They form their stars early and fast and then fade into red disks. Low-mass galaxies are known to form stars at a slower pace, but now we see that they also made their bars slowly over time," he says.

[Neverfly]

I'm a little confused... The references you gave did not answer your question?

Barred Spirals are a product of galactic evolution. Essentially, a spiral galaxy should grow a bar given time.

The bar is formed due to the immense gravity of the spiral hub. As stars move in their orbits, instability eventually leads to elliptical orbits. As more and more stars develop elliptical orbits, the bar becomes more pronounced.

The Milky Way will lose it's bar spiral status in about 5 billion years.

[William]

In reply to Neverfly, see Original Post: "I'm a little confused... The references you gave did not answer your question?

Barred Spirals are a product of galactic evolution. Essentially, a spiral galaxy should grow a bar given time.

The bar is formed due to the immense gravity of the spiral hub. As stars move in their orbits, instability eventually leads to elliptical orbits. As more and more stars develop elliptical orbits, the bar becomes more pronounced.

The Milky Way will lose it's bar spiral status in about 5 billion years."

Hi Neverfly,

Mass for Spiral Galaxy's Bars?
I do not see how gas can move from the mid point of a galaxy to form the bars. Where is the source of the gas? Extra galactic?

Remember the spiral arms for some odd reason have gas that has not formed stars.

As other authors have noted it is puzzling that the Milky Way's bulge has no gas whereas the spirals that move about a plane in the Milky Way have so much gas they create an optical zone of avoidance for astronomical observation. (i.e. There is no issue with astronomical observations through the Milky Way's bulge.)

As per the paper I quoted, the percentage of barred spiral galaxies increases with time, however, the percentage of barred galaxies, only increases for small galaxies. (i.e. The number of barred galaxies for large galaxies does not change with time.)

Spiral galaxies reach a maximum size
As I noted previously for some odd reason spiral galaxies reach a maximum size.

Event can remove spiral galaxy bars
As noted in the paper some event can happen that causes barred spiral galaxies to loss their bars.

What cause mass to move into galaxy centre?
Besides the issue of where does the mass come from to create the spiral galaxy bars there is the problem of the mechanism by which mass can move toward the centre of the galaxy.

In the formation of the sun and solar system there is a single large cloud of dust. Proto planets form and move toward the centre as there is a continuous disk of gas and particles that can interact as tidal forces slows down the proto planets.

In a galaxy there are vast spaces between stars and gas clouds. There appears to be no mechanism to dissipate the angular momentum and to pull the stars and matter into the centre of the galaxy.

What should form is an elliptical galaxy where there is a random distribution of angular momentum, rather than a spiral galaxy that has bars that revolve in a single plane.

There is quite obviously a different mechanism that is creating and constraining the spiral galaxy.

Comment:
Besides the above issues I thought it was interesting that spiral galaxy's that have bars can suddenly become star burst galaxies which is relevant as our solar system is in this particular galaxy.

As noted below it appears a group of galaxies have some peculiar property where by they can stop star formation in a lone galaxy that approaches them. Interesting the time required for the group of galaxies to stop star formation in the lone galaxy that approaches a group of galaxies is depend on the mass of the lone galaxy.

Strangulation Of Spiral Galaxies: ‘Missing Link’ Discovered

http://www.sciencedaily.com/releases...1124194936.htm

[Neverfly]

William,
I don't have much of solid answers to most of what you just said.
Hopefully some of the much more knowledgeable folks here can provide greater insight.

I'm going off some things I had read in books some time ago and don't have those books handy for referencing. Sadly.

[StupendousMan]

William,

You'll find the answers to many of your questions in a good graduate textbook on galactic astronomy. Please go read one. I suggest Binney and Tremaine, "Galactic Dynamics."

Understanding the formation of bars in galaxies due to self-gravitational instabilities requires a good deal of mathematical background. If you find the graduate-level texts too difficult, try starting with some advanced undergraduate texts, such as Shu's "The Physics of Astrophysics."

After you've read the chapter on spiral structure in one of these books, please come back and ask us any questions which remain.

[Buttercup]

Barred spiral galaxies are my favorite. Awesomely pretty.

[parejkoj]

While cleaning out my backlog of links and filling the papers into Papers¹, I re-ran into Barred Galaxies: an Observer's Perspective by Dimitri Gadotti. Figured it was relevant here.

1. If you do research and have a Mac, go get it right now! It's great - it understands ADS and arXiv and can perform searches within them, keeps track of what you've read and what you haven't, can produce BibTeX files from collections and "smart collections" which are like smart folders in Finder, iTunes or iPhoto and has a--currently limited--note-taking capability which is planned to be expanded into full hi-lighting and context-sensitive notes in the future!