Milky Way is a barred spiral

[Martin]

http://www.newscientist.com/article.ns?id=dn7854

 

"The Milky Way is not a perfect spiral galaxy but instead sports a long bar through its centre, according to new infrared observations from NASA's Spitzer Space Telescope.

 

Galaxies come in a wide variety of shapes usually thought to be produced by gravitational interactions with nearby objects. Some spiral galaxies look like pinwheels, with their arms curving out from a central bulge, while others have a straight bar at their centres."

 

Our galaxy's central bar is estimated to be about 27,000 lightyears long.

[MetaFrizzics]

This is bad news for us.

The galaxy has a much shorter life expectancy with the destabilizing bar, feeding the black hole at the centre. By the time we meet bizzarro superman on the other side of the galaxy, it will be all over.

[Martin]

This is bad news for us.

The galaxy has a much shorter life expectancy with the destabilizing bar' date=' feeding the black hole at the centre. By the time we meet bizzarro superman on the other side of the galaxy, it will be all over.[/quote']

 

Hi MetaFrizzics, my normal condition in life is not knowing stuff (NOT being an expert about a lot of things, in spite of getting to wear the hat of one) and also being skeptical.

 

so naturally I would like it very much if you would supply a link to a source

 

 

that tells about the barred spiral type decaying into some other type or whatever it does that lets you define the "lifetime" and say that it is short.

 

that should be very interesting to learn about

 

what is your estimate of barred spiral lifetimes, and what other type of galaxy (simple spiral, eliptical, whatever) does it decay into?

 

and what's a link to some journal article about it?

 

thanks,

 

Martin

[Martin]

for people who like journal article e-prints, you can get a PDF here

 

http://arxiv.org/astro-ph/0508325

 

this is the technical article on which the New Scientist popular article is based.

 

BTW----the black hole at the center of Milky is comparatively small, only about 2.5 million solar masses.

 

We at SFN have seen animation shots taken of stars orbiting this modest black hole. they whip around and swing out again. they don't immediately get gobbled up

 

Our galaxy has been around for roughly 10 billion earth years and (if these new observations are right) it still has its barred-spiral shape.

nothing much has happened to disturb that shape, apparently

 

and the central black hole is still pretty small as such things go.

 

so not being an astronomer I cant say but I would guess, just from common sense, that Milky's structure is pretty damn stable and slow-changing.

 

So I am skeptical of what MetaFriz says. he has to clarify what he is talking and give some technical source links, or i have to suspect its wrong.

Want to keep an open mind tho. Be delighted to see some evidence that Milky's "lifetime" however that is defined, exactly, is "short" whatever that means.

[MetaFrizzics]

While the Milky Way is obviously as 'old' as other comparable galaxies, it should be obvious that it cannot have had its 'bar' shape for its entire lifetime. Consider that strictly from the common-sense view of Newtonian physics (which is what astronomers rely upon alot), the 'bar' must have formed some time in the middle of the Milky Way's history. It is obviously an anomaly, and the disjoint structure created by it's combination with the rest of the galaxy bespeaks of a growth/decay process. Only one of two general scenarios seem probable by my understanding of the forces of rotating systems acting in a 'liquid' like flow pattern under gravitational forces:

 

(1) the 'bar' is expanding, eating alive the galaxy as it does so, by drastically changing the normally semi-circular orbits of the stars and systems at its radial border, pulling them out of orbit and into extreme / chaotic elliptical orbits similar to comets.

 

(2) the 'bar' is contracting, as stars at the outer edge fall back into a trailing spiral. This scenario may have greater promise of a 'stable' final form for the galaxy, which nonetheless mean huge changes in the gravitational field where the Sun is located.

 

That is to say, the bar is an artifact of 'turbulence': a type of turbulence which by nature must be destabilizing the motion of the galaxy arms. It seems unlikely to me from the viewpoint of large-scale entropy that the galaxy could be undergoing a 'reverse' process of stabilization of chaotic motion.

 

Bar Galaxy Research <-- click here

 

[Martin]

Bravo for you MetaFriz!

 

It is great to see a link to some research!

 

(However I think your interpretation is questionable)

 

The first thing that I respond to very positively (whether or not I am convinced by your reasoning) is that you have a link to a really fine source

the work of a an attractive young postdoc at Penn State.

Penn State, and the IGPG that she links to, is a great place and I've found their site to be a resource I go back to over and over again

 

You hit a motherlode of good information.

 

the particular postdoc is

kellyhb@gravity.psu.edu

Kelly Holley-Bockelmann

 

and she does COMPUTER SIMULATIONS OF GALAXIES

 

so she would be an excellent person to ask if there is anything unstable about Milky's bar-spiral form

and if it would be expected to evolve (over what timescale?) into some different galaxy type (like elliptical or pure unbarred spiral)

 

Kelly seems like a great person to ask about that.

 

 

But BTW even if our galaxy DID evolve gradually into some different type of shape it probably would not HURT.

I suspect that galaxies can even collide without disturbing most of the individual stars---most of the individual stars would hardly notice what is happening---two spiral galaxies can collide and merge into one elliptical galaxy---in the merger they kind of moosh each other up and they lose the nice spiral shapes.

 

This is what I SUSPECT, but I don't have source-links about computer simulations of galaxy collision and evolution of galaxy shape.

 

And since i only suspect it, and don't have sources to cite, I have to acknowledge that you could be RIGHT and I would be happy to be proven wrong, if you can find the articles to prove it.

 

A lot of galaxy simulation has been done, computer simulations of collision and that sort of thing. I've seen the frame-by-frame results---just dont happen to have links. Maybe you can find some links.

[Martin]

Just a reminder: if you like technical journal article e-prints, you can get a PDF here

 

http://arxiv.org/astro-ph/0508325

 

of the technical article on which the New Scientist popular article is based.

 

The black hole at the center of Milky has been observed and is comparatively small, only about 2.5 million solar masses. At one time i had a link to time-lapse observations that made a little animated movie of stars orbiting the hole. Does anybody still have that link?

 

I've also seen the graphic results of computer galaxy simulation studies where they set up, for instance, a collision of two galaxies and watch it evolve over several tens of millions of years.

 

Again at the moment I don't have a link to that stuff. Can anyone help out with sources?

 

My guess is that our galaxy's bar-spiral shape is very stable and beautiful, and that this news (aside from being aesthetically satisfying) is not of great consequence. A question came up whether one should be alarmed or not. I think not. Any comment on that?

[Martin]

another reminder: the link which Friz found was

http://cgwp.gravity.psu.edu/people/cgwp_kholley-bockelmann.shtml

and the friendly looking postdoc who is doing the computer simulations of galaxies address is

 

kellyhb@gravity.psu.edu

 

It might not be a bad idea, if anyone was interested, to simply write email to kelly and ask her a simple question like

 

Dear kelly, we at SFN liked the webpage you put up about your galaxy sims.

 

If you have time please answer this question: do barred spiral galaxies, like milkyway, decay with time into some other type like an unbarred spiral?

 

If anything weird happens to barred spirals, please tell us and give some idea of the timescale!

 

thanks,

[some posters at SFN discussion board]