Our Milky Way Galaxy is barred!

Actually, that was known for a while, but Spitzer Space Telescope has some great new data expanding on our previous knowledge.

Read all about it. And check out the amazing illustration they have. Quite pretty.

The news release text is here.

Truly amazing picture.

I wonder how accurately the spiral arms are depicted. Is it yet known how complete the arms are in the Milky Way? Because some galaxies have very intact arms, whereas the arms are very fragmentary in some galaxies.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Our group hosted a conference on barred galaxies about 8 years ago. As is customary, we scheduled some social events, including a tour of the nearby Moundville archaeological site and an outdoor barbecue (actual pork flesh cooked over flame with a sauce involving tomatos and peppers, none of the West Coast confusion in which the simple act of outdoor cooking qualifies). Anyway, at one such event, to honor recent discoveries from IR surveys, chief organizer Ron Buta handed everyone a

--- wait for it---





Milky Way bar.

Yes it is, although the temptation to alter that photo and replace "sun" with "you are here" is almost overpowering. Thanfully I'm 20 miles from my computer with Photoshop.

I own one of these t-shirts with that.
I like to wear it when I lead hikes, in case people are worried about getting lost.

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This is so cool. 8)

I was already enjoying the potential ramifications from this discovery, and now have even more goodies to bear in mind when pondering our appearance.

Darn skippy this changes things. I was brought up to think that spiral galaxies were the norm, since we live in one, and that barred, irregular, and ellipticals were exotic.

Pot and kettle.

Faultline

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OK, so what does this mean in the realm of the millions of galaxies we can see from afar?

Nick

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

"Stars in the spiral arms circle the galaxy in roughly circular orbits. But the old, red stars in the bar appear to be on more elliptical paths that take them more directly towards and away from the galaxy's core, where a colossal black hole is thought to lurk."

Why do the stars in the bar move in elliptical paths?

That was a bit of a simplification. A bar happens when the mass distribution is elongated; even a small disturbance can grow into a bar if the galaxy's mass distribution has the right profile. An individual star in a bar can have one of several kinds of orbits (and in fact can leak between these families in the way described by parts of chaos theory). It may have an elliptical path centered at the center (since the mass isn't all at the center, not quite as Kepler said). Different initial conditions give box orbits, which wander around in smooth versions of the skeleton of a box kite. There are also so-called X-orbits which cross the principal axes of the bar several times per orbit (they project like Lissajous figures). Farther out in the disk, the mass distribution is more symmetric (since the stars are farther from the bar) and the orbits are more neary circular (although orbits with any inclination to the disk aren't circular anyway; they bob up and down from the disk plane with a different frequency than the orbit).

Having a bar makes the Milky Way thoroughly normal. In de Vaucouleurs' version of galaxy classifications, about 1/3 of spirals have a strong bar, another 1/3 have a central bar which isn't so strong and you have to be primed to notice, and the other 1/3 have essentially no such oval distortion at the center. (These fractions change as you get to so-called late-type spirals, beyond about Hubble type Sc).

Thank you for your explanation

Looks like Richard Powell got it nearly right in his Atlas of the Universe website.

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Sorta like a kinder, gentler Total Perspective Vortex...

Too bad Douglas Adams isn't still around. What a follow up (or prequel) to The Restaurant at the End of the Universe: The Bar at the Center of the Galaxy. Make mine a double!

BTW, that's how the AP reported it.

Amazing job of surveying BTW, with stunning results. =D>

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If I may quote from the first paper reporting alcohol at the galactic center (B. Zuckerman et al, Astrophysical Journal Letters 196, L99, 1975), omitting embedded citations and the link since it has characters that BBCode doesn't like:

Ethyl alcohol has been of interest to manking since the dawn of te earliest civilizations. During early October of 1974 we detected a truly astronomical source of ethyl alcohol located in the general direction of the center of our Galaxy. Prelinminary estimates indicate that the alcoholic content of this cloud (Sgr B2), if purged of all impurities and condensed, would yield approximately 10^28 fifths at 200 proof. This exceeds the ttotal amount of all man's fermentation efforts since the beginning of recorded history.

A chance like that comes along at best once in most scientists' careers.

Amazing photo! =D> I just had no idea Spitzer had such an elliptical orbit. [sorry :-? had to say it.]

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Lighten up! This is a stellar board!

So ... wait, you mean the stars in the bar are almost entirely old (Pop II) stars? There's little no star formation going on in the bar?

That depends on what kind of barred galaxy and where in the bar. In late Hubble types (SBbc-SBc-SBcd) there are strong shocks among interstellar clouds driving star formation all along the bar. In earlier Hubble types (SBa-SBb), the bar falls off in density more strongly with distance from the core, making the orbits avoid such tight crossing. Star formation in these bars is confined to a tight, often spiral or annular region within the inner couple of thousand light-years. There are also barred S0 galaxies (SB0) whose bars really are solely composed of old stars.

The Milky Way may fit the pattern of centrally-condensed star formation, falling in Hubble type just about where these two kinds of bar change over. The outer bar is demonstrably rich in old stars, while there is lots of star formation right near the core.

Thanks.

BTW, my interest in star formation (or the lack there of) comes from the fact that old stars = low metallicity = no space aliens.

A year or two ago I zeroed in on this question for something I was writing for our astronomy club newsletter, and I was surprised at the variety of answers available on-line. Naturally, the closer spiral arms are better known than the more distant ones, of which there seemed to be some variety of opinion. But that's science.

Not necessarily. Keep in mind that the star-forming history was very brisk early on in galactic bulges, and that down near the galactic center there are some old red giants with spectroscopic metal abundances that may go above the solar value. This implies that there were several pretty rapid generations of star formation in the first few billion years, and that the synthesized products of early massive stars were trapped efficiently in the deep gravitational potential well of the core. That is, the normalization of "old = metal poor" changes as one moves inward or outward in many spirals. A bar may enter into this - bars provide for radial mixing of stars and gas, so that the common gradients in metal abundance are flattened (and sometimes completely so) across the radial extent of strong bars. (I don't know right away whether the IR spectroscopy in the inner Milky Way is adequent to suggest whether its bar is strong enough to have shown this - we do see such a gradient out around our position).

Now, i would like to know if the bar is a weak bar or a strong bar...

Once again the nature of our existence is changed forever. Do you think astrologers will start talking about the bar?

Boy howdy! They'll talk like it's been having an effect on people's lives here on earth all along. They'll describe its pivotal influences on destiny as if it were described in ancient (as ancient as new-age gets) texts written before anyone even knew!

How does the discovery of a half-dozen new planets(?) affect astrology?

But I do have an astronomy question to add here. If the "bar" rotates around the massive black hole at the center of the MW, and holds it's appearance over hundreds of millions of years, that means that the matter that makes up the inner end of the bar is revolving at the same rate (and slower velocity) than the matter on the outer ends.

I thought gravity didn't work that way. The outer-end matter must be travelling at incredible multiples of the inner-end velocity! What forces are at work other than gravity?

Faultline

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My son is my universe.

looks like i got me a new wallpaper for my desktop..
what is really mind blowing is if you blow it way up, our entire solar system isn't even as big as a single pixel.
yeah, we really matter a lot in the overall scheme of things. good thing God made us- and only us- to enjoy all this empty space..

I'm interested in that question as well. It would make sense to assume that there is some other force, but current theory doesn't recognize any other force than gravity. I guess the explanation must be that somehow there is other matter that pulls the stars in the outer part of the bar just in the right way so that it forms a bar, purely from gravitational force. But I'm not sure what that other matter would be. Maybe the beginning of the spiral arms or something like that?

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As above, so below

All,
That's a very pretty picture, But it is not a photo, just an artist's impression, drawn to illustrate new and interesting work and a new theory about the structure of our Galaxy that I am not competent to criticise.

But it's a drawing.

John

just a drawing?
i thought they put Hubble in a very highly elliptical orbit and snapped that pic when it was at it's maximun distance from earth..


yeah, i love the sarcasm....

I was pondering about the beautifulness of the artist's rendering, and then I recalled that there's a system of classification of spirals, called "Elmegreen arm class" (Elmegreen, 1982), that is divided into 12 categories, being AC=1 a flocculent spiral, and AC=12 a Grand Design spiral; I wonder how the Milky Way fits in that scheme, what arm class is assigned to it

Now let's annoy some candy companies by petitioning the IAU to change the name of the galaxy officially to Milky Bar. That'll sow discourd between them.