Guest wrote:For the life of me I cannot see the bar
Same here. I got my BS in Physics, and as part of the fun, took a 100-level astronomy course. Identifying barred spiral galaxies was nearly impossible for me, too. They need to have a mouse-over to indicate what, exactly, the bar is supposed to be here. That's the one exam question I missed. Then, I went on to grad school and had the unfortunate pleasure of being a TA for the same 100-level astronomy course. I never had to explain the difference to anyone, so I just let it go.
I think it's like those 3-d hidden picture things and we're the folks with only one functional eye. Or it's a big joke astronomers play on people 'not in the club.'
NGC 1672, a barred galaxy.
Photo: Robert Gendler.
M88, an unbarred galaxy. Jim Quinn/Adam Block/NOAO/AURA/NSF.
The bar of NGC 1672 can be described as the thick, curving, elongated dust lane that begins on either side of the nuclear region and winds out all the way through the yellow, elongated bulge of the galaxy. The (starforming) spiral arms seem to start at the ends of the bar.
M88, by contrast, has no bulge. The arms start winding out from deep in the center of the galaxy.
Consider two other galaxies, one barred and one unbarred :
NGC 1365, a strongly barred galaxy. Credit:
Credit: SSRO-South (R. Gilbert, D. Goldman, J. Harvey, D. Verschatse) -
PROMPT (D. Reichart)
Note the strong bar of NGC 1365, with the obvious, slightly curving dust lane running right through it. The spiral arms of NGC 1365 begin at either end of the bar. The rather weak central dust lanes running through the very spherical yellow bulge of NGC 1566 don't seem to affect the shape or location of the spiral arms at all.
Finally, many barred galaxies also have rings. The galaxy at left, NGC 6792, actually has a small bright bar inside its inner bright ring. Outside the inner bright ring there is a bar, and you can see the characteristic twin dust lanes winding their way through the yellow bar and bulge (here the bulge looks more like an oval). Outside that large bar there is a faint, quite non-circular bluish ring. So we have a galaxy with a bar within a ring within a bar within a ring.
But not all barred galaxies have rings, and not all galaxies with rings have bars.