by Ann » Mon Apr 06, 2020 6:07 am
Antony Rawlinson wrote: ↑Mon Apr 06, 2020 5:33 am
I don't see any "bar". What I do see is an asymmetric centre, with more bright material in the upper part (as seen in the image) of the central swirl than in the lower. What am I supposed to be looking for?
- Unbarred spiral galaxy M74. Descubre Foundation, Calar Alto Observatory, OAUV, DSA, V. Peris (OAUV), J. L. Lamadrid (CEFCA), J. Harvey (SSRO), S. Mazlin (SSRO), I. Rodriguez (PTeam), O. L. (PTeam), J. Conejero (PixInsight).
A galactic bar is an elongated structure running through the center of the galaxy. The spiral arms of a barred galaxy begin at the ends of the bar.
NGC 1672 is not as strongly barred as NGC 1300 (few galaxies are). But in the Hubble image of NGC 1672 processed by Steve Cooper, which I prefer over today's APOD because of its saturated colors that help bring out different structures of the galaxy, the bar is the dark orange central part. Arguably though, you could say that the bar on the right side of the nucleus extends "almost straight out" until it meets a major arm at upper right. At the same time, this side of the bar of NGC 1672 displays strong signs of star formation in the form of many pink nebulas and blue-white star clusters.
You can see two very pronounced dark dust lanes emanating from the core of NGC 1672 and running through the orange-colored bar. Such dust lanes are typical of barred galaxies. Look closely, and you can see them in NGC 1300, too.
Most galactic bars lack star formation, but there are galactic bars that are full of young stars. Take a look at
this Hubble image of NGC 1073. If you look carefully, you can see that the dust lane on the right side of the nucleus of NGC 1073 has formed many bright young clusters of blue-white stars.
Ann
[quote="Antony Rawlinson" post_id=301047 time=1586151211 user_id=142734]
I don't see any "bar". What I do see is an asymmetric centre, with more bright material in the upper part (as seen in the image) of the central swirl than in the lower. What am I supposed to be looking for?
[/quote]
[float=left][img3="Unbarred spiral galaxy M74. Descubre Foundation, Calar Alto Observatory, OAUV, DSA, V. Peris (OAUV), J. L. Lamadrid (CEFCA), J. Harvey (SSRO), S. Mazlin (SSRO), I. Rodriguez (PTeam), O. L. (PTeam), J. Conejero (PixInsight)."]https://i.redd.it/r3pikahipl541.jpg[/img3][/float][float=right][img3="Strongly barred spiral galaxy NGC 1300. NASA, ESA, and The Hubble Heritage Team STScI/AURA)"]https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg/1920px-Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg[/img3][/float]
A galactic bar is an elongated structure running through the center of the galaxy. The spiral arms of a barred galaxy begin at the ends of the bar.
[float=right][img3="NGC 1672: Barred Spiral Galaxy from Hubble. Image Credit: Hubble Legacy Archive, NASA, ESA; Processing & Copyright: Steve Cooper"]https://apod.nasa.gov/apod/image/1609/NGC1672_HubbleCooper_1080.jpg[/img3][/float]
NGC 1672 is not as strongly barred as NGC 1300 (few galaxies are). But in the Hubble image of NGC 1672 processed by Steve Cooper, which I prefer over today's APOD because of its saturated colors that help bring out different structures of the galaxy, the bar is the dark orange central part. Arguably though, you could say that the bar on the right side of the nucleus extends "almost straight out" until it meets a major arm at upper right. At the same time, this side of the bar of NGC 1672 displays strong signs of star formation in the form of many pink nebulas and blue-white star clusters.
You can see two very pronounced dark dust lanes emanating from the core of NGC 1672 and running through the orange-colored bar. Such dust lanes are typical of barred galaxies. Look closely, and you can see them in NGC 1300, too.
Most galactic bars lack star formation, but there are galactic bars that are full of young stars. Take a look at [url=https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Barred_spiral_galaxy_NGC_1073_%28captured_by_the_Hubble_Space_Telescope%29.tif/lossy-page1-1200px-Barred_spiral_galaxy_NGC_1073_%28captured_by_the_Hubble_Space_Telescope%29.tif.jpg]this Hubble image[/url] of NGC 1073. If you look carefully, you can see that the dust lane on the right side of the nucleus of NGC 1073 has formed many bright young clusters of blue-white stars.
Ann