by Ann » Fri Jun 06, 2014 7:44 pm
BDanielMayfield wrote:
Since the galaxy's bar is blue could it be a young galaxy, as galactic ages go?
That is an interesting question. I would guess that NGC 3319 definitely contains some very old stars.
http://en.wikipedia.org/wiki/I_Zwicky_18 wrote:
I Zwicky 18 is a dwarf irregular galaxy located about 59 million light years away.[2] The galaxy was first identified by Swiss astronomer Fritz Zwicky in a 1930s photographic survey of galaxies.[citation needed] Studies at the Palomar Observatory some 40 years ago led astronomers to believe that the galaxy erupted with star formation billions of years after its galactic neighbors. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. The Hubble Space Telescope, however, found faint, older stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.
So
dwarf galaxy I Zwicky 18 was believed to be a genuinely young galaxy whihc formed very recently, but as you can see from the Wikipedia entry, the Hubble Space Telescope revealed a population of old stars in this very young-looking galaxy. Therefore, I Zwicky 18 is no longer believed to be a very young galaxy, but rather it is thought to be an old galaxy that very recently erupted with intense star formation after, probably, billions of years of quiescence.
My guess is that NGC 3318 recently underwent some sort of "trauma" that caused it to form a great number of bars in its bar. Did it have a bar before? I would guess that it might have had an old, faint, yellow bar, which suddenly received a great inflow of gas and started forming young blue stars.
I own the book
The Galaxies of the Local Group by Sidney van den Bergh. In this book, he argues that
the bar of the Large Magellanic Cloud is younger than one billion years old, and that most of the stars in the LMC bar were born 4-200 million years ago. That suggests that there might have been a time when the bar of the LMC was as blue as the bar in NGC 3319 is today. Now the bar of the Large Magellanic is "middle-aged" and somewhat greenish.
But today most galactic bars are yellow. A few examples are
M109,
NGC 1300,
NGC 1365,
NGC 7427,
NGC 2903 and many others. For more examples of galaxies with yellow bars, check out
Adam Block's truly excellent galaxy page. Note two galaxies on that page with blue bars: NGC 1073 and NGC 7741. Check out
this Hubble image of NGC 1073, which shows star formation in the bar of the galaxy.
Ann
[quote]BDanielMayfield wrote:
Since the galaxy's bar is blue could it be a young galaxy, as galactic ages go?[/quote]
That is an interesting question. I would guess that NGC 3319 definitely contains some very old stars.
[quote]http://en.wikipedia.org/wiki/I_Zwicky_18 wrote:
I Zwicky 18 is a dwarf irregular galaxy located about 59 million light years away.[2] The galaxy was first identified by Swiss astronomer Fritz Zwicky in a 1930s photographic survey of galaxies.[citation needed] Studies at the Palomar Observatory some 40 years ago led astronomers to believe that the galaxy erupted with star formation billions of years after its galactic neighbors. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. The Hubble Space Telescope, however, found faint, older stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.[/quote]
So [url=http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/I_Zwicky_18a.jpg/300px-I_Zwicky_18a.jpg]dwarf galaxy I Zwicky 18[/url] was believed to be a genuinely young galaxy whihc formed very recently, but as you can see from the Wikipedia entry, the Hubble Space Telescope revealed a population of old stars in this very young-looking galaxy. Therefore, I Zwicky 18 is no longer believed to be a very young galaxy, but rather it is thought to be an old galaxy that very recently erupted with intense star formation after, probably, billions of years of quiescence.
My guess is that NGC 3318 recently underwent some sort of "trauma" that caused it to form a great number of bars in its bar. Did it have a bar before? I would guess that it might have had an old, faint, yellow bar, which suddenly received a great inflow of gas and started forming young blue stars.
I own the book [i]The Galaxies of the Local Group[/i] by Sidney van den Bergh. In this book, he argues that [url=http://jumk.de/astronomie/img/lmc.jpg]the bar of the Large Magellanic Cloud[/url] is younger than one billion years old, and that most of the stars in the LMC bar were born 4-200 million years ago. That suggests that there might have been a time when the bar of the LMC was as blue as the bar in NGC 3319 is today. Now the bar of the Large Magellanic is "middle-aged" and somewhat greenish.
But today most galactic bars are yellow. A few examples are [url=http://www.faulkes-telescope.com/files/faulkes-telescope.com/image/m109.large.jpg]M109[/url], [url=http://hd.wallpaperswide.com/thumbs/barred_spiral_galaxy-t2.jpg]NGC 1300[/url], [url=http://annesastronomynews.com/wp-content/uploads/2012/02/NGC-1365-the-Great-Barred-Spiral-by-Martin-Pugh.jpg]NGC 1365[/url], [url=http://annesastronomynews.com/wp-content/uploads/2012/02/NGC-7424.jpg]NGC 7427[/url], [url=http://i273.photobucket.com/albums/jj229/Astronomerica/SDSS-19/NGC2903-SDSS.jpg]NGC 2903[/url] and many others. For more examples of galaxies with yellow bars, check out [url=http://www.caelumobservatory.com/gallery/galaxies.shtml]Adam Block's truly excellent galaxy page[/url]. Note two galaxies on that page with blue bars: NGC 1073 and NGC 7741. Check out [url=http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2012/02/heic1202a.jpg]this Hubble image of NGC 1073[/url], which shows star formation in the bar of the galaxy.
Ann