APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

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APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by APOD Robot » Thu Dec 26, 2013 5:56 am

Image The Hydrogen Clouds of M33

Explanation: Gorgeous spiral galaxy M33 seems to have more than its fair share of glowing hydrogen gas. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies about 3 million light-years distant. Its inner 30,000 light-years are shown in this telescopic galaxy portrait that enhances the reddish ionized hydrogen clouds or HII regions. Sprawling along loose spiral arms that wind toward the core, M33's giant HII regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. To enhance this image, broadband data was used to produce a color view of the galaxy and combined with narrowband data recorded through a hydrogen-alpha filter, transmitting the light of the strongest hydrogen emission line. To see the monochromatic narrowband data alone, move your cursor over the image, or take this video tour of the hydrogen clouds of M33.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by owlice » Thu Dec 26, 2013 6:16 am

What a lovely image!
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Thu Dec 26, 2013 6:55 am

This is a great picture, and I'm so glad that Adam Block has been honored with another Astronomy Picture of the Day - he so richly deserves it!

A wonderful thing about this picture is that it gives us both a general overview of the structure and brightness of the inner part of M33 as well as a wonderful resolution into stars. For example, there is what looks like a sharp edge to the "upper part" of the blue disk of M33. But when we look at the full resolution of today's APOD, we can see that in places along this seemingly sharp boundary of the blue disk there appears to be just as many stars on both sides of the boundary, and the only difference is that the stars on the "wrong" side of the boundary are red and comparatively faint. This is particularly obvious at upper right in the picture, to the lower right of the great emission nebula NGC 604.

Another fascinating detail is how the inner yellow part of M33 appears to be bounded by thin inner dust lanes which keep the yellow stars contained as if by a series of fences. Outside these inner dust lanes, the disk population is generally blue. And yet, the brightest blue stars stand out on this blue background like a glittering multitude of tiny blue diamonds sprinkled somewhat unevenly across the face of M33. Two resplendent large rose-nebulae spread red petals all over the place, though mostly down the dust lane fairways.

What a lovely picture!

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Boomer12k » Thu Dec 26, 2013 9:55 am

Eewww....It's all Clumpy....

Is that because of mergers?

Is that because of various times of in-falling gas clumps??

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Thu Dec 26, 2013 12:00 pm

Boomer12k wrote:Eewww....It's all Clumpy....

Is that because of mergers?

Is that because of various times of in-falling gas clumps??

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Good questions. I wish I knew the answers.

I can say this, however. My gut feeling tells me that most dwarf galaxies are dwarf spheroidals, which contain no star formation whatsoever, and all their constituent stars are old. A good example of such a dwarf spheroidal is Leo 1, which can be seen in the direction of bright star Regulus. Galaxies such as Leo 1 stopped forming stars billions of years ago.
IC 10. Photo: Bill Snyder
However, while I believe it is true that most small (and smallish) galaxies are spheroidals, it is also true that some dwarf and smallish galaxies are extremely rich in star formation. An interesting example is IC 10, a starburst galaxy which is a little-known member of the Local Group.
http://en.wikipedia.org/wiki/IC_10 wrote:
The apparent distance between IC 10 and the Andromeda Galaxy is about the same as the apparent distance between the Andromeda Galaxy and the Triangulum Galaxy, which suggests that IC 10 may belong to the M31 subgroup.
So in a way, IC 10 can be thought of as the other Triangulum Galaxy (although IC 10 is in Cassiopeia). Fascinatingly, IC 10 can also be regarded as the other Small Magellanic Cloud:
http://en.wikipedia.org/wiki/IC_10 wrote:
IC 10 is the only known starburst galaxy in the Local Group of galaxies. It has many more Wolf-Rayet stars per square kiloparsec (5.1 stars/kpc²) than the Large Magellanic Cloud (2.0 stars/kpc²) or the Small Magellanic Cloud (0.9 stars/kpc²). Although the galaxy has a luminosity similar to the SMC, it is considerably smaller. Its higher metallicity compared to the SMC suggests that star formation activity has continued for a longer time period. The evolutionary status of the Wolf-Rayet stars suggests that they all formed in a relatively short timespan.
There is nothing in the Wikipedia article to suggest that IC 10 has merged with another galaxy. My complete amateur guess is that it might have picked up a lot of gas for one reason or another, or - and this is another interesting possibility - that IC 10 may have been born with a good supply of gas, and that, for one reason or another, much of this gas remained "untouched", so that it never collapsed into the kind of molecular clouds that give birth to stars. Much of its gas may have remained "unused", until something stirred it up and made it form new stars.
http://iopscience.iop.org/1538-4357/590 ... .text.html wrote:
It has become known that dwarf irregular galaxies generally have H I gas envelopes more extended than the stellar body that is observed in the optical wavelength (e.g., Huchtmeier, Sieradakis, & Materne 1981; Hunter & Gallagher 1985). Recently, the interplay of galactic and intergalactic material around dwarf irregular galaxies has been thought to be important in their evolution (e.g., Hunter et al. 1998; Wilcots & Miller 1998).
Sometimes small galaxies that exist in apparent isolation suddenly start forming stars at a furious rate for no obvious reason. A good example is the irregular galaxy NGC 1313. NGC 4395, at left, is a small spiral galaxy whose brightest parts are its largest emission nebulae.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by hohoho » Thu Dec 26, 2013 1:11 pm

"A prominent member...." You mean well-known, which is correct. But you gives the false impression that this is a big galaxy, as are our own, and Andromeda. In fact M33 is a tiny galaxy. Low mass! But, pretty as heck!

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by BDanielMayfield » Thu Dec 26, 2013 6:49 pm

hohoho wrote:"A prominent member...." You mean well-known, which is correct. But you gives the false impression that this is a big galaxy, as are our own, and Andromeda. In fact M33 is a tiny galaxy. Low mass! But, pretty as heck!
“Tiny” is relative, and probably an overstatement (or rather an understatement) for this galaxy.
Wikipedia wrote:The Triangulum Galaxy is a spiral galaxy approximately 3 million light years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598, and is sometimes informally referred to as the Pinwheel Galaxy, a nickname it shares with Messier 101. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, which includes the Milky Way, the Andromeda Galaxy and about 44 other smaller galaxies. It is one of the most distant permanent objects that can be viewed with the naked eye.
The article also states that M33 has about 40 billion stars, or about 40% as compared to the Milky Way. So in our neck of the universe, this galaxy is above average.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by geckzilla » Thu Dec 26, 2013 6:56 pm

Prominent
1. standing out so as to be seen easily; conspicuous; particularly noticeable

http://dictionary.reference.com/browse/prominent?s=t

Exactly as Triangulum is.

Maybe a new rule for Asterisk should be not to do guest account drive by ridiculous semantic arguments. It's pretty tiresome.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by MargaritaMc » Thu Dec 26, 2013 9:49 pm

Triangulum Galaxy (M33) - Deep Sky Videos
http://youtu.be/4shqOBkCki8
Click to play embedded YouTube video.
We're looking at various images of the Triangulum Galaxy - through world-class telescopes and quick backyard glimpses blighted by satellites. We also discuss why it does not display the usual central bulge of spiral galaxies.

This video features Marc Balcells, Mike Merrifield and Nik Szymanek.
With thanks to the Isaac Newton Group of Telescopes: http://www.ing.iac.es/
Nik Szymnak's website is: http://ccdland.net
Mike Merrifield is based the University of Nottingham: http://www.nottingham.ac.uk/astronomy/
M
PS. Off topic, this is a holiday greeting from the Isaac Newton Group of Telescopes with an image of NGC 660.
http://www.ing.iac.es/xmas/xmas2013.jpg
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
&mdash; Dr Debra M. Elmegreen, Fellow of the AAAS

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Tetrodehead » Thu Dec 26, 2013 10:03 pm

Brilliant.
In the mono, the upper left appears to contain planetary nebulae. New stars formed and blown spherical shells?

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Anthony Barreiro » Fri Dec 27, 2013 12:24 am

Tetrodehead wrote:Brilliant.
In the mono, the upper left appears to contain planetary nebulae. New stars formed and blown spherical shells?
I don't think so. M33 is 3 million light years distant from us, and this picture represents the inner 30,000 light years of the galaxy. At that scale, those ring nebulae would be about 750 light years across (I held a ruler up to my computer screen!). A typical planetary nebula is about one light year across, so these bubbles are almost three orders of magnitude too big. I'll leave it to somebody more knowledgeable to speculate about what formed those bubbles.

By the way, this is a breathtakingly beautiful and highly instructive image. I love seeing all the glittery stars and the pink emission nebulae. Thank you.

Along the same way, M33 is well placed for observation these evenings. It's rather faint, so you need a dark sky to see it. If you have a reasonably dark sky, you can see M33 in binoculars, but significant light pollution will completely wash it out. M33 appears bigger than the full Moon, so you need a wide field to see it. If you're using a telescope you need to use an eyepiece that gives you at least a one-degree field of view. If your field of view is smaller than one degree, M33 will completely fill your eyepiece, there will be no contrast with the background sky, so you won't see the galaxy at all. With a moderately large amateur telescope you can start to make out the spiral structure of the galaxy and to see the emission nebula NGC 604 as a slightly brighter region offset from the central bulge.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by geckzilla » Fri Dec 27, 2013 1:24 am

Anthony Barreiro wrote:
Tetrodehead wrote:Brilliant.
In the mono, the upper left appears to contain planetary nebulae. New stars formed and blown spherical shells?
I don't think so. M33 is 3 million light years distant from us, and this picture represents the inner 30,000 light years of the galaxy. At that scale, those ring nebulae would be about 750 light years across (I held a ruler up to my computer screen!). A typical planetary nebula is about one light year across, so these bubbles are almost three orders of magnitude too big. I'll leave it to somebody more knowledgeable to speculate about what formed those bubbles.
Strömgren spheres?
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Anthony Barreiro » Fri Dec 27, 2013 2:24 am

geckzilla wrote:
Anthony Barreiro wrote:
Tetrodehead wrote:Brilliant.
In the mono, the upper left appears to contain planetary nebulae. New stars formed and blown spherical shells?
I don't think so. M33 is 3 million light years distant from us, and this picture represents the inner 30,000 light years of the galaxy. At that scale, those ring nebulae would be about 750 light years across (I held a ruler up to my computer screen!). A typical planetary nebula is about one light year across, so these bubbles are almost three orders of magnitude too big. I'll leave it to somebody more knowledgeable to speculate about what formed those bubbles.
Strömgren spheres?
The examples listed in the wikipedia article on Stromgren spheres are at least an order of magnitude smaller than the big H II bubbles in M33. Maybe M33 is like Texas, and everything is bigger there.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by geckzilla » Fri Dec 27, 2013 3:21 am

Anthony Barreiro wrote:
geckzilla wrote: Strömgren spheres?
The examples listed in the wikipedia article on Stromgren spheres are at least an order of magnitude smaller than the big H II bubbles in M33. Maybe M33 is like Texas, and everything is bigger there.
There was only one example in that article.
http://en.wikipedia.org/wiki/H_II_region#Morphology
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Fri Dec 27, 2013 4:22 am

To me they do look quite a bit like Strömgren spheres. Bear in mind that the global properties of a galaxy like M33 are different than the overall properties of the Milky Way. There is definitely less overall gravity in M33 than in the Milky Way, which might possibly make it easier to form big Strömgren spheres. There may well be more turbulence as well as smaller amounts of available hydrogen gas per cubic kiloparsec in the Milky Way than in the Triangulum galaxy, and this might affect the size of the Milky Way Strömgren spheres negatively.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by geckzilla » Fri Dec 27, 2013 4:32 am

You can look at any Milky Way's bubbles with any H-alpha map.
http://www.astro.wisc.edu/~gostisha/pics/comp_big.jpg

Reading about Strömgren's model on Wikipedia, I don't see any reason why the overall size of the galaxy or its local gravity would affect the sizes of the spheres.
The hotter and more luminous the exciting star, the larger the Strömgren sphere.
The denser the surrounding hydrogen gas, the smaller the Strömgren sphere.
Edit: Although, the spheres are actually referring to the empty space, apparently. I have no idea what to call the hydrogen shells around them. They are obviously influenced by Strömgren's spheres, though.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Fri Dec 27, 2013 4:43 am

NGC 6822. Photo: Robert Gendler
Well, I'm not saying that David Malin necessarily knew those things, but he said that large round hydrogen bubbles formed more easily and grew larger in small galaxies like NGC 6822 than in the Milky Way.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by geckzilla » Fri Dec 27, 2013 4:46 am

Sure, there could be a correlation. But it would seem to have more to do with the density of hydrogen gas than with the galaxy's overall gravity.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Fri Dec 27, 2013 4:48 am

Yes, I may have been wrong to talk about gravity here. David Malin said about the hydrogen gas in the Milky Way that it is both more turbulent and more constrained than gas in galaxies like NGC 6922.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Wildbegonia » Mon Dec 30, 2013 3:25 pm

I really appreciate getting the monochromatic version by just moving over the cursor. If one would be navigating in space, would not be in its monochromatic state that we will see it?. Is it not all black out there in space? If so, I would like to suggest the site will offer this option to all the future entries from now on, that it is, the colour enhanced version and the monochromatic one.

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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Chris Peterson » Mon Dec 30, 2013 3:30 pm

Wildbegonia wrote:I really appreciate getting the monochromatic version by just moving over the cursor. If one would be navigating in space, would not be in its monochromatic state that we will see it?. Is it not all black out there in space? If so, I would like to suggest the site will offer this option to all the future entries from now on, that it is, the colour enhanced version and the monochromatic one.
Yes, visually we would never see any color. But keep in mind that the monochromatic image is just the hydrogen glow, and our eyes would see a lot of other light as well (but still without color). Also, the color isn't the only thing the image is able to enhance over our natural vision. We could also never see anywhere near so much detail. To our eyes, this would be an extremely low contrast structure.
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Re: APOD: The Hydrogen Clouds of M33 (2013 Dec 26)

Post by Ann » Mon Dec 30, 2013 9:44 pm

Wildbegonia wrote:I really appreciate getting the monochromatic version by just moving over the cursor. If one would be navigating in space, would not be in its monochromatic state that we will see it?. Is it not all black out there in space? If so, I would like to suggest the site will offer this option to all the future entries from now on, that it is, the colour enhanced version and the monochromatic one.
Any low-surface brightness object would appear gray. M33 certainly qualifies as a low-surface brightness object, so if we saw it while navigating in space, it would certainly appear just grayish. But parts of its large emission nebula NGC 604 has a high surface brightness, and it might appear slightly greenish to our eyes, but not red.

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