APOD: M33: Triangulum Galaxy (2016 Sep 17)

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APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by APOD Robot » Sat Sep 17, 2016 4:10 am

Image M33: Triangulum Galaxy

Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp composite image nicely shows off M33's blue star clusters and pinkish star forming regions along the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 1 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by Ann » Sat Sep 17, 2016 4:40 am

That's a fine and interesting picture!

The best thing is that M33 is so greatly resolved, so you can really get close up and personal with it. You can actually start counting the bright blue stars in it (not that you won't lose count soon). And the red supergiants also stand out, at least those within the arms. But there is a number of scattered stars(? clusters? galaxies?) that seem too bright to be supergiants in M33. At the outskirts of M33 there are several red stars(?) that could be Milky Way foreground stars, or background galaxies, but an irritating thing is that while they seem too bright to be M33 supergiants, they are strangely similar in brightness for foreground stars or background galaxies. And left of the faint yellow bulge of M33 is a line of three "stars" that are ever so slightly purplish in color and too bright and too scattered to be M33 supergiants. Similar "too-bright" purplish "stars" are seen elsewhere, too. Could they all be young clusters, emitting a mixture of blue starlight and red Ha light?

Note the bulge of M33. It's so faint! There is a small yellow brightening in the center of it, which must be the nucleus. It looks puny, too.

A picture like this makes it easy to believe that there is no supergiant black hole at the center of M33. This galaxy doesn't pack enough punch for such a scary singularity!
Image
NGC 4395. Photo: NASA/GALEX.
Elliptical M60, spiral NGC 4647 and tiny M60-UCD1.
NASA/Space Telescope Science Institute/European Space Agency.
Yes, I know, I know... small galaxies have massive black holes, too. NGC 4395, I'm just saying...

Or... M60-UCD1. Tiny galaxy, gargantuan black hole.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by De58te » Sat Sep 17, 2016 7:12 am

ANN, Foreground stars in the Milky Way tend to have diffraction points. Regarding the three purple stars in a line to the left of the central core, I enlarged the picture and enlarged my browser as much as possible to examine those stars. I can just make out a diffraction line in the middle star, with a hint of a halo in the lower star. So unofficially I conclude that those stars belong to the Milky Way.
Next, I also have read that astronomers suspect that there is no central black hole in M33.

heehaw

Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by heehaw » Sat Sep 17, 2016 1:40 pm

Do I recall arightly that M33 is a dwarf galaxy? (M31 is like our own galaxy, a big one.)

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by bystander » Sat Sep 17, 2016 1:51 pm

heehaw wrote:Do I recall arightly that M33 is a dwarf galaxy? (M31 is like our own galaxy, a big one.)
No, M33 is thought to be over 60,000 light years in diameter, contain more than 40 billion stars, and have a complement of dwarf companions. I think it qualifies as a full fledged spiral galaxy.
Last edited by bystander on Sat Sep 17, 2016 1:53 pm, edited 1 time in total.
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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by Chris Peterson » Sat Sep 17, 2016 2:33 pm

De58te wrote:ANN, Foreground stars in the Milky Way tend to have diffraction points. Regarding the three purple stars in a line to the left of the central core, I enlarged the picture and enlarged my browser as much as possible to examine those stars. I can just make out a diffraction line in the middle star, with a hint of a halo in the lower star. So unofficially I conclude that those stars belong to the Milky Way.
All that is required to see diffraction spikes is a bright enough source. They can show up around stars in other galaxies, around extragalactic clusters, even around distant galaxies themselves. I think these objects, being so apparently close together, are more likely associated with M33 than they are to be foreground bodies.
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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by MDB » Sat Sep 17, 2016 3:31 pm

Beautiful photo! How is it possible to resolve one star at the distance of a galaxy? If the M33 photo is 55 or 60 thousand light years across wouldn't even the smallest single point of light be light years across? Wouldn't the single points of light have to be a collection or group of stars?

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by Chris Peterson » Sat Sep 17, 2016 3:43 pm

MDB wrote:Beautiful photo! How is it possible to resolve one star at the distance of a galaxy? If the M33 photo is 55 or 60 thousand light years across wouldn't even the smallest single point of light be light years across? Wouldn't the single points of light have to be a collection or group of stars?
We cannot truly resolve any stars in other galaxies, and only a handful of nearby ones in our own. The confusion comes from what it means to "resolve" a star. One meaning of a resolved star is that we can magnify it enough to discern spatial structure on its surface. That's rare. But in another sense, it means nothing more than separating it from its background. That's something that we can quite easily do with many stars in other galaxies- if they're bright enough, or isolated enough. Remember that optically every star in that galaxy (and every foreground star, as well) is a point source. The stars only appear to be larger than single pixels because of diffraction, scatter, atmospheric seeing, and other effects that spread them out. The greater the apparent brightness of the star, the larger it will appear.
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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by neufer » Sat Sep 17, 2016 4:14 pm

Chris Peterson wrote:
De58te wrote:
ANN, Foreground stars in the Milky Way tend to have diffraction points. Regarding the three purple stars in a line to the left of the central core, I enlarged the picture and enlarged my browser as much as possible to examine those stars. I can just make out a diffraction line in the middle star, with a hint of a halo in the lower star. So unofficially I conclude that those stars belong to the Milky Way.
All that is required to see diffraction spikes is a bright enough source. They can show up around stars in other galaxies, around extragalactic clusters, even around distant galaxies themselves. I think these objects, being so apparently close together, are more likely associated with M33 than they are to be foreground bodies.
The two brightest stars in today's APOD are:
  • Milky Way Giant stars of apparent magnitude 8 (and absolute magnitude ~ 0).
The three purple stars in a line to the left of the central core are most likely:
  • M33 Supergiant stars of apparent magnitude ~ 18 (and absolute magnitude -7).
Art Neuendorffer

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by heehaw » Sat Sep 17, 2016 9:39 pm

bystander wrote:
heehaw wrote:Do I recall arightly that M33 is a dwarf galaxy? (M31 is like our own galaxy, a big one.)
No, M33 is thought to be over 60,000 light years in diameter, contain more than 40 billion stars, and have a complement of dwarf companions. I think it qualifies as a full fledged spiral galaxy.
Yes! But I have checked a bit further, and my memory has been jogged. Wikipedia gives the mass of M31 as 1230 billion solar masses, and that of M33 as only 50 billion solar masses, so M31 is 25 times more massive. A big number! What impresses me is that even with this huge mass difference, one gets in both cases a perfectly conventional spiral galaxy. The processes that produce the spiral effect seem to be independent of what size the eddy is (they sure look like eddies, anyway!)

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by neufer » Sun Sep 18, 2016 1:06 am

heehaw wrote:
bystander wrote:
heehaw wrote:
Do I recall arightly that M33 is a dwarf galaxy? (M31 is like our own galaxy, a big one.)
No, M33 is thought to be over 60,000 light years in diameter, contain more than 40 billion stars, and have a complement of dwarf companions. I think it qualifies as a full fledged spiral galaxy.
Yes! But I have checked a bit further, and my memory has been jogged. Wikipedia gives the mass of M31 as 1230 billion solar masses, and that of M33 as only 50 billion solar masses, so M31 is 25 times more massive. A big number! What impresses me is that even with this huge mass difference, one gets in both cases a perfectly conventional spiral galaxy. The processes that produce the spiral effect seem to be independent of what size the eddy is (they sure look like eddies, anyway!)
https://en.wikipedia.org/wiki/Triangulum_Galaxy wrote:
  • <<Triangulum may be home to 40 billion stars,
    compared to 400 billion for the Milky Way,
    and 1 trillion stars for Andromeda.>>
https://en.wikipedia.org/wiki/Dwarf_galaxy wrote:
<<A dwarf galaxy is a small galaxy composed of about 100 million up to several billion stars, a small number compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.>>
Art Neuendorffer

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by Ann » Sun Sep 18, 2016 5:37 am

heehaw wrote:
bystander wrote:
heehaw wrote:Do I recall arightly that M33 is a dwarf galaxy? (M31 is like our own galaxy, a big one.)
No, M33 is thought to be over 60,000 light years in diameter, contain more than 40 billion stars, and have a complement of dwarf companions. I think it qualifies as a full fledged spiral galaxy.
Yes! But I have checked a bit further, and my memory has been jogged. Wikipedia gives the mass of M31 as 1230 billion solar masses, and that of M33 as only 50 billion solar masses, so M31 is 25 times more massive. A big number! What impresses me is that even with this huge mass difference, one gets in both cases a perfectly conventional spiral galaxy. The processes that produce the spiral effect seem to be independent of what size the eddy is (they sure look like eddies, anyway!)
Infrared image of M31 by WISE.
Blue means stars, red means dust.
Image
Ultraviolet image of M31 by GALEX.
Blue means hot stars, yellow means cool stars.
M31 is a big galaxy, bigger than we think.
Wikipedia wrote:
Mass estimates for the Andromeda Galaxy's halo (including dark matter) give a value of approximately 1.5×1012 M[7] (or 1.5 trillion solar masses) compared to 8×1011 M for the Milky Way...

The total stellar mass of Andromeda is estimated to be between 1.1×1011 M.,[40][41] (i.e., around twice as massive as that of the Milky Way)...

Studies made with the help of the Hubble Space Telescope and published in 2015, have uncovered a large and massive halo of hot gas enveloping M31. This halo is estimated to contain half the mass of the stars in the Andromeda galaxy itself. As of May 7, 2015, the halo is about six times larger and 1,000 times more massive than previously measured...

M31 appears to have significantly more common stars than the Milky Way, seeming to predominate the old stars with ages >7×109 years,[42][clarification needed] and the estimated luminosity of M31, ~2.6×1010 L, is about 25% higher than that of our own galaxy.[50]
Image
M33. Photo: Alexander Meleg.
NGC 7331, a bluer and dustier galaxy than M31.
Note the obvious spiral arms.
Photo: Vicent Peris/ Calar Alto Observatory
Wikipedia points out that it is hard to know exactly how luminous M31 really is, due to its high inclination and dust absorption. In my opinion, M31 doesn't appear to be very dusty. Its far infrared ("dust") magnitude is 1.3 magnitudes fainter than its B magnitude, whereas, for example, NGC 7331, which is somewhat similarly in appearance and inclination to M31, is 1.3 magnitudes brighter in far infrared than in blue light.

There are also suggestions that M31 is a ring galaxy rather than a spiral galaxy, but most astronomers seem to agree that M31 is a spiral galaxy of Hubble type Sb.

Andromeda also has a very massive central black hole. Check out this list of the most massive black holes known. The supermassive central black hole of M31 is relatively far down that list, but at least it makes the list. Most Messier and NGC galaxies don't.

All in all, the large size, huge star populations, enormous halo, massive black hole, red colors and comparatively small dust content all suggest to me that M31 is a huge galaxy indeed.

M33, by contrast, has a definite spiral shape, but its arms are flimsy and irregular, and its bulge is faint. Its colors are blue, and its far infrared magnitude is only 0.1 mag fainter than its B magnitude, so M33 is (relatively speaking) dustier than M31. The size of M33, while not remarkably small, is clearly smaller than the sizes of both Andromeda and the Milky Way. And M33 contains only a small central black hole, if there is a black hole there at all.

All in all, and since there are no suggestions that M33 contains a whoppingly large halo, it is clear that relatively lightweight, whereas M31 is a Mike Tyson of galaxies.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by neufer » Sun Sep 18, 2016 12:18 pm

The only thing worse than Ann squeezing a quote to the side of a picture
  • is squishing a quote between two pictures. :evil:
Please stick your pictures within Wikipedia quotes
even if they didn't actually come from there...no one will mind.
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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by rstevenson » Sun Sep 18, 2016 5:26 pm

neufer wrote:The only thing worse than Ann squeezing a quote to the side of a picture
  • is squishing a quote between two pictures. :evil:
Please stick your pictures within Wikipedia quotes
even if they didn't actually come from there...no one will mind.
Or just put a carriage return before and after all pics and all quotes. Might create a few too many blank lines, depending on the phase of the Moon, but it's better than squished columns.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by geckzilla » Sun Sep 18, 2016 6:38 pm

Chris Peterson wrote:
De58te wrote:ANN, Foreground stars in the Milky Way tend to have diffraction points. Regarding the three purple stars in a line to the left of the central core, I enlarged the picture and enlarged my browser as much as possible to examine those stars. I can just make out a diffraction line in the middle star, with a hint of a halo in the lower star. So unofficially I conclude that those stars belong to the Milky Way.
All that is required to see diffraction spikes is a bright enough source. They can show up around stars in other galaxies, around extragalactic clusters, even around distant galaxies themselves. I think these objects, being so apparently close together, are more likely associated with M33 than they are to be foreground bodies.
A while back when I did the WISE Rho Oph mosaic, there was a very bright source (Antares) and its ghost / telescopic artifact was so bright it had diffraction spikes!
(I was so impressed I tweeted about it)
https://twitter.com/SpaceGeck/status/747651196199002112
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by Ann » Mon Sep 19, 2016 4:39 am

neufer wrote:The only thing worse than Ann squeezing a quote to the side of a picture
  • is squishing a quote between two pictures. :evil:
Please stick your pictures within Wikipedia quotes
even if they didn't actually come from there...no one will mind.
Right... there's famine, pestilence, war, terrorism, and Ann squishing quotes to the side of a picture or between two pictures.

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by neufer » Mon Sep 19, 2016 1:50 pm

Ann wrote:
neufer wrote:
The only thing worse than Ann squeezing a quote to the side of a picture
  • is squishing a quote between two pictures. :evil:
Please stick your pictures within Wikipedia quotes
even if they didn't actually come from there...no one will mind.
Right...

there's famine, pestilence, war, terrorism, and Ann squishing quotes to the side of a picture or between two pictures.
I'd probably order it:

famine, pestilence, war, Ann squishing quotes to the side of a picture or between two pictures and then terrorism.
Art Neuendorffer

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Re: APOD: M33: Triangulum Galaxy (2016 Sep 17)

Post by geckzilla » Mon Sep 19, 2016 8:13 pm

Haha, what? LOL
If your screen or browser frame is on the small side, it does squish the text into single characters per line between the two pictures. It's alright when there's more space. It is hilariously bad when squished, though. I just had a good laugh checking it out to see what would happen and if that's what Art was experiencing.
Just call me "geck" because "zilla" is like a last name.