APOD: M33: The Triangulum Galaxy (2022 Nov 03)

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APOD: M33: The Triangulum Galaxy (2022 Nov 03)

Post by APOD Robot » Thu Nov 03, 2022 4:05 am

Image M33: The 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 the Milky Way, this sharp image combines data from telescopes on and around planet Earth to show 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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Ann
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Re: APOD: M33: The Triangulum Galaxy (2022 Nov 03)

Post by Ann » Thu Nov 03, 2022 6:27 am


Wow, that's just a stunningly lovely picture of M33, the Triangulum Galaxy! The colors are pure eye candy, making M33 look like the loveliest pinwheel ever! And the resolution is so great that in the full size version, there seems to be a million stars popping out from the background like something you could sift through your fingers like grains of sand!
APOD Robot wrote:
...this sharp image combines data from telescopes on and around planet Earth...
The data acquisition is top notch, to say the least. And then all this data has been combined into one amazing image by Robert Gendler, who is an extremely skilled "processer".

I wouldn't want to change a thing about this image. Still, it is true that no one image can tell the full truth about an object as complex as a galaxy. For example, today's APOD is very bright indeed in Hα, hydrogen alpha, which glows pink and red in nebulas all over the disk of M33. The Hα is really there, no question, but how bright is it? Let's compare today's stunning image, which is the product of the collaboration of many telescopes and a man famous for his processing of images, with a picture of M33 that was taken by just one woman, Linda:

Where did all the red Hα go in Linda's image? We don't see much of it in her image because most of the Hα nebulas in M33 are not very bright. Actually, Linda did use an Hα filer for her image, but she made no effort to enhance the Hα in her processing so that it looked even nearly as bright as it does in today's APOD.

But one nebula stands out in Linda's image: NGC 604. We see it stand out very brightly in Sydney's image, too. It is much less noticeable in the APOD, where it fights for attention with all the other red emission nebulas.

You can see that the overall colors are very muted in Linda's image. Well, that's correct, too. Galaxies get their colors from stars and nebulas, but star colors are muted in themselves. Check them out in a telescope, and you will see.

M33 looks almost "ghostly wan" in Linda's image. The entire galaxy looks bluish to pearly white, and there is the barest hint of yellow in the center of M33 in her image. Well, I'd say that's correct, too. M33 has a rather faint central region, and this galaxy may not even contain a central black hole! :shock:
Wikipedia wrote about M33:

The nucleus of this galaxy is an H II region, and it contains an ultraluminous X-ray source with an emission of 1.2 × 1039 erg s−1, which is the most luminous source of X-rays in the Local Group of galaxies. This source is modulated by 20% over a 106-day cycle. However, the nucleus does not appear to contain a supermassive black hole, as an upper limit of 3,000 solar masses is placed on the mass of a central black hole based upon the velocity of stars in the core region.

Let's return to the color of Linda's image again. Shouldn't the center of M33 look more yellow in her image after all? No, I don't think so. Note that that there is a bright orange star in her image, HD 9687. This star is spectral class K5, similar to Aldebaran, and its B-V index is ~1.55. That's quite yellow. But the integrated B-V index of M33 is 0.55. That's a very big difference, even though the center itself is certainly a bit yellower than the galaxy as a whole. A likely B-V for the center of M33 might be 0.65, similar to the Sun.

M33 by Linda ac4lt detail annotated.png


So, no, the small and faint center of M33 that doesn't even contain a supermassive black hole shouldn't be portrayed as very yellow, if we want to imagine its "true" color.

But the color of the center of M33 is orange-yellow in the Hubble image of M33, isn't it? That's true, and I'm unimpressed. I don't think the center of M33 is as orange as it looks in the Hubble picture.


Ann
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Re: APOD: M33: The Triangulum Galaxy (2022 Nov 03)

Post by orin stepanek » Thu Nov 03, 2022 2:22 pm

opo9627c.jpg
star forming region in M33! I see a likeness of a dog! :mrgreen:
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Re: APOD: M33: The Triangulum Galaxy (2022 Nov 03)

Post by cmflyer » Thu Nov 03, 2022 3:15 pm

Hi,
I am wondering why the stars in the upper left have vertical/horizontal spikies, while the others are tipped 45 degrees. I assume they are all Milky Way stars, so thinking they are from different images.
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Re: APOD: M33: The Triangulum Galaxy (2022 Nov 03)

Post by Ann » Thu Nov 03, 2022 3:53 pm

cmflyer wrote: Thu Nov 03, 2022 3:15 pm Hi,
I am wondering why the stars in the upper left have vertical/horizontal spikies, while the others are tipped 45 degrees. I assume they are all Milky Way stars, so thinking they are from different images.
Craig
It is because the data for this image was acquired by several different telescopes.

Ann
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