Starship Asterisk*

M83: The Thousand-Ruby Galaxy

Explanation: Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. Prominent spiral arms traced by dark dust lanes and blue star clusters lend this galaxy its popular name, The Southern Pinwheel. But reddish star forming regions that dot the sweeping arms highlighted in this sparkling color composite also suggest another nickname, The Thousand-Ruby Galaxy. About 40,000 light-years across, M83 is a member of a group of galaxies that includes active galaxy Centaurus A. In fact, the core of M83 itself is bright at x-ray energies, showing a high concentration of neutron stars and black holes left from an intense burst of star formation. This sharp composite color image also features spiky foreground Milky Way stars and distant background galaxies. The image data was taken from the Subaru Telescope, the European Southern Observatory's Wide Field Imager camera, and the Hubble Legacy Archive.

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Beautiful galaxy! How similar to the Milky Way is it, ignoring the size difference? Is there a galaxy that better illustrates what the Milky Way looks like?
The renderings used to show what the Milky Way looks like always bother me since they are so fake looking - better to use a picture of a real galaxy, IMHO.

Wonderful galaxy, one of my favorites. The picture of the galaxy was the front page of the "Galaxies" book from Timothey Ferris from 1983 ... long time ago.

@FLPPhotoCatcher: M83 seems also to have a litte bar in it like the Milky Way. Here is a constructed view from above of the Milky Way: http://www.mpe.mpg.de/6872813/original- ... 31042f7e32.
We then should find a barred spiral which seems to look as this view. M83 doesn't match here very good.


I couldn't resist to unwind this galaxy to have a better look at the spiral arms: https://drive.google.com/file/d/18uzaaZ ... ya1wp/view

To see how chaotic the dust lanes are an inverted view is helpful:
https://drive.google.com/file/d/14gxKtj ... CyFsn/view

(More unwinded galaxies in the other thread: http://asterisk.apod.com/viewtopic.php?f=8&t=39558)

FLPhotoCatcher wrote: ↑Sat Jun 29, 2019 4:34 am Beautiful galaxy! How similar to the Milky Way is it, ignoring the size difference? Is there a galaxy that better illustrates what the Milky Way looks like?
The renderings used to show what the Milky Way looks like always bother me since they are so fake looking - better to use a picture of a real galaxy, IMHO.

The way I see it, you can't ignore the size difference. Interestingly, vigorous star formation is more often found in small galaxies than in large ones. Of course, a much greater part of the galaxy can be involved in vigorous star formation if the galaxy is small than if it is big. Both galaxies can have the same absolute amount of star formation, but the small galaxy will be dominated by it, while the large galaxy will not. But I will say that M83 forms more stars in absolute terms than the Milky Way does, based on its appearance alone.

Constellation Guide wrote:

The galaxy is undergoing more rapid star formation than the Milky Way, especially in its central region.

A huge difference between M83 and the Mlky Way is that M83 has hosted six supernovas in the last 100 years, whereas the Milky Way, during the same time period and as far as we know, has not seen a single one. (Or at least not a single one that was observed while it light should have reached us.)

The morphological classifications of M83 and the Milky Way are also different.

Wikipedia wrote:

The morphological classification of NGC 5236 in the De Vaucouleurs system is SAB(s)c,[3] where the 'SAB' denotes a weak-barred spiral, '(s)' indicates a pure spiral structure with no ring, and 'c' means the spiral arms are loosely wound.

The 'c' in SAB(s)c makes M83 different from the Milky Way. The 'c' denotes a galaxy with loosely wound spiral arms, and such galaxies are often dominated by their spiral arms (well, compared with other spiral galaxies). In my opinion, the Milky Way is not dominated by its spiral arms, and its spiral arms are less loosely wound than those of M83, and the Milky Way has a (relatively and absolutely) larger and brighter bulge than M83 does.

M83 is a "blue" galaxy, with B-V colors of 0.66. No one has been able to measure the B-V of the Milky Way, but my guess is that it is at least 0.85. The difference may not sound like much, but in terms of galaxy colors, it's a big difference.

So what does our own galaxy look like? Sue me. I'm going to have a guess.
























EDIT: Ooops! It turns out that NGC 4394 is a dwarf galaxy and a satellite of M85. That's not a good Milky Way twin. But how about galaxy M58 in the Virgo Cluster? M58 appears to be about twice as larg and bright as the Milky Way and obviously much, much larger and brighter than NGC 4394, but their morphologies are similar. I think that the Milky Way looks something like this, although perhaps with a bit more loosely wound arms. Another possible twin is NGC 7773, but I wonder if the arms of NGC 7773 are not too freely flailing.




























Ann

MoreInput wrote: ↑Sat Jun 29, 2019 6:46 am Wonderful galaxy, one of my favorites. The picture of the galaxy was the front page of the "Galaxies" book from Timothey Ferris from 1983 ... long time ago.

@FLPPhotoCatcher: M83 seems also to have a litte bar in it like the Milky Way. Here is a constructed view from above of the Milky Way: http://www.mpe.mpg.de/6872813/original- ... 31042f7e32.
We then should find a barred spiral which seems to look as this view. M83 doesn't match here very good.


I couldn't resist to unwind this galaxy to have a better look at the spiral arms: https://drive.google.com/file/d/18uzaaZ ... ya1wp/view

To see how chaotic the dust lanes are an inverted view is helpful:
https://drive.google.com/file/d/14gxKtj ... CyFsn/view

(More unwinded galaxies in the other thread: http://asterisk.apod.com/viewtopic.php?f=8&t=39558)

Thanks for your post, it's very helpful!

My personal opinion is that the dust lanes of M83 are relatively non-chaotic as major dust lanes of galaxies go.

The picture at left shows off the dust lanes of M83 very well. In several plases the dust lanes are long and relatively unbroken, although there are chaotic parts as well, particularly at around 3 o'clock.

The picture at left also demonstrates quite clearly that star formation preferentially takes place along the leading edge of dust lanes.

Ann

Two galaxies stand out at 9 o'clock. The upper one is fascinating. It appears to have a heavy bar and a huge ring. Any more information on it?

Smaller than the Milky Way; but beautiful nonetheless! Notice how the arms form a reverse giant 'S' !

So, I was reading up on today:s APOD and I am confused on the popular moniker of this galaxy. The brief article says that the reason it got its name is due to its blue clusters. However, aren't rubies red, not blue? o, would it not be called the *Thousand-Sapphire Galaxy* instead?

Thank you and have a great day,

Joey Cummens

How could you misspell "galaxy" (galaxx) in the title?? There are frequently misspellings and errors in APOD; don't you have spellcheck?

Never mind, I i think I misinterpreted it (I cannot go back and check since it does not seem to work on my end now for some reason).

MoreInput wrote: ↑Sat Jun 29, 2019 6:46 am Wonderful galaxy, one of my favorites. The picture of the galaxy was the front page of the "Galaxies" book from Timothey Ferris from 1983 ... long time ago.

Thanks for reminding me of that great book. We ran a planetarium show based on that book at one time, with Ferris providing narration. I've always thought a 2nd edition of that book with new pics from Hubble, VLT, etc., replacing the original ones, would be a wonderful idea.

Dr. Work wrote: ↑Sat Jun 29, 2019 2:00 pm How could you misspell "galaxy" (galaxx) in the title?? There are frequently misspellings and errors in APOD; don't you have spellcheck?

Hi, I actually logged in to mention that there is small, easy to understand typo in the title. Thank you so much for working at APOD. I appreciate you and your editing.

micahcff wrote: ↑Sat Jun 29, 2019 6:40 pm

Dr. Work wrote: ↑Sat Jun 29, 2019 2:00 pm How could you misspell "galaxy" (galaxx) in the title?? There are frequently misspellings and errors in APOD; don't you have spellcheck?

Hi, I actually logged in to mention that there is small, easy to understand typo in the title. Thank you so much for working at APOD. I appreciate you and your editing.

Thanks! It's fixed now.

NCTom wrote: ↑Sat Jun 29, 2019 11:19 am Two galaxies stand out at 9 o'clock. The upper one is fascinating. It appears to have a heavy bar and a huge ring. Any more information on it?

http://www.atlasoftheuniverse.com/galgrps/ngc5128.html I found this page & it lists many galaxies in this group.You may find the 2 galaxies you are curious about in this list/on this page.

joeycummens wrote: ↑Sat Jun 29, 2019 1:19 pm So, I was reading up on today:s APOD and I am confused on the popular moniker of this galaxy. The brief article says that the reason it got its name is due to its blue clusters. However, aren't rubies red, not blue? o, would it not be called the *Thousand-Sapphire Galaxy* instead?

Thank you and have a great day,

Joey Cummens

M83 is called the "Thousand Ruby Galaxy" because it is rich in gas and hot stars. Hot stars emit very strongly in the ultraviolet part of the spectrum, but they are also bright in the violet and blue part of the spectrum, and brighter there than in the orange and red part of the spectrum. Therefore these stars are bluish in color. However, it is their ultraviolet light that ionizes the gas near them and makes it shine red due to H-alpha emission.

But, to summarize: If a galaxy doesn't have a lot of hot blue stars, it will not have a lot of red emission nebulas either.

One more thing to remember is that the blue stars shine a lot brighter than the emission nebulas, at least in most cases. So a galaxy that contains a lot of red emission nebulas will nevertheless be more blue than red, because all the blue stars shine so much brighter than the red emission nebulas do.

Take a look at this picture of M83 by kennethtompkins167. The picture was made without a hydrogen alpha filter, so the red nebulas don't look very bright at all. But the blue arms of M83, full of hot blue stars, stand out.

Ann

Ann wrote: ↑Sat Jun 29, 2019 9:14 am

FLPhotoCatcher wrote: ↑Sat Jun 29, 2019 4:34 am Beautiful galaxy! How similar to the Milky Way is it, ignoring the size difference? Is there a galaxy that better illustrates what the Milky Way looks like?
The renderings used to show what the Milky Way looks like always bother me since they are so fake looking - better to use a picture of a real galaxy, IMHO.

The way I see it, you can't ignore the size difference. Interestingly, vigorous star formation is more often found in small galaxies than in large ones. Of course, a much greater part of the galaxy can be involved in vigorous star formation if the galaxy is small than if it is big. Both galaxies can have the same absolute amount of star formation, but the small galaxy will be dominated by it, while the large galaxy will not. But I will say that M83 forms more stars in absolute terms than the Milky Way does, based on its appearance alone.

Ann

Thanks for the info Ann (and "MoreInput").

NCTom wrote: ↑Sat Jun 29, 2019 11:19 am Two galaxies stand out at 9 o'clock. The upper one is fascinating. It appears to have a heavy bar and a huge ring. Any more information on it?

Unfortunately, no! But my software tells me that the galaxy below it is PGC 48132, and it shines at magnitude 15.6, which is very faint indeed. Bear in mind that M83 itself is magnitude 7.5 in our skies, so PGC 48132 is 8 magnitudes fainter! The galaxy above PGC 48132 is clearly fainter still.

My software says that PGC 48132 is an Sb-type galaxy, and my guess is that it is intrinsically brighter than M83.

As for the galaxy you are interested in, it has a strong bar and a ring. I think it is slightly similar to NGC 2523.

But check out a number of barred and ringed galaxies here, and check out a one-filter picture of 4253 here. Also look at the galaxies here, particularly the middle one.

Ann

Thanks, Ann and others, for the follow up. This kind of homework I can enjoy!

Unfortunately(and oddly) the link I posted did not include the 2 galaxies asked about in the list included.Those 2 galaxies look close enough to M83.. .you would think they would be included in the group M83 is a member of.I'm assuming most galaxies use an NGC before their designated number? I looked at the list and could not find the 2 galaxies.The list included other numbers..one leading to a dwarf galaxy.If someone checks out that list....maybe they can figure out what galaxy group they belong to.....or find them under a non NGC number.

sillyworm 2 wrote: ↑Sun Jun 30, 2019 12:40 pm Unfortunately(and oddly) the link I posted did not include the 2 galaxies asked about in the list included.Those 2 galaxies look close enough to M83.. .you would think they would be included in the group M83 is a member of.I'm assuming most galaxies use an NGC before their designated number? I looked at the list and could not find the 2 galaxies.The list included other numbers..one leading to a dwarf galaxy.If someone checks out that list....maybe they can figure out what galaxy group they belong to.....or find them under a non NGC number.

The reason why the two galaxies are not included in the list is because they are too faint. There are 13th magnitude NGC galaxies, but no 15th mag galaxies or fainter in the NGC catalogue.

Ann

Thanks Ann....maybe in the years to come we will be able to see these galaxies in greater detail.

NCTom wrote: ↑Sat Jun 29, 2019 11:19 am Two galaxies stand out at 9 o'clock. The upper one is fascinating. It appears to have a heavy bar and a huge ring. Any more information on it?

The upper one seems to have some bow shocks (just an enthusiast, so don't take that description literally). Makes it look like a Tie-Fighter, maybe we can name it the Tie-Fighter Galaxy