APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4530
Joined: Fri Dec 04, 2009 3:27 am

APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by APOD Robot » Fri May 26, 2017 4:06 am

Image Spiral Galaxy NGC 6744

Explanation: Big, beautiful spiral galaxy NGC 6744 is nearly 175,000 light-years across, larger than our own Milky Way. It lies some 30 million light-years distant in the southern constellation Pavo appearing as a faint, extended object in small telescopes. We see the disk of the nearby island universe tilted towards our line of sight. This remarkably distinct and detailed galaxy portrait covers an area about the angular size of the full moon. In it, the giant galaxy's yellowish core is dominated by the light from old, cool stars. Beyond the core, spiral arms filled with young blue star clusters and pinkish star forming regions sweep past a smaller satellite galaxy at the lower left, reminiscent of the Milky Way's satellite galaxy the Large Magellanic Cloud.

<< Previous APOD This Day in APOD Next APOD >>
[/b]

Boomer12k
:---[===] *
Posts: 2691
Joined: Sun Apr 22, 2007 12:07 am

Re: APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by Boomer12k » Fri May 26, 2017 6:31 am

Totally AWESOME!!!
Maybe I should have put a galaxy on the hood of my 240Z instead of a Dragon....hmmm.

:---[===] *

User avatar
Ann
4725 Å
Posts: 11724
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by Ann » Fri May 26, 2017 7:27 am

Wow, we're having a galactic bonanza here lately! I can't believe it!

I'll try to compare NGC 6744 with some of the other galaxies that have had their own APODs lately. But first. let's look at NGC 6744 itself.
NGC 6744 in optical light.
Photo: Don Goldman.
NGC 6744 in infrared light. Photo: WISE/NASA/JPL-Caltech/UCLA


















In infrared pictures of galaxies, blue areas mean red stars. Blue stars, by contrast, hardly show up in infrared images and are mostly invisible there. Green areas in this infrared image mean warm dust. Red-orange areas typically mean ongoing star formation. You can see a few bright orange-red splotches scattered in or near the interface between the inner, slightly yellow arm system, and the outer blue (or, in the WISE image, the green) one. (Note that the outermost blue arm of NGC 6744 and the little companion galaxy at 7 o'clock are mostly invisible in the WISE image.)

All but one of these orange splotches correspond to pink emission nebulas in Don Goldman's image, confirming the fact that these are sites of ongoing star formation. I must wonder what the brightest, reddest, roundest object is, at 2 o'clock. It doesn't correspond to any emission nebulas.
NGC 6744 in ultraviolet light. Photo: NASA/GALEX.
Let's look at one more picture of NGC 6744, this time showing the galaxy in ultraviolet light. Please note that this picture is upside down compared with the other two.

Note that the entire galaxy except the innermost center is glowing white to whitish-blue from ultraviolet light. The color is due to a mixture of stars of different temperatures. (Check out the full resolution 900 Kb image here.) Much of the ultraviolet light seen here is likely produced by relatively modest stars like Regulus, or even Vega or Sirius. Note that you can see the arm pattern of NGC 6744 exceptionally well. You can't spot the sites of star formation, however.
M101 in infrared light. Note the massive sites of star formation.
Photo: Spitzer.











How big is NGC 6744? It's big. Big. If it is 175,000 light-years in diameter, as today's caption says, then it is the same size as (or just possibly even somewhat bigger than) M101. And M101 is simply gigantic!

But M101 is a blue galaxy, dominated by flamboyantly hot, bright blue stars. Its B-V index is 0.450, which is tremendously blue. NGC 6744 is a much redder galaxy. Its B-V index hasn't been measured in the same way as that of M100, so some fits and guesses must be made, but it seems likely that it might be around 0.750 or 0.800, which is much redder.

To be so much redder, NGC 6744 must contain huge numbers of old red and yellow stars. In all probability, the wealth of small red stars in NGC 6744 means that it contains more stars than M101. NGC 6744 is likely also more massive than M101, since the copious numbers of small red stars add a lot of mass to NGC 6744.

So all in all, NGC 6744 is older, redder, more settled and more tired than M101, and, in my opinion, probably more massive. The Pinwheel galaxy, by contrast, is windblown, blue, brilliant and bellowing.

Ann
Last edited by Ann on Fri May 26, 2017 4:57 pm, edited 1 time in total.
Color Commentator

starsurfer
Stellar Cartographer
Posts: 4620
Joined: Thu Mar 15, 2012 7:25 pm

Re: APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by starsurfer » Fri May 26, 2017 9:09 am

Wow this image is nearly 11 years old! Love this galaxy!

douglas

Re: APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by douglas » Fri May 26, 2017 10:46 am

Ann wrote:
I'll try to compare NGC 6744 with some of the other galaxies that have had their own APODs lately. But first. let's look at NGC 6744 itself.
NGC 6744 in optical light.
Photo: Don Goldman.
NGC 6744 in infrared light. Photo: WISE/NASA/JPL-Caltech/UCLA
NGC 6744 in ultraviolet light. Photo: NASA/GALEX.
M101 in infrared light. Note the massive sites of star formaiton.
Photo: Spitzer.
After thankfully including these other wavelengths, we have a much better sense of the APOD's image processing. I searched for a radio image, but alas, was not presented one.

Any idea of Verschatse's exposure time? No overtly-detectable tracking errors.

There are diffraction spikes in foreground stars, so he used a reflector.

" .. a relatively low surface brightness disk .. "
http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf







How big is NGC 6744? It's big. Big. If it is 175,000 light-years in diameter, as today's caption says, then it is the same size as (or just possibly even somewhat bigger than) M101. And M101 is simply gigantic!

But M101 is a blue galaxy, dominated by flamboyantly hot, bright blue stars. Its B-V index is 0.450, which is tremendously blue. NGC 6744 is a much redder galaxy. Its B-V index hasn't been measured in the same way as that of M100, so some fits and guesses must be made, but it seems likely that it might be around 0.750 or 0.800, which is much redder.

To be so much redder, NGC 6744 must contain huge numbers of old red and yellow stars. In all probability, the wealth of small red stars in NGC 6744 means that it contains more stars than M101. NGC 6744 is likely also more massive than M101, since the copious numbers of small red stars add a lot of mass to NGC 6744.

So all in all, NGC 6744 is older, redder, more settled and more tired than M101, and, in my opinion, probably more massive. The Pinwheel galaxy, by contrast, is windswept, blue, brilliant and bellowing.

Ann

bls0326
Science Officer
Posts: 103
Joined: Tue Mar 26, 2013 10:18 pm
Location: USA, Texas, Amarillo

Re: APOD: Spiral Galaxy NGC 6744 (2017 May 26)

Post by bls0326 » Fri May 26, 2017 12:14 pm

Ann, thanks for the comments and pictures!

Brian