APOD: NGC 6744 Close Up (2018 May 31)

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APOD: NGC 6744 Close Up (2018 May 31)

Post by APOD Robot » Thu May 31, 2018 4:07 am

Image NGC 6744 Close Up

Explanation: 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, its galactic disk tilted towards our line of sight. This Hubble close-up of the nearby island universe spans about 24,000 light-years across NGC 6744's central region in a detailed portrait that combines visible light and ultraviolet image data. The giant galaxy's yellowish core is dominated by the visible light from old, cool stars. Beyond the core are pinkish star forming regions and young star clusters scattered along the inner spiral arms. The young star clusters are bright at ultraviolet wavelengths, shown in blue and magenta hues.

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by bystander » Thu May 31, 2018 5:03 am

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Ann » Thu May 31, 2018 5:04 am

NGC 6744 is a very interesting galaxy. Its bulge is huge and yellow, and somewhat similar to the giant yellow bulge of M81. A difference is that the bulge of M81 appears to be more dominant than the bulge of NGC 6744.

M81. Picture: Siegfried Kohlert


















But while M81 is a "grand design" galaxy with two long, sweeping spiral arms, NGC 6744 displays a multitude of small armlets. Then again, NGC 6744 has at least one long arm, and M81 does sport some extra arms.

NGC is forming stars at a respectable rate.
AsgardiaSpace.com wrote:

Furthermore, the team calculated that the star formation rate of NGC 6744 is between 2.8 and 4.7 solar masses per year, which is at least two times greater than that of the Milky Way. This value demonstrates that NGC 6744 is still actively forming stars.
So it is no wonder that NGC 6744 sports an extended set of admittedly disorganized spiral arms.

As for today's APOD, I personally don't much like the purple stars and purplish-tinged emission nebulas. I suppose that the strange colors have to do with the ultraviolet filter used for this image.

Ann
Last edited by Ann on Thu May 31, 2018 4:56 pm, edited 2 times in total.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by geckzilla » Thu May 31, 2018 5:30 am

I had some fun with these data while ago, too.
Image
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by ygmarchi » Thu May 31, 2018 7:04 am

Daily APOD image is more necessary than my cup of coffee.

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Ann » Thu May 31, 2018 7:35 am

geckzilla wrote:
Thu May 31, 2018 5:30 am
I had some fun with these data while ago, too.
Image
I like your version better, Geck!

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brucewilliams174

Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by brucewilliams174 » Thu May 31, 2018 11:19 am

So, if NGC 6744 is a universe is it one of the multiverses that is the latest thing in astronomy?

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by orin stepanek » Thu May 31, 2018 11:33 am

Galaxies are sometimes referred to as a universe! to me,all the galaxies are part of the universe! I believe that multiverse refers to universes that are beyond our understanding! This is my own humble opinion; and not necessary a fact!
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by BDanielMayfield » Thu May 31, 2018 1:08 pm

brucewilliams174 wrote:
Thu May 31, 2018 11:19 am
So, if NGC 6744 is a universe is it one of the multiverses that is the latest thing in astronomy?
orin stepanek wrote:
Thu May 31, 2018 11:33 am
Galaxies are sometimes referred to as a universe! to me,all the galaxies are part of the universe! I believe that multiverse refers to universes that are beyond our understanding! This is my own humble opinion; and not necessary a fact!
Orin's right. Calling another galaxy a universe is a dated holdover from the times when the Milky Way was thought to be the whole universe. If we can see it, it's in our universe.

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Chris Peterson » Thu May 31, 2018 1:59 pm

brucewilliams174 wrote:
Thu May 31, 2018 11:19 am
So, if NGC 6744 is a universe is it one of the multiverses that is the latest thing in astronomy?
A universe is not the same thing as the Universe. And more specifically, the term "island universe" is a synonym for "galaxy", commonly used with literary or poetic intent. Grammatically, "island universe" is a compound noun, meaning it is neither an island nor a universe, but an entity different from either. So your paraphrase of the caption is incorrect and changes its meaning.
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sunson

Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by sunson » Thu May 31, 2018 2:17 pm

Why does the stars on the edge one can see much clearer and well defined than the stars towards the center? Are they brighter? O perhaps what seems to be one star is in fact a bunch that seems to shine brighter and is more defined?

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Chris Peterson » Thu May 31, 2018 2:57 pm

sunson wrote:
Thu May 31, 2018 2:17 pm
Why does the stars on the edge one can see much clearer and well defined than the stars towards the center? Are they brighter? O perhaps what seems to be one star is in fact a bunch that seems to shine brighter and is more defined?
In the center you have a very high star density, and the individual stars are similar in color and brightness. So you don't have individually resolved stars. At the scale of this image, every single central pixel is receiving light from many stars. At the outer edges, the star density drops much lower, and you have individually bright ones that rise above the background intensity, so they show up by themselves.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by stevewiggins » Thu May 31, 2018 4:21 pm

Are we any closer to seeing more detail inside galaxies? Particularly the center. In this image of NGC 6744, one can see dust lanes beginning a tighter swirl around the center but what lies deeper within - at least one light year's span?

Uncle Jeff

Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Uncle Jeff » Thu May 31, 2018 4:35 pm

Are the brightest stars (the standouts with spikes) intervening foreground stars in our own galaxy (as is usual in these photos)?

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by neufer » Thu May 31, 2018 4:36 pm

stevewiggins wrote:
Thu May 31, 2018 4:21 pm

Are we any closer to seeing more detail inside galaxies? Particularly the center.
:arrow: Different wavelengths help.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by neufer » Thu May 31, 2018 4:37 pm

Uncle Jeff wrote:
Thu May 31, 2018 4:35 pm

Are the brightest stars (the standouts with spikes) intervening foreground stars in our own galaxy (as is usual in these photos)?
  • Yes.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Ann » Thu May 31, 2018 7:08 pm

sunson wrote:
Thu May 31, 2018 2:17 pm
Why does the stars on the edge one can see much clearer and well defined than the stars towards the center? Are they brighter? O perhaps what seems to be one star is in fact a bunch that seems to shine brighter and is more defined?

The Herzsprung-Russel diagram of stellar brightness versus color.
Illustration: Astronomy magazine.
Take a look at the Hertzsprung-Russell diagram at left.

When it comes to so called main sequence stars, which are stars that still fuse hydrogen into helium in their cores (like the Sun), they are hotter, brighter and bluer the more massive they are. Conversely, they are cooler, fainter and redder the less massive they are.

Massive stars quickly run out of fuel and evolve into giants, supergiants and, in a very few cases, hypergiants. These stars are extremely bright, but they burn out very quickly and explode as supernovas. Lightweight stars, by contrast, evolve slowly and shine steadily but faintly for billions and maybe trillions of years.

The bulges of massive galaxies are completely dominated by truly huge numbers of small yellow and red stars. There are also a number of red giants in the bulges of galaxies. These red giants are typically some 30-300 times brighter than the Sun. They are not thousands of times brighter than the Sun, certainly not in optical light. They are stars like Pollux and Arcturus, not stars like Antares and Betelgeuse. Red and yellow dwarfs far outnumber the red giants in the bulges of galaxies, but the red giants provide most of the light there.

In the arms of spiral galaxies, however, much of the light comes from bright main sequence stars of spectral class B. Even brighter are the main sequence stars of spectral class O, and supergiants of all spectral classes are the brightest of them all, except for the terrifically rare hypergiants.

All B- and O-type main sequence stars are young, and all the supergiants and hypergiants are young, too. But they reside in the outbacks of the galaxies, where the stars are few and far between. Even though many individual stars are so bright, they can't light up the terrible chasms separating them from other stars, associations and clusters. The arms of the galaxies are lit up intermittently by pinpricks of light, between which darkness reasserts its reign. The bulges of galaxies, by contrast, are the crowded cities, which are typically lit up by extreme numbers of small faint stars and moderate numbers of red giants.

Take a look at these two clusters, one globular cluster and one open cluster: :arrow:

It must be said that globular clusters are not like the bulges of galaxies. That is because galactic bulges contain stars of different ages, and the stars are usually rather metal-rich. By contrast, the stars of globular clusters are typically very metal-poor and so old that they are just a little younger than the Universe itself. In most cases, all the stars in a globular cluster were born at more or less the same time, too.

Nevertheless, both globular clusters and galactic bulges are dominated by huge numbers of small red and yellow stars. Most of the light, however, comes from a comparatively small number of red giants.

By contrast, most open clusters in the Milky Way are young. Not all are so young that they are dominated by blue stars, but many are. Some of them are rich in stars, like M11, but many contain just a smattering of bright stars. The open cluster in the picture at right is IC 2602, and all the bright stars are main sequence stars of spectral class B. You can see how sparse the cluster is. Think of the arms of spiral galaxies like conglomerates of clusters similar to IC 2602, but few and far between.

And that is why galactic bulges are often bright, but spiral arms are typically faint.

Ann
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by MikeA » Thu May 31, 2018 8:56 pm

Ann,
Your contributions are an absolute delight and sooo informative. Thank you for the time and effort you put into them.

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Chris Peterson » Thu May 31, 2018 9:59 pm

stevewiggins wrote:
Thu May 31, 2018 4:21 pm
Are we any closer to seeing more detail inside galaxies? Particularly the center. In this image of NGC 6744, one can see dust lanes beginning a tighter swirl around the center but what lies deeper within - at least one light year's span?
We can see much higher resolution than this. The Hubble is limited by a small mirror and correspondingly course pixel scale. The best ground based telescopes can resolve about one arcsecond these days- just over a light year at the distance of NGC 6744. And that's just getting better as telescopes get larger and adaptive optics gets better. (And using interferometric methods at millimeter and radio wavelengths we can see much finer still.)
Chris

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by geckzilla » Fri Jun 01, 2018 12:12 am

Chris Peterson wrote:
Thu May 31, 2018 9:59 pm
stevewiggins wrote:
Thu May 31, 2018 4:21 pm
Are we any closer to seeing more detail inside galaxies? Particularly the center. In this image of NGC 6744, one can see dust lanes beginning a tighter swirl around the center but what lies deeper within - at least one light year's span?
We can see much higher resolution than this. The Hubble is limited by a small mirror and correspondingly course pixel scale. The best ground based telescopes can resolve about one arcsecond these days- just over a light year at the distance of NGC 6744. And that's just getting better as telescopes get larger and adaptive optics gets better. (And using interferometric methods at millimeter and radio wavelengths we can see much finer still.)
Is there a typo here? I didn't think 1" was very impressive.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by neufer » Fri Jun 01, 2018 2:26 am

geckzilla wrote:
Fri Jun 01, 2018 12:12 am
Chris Peterson wrote:
Thu May 31, 2018 9:59 pm
stevewiggins wrote:
Thu May 31, 2018 4:21 pm

Are we any closer to seeing more detail inside galaxies? Particularly the center. In this image of NGC 6744, one can see dust lanes beginning a tighter swirl around the center but what lies deeper within - at least one light year's span?
We can see much higher resolution than this. The Hubble is limited by a small mirror and correspondingly course pixel scale. The best ground based telescopes can resolve about one arcsecond these days- just over a light year at the distance of NGC 6744. And that's just getting better as telescopes get larger and adaptive optics gets better. (And using interferometric methods at millimeter and radio wavelengths we can see much finer still.)
Is there a typo here? I didn't think 1" was very impressive.
https://en.wikipedia.org/wiki/Adaptive_optics#Wavefront_sensing_and_correction wrote:
<<An adaptive optics system tries to correct these distortions, using a wavefront sensor which takes some of the astronomical light, a deformable mirror that lies in the optical path, and a computer that receives input from the detector. The wavefront sensor measures the distortions the atmosphere has introduced on the timescale of a few milliseconds; the computer calculates the optimal mirror shape to correct the distortions and the surface of the deformable mirror is reshaped accordingly. For example, an 8–10 m telescope (like the VLT or Keck) can produce AO-corrected images with an angular resolution of 30–60 milliarcsecond (mas) resolution at infrared wavelengths, while the resolution without correction is of the order of 1 arcsecond.>>
https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Proposals_and_precursors wrote:
<<The history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzer's paper "Astronomical advantages of an extraterrestrial observatory". In it, he discussed the two main advantages that a space-based observatory would have over ground-based telescopes. First, the angular resolution (the smallest separation at which objects can be clearly distinguished) would be limited only by diffraction, rather than by the turbulence in the atmosphere, which causes stars to twinkle, known to astronomers as seeing. At that time ground-based telescopes were limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.05 arcsec for a telescope with a mirror 2.5 m in diameter. Second, a space-based telescope could observe infrared and ultraviolet light, which are strongly absorbed by the atmosphere.>>
https://jwst.nasa.gov/faq.html#sharp wrote:
<<With a mirror that is 2.75 times larger in diameter than Hubble the James Webb Space Telescope's angular resolution will be the same as Hubble's, but in the near infrared. Webb will have an angular resolution of somewhat better than 0.1 arc-seconds at a wavelength of 2 micrometers and ~1.3 arc-seconds at 28 microns.>>
Art Neuendorffer

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by Chris Peterson » Fri Jun 01, 2018 2:59 am

geckzilla wrote:
Fri Jun 01, 2018 12:12 am
Chris Peterson wrote:
Thu May 31, 2018 9:59 pm
stevewiggins wrote:
Thu May 31, 2018 4:21 pm
Are we any closer to seeing more detail inside galaxies? Particularly the center. In this image of NGC 6744, one can see dust lanes beginning a tighter swirl around the center but what lies deeper within - at least one light year's span?
We can see much higher resolution than this. The Hubble is limited by a small mirror and correspondingly course pixel scale. The best ground based telescopes can resolve about one arcsecond these days- just over a light year at the distance of NGC 6744. And that's just getting better as telescopes get larger and adaptive optics gets better. (And using interferometric methods at millimeter and radio wavelengths we can see much finer still.)
Is there a typo here? I didn't think 1" was very impressive.
Yes, I meant 0.01 arcsec (which also gives the 1 ly scale I mentioned).
Chris

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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by neufer » Fri Jun 01, 2018 3:18 am

Chris Peterson wrote:
Fri Jun 01, 2018 2:59 am
geckzilla wrote:
Fri Jun 01, 2018 12:12 am
Chris Peterson wrote:
Thu May 31, 2018 9:59 pm

We can see much higher resolution than this. The Hubble is limited by a small mirror and correspondingly course pixel scale. The best ground based telescopes can resolve about one arcsecond these days- just over a light year at the distance of NGC 6744. And that's just getting better as telescopes get larger and adaptive optics gets better. (And using interferometric methods at millimeter and radio wavelengths we can see much finer still.)
Is there a typo here? I didn't think 1" was very impressive.
Yes, I meant 0.01 arcsec (which also gives the 1 ly scale I mentioned).
The resolution of a 12 meter space telescope in the visible :?:
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by MarkBour » Fri Jun 01, 2018 4:08 am

neufer wrote:
Thu May 31, 2018 4:36 pm
Andromeda Galaxy M31 at different wavelengths
:arrow: Different wavelengths help.
Nice parallel comparison.
So, the heart of the galaxy dominates in all wavelengths until you get down to radio, at which range it looks pretty silent.
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Re: APOD: NGC 6744 Close Up (2018 May 31)

Post by neufer » Fri Jun 01, 2018 12:18 pm

MarkBour wrote:
Fri Jun 01, 2018 4:08 am
neufer wrote:
Thu May 31, 2018 4:36 pm
stevewiggins wrote:
Thu May 31, 2018 4:21 pm

Are we any closer to seeing more detail inside galaxies? Particularly the center.
:arrow: Different wavelengths help.
Nice parallel comparison.

So, the heart of the galaxy dominates in all wavelengths until you get down to radio, at which range it looks pretty silent.
  • Just so long as the giant central black hole has not recently been prodded.
https://en.wikipedia.org/wiki/NGC_383 wrote: NGC 383 is a double radio galaxy with a quasar-like appearance located in the constellation Pisces. Recent discoveries by the National Radio Astronomy Observatory in 2006 reveal that NGC 383 is being bisected by high energy relativistic electrons traveling at relatively high fractions of the speed of light. These relativistic electrons are detected as synchrotron radiation in the x-ray and radio wavelengths. The focus of this intense energy is the galactic center of NGC 383. The relativistic electron jets detected as synchrotron radiation extend for several thousand parsecs.>>
Art Neuendorffer