APOD: NGC 1309: Spiral Galaxy and Friends (2013 Jan 16)

APOD Robot · Post by **APOD Robot** » Wed Jan 16, 2013 5:06 am

NGC 1309: Spiral Galaxy and Friends

Explanation: A gorgeous spiral galaxy some 100 million light-years distant, NGC 1309 lies on the banks of the constellation of the River (Eridanus). NGC 1309 spans about 30,000 light-years, making it about one third the size of our larger Milky Way galaxy. Bluish clusters of young stars and dust lanes are seen to trace out NGC 1309's spiral arms as they wind around an older yellowish star population at its core. Not just another pretty face-on spiral galaxy, observations of NGC 1309's recent supernova and Cepheid variable stars contribute to the calibration of the expansion of the Universe. Still, after you get over this beautiful galaxy's grand design, check out the array of more distant background galaxies also recorded in the above, sharp, reprocessed, Hubble Space Telescope view.

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Ann · Post by **Ann** » Wed Jan 16, 2013 5:54 am

This is a very beautiful, reprocessed Hubble image! Thanks, Martin Pugh!

I don't have my software here so that I can check NGC 1309, but the galaxy looks smallish to me and very full of young blue stars. Note how broad the arms are. This means that new stars are being born "almost all over" in this galaxy, not just along narrow, sharply defined arms. Such broad arms are usually seen in galaxies that are smaller than the Milky Way. The bulge of NGC 1309 is small, not very bright at all, and not stikingly yellow (although that might be a consequence of the filters used). This is another clue that the galaxy is smallish.

Note the fantastic barred spiral at ten o'clock. Interestingly, although its bar is yellow, its arms are about as blue as the arms of NGC 1309. All other background galaxies are yellow due to distance and redshift. I have to wonder if this barred galaxy is far in the backgound, or if it is a small, marvellously shaped galaxy that is not so far from NGC 1309. Most likely it is really pretty far away from NGC 1309. Its shape suggests a substantial and therefore large dynamical structure. Its very blue arms, then, suggest very massive star formation giving birth very hot stars.

Ann

saturno2 · Post by **saturno2** » Wed Jan 16, 2013 11:26 am

The central core of NGC 1309 is very small, while the arms are dense and thick.
It look like a " teen-age" galaxy

Boomer12k · Post by **Boomer12k** » Wed Jan 16, 2013 12:45 pm

Wikipedia says its size is 75,000ly across, not 30,000.

There would appear to be either, many gas pockets that are coming in and attaching themselves to the galaxy, or it got "splayed" out from near collisions. The inner area appears very dense, the outer area, less dense, so much so, you can see through it. Like something happened to splay it out like that.

It reminds me of a HYDRA. There is a "head" on the upper right side, that looks like it has one red eye. The other "head" is lower left, looking down, and appears more feline. It has an "ear" above the orange galaxy, and above to the right is an "eye", and further to the right and down a "snout". The Hydras appear to be winding around a jewel, protecting it.

The background galaxies are awesome. Edge on, Face on, Elliptical, all over the place. And many seen through NGC 1309.

Are there any indications of Galactic Lensing here? Because with so many galaxies I would think there should be some.

:---[===] *

link5817b · Post by **link5817b** » Wed Jan 16, 2013 1:47 pm

I realize this may be a silly question for those using this forum, but...
can someone tell me what the yellow 'dot' is at the center of ngc 1309?
(eg is it a cluster of stars plus a likely black hole... or... ? )

Ann · Post by **Ann** » Wed Jan 16, 2013 2:47 pm

Boomer12k wrote:
Wikipedia says its size is 75,000ly across, not 30,000.

Interesting, Boomer12k. My software, too, says that NGC 1309 is about the same size as the Milky Way. Well, I'll keep insisting that it looks smallish, with its broad arms and rather faint bulge and nucleus.

It's quite blue, too. Its U-b index is -0.17 and its B-V is +0.44. Such blue colors are much more common among small galaxies than among big ones. There simply isn't that much "free gas" and star formation in the present-day universe, which is why it's easier for a small galaxy than for a big galaxy to be dominated by star formation. It simply doesn't take as much star formation to dominate a small galaxy as it takes to dominate a big one!

What is the U-B and B-V indexes of the Milky Way? That, frankly, is anybody's guess, since we can't see our galaxy from outside. But we can see the "integrated flux nebula", high "cirrus clouds" in the Milky Way which are believed to reflect the overall color of our galaxy. The Integrated flux nebula is pretty red, even though it's not the same color all over. The galaxy in the picture is NGC7479, by the way, and its color indexes are +0.15 (U-B) and + 0.72 (B-V). Maybe our galaxy has colors like those?

Ann

Ann · Post by **Ann** » Wed Jan 16, 2013 3:07 pm

link5817b wrote:I realize this may be a silly question for those using this forum, but...
can someone tell me what the yellow 'dot' is at the center of ngc 1309?
(eg is it a cluster of stars plus a likely black hole... or... ? )

It is almost certainly a black hole and a bright cluster of stars.

This is a very interesting picture of the central parts of the Milky Way. You can see a lot of turbulent gas, supernova remnants and a few clusters. Note, however, the tremendous cluster (in white) at four o'clock. This is almost certainly the biggest cluster in the Milky Way, and it is in orbit around our galaxy's central supermassive black hole.

Ann

neufer · Post by **neufer** » Wed Jan 16, 2013 3:42 pm

APOD Robot wrote: NGC 1309: Spiral Galaxy and Friends

If those other galaxies are "friends" how come they're all so distant

Chris Peterson · Post by **Chris Peterson** » Wed Jan 16, 2013 3:59 pm

link5817b wrote:I realize this may be a silly question for those using this forum, but... can someone tell me what the yellow 'dot' is at the center of ngc 1309? (eg is it a cluster of stars plus a likely black hole... or... ? )

There's probably a black hole, but we can't see that. The yellow dot is merely a region of increased stellar density- something seen in virtually all spiral galaxies at the center. It's not really correct to call it a "cluster", although it does resemble globular clusters in some respects. It probably isn't closely related to the central black hole- it is much too large. In part, it is an imaging artifact, as well. Most galaxies are inherently low contrast structures- in order to see them as we do in images, a strong "S" shaped transfer function is almost always applied to compress the range of the bright and dim regions, and to expand the middle. This also helps match the huge dynamic range of the object to the very limited dynamic range of our display devices. But it also significantly distorts the radial intensity profile of galaxies in images, so you can't fully trust what you're seeing in very bright regions like the core.

nstahl · Post by **nstahl** » Wed Jan 16, 2013 4:12 pm

It's a fine looking galaxy and its residents should be proud of it. Of course a lot of its residents surely don't realize it's a particularly fine looking galaxy, or even that it's a galaxy. And there doesn't seem to be anything to do about that.

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LocalColor · Post by **LocalColor** » Wed Jan 16, 2013 4:42 pm

"And friends' - love it. Hubble gives us "art" to appreciate!

neufer · Post by **neufer** » Wed Jan 16, 2013 6:32 pm

Chris Peterson wrote:
link5817b wrote:
I realize this may be a silly question for those using this forum, but... can someone tell me what the yellow 'dot' is at the center of ngc 1309? (eg is it a cluster of stars plus a likely black hole... or... ? )
There's probably a black hole, but we can't see that. The yellow dot is merely a region of increased stellar density- something seen in virtually all spiral galaxies at the center. It's not really correct to call it a "cluster", although it does resemble globular clusters in some respects. It probably isn't closely related to the central black hole- it is much too large.

It is interesting that both galaxies & globular clusters with suspected very large black holes
at their centers also have a noticeable concentration of stars near their centers:

http://en.wikipedia.org/wiki/Messier_15 wrote:
[b][color=#0000FF]M15 photographed by HST. The planetary nebula Pease 1 can be seen as a small blue object to the lower left of the core of the cluster.[/color][/b]
<<Messier 15 or M15 is a globular cluster in the constellation Pegasus. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.>>

http://en.wikipedia.org/wiki/Messier_87 wrote:

Messier 87 (also known as M87, Virgo A or NGC 4486) is a supergiant elliptical galaxy. At the core of this galaxy is a supermassive black hole (SMBH) with an estimated 6.6 × 10⁹ times the mass of the Sun and a diameter larger than the orbit of Pluto. This is one of the highest masses known for such an object. Surrounding the black hole is a rotating disk of ionized gas that is oriented roughly perpendicular to a relativistic jet. This disk is rotating at velocities of up to roughly 1,000 km/s, and spans a maximum diameter of 0.12 pc (0.39 ly). Gas is accreting onto the black hole at an estimated rate equal to the mass of the Sun every ten years.>>

Chris Peterson · Post by **Chris Peterson** » Wed Jan 16, 2013 6:42 pm

neufer wrote:It is interesting that both galaxies & globular clusters with suspected very large black holes
at their centers also have a noticeable concentration of stars near their centers.

Yes, there certainly seems to be a correlation. AFAIK, simulations have not done a very good job of explaining this. Of course, it doesn't help that we don't have a good idea how galaxies (or globulars) form in the first place- the role of dark matter, whether central black holes show up first or if they result from something later in galactic evolution, and many other questions.

It doesn't seem dynamically likely that a central supermassive black hole would create a central cluster-like region of this extent, but we can't really know without knowing more about how galaxies evolve. But it does seem very possible that both the central black hole and high central star density are both consequences of some single factor, not yet well identified.

Anthony Barreiro · Post by **Anthony Barreiro** » Thu Jan 17, 2013 12:14 am

Okay, I'll admit you see a bit more detail in this image than you see through a telescope eyepiece.

To see all those distant background galaxies scattered around and even behind 1309 is truly humbling.

Chris, thanks for the explanation about image processing affects the brightness of different areas in a picture of a galaxy.

Ann · Post by **Ann** » Thu Jan 17, 2013 5:30 pm

Chris Peterson wrote:
Most galaxies are inherently low contrast structures- in order to see them as we do in images, a strong "S" shaped transfer function is almost always applied to compress the range of the bright and dim regions, and to expand the middle. This also helps match the huge dynamic range of the object to the very limited dynamic range of our display devices. But it also significantly distorts the radial intensity profile of galaxies in images, so you can't fully trust what you're seeing in very bright regions like the core.

That is certainly true. In particular, I think it's common for photographers to "brighten the arms" and dim the center" in order to bring out as much detail as possible.

James D Wray, who took the UBV color images of "The Color Atlas of Galaxies", never fiddled with the surface brightnesses of galaxies. What you saw was what you got. It's quite interesting to look at Wray's image of famous barred spiral galaxy NGC 1300, for example. In Wray's image, NGC 1300 looks like a bright, almost circular yellow bulge, with some grayish "fuzz" far from the bulge on both sides of it!

What about NGC 1309? In Wray's image, its surface brightness is quite high, and the two most obvious arms are bluish and very broad. Its inner disk is greenish (from A-type stars) and its yellowish bulge is very small and not particularly bright at all. Admittedly its nucleus is sufficiently bright to look white. Wray wrote:

From an evolutionary perspective we note that the galaxy is dominated by a present burst of star formation activity which, on the basis of the general lack of any significant yellow disk population, may be unprecedented in its evolutionary history. A small blue galaxy is visible at 31.3.

That small blue galaxy is the fantastic barred spiral so gloriously portrayed in this Hubble image, processed by Martin Pugh.

Ann

bystander · Post by **bystander** » Mon Feb 04, 2013 8:52 pm

NGC 1309: Stepping Stone to the Universe
Slate Blogs | Bad Astronomy | Phil Plait | 2013 Feb 05

Starship Asterisk*

APOD: NGC 1309: Spiral Galaxy and Friends (2013 Jan 16)

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