APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

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Expand view Topic review: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by JohnD » Sat Feb 19, 2011 9:00 pm

Thank you Ann!

Have to say though that comparing Hoag's with the galaxy you mentioned they look awfully alike.

Image

Uploaded with ImageShack.us

JOhn
PS Slight cheat - I expanded the second galaxy pic in one dimension to make it as circular, polar-viewed, as Hoag's.

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by Ann » Sat Feb 19, 2011 7:21 pm

JohnD wrote:
Is the central region as empty of stars or dust as it looks?
Yes, I'd say it almost certainly is. Very many spiral galaxies really look like this - there is a yellow bulge apparently completely devoid of dust, and then, quite suddenly, the starforming dust appears. This is particularly common in flocculent galaxies, that is, starforming galaxies with dust but no clear spiral pattern. A particularly striking example is galaxy NGC 2775:
This looks like a Hubble color photo where the color is horribly shifted to the blue. You can be sure that the bulge of NGC 2775 is yellow, not blue, as it appears to be here. Nevertheless, the lack of dust in the bulge and the very dusty structures outside the bulge are very obvious here. Note, too, the suddenness of the transition.
And the central glow - is that a dense ball of stars? Or what? Can we guess at a BH in there?
The bulge is full of old yellow stars. There is no star formation here, because stars need gas and dust to form, and there is none of that in the bulge. Closer to the center there is often dust and some quite intense star formation, but there is probably not a lot of central star formation in either NGC 2841 or in NGC 2775. There may be no central star formation in these galaxies at all.

The very center of a galaxy is always very densely packed with stars, at least the centers of all massive galaxies. And NGC 2841 is massive, so we can be sure that its center is densely packed. How dense is it? Well, at least it will be denser than a globular cluster:

http://apod.nasa.gov/apod/ap070419.html

Omega Centauri is dense, but the center of a large galaxy is considerably denser.

And is there a black hole in there? Not in Omega Centauri, but in NGC 2841, yes, definitely. All large galaxies have a central black hole, and NGC 2841 is large and massive. Since this galaxy is larger and more massive than the Milky Way, chances are that, if anything, the central black hole of NGC 2841 is bigger than the one in the Milky Way. So it will probably weigh more than four million solar masses, which is the mass of the black hole in our own galaxy.
If we could see this from its galactic pole, wouldn't it look like Hoag's Object, with a smaller, less empty central region?
http://apod.nasa.gov/apod/ap040815.html
No, almost certainly not, at least not in my opinion. Neufer might disagree. The way I see it, there is no "gap" between the yellow bulge and the dusty star forming region in NGC 2841.

This is a pole-on view of another flocculent galaxy, NGC 7217: http://www.caelumobservatory.com/mlsc/n7217ms.jpg

As you can see, NGC 7217 has a large yellow bulge, but interestingly, the bulge has a complex dusty spiral pattern that penetrates almost, but not quite, all the way to the center of the galaxy. This dusty flocculent spiral pattern in the bulge displays some star formation. Outside this yellow bulge with its dusty spiral pattern is a blue starforming ring. Importantly, however, there is no gap between any of the components of this galaxy.

Ann

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by JohnD » Sat Feb 19, 2011 6:12 pm

Wonderful picture!

Is the central region as empty of stars or dust as it looks?
And the central glow - is that a dense ball of stars? Or what? Can we guess at a BH in there?
How does this central region compare with the Milky Way, which I thought was denser and denser at the centre?

If we could see this from its galactic pole, wouldn't it look like Hoag's Object, with a smaller, less empty central region?
http://apod.nasa.gov/apod/ap040815.html

A theory on the formation of Hoag's and other ring galaxies is that they are the product of collisions.
So, Victor, no!

John

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by VictorB » Sat Feb 19, 2011 5:50 pm

The lack of large intense star forming regions is a result of no collisions with small companion galaxies????

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by neufer » Sat Feb 19, 2011 4:32 pm

dawg64 wrote:
What would happen to a planet similar to Earth located in NGC 2841 if a plume of multimillion degree gas passed over it?
Been there done that:
http://en.wikipedia.org/wiki/Solar_wind wrote:
<<The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 10 and 100 keV. The stream of particles varies in temperature and speed over time. These particles can escape the Sun's gravity because of their high kinetic energy and the high temperature of the corona.

The solar wind is divided into two components, respectively termed the slow solar wind and the fast solar wind. The slow solar wind has a velocity of about 400 km/s, a temperature of 1.4–1.6×106 K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of 750 km/s, a temperature of 8×105 K and it nearly matches the composition of the Sun's photosphere. The slow solar wind is twice as dense and more variable in intensity than the fast solar wind. The slow wind also has a more complex structure, with turbulent regions and large-scale structures.

The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt". Coronal streamers extend outward from this region, carrying plasma from the interior along closed magnetic loops. Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred between latitudes of 30–35° around the equator during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the minimum waned. By the time of the solar maximum, the poles were also emitting a slow solar wind.

The fast solar wind is thought to originate from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field. Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 kilometers above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.

Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called interplanetary coronal mass ejections, or ICMEs. ICMEs are the interplanetary manifestation of solar coronal mass ejections, which are caused by release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. ICMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME.

When an CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora.

ICMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Faster-moving streams tend to overtake slower streams that originate westward of them on the sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs.>>

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by dawg64 » Sat Feb 19, 2011 4:12 pm

What would happen to a planet similar to Earth located in NGC 2841 if a plume of multimillion degree gas passed over it? Does the Milky Way Galaxy emit plumes of such gas? If so, could it be a cause of global warming? Just curious.

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by Ann » Sat Feb 19, 2011 2:04 pm

Check out http://en.wikipedia.org/wiki/Cosmic_dust to learn a lot about dust in space! 8-)

Ann

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by rstevenson » Sat Feb 19, 2011 1:43 pm

GoBears wrote:In photos like this of distant galaxies, people talk about "dust." I am aware that there is certainly interstellar dust that is probably as fine as. . .well, as fine as dust. But is not the "dust" in these photos actually billions of stars that are too far to resolve into individual points but instead look like dusty haze? Is it not inaccurate to talk about these intragalactic structures as "dust" when we can't know what's between those stars? Or is "dust" some kind of secret astronomer code word, maybe coined by Asimov, for "lots of stars?"
The Stars, Like Dust is a story by Asimov. :lol:

But to your question... That central golden ball of light is indeed the glow of stars too small to be seen individually. That's not the dust that's being referred to. In images like this the dust must be inferred. As Ann mentioned above it can be inferred where it reflects the blue light back at us from the far side of the galaxy and it can be inferred where it filters the light, allowing mostly red through, between the galaxy and us.

And thanks, Ann, for mentioning those white dots. I wasn't sure what they were but perhaps vaguely thought of them as nearer stars. Seeing them instead as globular clusters brings me a whole new appreciation of the scale of this galaxy.

Rob

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by GoBears » Sat Feb 19, 2011 1:10 pm

I am strictly an amateur, so forgive me if I am wrong about this:

In photos like this of distant galaxies, people talk about "dust." I am aware that there is certainly interstellar dust that is probably as fine as. . .well, as fine as dust. But is not the "dust" in these photos actually billions of stars that are too far to resolve into individual points but instead look like dusty haze? Is it not inaccurate to talk about these intragalactic structures as "dust" when we can't know what's between those stars? Or is "dust" some kind of secret astronomer code word, maybe coined by Asimov, for "lots of stars?"

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by orin stepanek » Sat Feb 19, 2011 12:53 pm

Indeed; Hubble brings us detailed photos of distant galaxies to our visual doorstep! Wonderful! 8-) Here is another APOD of the same galaxy. :)

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by Ann » Sat Feb 19, 2011 7:27 am

NoelC wrote:You've just got to love how the Hubble makes a 46 million light-year distant galaxy look like the Great Andromeda galaxy that's almost 20 times closer.

-Noel
Indeed, this is Hubble at its best. The resolution is wonderful, and the colors are just great. Note, for example, how the dust on the far (right) side of the bulge looks blue, while the dust on the near, left, side looks brownish. This is typical of spiral galaxies whose bulges are seen at an angle. The dust on the far side of the bulge reflects the light from the bulge back at us, and since it preferentially reflects blue light, the dust looks bluish. The dust on the near side, on the other hand, blocks the light from the bulge and looks brown and dust-reddened.

Another delightful aspect of this image is that the large version of it shows many small whitish "stars" scattered in front of the bulge. Because they are so similar in color and brightness, I believe that they are globular clusters.

It has been said that NGC 2841 lacks pink emission nebulae, but that is clearly not true. The large version of this image reveals a multitude of small pink knots and dots. But, indeed, they are small. The vast majority of those pink HII regions will have only one O star inside them, or indeed, they may contain no O star at all, just a small number of early B-type stars, or even just a single early B-type star. NGC 2841 is not a galaxy with no star formation (like most ellipticals and lenticulars), but it is indeed a galaxy with only a modest amount of star formation. There are few if any "Orion Nebulae" in this galaxy, and clearly no equivalents to the Eta Carina star forming region or to NGC 3603.

This may be a typical HII region in NGC 2841, although this particular nebula is in the Milky Way, of course. The nebula is centered on a single early B-type star:
Personally I would love to see the Hubble image a few other spiral galaxies whose ability to form stars seems limited. I'm thinking of galaxies like NGC 2613 and NGC 4274.

Knock, knock, are there any baby stars here?

NGC 2613: http://www.physics.uci.edu/~barth/gallery/ngc2613.png

NGC 4274: http://lh4.ggpht.com/_hrpzshl95ms/RtO2x ... A/Disc.JPG

It would definitely be interesting to see Hubble take a look at those two galaxies!

Ann

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by NoelC » Sat Feb 19, 2011 6:29 am

You've just got to love how the Hubble makes a 46 million light-year distant galaxy look like the Great Andromeda galaxy that's almost 20 times closer.

-Noel

Re: APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by bystander » Sat Feb 19, 2011 6:20 am

APOD: Spiral Galaxy NGC 2841 Close Up (2011 Feb 19)

by APOD Robot » Sat Feb 19, 2011 5:06 am

Image Spiral Galaxy NGC 2841 Close Up

Explanation: A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way, but this close-up Hubble image spans about 34,000 light-years along the the galaxy's inner region. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

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