So just a few days after my previous Astrobite summarizing the ASA meeting I got a surprise when I woke up to an email from the Astrobites scheduler saying that he'd posted my Astrobite I wrote for the queue back in February. This one deals with an interesting problem I'd never heard of before called the “Satellite Planes of Galaxies problem.” Observations of he Milky Way, the Andromeda Galaxy, and Centaurus A show that a significant fraction of the satellite galaxies around them tend to orbit in correlated planes. Yet similar-looking structures are vanishingly rare in simulations, to the point where it would be exceedingly unlikely to find them around three galaxies so close to each other. It's pretty interesting as while we've had hints of theses planar structures around the Milky Way for a few decades and Andromeda for a little less it's only recently that we've really been able to confirm them and discover the one around Centaurus A.
Something amusing I found in this paper was the name for the structure around the Andromeda Galaxy, which is called the “Great Plane of Andromeda.” This sounds like a reference to a very old name for the Andromeda galaxy, several hundred years ago when it was known as the Great Nebula in Andromeda. I just like the idea that anything associated with the galaxy becomes known as the “Great ____ in/of Andromeda.” A hui hou!
Showing posts with label Andromeda. Show all posts
Showing posts with label Andromeda. Show all posts
Saturday, July 14, 2018
Saturday, March 31, 2012
Two Clusters for the Price of One.
I was digging through my astrophotography folder recently and discovered a picture of the Double Cluster in Persues I'd taken last November that I hadn't reduced yet. I speedily corrected that, and now have a picture of the Double Cluster for your perusal.
The Double Cluster is a pair of open clusters cataloged as NGC 884 and NGC 869, respectively. (They also have the older names of χ Persei [that's the Greek letter chi] and h Persei.) Located in the constellation Perseus, they appear very close to each other on the sky. These two clusters are pretty easisly visible as a faint misty patch close to the border with Andromeda. They are located at distances of 7,600 and 6,800 light-years from Earth, so they are also not too far apart in space.
Anyway, enough exposition, have a picture!
Being open clusters, there really isn't that much more I can think to say about them (since they don't have any stand-out features like a planetary nebula in from of them). They were apparently known from at least as early as 130 B.C. (though what they were wasn't know, of course). William Herschel, of Uranus-discovering fame, was apparently the first person to realize that they were two distinct clusters instead of one. Interestingly, they don't have a Messier number, so Messier either never came upon them, or, more likely, found them sufficiently obviously un-comet-like that he felt no need to include them in his list. Considering they can be made out with the naked eye, I'm guessing the latter is more likely.
The Double Cluster is a pair of open clusters cataloged as NGC 884 and NGC 869, respectively. (They also have the older names of χ Persei [that's the Greek letter chi] and h Persei.) Located in the constellation Perseus, they appear very close to each other on the sky. These two clusters are pretty easisly visible as a faint misty patch close to the border with Andromeda. They are located at distances of 7,600 and 6,800 light-years from Earth, so they are also not too far apart in space.
Anyway, enough exposition, have a picture!
 |
| NGC 884 (left) and NGC 869 (right), the Double Cluster in Perseus. |
Being open clusters, there really isn't that much more I can think to say about them (since they don't have any stand-out features like a planetary nebula in from of them). They were apparently known from at least as early as 130 B.C. (though what they were wasn't know, of course). William Herschel, of Uranus-discovering fame, was apparently the first person to realize that they were two distinct clusters instead of one. Interestingly, they don't have a Messier number, so Messier either never came upon them, or, more likely, found them sufficiently obviously un-comet-like that he felt no need to include them in his list. Considering they can be made out with the naked eye, I'm guessing the latter is more likely.
Monday, October 31, 2011
The Great Galaxy in Andromeda
Saturday night while I was up at the Vis I decided to take a break from imaging globular clusters to try my hand at what probably pretty much every astrophotagrapher ever has broken their teeth on: Messier 31, the Great Galaxy in Andromeda.
The Andromeda Galaxy is located in the direction of the constellation Andromeda, about 2.5 million light years away. It's not the closest galaxy to our own Milky Way, but it's the closest spiral galaxy and the one closest in size to the Milky Way in our Local Group of about 30 galaxies. (Intriguingly, although Andromeda is larger in size than the Milky Way, recent studies indicate that the Milky Way may have more mass. It also has a higher star formation rate, and a higher rate of supernovae.)
While Andromeda may or may not be the most massive galaxy in our Local Group, there is no doubt that it's the brightest galaxy in the northern hemisphere. It's also the largest on the sky. In fact, if we could see it all, it would appear as wide as six full moons on the sky! Its huge size, however, is paradoxically what makes it so hard to see. All that light is spread over a large area, making it exceedingly faint. What you're seeing in this picture is no more than the central third of the galaxy; it stretches out on both sides almost as far again as seen in this picture (mostly because I didn't have a lot of time to image it, so I took the longest exposures I did in the time available).
Being as it is the largest on the sky and brightest in the northern hemisphere, Andromeda was the first galaxy to have its spectra taken (by Vesto Slipher in 1912) and the first galaxy to be confirmed as such (i.e. a system of star not materially associated with the Milky Way), by Edwin Hubble in 1922-23. This discovery increased the size of the known universe by several times, and was instrumental in the development of our current picture of the universe.
The Andromeda Galaxy is a fascinating star system, and I could write pages more on its various interesting features, but it's getting late here and I ought to get some sleep. After seeing how this picture came out, I'm tempted to try again and get a longer exposure to show fainter details, so perhaps I'll write more about it if I do.
Edit (11/5/11): Due to a suggestion from a master imager, I went back and re-reduced the data for this picture, stretching the light curve in a different manner to get better results. DeepSkyStacker, the program I use to do the data reduction, lets you apply different light curves to your photo after it does all the work to reduce the noise in the image. Basically, different light curves are better for bringing out different features. The one I chose (called "cube root") helped show the faint nebulosity better without simultaneously blowing out the the bright, dense core. So, here's the same picture, version 2:
If you compare the two pictures, you can see that the second one shows a lot more detail. I'm glad I learned how to apply different light curves, as my typical globular cluster shots didn't usually change much when I played around with them before so I wasn't quite sure what it did. But as you can see, it works wonders with nebulous subjects! (And since there aren't as many globular clusters to image during the winter, I'll probably be taking a little break from them to image some of the other cool objects in the night sky...)
The Andromeda Galaxy is located in the direction of the constellation Andromeda, about 2.5 million light years away. It's not the closest galaxy to our own Milky Way, but it's the closest spiral galaxy and the one closest in size to the Milky Way in our Local Group of about 30 galaxies. (Intriguingly, although Andromeda is larger in size than the Milky Way, recent studies indicate that the Milky Way may have more mass. It also has a higher star formation rate, and a higher rate of supernovae.)
 |
| The Great Galaxy in Andromeda, Messier 31. Technically, only the innermost part of it. M32 (at top) and M110 (at lower left) are also visible. |
While Andromeda may or may not be the most massive galaxy in our Local Group, there is no doubt that it's the brightest galaxy in the northern hemisphere. It's also the largest on the sky. In fact, if we could see it all, it would appear as wide as six full moons on the sky! Its huge size, however, is paradoxically what makes it so hard to see. All that light is spread over a large area, making it exceedingly faint. What you're seeing in this picture is no more than the central third of the galaxy; it stretches out on both sides almost as far again as seen in this picture (mostly because I didn't have a lot of time to image it, so I took the longest exposures I did in the time available).
Being as it is the largest on the sky and brightest in the northern hemisphere, Andromeda was the first galaxy to have its spectra taken (by Vesto Slipher in 1912) and the first galaxy to be confirmed as such (i.e. a system of star not materially associated with the Milky Way), by Edwin Hubble in 1922-23. This discovery increased the size of the known universe by several times, and was instrumental in the development of our current picture of the universe.
The Andromeda Galaxy is a fascinating star system, and I could write pages more on its various interesting features, but it's getting late here and I ought to get some sleep. After seeing how this picture came out, I'm tempted to try again and get a longer exposure to show fainter details, so perhaps I'll write more about it if I do.
Edit (11/5/11): Due to a suggestion from a master imager, I went back and re-reduced the data for this picture, stretching the light curve in a different manner to get better results. DeepSkyStacker, the program I use to do the data reduction, lets you apply different light curves to your photo after it does all the work to reduce the noise in the image. Basically, different light curves are better for bringing out different features. The one I chose (called "cube root") helped show the faint nebulosity better without simultaneously blowing out the the bright, dense core. So, here's the same picture, version 2:
 |
| The Andromeda Galaxy, Messier 31. Now much prettier! |
Subscribe to:
Posts (Atom)