It’s been a while since I’ve posted a gorgeous shot of a weird and beautiful galaxy, and I have one that fits the bill perfectly: NGC 660, what’s called a polar ring galaxy:
How awesome is that? [Click to galactenate.]
This picture, taken using the Gemini 8-meter telescope and put together by my old pal Travis Rector, is really pretty, and really pretty weird. Reading about it, in fact, I learned something! Learn it with me:
Ring galaxies are odd. I’ve always thought they were the result of galactic collisions, literally where two galaxies collide. If one is smaller, traveling rapidly, and pierces right through the heart of the other, the weird gravitational effects wind up creating a gigantic ring of material, and you get something that looks like a fried egg. The best and coolest example I know of this is Hoag’s Object, seen here in a Hubble image (put together by another friend of mine, Tiffany Davis).
In general with these kinds of objects, there are tell-tale signs of the collision. The gas in the galaxies gets slammed around a lot, which means it can collapse and form lots of stars, for example. Usually, the ring is perpendicular to the central galaxy, too – that’s why they’re called polar ring galaxies.
But NGC 660 is an oddity. It shows the ring – which is 40,000 light years across, a little less than half the size of our Milky Way – and it has lots of star formation: the ring is studded with red gas clouds, stellar factories, furiously churning out stars. But the ring isn’t aligned right; it’s tilted at a funny angle. It’s shape is off-kilter, too. Plus, although you can’t see it in this image, other observations show that the central galaxy is creating lots of stars in its core too. That’s not easy to explain in the head-on collision scenario, and is weird all by itself, since usually the cores of galaxies stopped forming stars billions of years ago.
But here’s where I found out something new to me: some polar ring galaxies are formed when two galaxies pass near each other. The gravity from one galaxy can strip the gas from the other, and if the geometry is right that gas can form a huge, long arm which wraps around the first galaxy. That can form a ring of material that cranks out stars… just like in NGC 660.
Also, a near pass like that tends to be slower than a head-on collision. That means there’s more time for the gravity of the two galaxies to shake each other up. That dumps gas into the center of the galaxies, where it can form stars. So this explains why we see newborn stars in NGC 660, too.
Well, that was new to me! I’ve written about galaxy collisions before, and the distorted but elegant and lovely shapes they take on (see Related Posts below). And it’s obvious to me now that the disturbed material can form a ring, but it’s just something I’d never run across before. So I learned something.
And now you did too.
So there you go. A picture of a galaxy with a big telescope is high art, beautiful and graceful. But there’s a whole lot of science behind it, too. So, as usual, the appreciation you can have for something like NGC 660 only gets deeper and better when you understand what’s actually going on. You’re seeing two entire galaxies colliding, hundreds of billions of stars, octillions of megatons of gas being tossed around, new stars being born… and all because they are held sway under the invisible grasp of gravity.
See? Isn’t that cooler than just seeing a pretty picture?
Image credit: Gemini Observatory/AURA
In a funny coincidence, my friend Travis Rector, an astronomer at the University of Alaska who takes amazing and incredibly beautiful astrophotographs, posted an image that may look familiar. It’s of NGC 6751, a planetary nebula about 5000 – 7000 light years away:
[Click to embiggen, and note I rotated the image 90° to make it fit better on the blog.]
It’s very pretty, but also very complex. Planetary nebulae are actually gaseous structures created when stars a bit more massive than the Sun die. When they turn into red giants they blow a dense, slow wind of gas into space — that can be seen in NGC 6751 as the big blue halo surrounding the whole thing. The edge is a bit brighter as it slams into gas floating in between the stars and piles up a bit. The halo is probably something like 1.5 light years across.
The interior part is actually the most interesting, You can see the star in the center. About halfway out to the big halo is a ring of material that looks like it’s broken up into individual knots like pearls on a necklace. Inside that ring is something that looks like a disk seen face-on, with faint filaments stretching from the central star out to the ring.
Studies of this object indicate this is in fact the case. Although it’s not clear, I suspect the central star may have enveloped and swallowed a companion star or giant planet, spinning it up to a much faster rotation speed. Otherwise, it’s hard to explain why it has a ring and disk of material; a solitary star could never spin fast enough to eject such a structure. This would also explain some of the more complex features of the nebula as well. If this is true, we’re nearly roughly down on the pole of the star (or maybe off by 20° or so), since the disk is very close to being a circle; if the system were tilted by much more the ring would be more elliptical, like looking at the rim of a glass from an angle.
Anyway, I said this nebula may look familiar; that’s because I recently posted a picture of the star U Cam, which is much like the Sun but a lot older. Like the central star of NGC 6751, it too is dying, but in the case of U Cam it’s blasting out shells of material on a very short timescale. The ring we see around it is only about 700 years old, and was created in an event that lasted mere decades. The shells and rings in NGC 6751 took thousands of years to make, and the halo is probably more than 50,000 years old!
And while both huge structures are the results of dying stars, and both have an overall similar appearance, they’re very different in actual shape and origin. The halo around U Cam is like a soap bubble: a thin shell that has a sharp edge but is probably mostly empty on the inside. Astronomers call this a "detached shell". NGC 6751, on the other hand, is more like a balloon filled with gas. And down near the star NGC 6751 has that complex disk/ring affair going on, while U Cam is probably mostly empty space all the way down to the surface of the star. The gas making up the shell of U Cam has about the same mass as the Earth, while the nebula in NGC 6751 is tens of thousands times more massive!
There are lots of other differences between them as well, but I find it remarkable (literally, since I’ve been sitting here remarking on it!) that two objects with such similar appearance – and both caused by the efforts of dying stars – can actually be so different. Nature is filled with such things, of course. Spiral galaxies look similar to swirls of cream in a coffee cup, though the physics is entirely different. Stars and drops of water are spherical, but for two different reasons (gravity for the stars, surface tension for the droplets).
Sometimes moons look like Death Stars, but that may be pushing this a bit too far.
I think that’s cool. Shapes of objects can be revealing of their nature, but you have to be careful when making judgement based on shape alone. You have to look deeper to reveal the true nature.
If there’s a life lesson in that, feel free to find it on your own.
Image credit: D. Tran (PAL College), T.A. Rector (University of Alaska Anchorage), T. Bridges (Queen’s U.) and the Australian Gemini Office
My old friend Travis Rector is a professional astronomer at the University of Alaska. He’s also a gifted astrophotographer, and has made countless stunning images of astronomical objects over his career. If you’ve been reading my blog for any length of time at all you’ll have already seen many of his images, since a lot of news items involve objects he’s observed (see Related Posts below for more). And they’re all incredible! Like, say, this relatively random one I grabbed from his gallery, a ridiculously beautiful picture showing the interacting spiral galaxies NGC 5426 and NGC 5427:
See what I mean? [Click to galactinate.] I could’ve shown any of dozens of images like this, and they’re all amazing.
He’s decided to release a new image every Monday during 2012, putting it in his gallery with a description of what you’re seeing. Trust me, you absolutely want to keep track of what he’s up to. You can see the latest weekly image on his Facebook page or you can go straight to his gallery.
But I don’t recommend it unless you have plenty of time in your schedule. I won’t be responsible for people getting lost looking at his work.
If you were wondering what was going on with the bright new supernova in the spiral galaxy M101, it’s now getting very difficult to observe due to its proximity to the Sun in the sky. But happily my friend, the accomplished astronomer Travis Rector, got a shot of it using the Mayall 4-meter telescope at Kitt Peak National Observatory. I would venture to say it’s one of the prettiest ones I’ve seen so far:
[Click to Chandrasekharenate.]
This was taken on September 18th, and the supernova is the bright blue star above and to the right of the center of the picture (to the left of the fuzzy red nebula). Pictures like this are important in pinning down the exact location of the supernova in the galaxy, so that after it fades the potential prescursor star can be found (though in this case, we already have pretty decent Hubble images of the field). Also, of course, big telescopes with sensitive detectors can give very accurate brightness measurements, which are absolutely critical in understanding how these objects change with time. This particular flavor of supernova is key to our understanding the size and scale of the Universe itself, so the more data — and the more accurate the data — we have, the better.
Image credit: T.A. Rector (University of Alaska Anchorage), H. Schweiker & S. Pakzad NOAO/AURA/NSF
- AAS 15: Travisty of astronomy (links to many of Travis Rector’s must-see photos!)
- Supernova update: it’s peaking now!
- M101 supernova update
- AstroAlert: Type Ia supernova in M101!
- Dwarf merging makes for an explosive combo
- Hubble delivers again: M101
[Click to ennebulenate.]
That’s really cool. As I pointed out in the earlier post, these are called planetary nebulae, and are the results of the dying stars blowing off winds of gas. They are very rarely circular, instead coming in all kinds of fantastic shapes. It’s thought that you might not get a PN unless the star is binary or swells up to eat its planets as it dies; when that happens the star can get spun up and eject the gas more easily.
It’s not really a circle, of course: it’s a sphere, or more properly a spherical shell. It really is like a soap bubble! The bright edge is due to an effect called limb brightening, which I explained in that earlier post.
This isn’t really well understood, but to get one this symmetric the star must be a loner, and spherical ones are pretty rare. Read More
I’ve been posting a lot of nice astronomical images lately, but sometimes one comes along and blows me completely away. How fantastically gorgeous is this?
Holy Haleakala! [Click to galactinate.]
That spiral galaxy is NGC 6872, and as you can see in this image from the Gemini South telescope it’s getting its clock cleaned by the littler spiral — IC 4970 — just to the right. The two are undergoing a galactic collision, a colossal event playing out over hundreds of millions of years. NGC 6872 is currently the victim here; its spiral arms are clearly distorted and being flung wide by the gravitational interaction. However, the smaller IC 4970 will be the ultimate loser in this battle: it will fall into the bigger galaxy, be torn apart, and eventually consumed in its entirety, becoming a part of NGC 6872. Bigger galaxies do this to smaller ones all the time; the Milky Way is in the process of eating several small galaxies even as you read this (I have details in articles linked below; see Related Posts).
This pair has been observed by other telescopes, including the composite picture here of images by the Spitzer Space Telescope (which sees in the infrared), The Very Large Telescope (visible light), and Chandra (X-rays), which I rotated to match the Gemini shot and rescaled a bit.