Tag: dust

Ceci *est* une pipe

By Phil Plait | September 20, 2012 7:00 am

Oh, have I got a treat for you today. Behold the brain-busting beauty of Barnard 59!

[Click to ennicotianatabacumenate – and seriously, do it! – or stick the gargantuan 16,000 x 15,000 pixel version (!!) into your pipe and smoke it.]

This incredible picture was taken by the MPG/ESO 2.2-metre telescope at the European Southern Observatory’s La Silla Observatory in Chile. The chunk of sky shown in this image is pretty big for a deep sky photo – about 6 arcminutes on a side. For comparison, the Moon is about 30 arcminutes across, so we’re still talking just a teeny region. But look at all those stars!

Of course, it’s not the stars that draw your attention: it’s the not stars. This region of the sky, in the constellation Ophiuchus, is toward the center of the galaxy, and is lousy with gas and dust – the latter of which is actually composed of complex chains of molecules. These form grains astronomers call dust, though they’re not like the bunnies you find under your dresser: these are more like particles of smoke in size. Ethereally thin by earthly standards, they form clouds that are still so large, light years across, that they are effectively opaque. They block the light coming from stars behind them, so in rich star fields like this one the dust clouds are made visible by their silhouettes.

What you’re seeing here is one particular complex of dust in the much larger cloud called the Pipe Nebula. The picture inset here shows the whole thing, and the reason for the name is obvious. Barnard 59, seen in incredible detail above, is the mouthpiece of the pipe.

You really need to take a look at at least the medium resolution image. You can see tendrils, wisps, and many other features. One of the neat things that you might miss at first is how the dark clouds change the colors of stars behind them. Start in the center of the cloud, then look near the edge, where the cloud starts to thin out, and you can see stars once again. See how the stars along the edge are redder than the stars farther out? Dust scatters blue light – a blue photon sent straight at us by a star can hit a dust grain and be sent off in another direction, missing us. There’s enough dust at the edge of the cloud to do that.

But toward the center of the cloud we’re through a lot more of that floating junk, so much that it absorbs the light coming from behind it. This effect is called interstellar extinction, and it’s kind of a pain when you’re trying to look at stuff through a cloud. However, it does make for a very pretty effect in pictures like this.

One more thing. See those fuzzy stars in the center of the cloud? Those are stars being born right before your eyes! These clouds can have very dense, cold clumps of material which can collapse to form stars. Usually invisible to optical telescopes – these ones are on the near side of the dust cloud, which is why we can see them at all – they glow brightly in infrared, and telescopes that can see out past the visible part of the spectrum see these very clearly. And yeah, you really want to click that link. It’s eerie and beautiful and spectacular.

All of this is another reason I love astronomy. One person’s meat is another person’s poison. If you want to study stars, dark nebulae are a pain. But if you want to study how stars form, they’re the first place you want to look!

Image credit: ESO; ESO/Yuri Beletsky


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CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

Temba, his spiral arms wide

By Phil Plait | September 3, 2012 7:02 am

Lying roughly 50 million light years from Earth is the magnificent spiral galaxy NGC 5033. Although that distance is a soul-crushing 500 quintillion kilometers, it’s actually relatively close by on the cosmic scale. Close enough that a lot of detail can be seen in the galaxy… and it also makes for a stunner of a picture:

[Click to darmokenate.]

This shot was taken by friend-of-the-BA-blog Adam Block using the 0.8 meter Schulman Telescope on Mount Lemmon in Arizona. It’s a whopping 13 hour exposure taken in near-true color.

It’s amazing what you can see in just this picture if you know what to look for. The spiral arms of the galaxy are fairly open, which is common enough, but the outer ones stick out a bit more than you might expect. The nucleus is very small and bright, more so than I’d expect for a typical spiral as well. Both of those things led me to expect this is an active galaxy, and that turns out to be the case.

Every big galaxy – ours included – has a supermassive black hole in the center. The Milky Way’s is 4 million times the mass of our Sun! In some galaxies, like ours, happily, the black hole is just sitting there. But in some there is gas actively falling into the hole. It spirals around and forms a very hot and very large disk, which glows fiercely as the matter is heated to temperatures of millions of degrees. They disk can blast out light from radio waves up to X-rays, and we say that the galaxy is "active".

A quick search of the literature didn’t turn up any measurements for the mass of black hole in NGC 5033, but it does confirm that it’s an active galaxy. Interestingly, the black hole is not located in the exact center of the galaxy! That’s very unusual, and indicates that NGC 5033 recently merged with another galaxy, probably a smaller one. It’s a cannibal! But then, most big galaxies are. It’s how they get big… and you’re living inside a big one, so there you go.

This may explain the wide arms on the galaxy as well; a collision and merger can distort the shape of the galaxy. Also, check out all the pink blobs along the arms: those are sites of furious star formation, the hot energetic massive young stars lighting up the gas around them. That also is common after a big collision.

Finally, one more nifty thing. You can see long ribbons of dark dust festooning the galaxy in the inner region. Dust absorbs light from stars behind it. But see how the dust looks like it’s only on one side of the galaxy, the half in the picture below the center? That’s an illusion, sortof. In reality there’s dust orbiting all around the center. However, there are stars above and below the disk of the galaxy, and the ones between us and the far side fill in the darkness a little bit, so the dust is less apparent. I’ve written about this before, and it does happen in quite a few spirals. Click the links in the Related Posts section below to see more gorgeous galaxies with this feature.

It’s funny how much information you can squeeze from a single picture! You have to be careful and not over-interpret it, and of course a lot of the things I’ve written here wouldn’t have been known without other observations of NGC 5033 using different telescopes and different methods in different types of light.

But even just one picture can tell you a lot. And in my opinion – and I tend to be right about these kinds of things – the wave of beauty that flows over you when looking at this picture is only enhanced by knowing more about the galaxy itself… and is boosted in no small way by the fact that we can know these things.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona


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CATEGORIZED UNDER: Astronomy, Pretty pictures

Star birth in the Scorpion

By Phil Plait | August 17, 2012 7:00 am

We live in the outskirts of our disk-shaped galaxy, our Sun and planets located about halfway from the center to the edge. This is a bit like living a few kilometers away from a city, in the suburbs. From that distance, when you look toward the city, you see more buildings, more activity, just more stuff going on.

The same thing is true for us on Earth: the center of the galaxy (downtown) is located toward the constellations of Sagittarius and Scorpius, so when we look in that direction there’s lots of fun things to see: more stars, more gas and dust, more clusters, more stellar nurseries.

And when you point the monster Very Large Telescopes ginormous 8 meter mirror in that direction you can see amazing details in that buzzing hubbub, like this lovely shot of the nebula NGC 6357:

[Click to ennebulanate, or grab the 3760 x 1560 pixel version. note: I rotated the image to make it fit the blog better and so you can see it more properly embiggened here.]

This piece is actually part of a much larger complex of gas and dust, but shows some nice features. The whole place is lousy with hydrogen gas, glowing rosy red due to energy pumped into it from young, massive, hot stars. Those stars are forming from that very gas, so they’re lighting up their own nursery. Running right through the middle is a river of interstellar dust – not like the dust bunnies under your bed, this is actually more like soot, and made up of complex clumps of organic molecules. This dust absorbs and blocks light behind it, so it looks like it’s splitting the gas cloud in half.

You can also see some structures in the dust, like the "fingers" of material at the top pointing to the center of the gas. Those are actually dense clumps of material being slowly blasted away by the fierce, intense ultraviolet light from newborn stars. Think of them like sandbars in a river getting eaten away by the current. They point right at the stars doing the deed, a cosmic "j’accuse!"

Nebulae like this are among my favorite objects in the sky. They’re beautiful, they’re fascinating, and it’s more than a little mind-blowing to know that there are dozens, hundreds, maybe thousands of stars being born in these objects even as we watch. And it also gives me a bit of a shiver to know that these objects are ephemeral, too: the stars being born really are slowly eating away at the material… and many of these stars will explode as supernovae someday, and that destruction won’t be slow anymore! The onslaught of high-energy radiation and material moving outwards from those stellar blasts at thousands of kilometers per second will make short work of this nebula. So take a look while you can. In a million years or four, this whole thing will be gone.


Related Posts:

Cold fire threads Orion’s belt
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CATEGORIZED UNDER: Astronomy, Pretty pictures

The darkness and the light

By Phil Plait | May 9, 2012 6:32 am

The sky is not as it seems.

Certainly, gazing upon it on a clear night you see so much: stars, planets, the glow of hot gas here and there… but there’s also darkness. Look at the Milky Way, its stream split down the middle by a rift of black. Gape at a gaudy nebula, and you’ll see it pocked here and there by pools of black.

But what is inky pitch to our eyes glows with a cold light to those attuned to it.

Tell me, what do you see here?

The bright star is obvious enough, but you can also, dimly, see a feathered stripe of black splashed across the vista, blocking, absorbing the light from stars behind it. Details are muted, structure difficult to ascertain, and you strain to see features that your brain cannot interpret.

But that’s with your eyes. Try again, look at it, but this time, widen your view. See it now?

Well done! Where before you saw material absorbing light, now it emits! Of course, unbeknownst to you, you had some help: the ESO APEX telescope in Chile. It sees into the far, far infrared, where light is so stretched out it is entirely invisible to humans. In fact, the wavelength of light is so wide there that if it were a vibrating string, you could physically see the crests and troughs, since each would be separated by the next by nearly a millimeter. The light your eye can see has a wavelength only a thousandth that wide.

When APEX looked at this ribbon of dark, frigidly cold dust, it sees the material glowing. What we see as dark, it sees as bright. You can even compare the two directly, using a slider over the two versions of this picture, unveiling precisely what your now-expanded vision can take in.

Cold dust is the bane of the astronomer who uses merely visible light, since it blocks the view behind it. But one person’s poison is another’s meat, and if you study the material that wends its way between the stars — and sometimes comes together to form them — then the view from APEX is sustenance for you. This material is barely above the ultimate freezing point of absolute zero, and you might think it dead and useless. But from such stuff are you and I descended, and everything you see around you.

So when you do peer around you, and take in your environment, your surroundings, your home, look again. You are surrounded by the invisible, permeated by it… but always remember, it was invisible only until we chose to look for it. We created the means necessary to do so, and when we did the Universe opened up before us.

Image credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin.


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Cold fire threads Orion's Belt

By Phil Plait | May 2, 2012 6:00 am

Orion is the gift that keeps on giving. When you look toward that constellation in the sky, you’re facing a region of massive ongoing star formation. A sprawling cloud of gas and dust occupies Orion’s midsection, most of it thick and opaque. Some of it is illuminated by stars embedded inside, and some by the reflected light of nearby stars.

M78 is a section of the cloud just above Orion’s Belt that’s evidence of the latter. But even then, much of the dust is dark to our eyes. But if you look in the far, far infrared, where warm material glows, a different — and spectacular — view appears:

[Click to blackbodyenate, or grab the 2300 x 3500 pixel version.]

This is actually a combination of two views: one in visible light from the Digitized Sky Survey, and the other from the APEX telescope, which can see light in the submillimeter wavelength range — 1000 times the wavelength the human eye can see. Only cold, cold objects emit at this wavelength, things a few degrees above absolute zero.

The blue material in the image is gas and dust reflecting starlight from nearby blue stars, so it can be seen in visible light. The cold dust, though, threads in front and behind the visible material, and can only be seen by APEX’s eye, tuned as it is to the far infrared. Falsely colored in this image, it glows an eerie orange like fire running through cracks in the nebula.

But it turns out the cracks are the fire itself…

Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: APEX, dust, M78, Orion, star formation

Desktop Project Part 17: Sculpting Martian dunes

By Phil Plait | April 11, 2012 6:30 am

[I have a lot of astronomy pictures I’ve saved to my computer’s desktop, so I’ve pledged to post one every day in an attempt to regain control of my machine. I call this my Desktop Project.]

Speaking of Martian winds…

Mars is a pretty interesting place. A lot of the surface is covered in dust and sand, and while the air there is very thin, it can move with terrific speed. That gives it enough momentum to push that solid material around. The small-grained dust is far easier to pick up and get blown around by that wind, and we see lots of clear (and gorgeous) evidence of that in pictures from Mars. But the bigger, heavier basaltic sand is harder to move. Until recently there was no evidence of bulk dune motion at all on Mars*!

But the fantastic HiRISE camera on board the Mars Reconnaissance Orbiter has found that evidence: the motion of a Martian sand dune that took nearly two years to see:

[Click to barsoomenate.]

The animation shows the barchan (horseshoe-shaped) dune on June 25, 2008 and May 21, 2010. During that time, the sand was blown a few meters, and you can see the difference. It’s most obvious in the crescent-shaped part, but if you look closely (especially at the embiggened picture) you’ll see the rippling has moved as well, sculpted by the moving Martian air.

This fantastic image brings home (so to speak) an important point. There are, broadly speaking, two kinds of planetary missions: ones that fly past their target, like when New Horizons will blow past Pluto in 2015; and ones that go to their destination and stay. Flybys give us a great opportunity to see other worlds, and aren’t as expensive — you don’t need to bring all that fuel to slow down (like Cassini did) or pack parachutes and a lander. But as great and important as they are, we only get a fleeting glimpse of the target.

But when we go to stay, we get a long, long view. Long enough, in most cases, to see change. Mars is a dynamic, ever-evolving planet. And sometimes that change is slow, so we need the time to see it. And when we do, we see dust devils, landslides, meteorite impacts, and the march of dunes across the Red Planet’s surface.

It’s more expensive, and it’s harder, but it’s worth it to go someplace and settle in. Otherwise, you might miss something really cool.


* There’s evidence that the ripples on dunes have moved, but not that the dunes themselves have been moving as wind pushes them.

Image credit: Image credit: NASA/JPL-Caltech/Univ. of Ariz./JHUAPL


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CATEGORIZED UNDER: NASA, Pretty pictures
MORE ABOUT: dunes, dust, HiRISE, MRO, sand

Desktop Project Part 2: Unicorn, rainbow… soot?

By Phil Plait | March 27, 2012 7:00 am

[Over the past few weeks, I’ve collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside… but I decided my computer’s desktop was getting cluttered, and I’ll never clean it up without some sort of incentive. I’ve therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they’re gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]

Did you know there’s a unicorn in the sky? There is: the constellation Monoceros (literally, one-horn). Located near Orion, when we look in that direction we’re peering into the disk of our Milky Way galaxy, and that means seeing lots of gas and dust. And when you do that with a telescope like WISE that sees into the far-infared, what you get is, well, magic:

This is SH2-284, a star forming nebula. The image is false color, but each hue represents a different part of the infrared spectrum. Blue and teal is mostly coming from stars, while red and yellow is dust. Green comes from a very specific kind of material called a polycyclic aromatic hydrocarbons — long-chain carbon molecules which are essentially soot. PAHs are made in various ways, but are abundant where stars are being born, and that’s what we’re seeing here.

There’s a cluster of young stars in the center of this cloud, and they’re so hot they’re eating out the inside of the cloud, creating that cavity you can see. Like so many of these structures, the clock is ticking: many of those stars will explode, and when they do they’ll tear the cloud apart. So take a look while you can… this unicorn rainbow cloud only has a few million years left before it’s extinct.

Image Credit: NASA/JPL-Caltech/WISE Team


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CATEGORIZED UNDER: Astronomy, Pretty pictures

Alphas in the heart of the Omega

By Phil Plait | January 5, 2012 7:00 am

After having recently posted an interesting picture of the results of star formation in a nearby galaxy, here’s another example, but far closer: an incredibly detailed image of the heart of the Omega Nebula, where stars are being born from huge clouds of gas and dust:

[Click to ennebulenate, or grab an even bigger version.]

This image was taken using the 8.2 meter Antu telescope, one of four making up the European Southern Observatory’s Very Large Telescope in Chile. What you’re seeing here is the central region of a much larger complex of gas and dust located about 6500 light years away toward the center of our galaxy. The whole thing is about 20 light years across, and perhaps as many as 1000 stars are in the process of being born or were recently formed there.

The red color is due to the presence of warm hydrogen gas, the basic building material of stars. It’s being lit up and is glowing due to very young, massive and hot stars — the alpha dogs, if you will — flooding the nebula with ultraviolet light. The dark material is actually dust, which is opaque in visible light, so it blocks the glow from material behind it.

That dust really caught my eye: some of it is not shapeless and random, but has been sculpted into very long, very thin wisps and tendrils. Most of these are parallel, which is a big clue to what causes them. They are most likely being shaped this way by shock waves; supersonic material blasted out from those same young, hot stars. These powerful stellar winds of subatomic material race out and slam into the surrounding material, compressing it. Waves from various stars can also collide, creating very thin streamers like this. Some are so narrow they’re barely resolved in the picture at all.

Read More

CATEGORIZED UNDER: Astronomy

Sometimes a cigar galaxy is just a cigar galaxy

By Phil Plait | January 3, 2012 7:00 am

Astronomical imagery is a tricky business. Different objects behave differently, emitting light in different ways. So, for example, a cool dinky star might give off very little blue light — through a blue filter it virtually disappears — while a hot, massive star blasts out blue light. Your choice of filter can drastically change the way an object looks.

Having said that, I recognized right away that this image is the core of the nearby galaxy M82… but it still looks funny to me:

[Click to galactinate, or grab the huge 12.5 Mb image.]

One reason this new image from Hubble looks funny to me is that there aren’t as many stars in it as I expect. M82, also called the Cigar Galaxy due to its elongated shape, is pretty close as galaxies go, about 12 million light years away. It’s one of the closest large galaxies in the Universe, and a Hubble image usually shows it littered with stars, so closely packed they form a bluish background glow in most pictures.

And while that background of stars is there, it’s more diminished than usual because in this image astronomers used a series of filters that accentuate the light emitted by gas. While stars put out this kind of light as well, these filters downplay starlight and crank up the volume on, um, gaslight. Specifically, blue and green are from oxygen, red is from sulfur, and teal is hydrogen. The dark material is dust: long-chain molecules that absorb starlight. They also tend to redden light coming from behind them, similar to the way haze in the air makes sunsets look red.

Clearly, M82 is lousy with gas and dust in its core. Read More

A nearby star rings in the new year

By Phil Plait | January 2, 2012 7:00 am

I am fascinated by junk floating around stars. And no, not paparazzi, har har. I mean circumstellar material, literally gas and dust orbiting other stars. We see it around stars that are dying, we see it around stars being born, and we see it even after stars are well into their youth.

One such young’un is the bright and shiny HR4796, a star 240 light years away, with about twice the mass of the Sun. It’s known to be less than 10 million years old — compare that to the Sun’s age of 4.56 billion years; we’re 450 times older! — and has also been known for some time to have material around it in the shape of a ring. New observations by Japan’s huge 8.2 meter Subaru telescope have provided some of the sharpest views of this ring ever taken, and revealed some surprises.

Isn’t that lovely? [Click to enannulusenate.]

This picture is in the infrared, well outside what the human eye can see. The star itself is so bright it’s saturated, overexposed. That part of the picture is blocked out to make it easier to see details around it, but the star’s position is marked with a dot. The tendril-like structures radiating outward are not real, but are artifacts of the image processing techniques. You can ignore them.

The important thing is the ring itself, which is easy to spot. It’s almost certainly a circle, but we’re seeing it at an angle (about 13° from edge-on) so it looks like an ellipse. It’s huge; 22 billion km (14 billion miles) across, more than twice as wide as our entire solar system.

Again, the ring has been known for some time; for example it was seen in Hubble observations back in 2009 [NOTE: as astronomer (and my friend) Glenn Scheider points out in the comments below, HR 4706’s ring was seen long before 2009. I wasn’t clear when I wrote the previous statement; I was only alluding to one particular earlier observation, but it wound up sounding like it was the earliest such observation. My apologies for any confusion.]. But there is some new stuff here. For one, if you look along the long axis of the ring, you can see it looks fuzzy. That’s real! The ring is made of dust grains of various sizes, probably the result of bigger clumps colliding with each other and grinding themselves up into ever-smaller pieces (the authors of this reasearch (PDF) call this a "collisional cascade", my new favorite phrase for 2012). These grains of dust orbit the star, and the smaller ones get blown away from the star due to the pressure of its fierce light. Bigger grains are less affected, so they tend to stay in place.

So the main ring is made of bigger grains, while the smaller ones are blown back, forming a larger, extended ring. That fuzzier outer ring is fainter and harder to see, but we see it more easily along the long axis because of geometric effects (similar to why soap bubbles and giant shells of cosmic gas look like circles in space). So even though we only see a part of this outer ring, the fact that we only see it in those two spots is what makes it clear we’re seeing a ring at all! Funny how that works.

Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: dust, HR4796, infrared, ring, Subaru
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