[The Desktop Project is my attempt to clear off all the amazing images I’ve been collecting on my computer’s desktop over the past few weeks – I’ll post one great picture every day until they’re gone. That way, I clear off my computer and you get to drink in a beautiful image and some science. Everyone wins!]
I love globular clusters. They’re amazing objects: hundreds of thousands of stars all orbiting each other like bees around a beehive, incredibly old (most are well over 10 billion years and counting), and are a laboratory of how stars age and die. And I used to love looking at them through my own telescope when I was a kid, avidly going from one to another.
M9, though, isn’t one that I remember observing. I’m not sure why. It’s easily bright enough to see, and big enough to get a sense of its globularness. But even if I had seen it, I don’t think it would’ve looked quite as amazing as this shot from Hubble:
[Click to hugely apiaryenate.]
Yegads. Funny though: all in all, as globulars go, M9 is rather unremarkable. It’s average in size, in distance (about 25,000 light years from Earth), and in most other ways. It does have the distinction of being the globular cluster nearest the center of the Milky Way, lying less than 6000 light years from the core. But that’s a bit of a cosmic coincidence: globulars orbit the Milky Way, so whichever one is closest is just a matter of orbital characteristics and time.
Still, hmmm. I imagine M9’s orbit must be pretty elliptical to bring it that close in, though. Some globulars orbit very far out on paths that never take them too close to the center. So perhaps in this way it is interesting. Why is its orbit shaped like that? Did it interact with some other object billions of years ago, changing a circular orbit into one that’s elongated? Its velocity through space is relatively high (PDF) as you might expect from an object at the bottom of its orbit– a position called perigalacticon, if you want to impress your friends at parties.
And yet, for all its unremarkableness, look at it! It’s gorgeous! Even the mundane in astronomy possess surpassing beauty. It’s another reason I love this science so much.
Image credit: NASA & ESA
I just got back from a week of travel, and I’m facing down a hundred emails, tons of news, about a billion things to write about, and then more travel later this week.
So when I see the folks at Hubble have posted a picture of a weird, pretty spiral, I figure it makes my job easier. I can just post a cool picture! So here it is:
[Click to galactinate.]
But dagnappit, I can’t leave it at that. I never can.
This is NGC 4980, a spiral about 65 million light years away or so. Most spirals have well-defined arms, but this one is just… odd. The arms are indistinct, and also fairly asymmetric. If I had to guess I’d say it recently suffered a collision with another galaxy, but apparently there are no other galaxies near it! I was rather surprised to find that there isn’t much in the professional literature about it; it’s close and bright, and worthy of some study.
The arms of the galaxy are there, and appear blue from the combined light of billions of young, massive, hot stars. As with many spirals, there are older, redder stars in the center; those are in the arms as well, but outshone by the brighter blue stars. Usually, the cores of spiral galaxies long ago ceased making stars, so all the big blue ones have long-since exploded, leaving behind the cooler, redder stars.
Note that the very core of the galaxy is a pin-point source of light. I saw on some websites that NGC 4980 is an emission line galaxy — it emits light at very specific colors, like a neon sign — which is a clear indication that a supermassive black hole is gobbling down matter there in the galaxy’s heart. As matter swirls in, it forms hot, flat disk (too small to see here) that is incredibly bright. This lights up clouds of nearby gas, which respond by glowing at those narrow slices of color. There aren’t too many of these "active galaxies" near us on a cosmic scale, so again I’m rather surprised this hasn’t been studied more!
So there you go. A lovely spiral to start your week, and one that’s also a little bit on the odd side. Frankly, lovely and odd is how most of my weeks start, so I’m happy to share.
This is a galaxy?
Yup. It is! [Click to galactinate.]
This is the dinky Antlia Dwarf Galaxy (located in the southern constellation of Antlia, the "pump"), technically called a dwarf elliptical. It’s so faint and sparse that it wasn’t discovered until 1985 (and confirmed as being a galaxy in 1997), even though it’s only 4 million light years from Earth… not terribly farther than the Andromeda Galaxy, which is so big it’s visible to the naked eye! Antlia may be a member of the Local Group, a loose collection of a few dozen mostly small nearby galaxies; the Milky Way and Andromeda are the two biggest members.
This image is from Hubble, and shows just how dim a bulb this galaxy is. It only has a few million stars in it — our Milky Way has over a hundred billion, by comparison — and it’s only a few thousand light years across. The Milky Way is a full 100,000 light years in diameter, so if you put Antlia next to it you’d probably miss it entirely. Note that in this picture you’re only seeing the brightest stars in Antlia. At this distance, a star like the Sun in Antlia would be a tough object to see, even with Hubble. Most of the stars you see here are red giants, stars near the ends of their lives and thousands of times more luminous than the Sun.
But it’s an intriguing little bugger. For one thing, some of its stars are clearly very old, ten billion years or so. But other stars are just as clearly young, having been formed only a hundred million years ago or so (and I found a paper claiming it may have younger stars yet). That means Antlia has had more than one episode of star birth… but it doesn’t appear to be actively churning out stars now. If it did, the bright pinkish-red nebulae that form stars would be really obvious, especially in a galaxy this close by (like in, say, NGC 1427A).
I love a good coincidence. On Monday morning, I posted a gorgeous picture of the planetary nebula Abell 31, an object formed when a dying star blows off its outer layers in a series of winds which collide with each other. I mentioned that these nebulae are usually symmetric — Abell 31 happens not to be because it’s moving rapidly through space, and the gas through which it moves is compressing one side of it. But events like that are not the norm; most planetaries show stunning symetric features… like Henize 3-1333, as you can see in this nice Hubble image of it:
[Click to ennebulenate.]
It looks like a flower, doesn’t it? The petals you see are actually sculpted lobes of gas. I’m guessing it undergoes periodic episodes where it blows out gas in focused beams, which then move outward and form those features as they plow into gas previously blown out by the star. It’s a guess, but it fits what’s known about the inner regions of the cloud near the central star. There’s a thick disk of material surrounding the central star, something like 30 billion km (20 billion miles) across, far larger than our solar system. Every six years or so, the central star appears to dim, which may be due to the inner part of the disk itself becoming unstable and puffing up, blocking the light. This disk may also be responsible for shaping the outflow of the gas from the star, forming those petals.
If you’re wondering just how much material the star is blowing out, it turns out to be about the mass of the Earth every year! That’s a tiny fraction of the star’s mass, but it blows out this much every year for thousands of years. Eventually that wind will turn off, and all that will be left is the very hot (30,000° C or about 55,000° F) core of the star, which will then cool over the next few billion years. Long before then the expanding gas around it will dissipate, and all that’ll be left is a very diffuse cloud of material that will mix with the ethereally thin matter between the stars.
Well that, plus images like this one. And, of course, the knowledge we’ve gained studying how stars die.
Credit: ESA/Hubble & NASA
Sometimes, I like to think of a photon of light as a car on a road. As the road dips and curves, a car has to follow that path, dipping and curving as well. It might be weird to think of space as curving, but it does. Gravity from massive objects warps space, and a beam of light moving through that curved space curves along with it.
This is the principle behind what’s called gravitational lensing. A beam of light passing by an object — a big galaxy, say, or a cluster of galaxies — bends one way. A beam headed in a slightly different direction bends a slightly different way. This can really mess with what we see… which I can prove! Check this out: a Hubble image of the galaxy RCSGA 032727-13260.
What a mess! All those arcs and blue smudges are images of that one galaxy. The light from that galaxy traveled nearly 10 billion light years to get here! But when it was halfway here, that light passed by the big cluster of galaxies — the red fuzzballs — in the middle of the image. As it did, the curvature of space distorted and warped the light from the galaxy, and by the time it reached us here at Earth the image looks like this. The outstretched, smeared-out arc is amazing; I’ve never seen one that long and well-defined before.
Not only that, but the image gets broken up into several separate images. There are no fewer than four different repetitions of the background galaxy in the big image. To show that, I put three of them together here. It’s goofed up, to be sure, but you can kinda sorta see they are the same galaxy, flipped over and/or smudged out.
The cool thing about this is we can learn about the more distant galaxy by examining these images. Read More
There is just something wonderful when Hubble points to nearby spiral galaxies. Sprawling and detailed, we get both great resolution on smaller features as well as a jaw-dropping overview of a grand spiral… like, say, NGC 1073:
Yeah, I know. [Click to galactinate — I had to shrink it to fit here, and it lost a lot of the coolness when I did — or grab the 3900 x 3000 pixel version.]
NGC 1073 is a decent-sized spiral galaxy about 60 million light years away. It’s actually part of a small, tight group of galaxies many of which are far more famous (like NGC 1068). But 1073 is important because of a simple property: it looks like us.
While it’s not a perfect match, NGC 1073 does bear an interesting resemblance to our Milky Way galaxy (UGC 12158 looks more like our galaxy, but is far bigger, for example). Both have large, rectangular bars going across their centers. Bars are a bit odd, since you’d expect the arms just to wind all the way down to the center. But the gravity of a galaxy isn’t like the gravity of a solar system, with a big heavy star sitting in the center. Galaxies have their mass spread out over a long distance, so what gas and dust clouds and stars feel in the way of gravity is different, and bars are a natural outcome of that. However, they’re still not perfectly understood. Bars may form when galaxies collide, and they might be an indication of a galaxy reaching middle age. Perhaps there are other factors as well.
Studying galaxies like NGC 1073 will help us understand how bars form, and why we have one too. Remember, we’re stuck inside our galaxy and can’t see it from the outside (that picture above is an illustration based on detailed observations). It really helps our understanding of the Milky Way to observe galaxies like ours.
An important thing too is that the two galaxies are different in some ways: NGC 1073 has more open arms, for example, compared to our more tightly wound arms. Those differences are telling us something as well. What is it that makes one galaxy hold its arms closer in, and another to fling them out? Why does this galaxy have two arms, and that one three? If you can look at two galaxies that are alike except in one way, it’s easier to isolate the cause. So studying NGC 1073 is a great way to study ourselves.
It always makes me think of Nietzsche, who wrote on the nature of man, "And when you gaze long into an abyss, the abyss also gazes into you."
But on the nature of the Universe, it changes: "And when you gaze long into an abyss, your gaze falls back on yourself."
Well, this is depressing: Fomalhaut b may not exist.
Fomalhaut is one of the brightest stars in the sky, and is only about 25 light years away — that’s close, on a cosmic scale. It’s young, not more than a few hundred million years old, and surrounded by a vast ring of dust, leftover from the formation of the star itself. The ring is about 20 billion km (12 billion miles) in radius, and has a sharp inner edge.
That last bit is important: the easiest way we know to make the inside edge that well-defined is if a planet is orbiting the star just inside the ring. Its gravity would draw in particles, sculpting what would otherwise be a fuzzy boundary into a clean-cut ring. Not only that, but the ring is off-center; again, that’s likely due to the gravitational influence of a planet.
In 2008, astronomers announced they had found that planet: it appeared in two different Hubble Space Telescope images (shown above; click to embiggen) separated by two years. During that time, it had moved a little bit, by just what you’d expect for a planet at that distance from the star. The news came out the same day as other planets were seen around a different star, and I, along with lots of other folks, made it a headline (see the gallery at the bottom of this post showing all the planets we’ve been able to detect directly in images). This was, after all the first direct detection of a planet orbiting a Sun-like star!
Except, maybe not so much. A new paper has come out (PDF) trying to see Fomalhaut b using the Spitzer Space Telescope. Spitzer is sensitive to infrared, where the planet is far brighter.
And what did they see? Nothing.
This image is pretty damning for the existence of Fomalhaut b. It’s the Spitzer infrared observations of the star, with the star’s light carefully removed. On the left is the actual image, and on the right they artificially added a point of light calculated to be equal to what the planet would emit, in the same position the planet should be — that’s what Arrow 1 is pointing at. It should be one of the brightest things in the image (Arrow 2 points to an unrelated bright spot). And while it’s obvious on the right, nothing can be seen on the left, in the real image. In other words, the planet isn’t seen.
Looking over the paper, it’s clear the astronomers were very careful, and did a number of tests. There’s no known way to make a planet as bright as what was seen in the Hubble images yet invisible in the Spitzer images. If the planet were there, they should’ve seen it. Also, a recent study has shown that if the two images show the planet moving, it would be on an orbit that crosses the ring! That seems extremely unlikely, if not outright impossible. A planet that big and massive — more massive than Jupiter — would disrupt the ring in short order if it physically crossed it. That really does make it very, very likely this is not a planet*.
So what is it? It’s probably a clump of dust orbiting the star, reflecting light from the star enough to show up in the Hubble images but not warm enough to show up in the infrared observations.
That’s too bad. If this is true — and it probably is — then that takes away one of the very few planets directly seen in telescopic observations. However, there are still plenty more, and those have been confirmed (again, see the gallery below). And that number will tend to increase as time goes on, even if every now and again it drops by one or two.
Hmph. I once wrote that destroying a planet is hard. Sometimes, all you need to do is try to observe it a different way, and poof! It’s gone.
And now I have to update that gallery, and all my previous pages about it too. Dang science. Always learning more stuff and changing what we thought we knew.
Image credit: Paul Kalas, U C Berkeley; NASA/Spitzer/Markus Janson et al.
* I chatted with an astronomer friend of mine about this, and he agreed with the authors of this new study. "Overall," he wrote me, "it smells like fish.". I couldn’t help myself. I wrote him back: "Of course it does. Fomalhaut is the brightest star in Pisces!"
[Below is a gallery of exoplanets that have been directly imaged using telescopes on ground and in space. Click the thumbnail picture to get a bigger picture and more information, and scroll through the gallery using the left and right arrows.]
What would sunset look like if you were on the planet HD209458b, a gas giant orbiting a star 150 light years away? According to exoplanetary scientist Frédéric Pont, it looks like this:
Isn’t that pretty? And there’s quite a bit of science in that, too.
First things first: HD209458 is a star pretty similar to our Sun. It was one of the first stars determined to have a planet orbiting it (way back in 1999) — the aforementioned HD209458b, nicknamed Osiris — and it turns out the planet’s orbit is so close to edge-on as seen from Earth that we see that planet passing directly in between us and that star once per orbit. When the planet transits that star the amount of light we see dips a little bit. From that we can get the period of the orbit and the size of the planet (a bigger planet blocks more light).
But we can get more, too. There’s a camera on board Hubble called the Space Telescope Imaging Spectrograph, or STIS. It can take the light from an object and break it up into thousands of separate narrowly sliced colors, called a spectrum. By analyzing that spectrum we can find out an astonishing amount of things about astronomical objects: their temperature, rotation, even their composition!
Shortly after HD209458b was discovered to be a transiting exoplanet, STIS was pointed at the star. The camera took hundreds of very short exposures during a transit in the hope of being able to detect the atmosphere of the planet. Osiris was known to be massive, about 70% as massive as Jupiter, so it most likely has a thick atmosphere. It also orbits so close to its parent star — 6.7 million km (4 million miles), much closer than Mercury orbits the Sun — that the heat from the star puffs the atmosphere up, making it easier to see.
In fact, the spectra did reveal the presence of an atmosphere; the first time the atmosphere of an alien planet was ever observed. Different elements and molecules absorb light at different colors, so in the spectrum there are dark spots where the planet’s air absorbs the light from the star behind it during a transit, and how dark that spot gets tells you how much light is absorbed.
It’s this information Prof. Pont used to create the image above (inspired by investigation and an animation done by Alain Lecavelier des Etangs). By knowing the color of the star itself, and using the way the planet’s atmosphere absorbs light, he created this image of the star using sophisticated computer modeling. Read More
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