The galaxy we live in, the Milky Way, is a large spiral galaxy that lives in a small cluster of other galaxies called the Local Group. The other big member is the Andromeda galaxy, located about 2.5 million light years away. That’s a long way off, but we’ve known for a long time that Andromeda is heading more or less toward us at a speed of roughly 100 km/sec (60 miles/second).
The question is, is it headed directly at us, or does it have some "sideways" motion and will miss us? New results announced today by astronomers using Hubble show that — gulp! — Andromeda is headed right down our throats!
But don’t panic. It won’t happen for nearly 4 billion years.
This is a pretty cool result. They used Hubble to look at stars in Andromeda’s halo, the extended fuzzy region outside the main body of the galaxy. By very carefully measuring the positions of the stars over seven years, they could directly measure the motion of those stars. Extrapolating that into the future has allowed the motion of the Andromeda galaxy itself to be determined for the first time.
So what’s going to happen?
First, watch this awesome video of the collision based on the observations:
So here are the details:
I worked with Hubble Space Telescope data for about ten years, and one of the most amazing things about that was seeing the images fresh off the mirror. Knowing that no human on Earth had ever seen that particular object that sharply was a thrill.
Not every Hubble observation gets turned into a gorgeous image, though. A lot of them don’t need to be for scientific publications, for one thing, and for another not every observation is of a targeted object for a specific purpose. Because of that, there are probably hundreds and hundreds of amazing objects — galaxies, nebulae, star clusters — buried in the data, waiting to be found.
That’s where you come in: the folks at the European Space Agency’s Hubble HQ are holding a contest they call Hidden Treasures. You can look through the Hubble observation archive for images and tweak them using online tools they provide, or you can really roll up your sleeves and use professional astronomical software to prettify the images. They’ve made a video explaining the Hubble archive, which may help.
The contest has nice prizes (an iPod Touch, an iPad, and other "goodies"), but you have to hurry: it ends May 31. I know, I’m late to the game here, and I apologize. But if this sounds like something you’d like to do, go dive in! I can tell you as someone with (a lot) of first-hand experience here: it’s huge fun. And who knows? You might find something beautiful, something interesting, or even something no one has ever seen before.
Messier 106 is an elongated spiral galaxy, seen by us at a low angle, in the constellation of Canes Venatici (CANE-eez ven-AT-ih-sigh, the hunting dogs). It’s about 25 million light years away, give or take. That may sound far — 250 million trillion kilometers! — but for Hubble, that’s considered close. So if you take a stack of Hubble images of M106 and put them together, as amateur astronomer Andre vd Hoeven did, you get a lovely picture it!
[Click to galactinate and get access to a zoomable version -- and you want to. I shrank the image considerably to get it to fit here. (UPDATE: there's a HUGE version at Flickr.)]
M106 looks a bit odd to my eye. The overall structure is pretty typical for a two-armed spiral seen at this low angle, but still… those red spots mark the location of busy star formation. The hot young stars heat up their surrounding gas, and the hydrogen in them reacts by glowing. Usually you see star formation that intense over a large region of the galaxy, or a small region, but not somewhere in between like this.
Not being familiar with the galaxy, I looked it up, and found the image inset here (which I’ve rotated to better match the Hubble image above). Right away we see something really weird: there are two more arms invisible in the Hubble shot!
What the what?
The inset picture is a combination from a lot of telescopes and wavelengths: visible light (displayed as gold), infrared (red), radio (purple) and X-ray (blue). The visible and IR line up well with Hubble’s view, but the radio and X-ray clearly show those extra arms. X-rays are emitted by very hot gas — like, million degrees hot — and radio is emitted by gas with a strong magnetic field permeating it. That’s a hint about what’s going on. Another is that the core of the galaxy is very bright, glowing more fiercely than you’d expect from a normal galaxy.
[The Desktop Project is my way of clearing all the pretty pictures off my computer's desktop, by posting one per day until they're gone. I think this week is it - I'm almost out!]
Dark matter is funny stuff. We’ve known about its existence for many decades, and the more we look the better our evidence gets. We know it has mass, and therefore gravity, but we don’t know what it is! We do, however, know what it isn’t: normal matter of any kind, like cold gas, rogue planets, black holes, dead stars, or anything else made of protons, neutrons and the other types of particles we deal with in everyday life.
Since careful observations have shown clearly it can’t be any kind of normal matter, it therefore must be some sort of exotic flavor of matter, some kind of particle we haven’t yet seen.
One thing we’re pretty sure about it, though, is that it doesn’t interact with normal matter except through gravity. Dark matter can pass right through you and you’d never know it. But put enough of it in one spot, and its gravity will reveal its presence.
Which is why the galaxy cluster Abell 520 is such a mystery. Here’s the beauty shot:
Pretty, isn’t it? Abell 520 is a galaxy cluster about 2.4 billion light years away, and a mass of several trillion times our Sun’s — it’s made of galaxies, each with billions of stars in them. And a galaxy cluster is a collection of hundreds or even thousands of galaxies bound together by their gravity. In fact, Abell 520 is more than one cluster: it’s actually a collision between two or more clusters! As they move through space, clusters can collide, and actually quite a few of these cosmic train wrecks are known.
When clusters collide, a lot of things happen. The gas clouds in between galaxies in the two cluster slams into each other, heating up to millions of degrees and glowing in X-rays. In the picture above, that gas has been colored green so you can see it (invisible to the eye, the X-rays were detected by the Chandra Observatory). The orange glow is from stars in galaxies (as seen by the Canada-France-Hawaii and Subaru telescopes). The blue is actually a map of the dark matter made using Hubble observations. The gravity of dark matter distorts the light passing through from more distant galaxies, making it possible to map out the location of the otherwise invisible stuff (you can read about how that’s done here and here).
Since dark matter doesn’t interact with normal matter, we expect it to simply pass through the collision point, sailing on as if nothing had happened. That’s been seen in a half dozen other galaxy cluster collisions, including the Bullet Cluster — hailed as definitive proof of the existence of dark matter — as well as Abell 2744 aka Pandora’s cluster (seen here on the right), and the newly found Musketball cluster.
But Abell 520 isn’t like those others. The problem is, there’s a clear peak in the dark matter right in the middle of the cluster, not off to the sides as you might expect. It looks as if the dark matter slammed to halt in the middle of the collision instead of sailing on.
Here’s the thing: this does not mean dark matter doesn’t exist, or we’re wrong about it. The other clusters I mentioned above make it clear we do have a pretty good grip — so to speak — on the behavior of dark matter.
[This is another in a series of posts I'm doing to help me clear off the zillions of cool astronomy pictures I have sitting on my computer desktop. I've been posting one of these every day and will continue until my desktop is cleared!]
One important aspect of science is its ability to question its own tenets. Some people think that’s a weakness, but it’s a strength! A stiff tree breaks in the wind, but a flexible one survives.
There are, of course, a lot of basic things we do know pretty well. Evolution is real, the Universe is expanding and billions of years old, and so on. As we observe nature more, we learn more, and we can add to these ideas, fill in the details. Sometimes, of course, we learn something that means our models may be wrong, or need to be modified. Again, this is a strength of science: it improves our understanding. We don’t want to think something wrong is true! We need to be flexible.
Which brings us to the weird little galaxy I Zwicky 18, which is so odd-looking I thought at first this Hubble image of it was a drawing!
But no, this is real! [Click to galactinate.]
It’s an amazing shot: it’s the sum of nearly 200 separate Hubble observations of the galaxy, giving a total exposure time of 243,000 seconds: nearly three solid days!
Wow. When I worked on Hubble, many of the images I analyzed had exposure time of only a few minutes. So yeah. This is a deep image.
[Note: This is a repost of what I wrote on February 23, 2007, the 20th anniversary of the day light reached us from Supernova 1987A, the brightest supernova that had been seen for centuries. Not a whole lot has changed since I posted this, including my opinions on it, so I figure I'll give it a second chance (I kept all the dates the same as they were five years ago, so be aware of that as you read it). That exploding star 1.6 quintillion kilometers away certainly changed my life - I could even say I got married because of it, though that's a story for a later time - and it's all been pretty good, I must say.]
Has it really been 20 years since Sanduleak -69 202 blew up? Wow.
Of course, that’s Supernova 1987A to you. And if that doesn’t ring a bell, this image might:
That image, from Hubble, was released as part of the 20th anniversary of the closest supernova in 400 years. It’s amazing– we know so much about this event now, and I know a lot of people — including me — who would have killed for this knowledge back in, say, 1990. But we still don’t understand a lot about it too.
If you want a history of this object, I won’t belabor it here, since I have details in an article I wrote about 87A. In fact, that is the first part of a series of short articles I wrote about the supernova (at the end of each is a link to the next). But the early days were very confusing. It was thought only red supergiant stars could explode, but this one — named Sanduleak -69 202 — was clearly blue when it detonated. It emitted ultraviolet light as expected, but the amount was weird– it got brighter and fainter in an odd way, as if it had a cloud of gas around it. The best images we could do, pre-Hubble, did show some sort of elliptical envelope of gas, but the UV light didn’t match the shape seen.
It wasn’t until we got the Hubble images in 1990 that we saw that inner ring, and things made a little more sense. We could see that it wasn’t a complete shell (like a football), it was a flat ring! But then we realized we still had a problem: how did that ring get there? And what were those fainter arcs above and below it?
I was in the thick of it back then. I had just started my PhD research, signing on with a large project to look at exploding stars with Hubble. I signed up just before launch, so I got to live through the trauma of learning about the flawed mirror, and getting the fuzzy data. I spent months learning how to clean up the data, and wishing for just a few more photons, and lying awake at night (after getting our first meager data on 87A) staring at the ceiling trying to figure out just what the heck that ring was.
Lots of false starts. Lots of dead ends. Lots of great ideas smashed by reality. Lots of math. Lots more math. Lots of meetings, lots of talking, lots of sitting in front of a computer learning about deconvolution, pointing constraints, spectral analysis, Fortran, IDL, Unix.
In the end, I was able to cobble enough together to write a scientific paper and get my PhD in 1994. A lot of what I (and my collaborators of course) were able to figure out turned out to be right, and some turned out not to be. No matter how you slice it, Supernova 1987A is a weird object. For a long time we knew of nothing else like it, but eventually (really, quite recently) people found similar objects. Not that we understand how you can get those three rings like that– that’s still a mystery, even after 20 years.
Wow, 20 years. Well, the Universe ticks on. During that time, the inner ring faded as the initial blast of light from the explosion wore down, but then it rebrightened years later as gazillions of tons of hot gas from the exploded star begin to reach the ring. The supernova itself was at first an unresolved dot, but as you can see from the image above it’s expanded greatly over two decades. It’s an elongated cylinder of material now, getting bigger every day.
And it won’t stop, not for thousands of years. After 7305 days, it’s stretched out to be a goodly fraction of a light year, but it’s still screaming along at thousands of kilometers per second. It’ll slam into the inner ring, eventually dispersing it (that’ll take decades, probably). A few hundred years later it’ll reach the outer rings, and blast them apart too. Maybe eventually it’ll look like the Crab Nebula; there’re some indications the explosions were a bit similar. Even then it’ll go on, getting bigger and fainter, looking like the Vela remnant, and then Simeis 147, and then it’ll fade, mix, and merge into the ambient gas surrounding the other stars in the outskirts of the Tarantula nebula, where the star that made the supernova was born. No doubt by then more of the stars in its neighborhood will blow up; the place is lousy with massive stars just waiting to go off. They’ll have their turn, and future astronomers can marvel over them, as well.
I hope they have as much angst, sleepless nights, head-scratching, wonder, joy, awe, and fun as I did looking at Supernova 1987A. Isn’t that the point?
Note added after I edited this, but before I posted it: Amazingly, while looking up some info about the star that exploded, I stumbled on the announcement that the mystery of the origin of the three rings may be solved! It’s been speculated for a while that the star that blew up was originally a binary star, two stars orbiting each other. If one was more massive than the other, then it could have literally swallowed the smaller one up when it expanded into a red supergiant (it turned blue later). The smaller star spiraled into the bigger one, eventually reaching and merging with the more massive star’s core. As it spiralled in, it "spun up" the more massive star, making it rotate faster and flattening the equatorial regions into a disk. That’s how the inner disk may have formed. Eventually, much of the outer gas of the merged stars was ejected in various stages, and the complicated ejection mechanism may have formed the outer rings. New models by Podsiadlowski, Morris, and Ivanova appear to confirm this idea mathematically, which is fantastic news! It’s not 100% certain, of course, but it’s a great step toward understanding. And that, most certainly, is the point.
Update (late on February 23): the wonderful and talented Jennifer Ouellette, whose name I cannot type correctly on the first try no matter how much I want to, has much more meaty info on this.
Image criedt: NASA, ESA, P. Challis & R. Kirshner (Harvard-Smithsonian Center for Astrophysics); Hubble & Plait
There are quite a few mysteries in astronomy; things we don’t understand. The vast majority of them are smallish in scope, things that can probably be solved with a little more work, more observations. These are more like questions than outright mysteries; things we just don’t have the answers to quite yet.
But then there are some that really are mysteries: unexpected oddities that, for now, defy explanation. One of these reared its head again recently, when observations by the ground-based Subaru and Keck observatories were combined with those from the space-based telescopes Hubble and Spitzer. It doesn’t look like much of a mystery — just a red smudge — but it pushes the boundaries of what we think the very Universe itself can do.
[Click to enbigbangenate.]
First, holy cow, what an image! Incredibly, nearly every single object in that picture is an entire galaxy, a vast collection of billions of stars. They’re also very distant; I doubt any of the bigger ones are closer than several billion light years away.
And lurking off to the side, where you’d hardly notice it, is that little red guy. Named GN-108036, it’s at the soul-crushing distance of 12.9 billion light years away. That means that the light we see here left that galaxy when the Universe was only a few hundred million years old.
As you might imagine, it may look faint, but at that distance it’s remarkable we can see it at all. But we do, because it’s amazingly luminous, perhaps the most intrinsically bright galaxy seen at that distance ever found. Of course, we don’t see too many galaxies farther away than this! And that’s part of the mystery.
So you saw my gallery yesterday of gorgeous pictures from 2011, right? And then you read my post this morning where I whine about how Chandra releases an awesomely cool picture the day after I put up my gallery?
Right. So of course Hubble releases an image today that is so insanely amazing I hardly know where to start with it.
So I’ll start by showing it to you. Behold, Sharpless 2-106:
Are. You. Freaking. Kidding. Me? [Click to ennbulenate, and yes, you really want to.]
This devastatingly beautiful image shows the birth pangs of a massive star. Called IRS 4 (for Infrared Source 4; it was first seen in IR images), it’s the really bright star just below center where the two blue lobes come together. It’s a bruiser, an O-type star with at least 15 times the Sun’s mass — 30 octillion tons! — and is a staggering 10,000 times as bright. It’s still in the process of forming, but it’s nearly there.
Located about 2000 light years away, IRS 4 is surrounded by an enormous cloud of gas and dust that may have a mass as high as 25,000 times the mass of the Sun. When the star first ignited, fusing hydrogen into helium in its core, the vast amount of energy it started pouring out lit up the cloud in the immediate vicinity around it. Most of the cloud is still dark and cannot be seen here, but everything within a few light years of the star is being illuminated, if not ionized, by the fierce ultraviolet light from the star.
Generally, very young stars are still surrounded by the thick disk of material from which they formed. That’s true of IRS 4; the dark line on the left of the star is actually the shadow of that disk on the gas and dust around it.
At this point, things get weird.
I will never, ever get tired of insanely gorgeous images of globular clusters.
Holy. Haleakala. [Click to embiggen, or get the ridiculously huge 3900 x 4000 pixel version.]
That is Hubble’s view of M 53, a cluster of several hundred thousand stars crammed into ball about 60,000 light years away — well outside the Milky Way itself, but bound to it, orbiting our galaxy. It’s probably 12 billion years old, but it looks like some of the stars in it have opted for a little cosmetic surgery…
In our galaxy, stars are so far apart that collisions between two of them almost never happen. But in globular clusters stars are so closely packed that many of them have apparently literally collided with each other, merging into objects called blue stragglers. Globulars are old, so having blue, massive stars is weird; they have short lifespans, and should’ve all blown up as supernovae or at least turned into red giants billions of years ago.
When these objects were first discovered in globulars they were really surprising, and while we still don’t understand everything about them, it’s a fair bet they result from two stars having a very, very close encounter. If two older, low mass red stars pass close to each other at low speed, their gravity can cause them to become bound to each other (it helps if a third star is involved; it can steal away energy from the other two, making it easier for them to become stuck together). Over time, they can spiral together and merge, forming a single, more massive, hotter object: a blue straggler. They’re seen in many globular clusters, and tend to be more common where stars are thickest, as you’d expect.
Over 200 of them have been found in M 53 alone, and at first glance, if you didn’t know better, you’d think they were far younger than the ancient stars around them. In a way, I suppose, they are.
But don’t judge. If you were a 12 billion year old star, you might want a facelift, too.
Image credit: ESA/Hubble & NASA