One of my favorite things to do in the whole world is look at astronomical images. They are a source of great beauty, insight into our Universe, and wonder that we can understand them.
As it happens, I spent a solid chunk of my professional research career looking at supernovae remnants, the expanding debris after a star explodes. Everything about them is cool: the extraordinary energy released, the amazing beauty and symmetry they posses, the fact that many of the elements necessary for life are created in them.
So I’m pretty familiar with images of these things. Which is why I got a good surprise when the European Space Agency posted this picture of the supernova remnant G272.2-03.2, taken with the XMM-Newton observatory:
[Click to corecollapsenate.]
This is actually a composite image; the starry background is from an optical telescope, but the remnant itself is seen in X-rays by XMM-Newton. X-rays are emitted by very hot gas – heated to a million degrees or more – so you know right away this was an energetic event. I mean, duh, a star exploded.
The two colors (green and orange) tell you the gas is at two different temperatures. The outer rim is probably a thin shell of gas compressed as it slams into the very thin material between stars, while gas heated by shock waves fills the shell. My eye went right away to the bright bit at the right. That’s very common in objects like this when the expanding gas rams into a slightly denser part space (like some other floating cloud of gas) – you get a "dent" in the shell and it gets a bit brighter.
What surprised me most about this particular object is that I had never heard of it! That’s a little unusual; I try to keep up with such things. Then I found out this image was taken in 2001! So it’s not like I ever had a chance to see it. Weird.
So I did what I always do in these situations: looked for references to it in professional journal research papers. And what I found was… almost nothing. There’s a good paper analyzing it by my friend Ilana Harrus, but not much else. Her paper came out a few months before this XMM-Newton observation though, and I couldn’t find a paper with these observations in it.
So I don’t have a lot of information about it. It’s probably about 5000 years old, and may be somewhere between 6000 and 16,000 light years away; pinning down these numbers is very difficult. The star that blew up was probably 8 – 10 times the mass of the Sun, actually a bit of a lightweight for a supernova progenitor. The nebula itself is clearly a shell with hot gas in the interior, but it’s hard to know much more about it. From Ilana’s paper I read that it has some features that make it look old, others younger. But the lack of deep observations keeps this object something of a mystery. I’d love to see some long exposures from Hubble or the Very Large Telescope in Chile. There really aren’t very many good examples of moderate age supernova remnants, and this looks to be a pretty nice example of one.
But geez, next time, someone let me know before a decade passes, OK?
Image credit: XMM-Newton/ESA
One of the most amazing things I can think of can be stated simply: some stars explode.
That’s incredible. An entire star, millions of kilometers across and massing octillions of tons, can go supernova, tearing itself to shreds. The explosion is so huge that it releases more energy in a few months than our Sun will over its entire lifetime.
And yet, when seen from a distance, supernovae can produce structures of astonishing subtlety and beauty. About 11,000 years ago, a star over 800 light years away exploded in the constellation Vela, producing an expanding gas cloud. Here is one small part of that nebula:
[Click to chandrasekharenate, or grab the ginormous 8300 x 8300 pixel version.]
That gorgeous structure is NGC 2736, also called the Pencil Nebula, part of the much larger Vela supernova remnant. This picture was taken using the 2.2 meter MPG/ESO telescope in Chile. As the debris from the titanic explosion expands, it rams into the interstellar gas surrounding it. That compresses the gas, and drives a shock wave through it. A shock wave occurs when an object moves at supersonic speed through some other material – although the gas in space is thin, in some places it’s thick enough that atoms and molecules in it do collide. It’s still a thin vacuum by our standards, but physics will not be denied.
Think of it this way: imagine two people standing a few meters apart, holding a rope between them. One of them snaps their end up and down sharply. A wave is created which moves down the rope, and a second or so later the other person feels the tug. The information that the first person moved the rope took some amount of time to travel down the rope in the form of that wave.
Sound is similar, in that it’s a compression wave. When something happens to make a sound – like a tree falling in a forest – it compresses the air, and that compression moves outward at (duh) the speed of sound. It’s a way of transmitting information from one spot to another.
But now imagine something moving faster than sound. Instead of hearing the sound first, the supersonic object would actually travel past you before its sound would. Because you didn’t hear anything first, that event would surprise you, right? You might even be… shocked.
Hence the term shock wave.
And that’s what’s happening in NGC 2736. The gas from the supernova is expanding far faster than sound in the surrounding gas, so the gas is shocked. It gets hugely compressed, and forms those thin filaments and ribbons. You see this a lot in space where one thing is slamming into another (see Related Posts below). The energy of the shock wave heats up the gas, which then glows, and from a safe distance we see it as a thread of light, finely detailed and structured.
They say that in space, no one can hear you scream… but in reality, if you pick the right place and scream hard enough, you can make yourself heard across thousands of years in time, and trillions of kilometers in space.
Image credit: ESO
[NOTE: Whenever I write about actual cosmic events that might possibly affect us on Earth, I get scared emails from some folks. So let me be up front: there are no stars close enough to Earth to hurt us should they explode. Nothing I write in this post changes that; I'm talking about a star that can go supernova that's closer than I thought any was, but still much too far away to do much to us. So don't panic. But do please enjoy the over-the-topness of what happens when a star explodes. Because it's cool.]
On May 13 I tweeted this one: BAFact: A supernova has to be less than about 75 light years away to hurt us. No star that close can explode, so we’re OK. The distance may actually be somewhere between 50 – 100 light years, and it depends on the kind of exploding star, but I have to keep these factoids to about 110 characters to tweet them. Nuance is at a premium.
I got so many replies about that one that I decided to do a theme week, and stick with supernovae. The next day I tweeted this: BAFact: The nearest star that can go supernova is Spica – it’s 260 light years away, so we’re safe, and I linked to a video I did a few years back this.
A few minutes later I got a tweet from Nyrath, saying that he thought the nearest star that could explode was IK Pegasi, 150 light years away.
I looked this up, and here’s the thing: he’s right! I had never heard of IK Peg, so I didn’t even know it existed. And it turns out it is the nearest star that can explode, though technically it probably isn’t.
And you know when I say something weirdly oxymoronic like that there must be a good story here, right? Mwuhahahaha. Yes. yes, there is. Stick with me; this is long, but also awesome.
It’s been known for a while that IK Peg is a weird star (you can read quite a bit about it on the ESO website, though the formatting is a bit messed up). It looks like an A-type star — that is, more massive, hotter, and bigger than the Sun. It’s not nearly enough to explode — stars need to be at least 8 times the Sun’s mass to do that, and this star is only about 1.7 times heftier than the Sun.
It pulsates, getting brighter and dimmer on a pretty rapid timescale: each cycle only takes about an hour. A lot of stars do this, but typically when one does it means it’s nearing the end of its life. In a few dozen million years it’ll swell up into a red giant, blow out a strong wind that’ll strip its outer layers away (creating a gorgeous planetary nebula), and eventually retire as a white dwarf; small, dense, and hot, cooling slowly over billions of years.
Except… there’s a monkey in the wrench. The star isn’t alone.
It has a companion. And this is where things get interesting.
[The Desktop Project is my way of forcing myself to write a post about the astronomical images I've been saving to my computer's desktop and then ignoring. I've been posting one every day for nearly a month, and this, my friends, is it. The last one. And I saved it for this occasion, because it's ridiculously awesome. Thanks for bearing with me as I did this bit of housecleaning.]
The constellation Carina is a mess. It represents the keel of a ship, but in the sky it happens to be in the direction of the disk of our galaxy, which is like having a window in a building facing downtown in a busy city. And like an urban center, the Milky Way in that direction is lousy with gas, dust, stars… and much of this is chaotic, disturbed, and, well, messy.
Oh, but what a glorious, glorious mess. Behold! The Carina Nebula!
[Click to ennebulenate, or grab this ridiculously huge 13,000 x 9000 pixel monster version. And yes, you very, very much want to make this bigger.]
Holy wow! I love this image! It’s got it all: stars of every color studding a riotous background of gas, itself glowing red or reflecting blue, silhouetted in great ostentatious sweeps of dust. Shock waves riddle the gas, compressing it here and there in arc, loops, streamers, and filaments.
It’s ridiculous, and spectacular.
The image was taken using the HAWK-1 detector on the European Southern Observatory’s Very Large Telescope. This is an infrared picture, using colors outside what the human eye can detect. In the picture, what you see as blue is actually light at 1.25 microns, green at 1.65, and red at 2.2 microns. For comparison, the reddest color the eye can see is about 0.7 microns. Amazingly, in visible light this region is even more chaotic looking.
The Carina Nebula is about 7500 light years away, and is the site of a lot of star formation. Many of the stars being born are very massive, which makes them hot, blue, and frighteningly luminous. See that bright star in the lower left? That’s Eta Carina, one of the most massive stars in the galaxy. To give you an idea of how stupid violent and unstable that star is, in 1843 it erupted in an explosive event that rivaled a supernova. The star held together, barely, but it ejected two lobes of matter that have about as much mass as the Sun. Each. And they’re expanding at 700 km/sec (400 miles per second), fast enough to cross the continental United States in 12 seconds.
And one day Eta Car will explode. It’s too far away to hurt us, but what a sight that’ll be! And even now, just sitting there not exploding, it still shines about 4 million times brighter than the Sun. Four million. If the Earth were as close to Eta Car as we are to the Sun, we’d be vaporized into an ionized memory.
The HAWK-1 image is actually high enough resolution to get a lot of detail. Here’s a collection of nine interesting regions:
This is very exciting: the star that blew up to form Supernova 2012aw may have been seen in an older Hubble image!
First, here’s a lovely shot of the galaxy and supernova:
[Click to galactinate.]
This is not from Hubble! It’s from Adam Block, a frequent contributor of stunning pictures to this blog, who took it using the 0.8 meter (32") Schulman Telescope at Mt. Lemmon on March 20. The supernova is the bright bluish star sitting on a spiral arm to the right and just below the core of the galaxy.
M95 is a relatively nearby barred spiral galaxy just about 37 million light years away, so we can see a lot of detail in it. In fact, it’s close enough that with big telescopes, individual stars can be seen in it. Once the supernova was spotted and its location determined, astronomers found a picture of M95 taken with Hubble a few years ago, long before the supernova event, and combed through it. Sure enough, they found a star sitting right where the supernova went off! It’s almost certainly the progenitor of SN2012aw.
Interestingly, given the color and brightness of the the star in the Hubble image, it was not terribly massive, maybe 8 times the mass of the Sun. That’s at the lower limit for how much mass an exploding star of this type can have. It’s probable the star had more mass when it was younger, and shed a lot of it during its short, furious life. I poked around online and found another example like this; SN2003gd was a supernova in the nearby galaxy M74, which is also close enough that a progenitor star was found in older images. Interestingly, it too had about 8 times the Sun’s mass, and had other characteristics similar to this new supernova.
Being able to find the star that blew up in older images is terribly exciting! It’s not that common to find them — they have to be in nearby galaxies, or else they’re too faint to see. And they really help constrain the physics of the explosion. We have a pretty good grasp of the basics on how high-mass stars explode, but the devil’s in the details. The mass of the star right before it blows up, how bright it is, what color it is, what kind of environment it’s sitting in — all these things help astronomers understand better how and why stars like this explode. In fact, Supernova 1987A sparked a revolution of sorts in supernova astrophysics because it was found to be a blue supergiant when it went off — before that, it was thought only red supergiants could explode.
So SN2012aw joins the short — but growing — list of supernovae that have a star identified as the culprit. The more we find, the merrier astronomers will be.
Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona. Tip o’ the Chandrasekhar limit to DeepSkyVideos on Twitter.
- Supernova 2012aw: the pictures!
- Breaking: possible supernova in nearby spiral M95
- Supernova update: it’s peaking now! (about a supernova in galaxy M101 in 2011)
- Supernovae popping off like firecrackers in Carina
I just learned that there’s a possible (but nearly certain) supernova on the rise in the relatively nearby spiral galaxy M95. This is exciting, because it should get bright enough to spot in small telescopes! By coincidence, Mars happens to be sitting in the sky very close to the location of M95; that makes it easier to find in that you have an obvious landmark in the sky, but tougher because Mars is so close and so bright it swamps the region with light!
Right now, the supernova is still at roughly 12th magnitude, making it too faint to see without bigger ‘scopes, or smaller ones with digital cameras. However, it was only discovered on March 16, so it’s most likely going to get brighter. The galaxy itself is about magnitude 9 or 10, so the supernova may get that bright.
There are quite a few pictures of the galaxy+supernova on Flickr, but most
are copyrighted aren’t free license so I can’t post them here. However, searching the site for "M95 supernova" yielded a few of them. You can also find a list of links here. I think this one in particular is cool; it has bright lines going across that’s scattered light from nearby Mars!
However, by a funny coincidence (?), the European Southern Observatory chose a Very Large Telescope image of M95 as its Picture of the Week just this morning:
[Click to galactinate.]
I say it’s a coincidence because there’s no mention of the supernova in the caption. Anyway, M95 is a gorgeous barred ring spiral: the bar is the rectangular feature in the middle, and the ring around it of gas and stars is not uncommon in galaxies (like here and here). M95 is about 35-40 million light years away, and is part of a small group of a couple of dozen galaxies called the Leo I group. M96, another spiral in the group, is even prettier!
Back to the supernova, DeepSkyVideos put together a very quick-and-dirty video about it which manages to be very informative and good despite being put up so quickly:
If you have a good telescope and detector, the coordinates of the supernova are online. Astrobob has a good finder chart for it. I’ll note that observations right now are critical; the physics of the explosion are best characterized by how rapidly it brightens. At this point, we don’t even know if it’s a Type I or Type II! So observe it if you can. And if you take good pictures or see any online that are
not copyrighted freely licensed, please let me know!
And as a final note for now: we’re in no danger from this. I normally wouldn’t bother writing that, but a lot of people seem jittery due to 1) the 2012 nonsense, b) the recent (coincidental) solar flares, and γ) the asteroids (DA14 and AG5) I wrote about last week. So to proclude any fear-mongering, I’ll just say this supernova is something like 400 million trillion kilometers away, and probably won’t even get bright enough to see in binoculars. I hope that helps assuage any fears.
Image credit: ESO
A few years back, when I was working on using NASA satellite data to create educational materials for kids, we had this idea of using the steady beats from pulsars in a song. Pulsars are the rapidly-spinning über-dense fantastically-magnetic collapsed cores of exploded stars. As they spin, they emit beams of matter and energy that sweep out into space much like a lighthouse beam, and we see a blip of light when that beam passes over us.
Some pulsars spin hundreds of times per second, some take several seconds to spin once. If you take that pulse of light and translate it into sound, you get a very steady thumping beat with very precise timing. So making it into a song is a natural thought.
But we certainly didn’t take it as far as the German band Reimhaus did, making a music video out of it! They used several pulsars for their song "Echoes, Silence, Pulses & Waves". So here’s the cosmic beat:
Pretty clever. Lots of other people have turned cosmic phenomena into sounds and music, including the Perseid meteor shower, the Phoenix Mars Lander descent, the Earth’s aurorae, and even the aurorae from Saturn!
Image credit: NASA. Tip o’ the magnetar to Elkin Fricke for sending me the link to the video.
If you’re a fan of over-the-top ridiculously huge violent explosions, then you won’t do any better than gamma-ray bursts. With apologies to Douglas Adams and Eccentrica Gallumbits, GRBs are the Universe’s largest bangs since The Big One. When they were first discovered, during the Cold War, it was unclear what caused them. There were more theories than there were observations of them! Now we’ve observed hundreds of these things, and we’ve learned quite a bit about them, like a) every one of them is different, 2) they have lots of different sources, and γ) even after five decades they can still surprise us.
Last year on Christmas, the light from a gamma-ray burst reached Earth and was detected by NASA’s orbiting Swift satellite. Designated GRB 101225A, it was weird right off the bat: it lasted a staggering half hour, when most GRBs are over within seconds, or a few minutes at most. Followup observations came pouring in from telescopes on and above the Earth, and the next weird thing was found: the fading glow from the burst seemed to be coming from good old-fashioned heat: some type of material heated to unbelievable temperatures. Usually, the afterglow is dominated by other forces like rapidly moving super-intense magnetic fields that accelerate gigatons of subatomic particles to huge speeds, but in this case it looked like a regular-old explosion.
Both of these things are pretty dang weird. So what could have caused this burst?
Normally, we think GRBs are the birth cries of black holes. When a giant star explodes, or two tiny but ultra-dense neutrons stars merge, they can form a black hole and send vast amounts of gamma rays (super high-energy light) sleeting out into the Universe. In this case, though, something different happened, and two ideas of what was behind it are emerging…. but both involve neutron stars. And I’m not sure which idea is cooler.
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
Some new research just released asks a question near and dear to me: are there thousands of spinning white dwarfs in our galaxy, just waiting to explode as they gradually slow their rotation?
The answer is very probably yes. Let me be clear, as I always must be when covering topics like this: we’re not in any real danger from these things. Space is vast, and supernovae are few. If these things were that volatile we wouldn’t be here to talk about them in the first place.
But it’s still a very cool scientific question, and actually a fairly simple concept. Here’s how it works.
Imagine a binary system of two stars like the Sun, orbiting each other. One star nears the end of its life, swells up into a red giant, and blows off its outer layers. After a few millions years, all that’s left is its core: a dense, hot ball called a white dwarf. The size of the Earth but with the mass of a star, white dwarfs are pretty weird. They have incredibly strong gravity, which wants to crush them down even further, but they are supported by the electric repulsion of electrons, which is a pretty mighty force. It’s an uneasy truce.
It’s made even uneasier by the other star. It too eventually swells up, and can start to dump matter onto the dwarf (like in the picture above). If enough mass piles up, the immense gravity of the dwarf can induce nuclear fusion. Sometimes the material explodes, flaring in brightness, and we get a nova. Other times, if enough matter piles up — making the total mass of the white dwarf a bit more than 1.4 times that of the Sun — the ignition of fusion can cause a runaway reaction in the star, disrupting it entirely. The white dwarf tears itself apart, and you get one of the biggest and most violent explosions in the Universe: a supernova.
But there’s a hitch. Read More