death star supernova

Chaos has reigned chez Piquant this week, as a crew of workmen descended on our quiet DC retreat and proceeded to cover everything in plastic, strip, sand, paint, install new bathroom vanities, and replace the old drafty windows that may very well date back to 1918. So we very nearly missed the chance to wish a happy birthday to the scientists who, 20 years ago today, first detected the explosion of a supernova dubbed 1987A. It's not the catchiest moniker, granted, but at least it's easy to remember. Along with other known supernovae in the universe, 1987A is still being studied by various teams of scientists, still offering a few surprises to prompt us to re-think our working models for how these amazing celestial objects evolve.

Supernovae are essentially exploding stars. On February 23, 1987, a Canadian astronomer named Ian Shelton was manning the telescope at Las Campanas Observatory in Chile, taking images of a small galaxy some 167,000 light-years from called the Large Magellanic Cloud.  He noticed an extremely bright star on one of the photographic plates that hadn't been present in prior images of the same region.

Shelton joins a long line of distinguished astronomers who've observed supernovae. For instance, more than 400 years ago, Johannes Kepler spotted a bright new object in the night sky, brighter than the planet Jupiter, so bright it was visible even without a telescope (which had not yet been invented). It stayed that bright for several weeks, gradually dimming. Today we know it as the Kepler remnant. (Jen-Luc wonders if perhaps 1987A might one day bear Shelton's name. It seems only fair.) But until  the light from 1987A's explosion finally reached us, our understanding of the actual mechanisms at work were a bit on the vague side.

The new Conservapedia alternative to Wikipedia (that radical liberal bastion!) has been roundly mocked by science bloggers this past week, and rightly so. I mean, this is a site whose entry on Einstein basically says his work had nothing to do with the development of nuclear weapons. The degree of ignorance required to make that sort of statement simply boggles the mind. Does E=mc2 ring a bell? (If it doesn't, Mark Trodden of Cosmic Variance just wrote a spiffy primer post.) How about the sun? That whole energy/mass conversion thing that Einstein cobbled together in 1905 in his spare time -- when he wasn't doing Nobel-Prize-winning work on Brownian motion, and coming up with special relativity -- is pretty critical to human life, considering it's at the heart of nuclear reactions, and nuclear reactions are what make stars like our sun shine.

Take it from They Might Be Giants: "Oh the sun is a mass of incandescent gas/A nuclear furnace/Where hydrogen is fused into helium/At temperatures of billions of degrees." That energy warms the earth, and also keeps the sun's layers from collapsing down into its core. Eventually the fuel runs out, however, and that's when the fireworks can start. All stars die -- even our sun will die one day -- but really massive ones die in particularly spectacularly ways. Here's the conventional scientific explanation: As the hydrogen runs out, fusion slows down, and gravity causes the core to contract, raising temperatures even further, sufficient to give rise to a brief, shorter phase of helium fusion. What happens next depends on a star's mass. Smaller starts gradually cool to become white dwarfs, and those white dwarfs may turn into Type IA supernovae (like 1987A) if there is a near companion star. 

Much larger stars (greater than 8 solar masses) will create temperatures and pressures so high that the carbon in the star's core begins to fuse once the star contracts at the end of the helium-burning stage.  This halts the core's collapse, at least temporarily, and this process continues, over and over, with progressively heavier atomic nuclei. So the cores of those supernovae begin to resemble an onion, with layers upon layers of elements -- the outermost layer is hydrogen, which surrounds a layer of hydrogen fusing into helium, surrounding a layer of helium fusing into carbon, and so on. In fact, most of the heavy elements in the periodic table were born in the intense furnaces of exploding supernovae that were once massive stars.

Supernovae also make great "standard candles" to help astronomers determine distances in space, because they burn so steadily and brightly -- and predictably. In fact, the use of supernovae as standard candles is what enabled two separate teams of physicists in 1998 to determine that the expansion of the universe is actually accelerating... pretty much revolutionizing the field of cosmology in the process, and starting the whole "dark energy" craze.

All kinds of fascinating new results related to supernovae were reported at the 2007 meeting of the American Astronomical Society (AAS) meeting last month in Seattle. For instance, apparently stars can blow bubbles. The powerful stellar winds produced by extra-massive stars push away nearby gas and dust and form low-density cavities inside expanding bubbles. When such a star dies in a big explosion, the energy from its death throes enlarge the bubbles into huge supernova remnants (yes, just like the Kepler remnant.) If enough cavities overlap, they can form a superbubble. Scientists at the University of Illinois at Champaign-Urbana announced their observation of a superbubble in the midst of forming, which could yield new information about the formation of planetary systems among other insights.

Another hot topic at the AAS meeting: a team of researchers from the University of Notre Dame reported detection of a light echo from a Type Ia supernova called 1995E. Light echos can occur when light from a supernova is redirected towards the earth by grains of dust in the host galaxy. The explosive event is the direct rays we see, but delayed light echos from a different location because they took a more circuitous route -- much like the delay between a direct flight from LA to New York versus a changeover in Chicago.

As for 1987A, University of California, Berkeley astronomer Nathan Smith announced his alternative theory for the origin of the strange, triple-ring nebula surrounding the object, produced by the star a few thousand years before it exploded. The working theory was that the original red supergiant merged with a companion and started spinning rapidly (ejecting the material that produced the strange shaped nebula), then turned into a blue supergiant and finally exploded. The sticking point for this neat little theory is that red supergiants are just too darn big to spin that fast. Smith argues that the progenitor star of 1987A might have been an unstable blue supergiant (called luminous blue variables). Such stars eject material from their surfaces in recurring eruptions, like volcanoes, before dying in a supernova explosion. His evidence: he recently discovered two such stars that have similar clouds of gas and dust.

Oh, and remember the Kepler remnant I mentioned earlier? Kepler might have lacked even a rudimentary telescope, but thanks to advanced instruments like Hubble and the Chandra X-Ray Observatory, astrophysicists are still studying it and learning new things. Chandra in particular announced a stunning new image at the AAS meeting in January, achieving unprecedented details by combining nearly nine days of observations, and determining once and for all that the Kepler remnant is the result of a Type Ia supernova. (There had been some debate about that, since prior conflicting data from radio, optical and X-ray telescopes made it difficult to determine whether it was a Type Ia, or a Type II (which results form the collapse of a single massive star that sheds material before exploding). It could also help astronomers further improve the reliability of using such objects as standard candles -- and hopefully tell us more about that mysterious dark energy.

There's yet another area in which supernovae can help solve some of astrophysics' most puzzling mysteries: neutrino physics. All stars emit these so-called "ghost particles" -- our sun bathes us in billions of neutrinos every day, which interact with matter so weakly that they pass right through us without being noticed. Physicists have built deep underground laboratories that have managed to detect the odd solar neutrino or two, but such events are rare; only a tiny fraction of the sun's neutrinos are detected. Supernovae like 1987A emit 1000 times more neutrinos than the sun will produce in its entire 10-billion-year lifetime. When it was first observed 20 years ago, the Super-Kamiokande detector in Japan picked up a few extra neutrinos: 19, to be exact. That's not much compared to how many neutrinos the supernova actually emitted, so it merely provide a few initial clues to the mystery of how supernovae really work.

And 1987A continues to reveal new secrets. NASA issued a press release this morning reporting that the XMN-Newton X-ray telescope has taken images showing that the supernova keeps brightening -- at least since the ROSAT telescope first detected X-rays emitted by 1987A in 1992. Our plucky little Death Star Supernova now outshines all other X-ray sources in its immediate vicinity. Maybe even the curmudgeonly Simon Cowell of American Idol would be impressed.

Comments

[Phil Plait, aka The Bad Astronomer]

Very lovely, as usual. I linked to you from my own blog about my personal experience getting my Phd with this very supernova. Hint hint. :)

[Blake Stacey]

"Smaller starts gradually cool to become white dwarfs, and those white dwarfs may turn into Type IA supernovae (like 1987A) if there is a near companion star."

Everything sounds right about this except the parenthesis. As Phil Plait has written, the star which blew up to become SN1987A (Sanduleak -69 202) was a blue supergiant. SN1987A is properly considered a Type II supernova; although it probably originated as a binary system, with one star swallowing another about 20,000 years ago, the thing which blew up was not a white dwarf.

"Physicists have built deep underground laboratories that have managed to detect the odd solar neutrino or two, but such events are rare; only a tiny fraction of the sun's neutrinos are detected. Supernovae like 1987A emit 1000 times more neutrinos than the sun will produce in its entire 10-billion-year lifetime. When it was first observed 20 years ago, the Super-Kamiokande detector in Japan picked up a few extra neutrinos: 19, to be exact. That's not much compared to how many neutrinos the supernova actually emitted, so it merely provide a few initial clues to the mystery of how supernovae really work."

The ghostly nature of neutrinos is both a benefit and a curse. The curse part is easy to understand: it makes the little things incredibly difficult to detect! You have to put a lot of matter in their way if you hope to catch any. By "a lot", I mean that Super-Kamiokande uses 50 kilotons of water in a tank under a mountain (and you thought "kiloton" only referred to atomic bombs!). The IceCube detector currently being constructed will use one cubic kilometer of Antarctic ice; they expect to finish in 2011, and at an estimated price tag of $271 million, it works out to a very economical 25 cents per ton!

The blessing of neutrinos is a little more subtle. A supernova produces vast quantities of them, radiating more energy in neutrinos than across the entire electromagnetic spectrum combined. Because neutrinos are so slippery, they can "ghost" their way through the expanding gases of the exploding star, while light is still trapped behind. Nobody knows for sure, but a neutrino signal could arrive at Earth several hours before telescopes could spot it in the sky. If all the neutrino detectors around the world ring at once, we'd better start looking up!

And here's where I plug my colleagues and friends in the Supernova Early Warning System cabal:

http://snews.bnl.gov

A technical description of the project and its methods is available via New J. Physics:

http://www.iop.org/EJ/abstract/1367-2630/6/1/114/

[Joshua R]

oh conservipedia how i love thee

[Brandon Swift]

Blake is correct: 87A was a Type II supernova, the M >~8 solar masses variety.

Also, it is the Type Ia supernovae that make the best standard candles, which led the the 1998 discovery of the acceleration.

[DrNathaniel]

Actually, it wasn't Super-K that saw neutrinos from 1987a.. it hadn't been built yet. Neutrinos were seen in the water-chereknov detectors of the time, namely IMB and Kamiokande.

This is important.. for the next supernova, you want multiple detectors running. Partly for coverage (since no detector is live 100% of the time), partly for extra information (SNO would have provided a wealth of SN data if it caught one!) and partly for coincidence... the SNEWS watch works only if it has multiple coincidece signals. Neutrinos see a supernova _first_, which is important. If we (neutrino physicists) see a supernova, we will notify the astronomical community, which mobilizes every telescope on the planet to try to see the thing.

Unfortunately, Super-K is just about the only big experiment sensitive to supernova neutrinos that is operating right now. That's one of the reasons we want to build UNO.

---Nathaniel

[Joshua Zucker]

The TMBG quote is at a temperature of *millions* of degrees (not billions). But whatever, way way way hot.

[The Science Pundit]

Nice post, as usual. FYI, Karmen (Chaotic Utopia: Jan 26 post) has a link to the original by Tom Glazer.

[Jim Kakalios]

Off Topic:

Major, major kudos on the excellent review in this week New York Times Book Review section of The Physics of the Buffyverse! A positive stand alone review, with a cute graphic! You should be justifiably proud.

And while I'm still off topic, but back to the blog: I would also commend you on the extend and quality of the writing you post up here, gratis, week in and week out. I am aware of the effort involved in writing just one essay, and the high quality product that you consistently put out is impressive.

Cheers,

Jim

[michael autin]

Actually the "fuel" of stars does not "run out". It is more like a spring being compressed. As protons are converted to neutrons and when the amount of neutrons exceeds about 68% of the mass then gravitational cohesion evaporates and the stars explode as neutrons do not attract as much as Repel by that failure to attract. BUT a lovely descriptive blog posting you have, thanks.

[michael autin]

As to neutrinos, to me and my understanding of 100 years of physics; which has developed into a quantum understanding of astrophysics: they seem to be the lynch pin for gravitational (Natural) fusion which is that as protons are compressed into smaller volumes, the neutrino acts like a pin for the electron to a proton to yield a neutron, which at a lifespan of 15 minutes disintegrates (WITHOUT gravity to keep it "pinched") into a proton and electron and neutrino. I may not be EXACT as to this point and the above point, but I am logical enough to say that I am accurate in my scientific vocabulary to have confidence in what I write in this regard. Of course I use multiple equations for electromagnetic (electron-nucleus vibrations or light) and for gravitational (nucleus vibrations). Of course non math/science people may read this open conversation and I will hear the "social-echo" on the streets of Major cities for seconds, minutes, hours, days, months, years, decades... and probably get fed up with sophisicated "traps" to test accuracy, or even just joke around. At least there are places where people can tell REAL science from ideas from other books written BEFORE observed science was written and lead to discrepancies that make communication between us mortals occasionally tough.

[Nick Johnson]

Off-topic ::

What if... and this ia a big if, our universe acted in the same ways that stars do and blackholes? Where they expand, collapse, expand, collapse, ect... multiple times? Man would that change my perception on time.

Also, when I was in AP Physics back last year in highschool my teacher Mr. Rich explained the process of a stars death, he informed us that many of the bigger stars supernova and turn into blackholes... such as Betelguise(sp?) and that at the moment we're looking at the last minutes of that particular star's life. I am interested in a field in astronomy and cosmology, but the lack of pay definitely directs me elsewhere.

Anyway, good morning read at work (stupid call centers) and even cooler comments. LOVE this site, and thats impressive coming from a 19 year old (we are sometimes hard to entertain).

[djlactin]

actually, Einstein won his Nobel Prize for explaining the photoelectric effect.

[Stephen]

I thought Einstein's Nobel Prize was on the photo electric effect. Wikipedia agrees. His Brownian Motion stuff was interesting too - proving that atoms exist at a time when there was some doubt about it. But the Photo Electric Effect led to Quantum Mechanics. You know - the guys who work on those little tiny cars... that are incompatible with Einstein's General Relativity.

[Blake Stacey]

Nick Johnson:

It's "Betelgeuse". ;-) It comes from the Arabic "yad al-jauza", meaning "hand of the Central One".

You might be interested looking up the "cyclic model". This is an idea which has been floating around for decades, and is currently being worked out by some string-theory people. The Wikipedia article on the topic is a little technical (what in blazes is an "orbifold" or an "ekpyrotic scenario", you may well ask), but it might give you a starting point:

http://en.wikipedia.org/wiki/Cyclic_model

[Quasar9]

Hi Jen Luc, rich & exciting post.
The beauty about modern technology is that one can ammend errors on posts online in a jiffy.

"although it probably originated as a binary system, with one star swallowing another about 20,000 years ago, the thing which blew up was not a white dwarf." - Thanks Blake Stacey

"Actually, it wasn't Super-K that saw neutrinos from 1987a.. it hadn't been built yet. Neutrinos were seen in the water-chereknov detectors of the time, namely IMB and Kamiokande." - Thanks Dr Nathaniel

"The TMBG quote is at a temperature of *millions* of degrees (not billions). But whatever, way way way hot." - Thanks Joshua Zucker

"actually, Einstein won his Nobel Prize for explaining the photoelectric effect." - Thanks djlactin

Blake I know you didn't mean it literally, but the Cyclic model is the preferred model of the other cabal (and has some ST people working on it) - but cannot be compared to a Supernova - where would we earthlings be 'sitting' to observe it. And where would all those neutrinos go? - to outer space?
Mind you maybe the (this) universe is short of a neutrino or ninetten, or is it 42.

[Blake Stacey]

Quasar9,

I was just trying to give a little context to NJ's query about Universes which "expand, collapse, expand, collapse, etc... multiple times".

[Johan Richter]

Actually; I have heard the claim that E=MC^2 has nothing to do with nuclear weapons from an actual physicist as well. His reasoning was basically like this:"Of course the formula doesn't just apply to nuclear reactions. It is equally appliable to chemical reactions, giving an equivalance between losing mass and giving of energy. But no one claims that Einstein should be thanked for all chemical reactions that are performed since relativity theory is pretty useless for predicting what chemical reactions will happens. Likewise, you don't actually need E=MC^2 to come up with the idea of nuclear reactions. Standard non-relativistic quantum mechanics works just fine."

Not being a physicist I won't judge his argument, which I anyway might have misunderstood in certain details. I would like to hear your opinion on it however.