supernova

Arthur C. Clarke suggests, in a half joking manner, that supernovae may be industrial accidents of alien civilizations who were tinkering with a technology they didn't understand.

It reminds me of the time that there was an advance in particle physics, and some new TeV collider was being built. Some people thought that if a certain particle would be created there would instantly be a massive black hole where Earth was. After checking the figures vigorously, they realized that that conclusion was false.

• A supernova can briefly outshine the rest of the galaxy it is a part of.
• They occur about once every two hundred years per galaxy, and ones within our galaxy (but not too close!) can usually be seen by the naked eye, often even during the day.
• They are the main process in the universe which creates elements heavier than iron, and in fact all the matter heavier than helium in our Solar System was thought to have been formed in a massive star's core, or in it's final supernova.
• They can result in a neutron star, which is the core of the old star compressed under gravity so much that it's matter is almost entirely composed of neutrons, or for larger stars, a black hole.
• The glow which is visible around one for several weeks after the main event is mainly the result of the decay of radioisotopes formed in the cataclysmic blast.
• The escaping outer layers of the former star tend to form planetary nebulae.
• And you don't want to stay too close to one, either.
• It has been calculated that it is likely that at least one supernova has occurred close enough to the Earth to have caused a mass extinction, by dint of bathing the Earth with large amounts of cosmic rays and other radiation.
• It has been theorised that the largest mass extinction in Earth's history was in fact caused by one of these nearby supernovae.

Generally when a star is born with a mass of 8 times that of our sun, it will end its life with a type II supernova explosion.

It is at the core of such a star where the fusion of hydrogen to make helium takes place, this relatively small region releases enough energy to stop the star collapsing under it's own gravity. Eventually the fuel runs out and gravity collapses the star. If the star is massive enough, gravity can compact the core to such an extent, that enough energy is available to continue the fusion process, fusing progressively heavier elements than hydrogen towards the core. (Shown below, outmost layers to innermost)

H => He

He => C,O

C => Ne, Mg

O => Si, S

Si, S => Fe

When sulphur fuses with silicon to make iron the process stops, as to fuse iron, you have to put more energy in than you can get out. (Please see Wrinkly's write up 'Transferric element' for more.) Gradually a core of iron 'ash' will build up....

When the iron core exceeds 1.4 solar masses gravity overcomes electron degeneracy pressure and the core collapses from perhaps 5000 miles to perhaps only 10 miles, in seconds. Enough energy is released at this point to power 50 stars like our own for 20 billion years, longer than the current age of the universe.

Most of this energy is carried away by neutrinos, only a small percentage of the energy is absorbed by the outer layers of the star, and this is what powers the actual supernova explosion. The enormous shockwave created slams into the outer layers of the star, ejecting the material at up to 10 million miles per hour, this provides enough energy to fuse together much heavier elements than iron. Within a day or two the shockwave has reached the outer surface of the star, and it's brightened by a billion times or more, sometimes outshining the galaxy the star is in. The core, however has become a very compact massive object, a neutron star, or if massive enough a black hole

The envelope continues to expand, glowing brightly in x-ray light. The glowing cloud of gas left makes for some of the most beautiful astronomical photographs, indeed it's supernova that make the photograph possible; the silver and other chemicals used to make the negative, and photographer, can only be made in a supernova explosion.

Type I Supernovae: All type I supernovae are classed so because they lack hydrogen (H) bands in absorption or emission when they are at maximum light. That is, the most common element in the universe is not present in these explosions.

Type Ia Supernova: Believed to originate from the explosion of a white dwarf star, these are distinguished by the silicon (Si) content of their ejected matter. Stars do not become white dwarves until they burn off all fusionable material, which explains the type Ia lack of H and the presence of the heavier Si. Type Ia supernovae occur in all types of galaxy: elliptical, spiral, and irregular. Because they are both bright and common, Ia supernovae have replaced cepheid variable stars for use as a standard candle.

Type Ib Supernova: These lack Si, and are rich in helium (He). In these stars hydrogen has been lost either through solar wind or interaction with another star in a binary star system. A type Ib supernova has never been seen in an elliptical galaxy.

Type Ic Supernova: Like a type Ib supernova, only the star's helium mantle has also been partially stripped away in whatever way its hydrogen mantle was. Type Ic supernovae are also not present in elliptical galaxies.

Type II Supernovae: All type II supernovae have H bands in their absorbtion or emission spectra. All of these occur only in the arms of spiral galaxies, and all are theorized to leave behind a neutron star after explosion.

Type IIb Supernova: He is dominant over H in the spectrum, though H is clearly present.

Type IIL Supernova: H is dominant over He, and the brightness drops off linearly after its peak. The L in the title is for linear.

Type IIP Supernova: H is dominant over He, and the brightness hits a three month (or so) plateau after its peak. It should be no shock that the capital P stands for plateau. SN 1987A is generally considered a type IIP, but a large faction of cosmologists contend that it was instead a IIpec.

Type IIn Supernova: These have weak or absent H absorption, and tend to be most measurable by their radio and X-ray emission. This classification was proposed in 1990 and is not universally accepted.

Type IIpec Supernova: This is a catch-all category for supernovae that have spectral hydrogen, but don't fit obey the properties of any of the above classifications. It was proposed in 1985 to take the place of three classes from the previous standard supernova classification.

Lexx 2.0: Supernova

Having stolen the Lexx and escaped from the forces of His Divine Shadow into the Dark Zone, a universe parallel to the one they lived in, our heroes Stanley Tweedle, Zev, and Kai decided to search for a home. Zev is set on finding Brunus, the home of Kai's ancestors before they moved to the Light Universe. She thinks that something there could provide a clue to bring him back to life. So she has instructed 790 to scan all planets to determine which one it might be.

The planet is of course abandoned because its inhabitants moved away over 2000 years before, but they set up stabilizers to prevent the sun from exploding and left a museum of their culture. The museum had been taken over by Poet Man (played by Tim Curry), who was left behind in the migration because he got too drunk and slept through it. So he re-recorded all the holographic messages and reprogrammed some of the equipment so he would be the one remembered in the future. There is also a strange blue star previously unknown to Kai even though he'd been taught everything about this planet.

Zev drags Kai into a room called "Burst of Life," hoping it is what she's looking for, but it turns out those who enter have their memories recorded on discs and their bodies cut in half, leaving a thin slice out of the center to hang in a gallery with the disc. Stan, bored, decides to enter a room called "love," where he is misdiagnosed as a female, thus activating Poet Man's program to have someone implanted with his sperm so his line could live on.

Meanwhile, on the Lexx, Gigerota crawls out of the depths where we thought she'd died. The Divine Predecessors convince her to bring back Stan's hand so they can control the Lexx, and in return they will take her to a planet of succulent young men she can eat. So she goes down to the planet and rescues Stan from Poet Man, only to then cut off his hand and deactivate the solar stabilizer. When she gets back to the Lexx, the Divine Predecessors tell her they need the whole Stan because his voice is also part of the control mechanism, but when she leaves they simulate his voice and get the Lexx to leave.

Back on the planet, Stan manages to reactivate the stabilizer, then goes looking for Zev and Kai. A message from the Time Prophet in the memory chamber leads him to them, and although Kai has already been cut in half, a ray of light reflected off his memory disc hits him and gives him the impetus to put himself back together and save Zev.

Gigerota has already deactivated the stabilizer again, and by the time they turn it back on, it is too late to stop the supernova. She tries to fly back to the Lexx in the moth, but it won't let her in because she ate a piece of it.

Our heroes think there is no hope left, so they gather to watch the supernova. When the time comes that it ought to happen, the sun and the blue star freeze in place, speak to our heroes, and force the Lexx to come back for them. It turns out the two stars are in love and are ready to die together, so as soon as the Lexx is out of range, they explode, and Gigerota dies a fiery death. Poet Man's machinations are all for naught, and he will exist only in the memory of our heroes.