'What's the blast radius of a supernova?'

StilLearning

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#1
What's the blast radius of a supernova.jpg


Hi there everyone, thanks in advance for your thoughts. Those of you coming at this from the thread ‘fighting fire in microgravity’ will know that my current (much, much, stalled) project is a document to help authors who want to write some (just some!) realistic physics into their science fiction. I do this in-person for a few authors already as I've got good qualifications in physics and space technology, and my day job is a physics tutor.

Based on previous feedback I've put up parts of chapter 2 here: The factsheet and a sample of the science section. The full chapter contains more detail on how super nova happen, a ‘what does this mean for a writer’ section that focusses more on descriptions and experiences, and a list of the sources I’ve used. I'm looking for any and all feedback, and if anyone wants to see more of a section, or the sources list, feel free to PM me.

Many thanks again!

1.2: What’s a supernova’s blast radius?


Factsheet:

  • Supernova candidates are easy to spot but unpredictable. They come in different types, but by far the most common are:
    • The corpse of a star that steals fuel from a living companion, reignites itself, and then becomes unstable and explodes (Type 1a).
    • A ‘classic’ big, old, star that becomes unstable due to age and explodes (Type 2).
  • Type 2 supernova give off a massive pulse of subatomic particles called neutrinos about 3 hours before they blow. Type 1a are less well understood.
  • A supernova fireball is full of rapidly decaying radioactive elements – so it actually keeps getting hotter for weeks after the explosion. It expands at around 10% of lightspeed (30,000 km / sec.
  • An Earth like planet would be reduced to a cinder and thrown into interstellar space, even if it were thousands of times further from its star than Earth is from the Sun. Further out…
    • At 2 to 5 light years: A bright blue point of light appears in the sky, growing to sun-like brightness over 14 to 30 days. Effects include increased surface temperatures, wildfires, extreme weather, melting of ice caps, lethal radiation levels, total ozone layer loss, and chemical changes to the atmosphere.
    • At 20 to 50 light years: The blue light outshines a full moon a thousand times. Radiation levels cause cancers, sterility, birth defects, massive ozone layer loss ( 50% +) , high altitude nitrous oxide smog, increased cloud cover, loss of satellite networks, and lethal radiation dose to astronauts. Other possible effects include an worldwide lightning storms and dementia in humans and animals.
    • At 100 to 250 light years: The blue light is comparable to full moon, and radiation causes a measurable spike in cancer and birth defect rates. Other effects include satellite disruption similar to the worst solar storms, increased frequency of lightning strikes, erratic behaviour and memory loss in mammals, and disruption to circadian rhythms.
  • A world within 20 light years of the supernova may be engulfed in the expanding cloud of radioactive debris. This will cause more long term effects, including global cooling and an increase in background radiation levels.


The Science:

‘What’s the lethal range of a supernova’ isn’t such a simple question, for a few reasons. The main one is that ‘supernova’ is a term covering a bunch of different kinds of explosions that have one thing in common: Unimaginable size and power….

[the first few paragraphs give a rough run down of how the two most common types of supernova occur, and there’s a list and descriptions of the rarer, exotic, types like hypernova at the end of the chapter]

….that’s what supernova are. But just how far do you need to run to survive?

Thousands of times further away than the Sun from Earth:

This is a good range to start with since, because they are so much bigger and hotter, it’s the kind of distance the habitable zone of a supernova candidate star will be at – although such stars are notoriously badly behaved, so how habitable that would be to humans is debateable. In any case, despite all that extra distance, a planet in the habitable zone would suffer what astrophysicists refer to as ‘massive physical damage’ . In other words: Its surface would be heated until the rock vaporised, then it’s new evaporated rock atmosphere would get stripped away by pummelling by waves of plasma, peeling the planet.

Think a big gobstopper getting the full blast of a flamethrower.

A much shrunken remnant might be left, depending on the specifics of the blast, but for all practical purposes the planet joins Alderaan in the planetary afterlife. Without the gravity of the destroyed central star any remains would drift into interstellar space – so weeks of nuclear fire would be followed by cosmic night and eternal cold.

One to five light years:

With a light year (for reference, one light year is roughly 63000 times the Earth-Sun distance) of range the planet should survive – as in ‘the rocks won't actually melt underfoot’. But even with a two light year gap that’s about as good as the good news gets – the immediate effects of a supernova at that distance are described in the literature as ‘sterilising’: Starting as a purple-blue pinpoint, many times brighter than a full moon, it might take over three weeks to hit its peak, Sun-like, levels of brightness. But the majority of the supernova’s energy isn’t in heat and light but high energy gamma rays, X rays, and high speed sub atomic particles. As the intensity of the blue point grows, the high energy gamma rays would turn the ozone layer into a worldwide smog of nitrous oxide. Truly zero ozone means severe sunburn after 10 minutes of exposure, and if sunburn doesn’t sound so bad, know that we are talking a true ‘clinically severe’ sunburn: Blisters covering large areas, excruciating pain, swelling (especially the face and lips), a blinding headache, dizziness, confusion, disorientation, fever and chills, nausea, vomiting, and dehydration.

Surface radiation levels will rise until standing outside would be the equivalent, radiation dosage wise, of being within a mile of a 10 kiloton nuke - and this would go on for weeks. At its peak standing under the supernova light would mean burns, cancer, sterility, and birth defects. Exactly how much hotter, in the degrees Celsius or Fahrenheit sense, the surface would get depends on exact range and size of the blast – but, given that current climate change fears are based on an overall temperature increase of less than 7 degrees Celsius, imagine the effects of a worldwide 20% temperature increase that lasted for months: Wildfires, and melting of ice caps, massive changes to weather patterns and ocean currents would be the tip of the melting iceberg. Those are major immediate effects*.

This doesn't end with the immediate effects.

Once the supernova has faded there would be a new feature in the sky, above the clouds of smog: Where once there was the brightest, bluest star in the sky would be a nebula - a cloud of superheated plasma and radioisotope bearing dust, expanding at around 10% of light speed. It’d take decades or even centuries to engulf a nearby world, but when it did… Well, an Earth like planet is protected from the natural space radiation by two magnetic fields: Its sun’s, which extends well beyond Pluto in our solar system, and its own smaller but more intense one. As the nebula engulfed a luckless solar system it would collapse the sun’s bubble, exposing a planet in the habitable zone to both the radiation of space and the radiation of the cloud itself. Food chains would collapse as radiation-vulnerable species die off, and the cloud, which is mainly ionised hydrogen and helium, mixes with the upper atmosphere to produce water vapour. The influx of water vapour would build, increasing cloud cover – an effect compounded by interstellar radiation, which has been shown to trigger excessive cloud formation - triggering an ice age. A ‘nebula winter’ as opposed to a nuclear one.

So, at one to five lightyears, your planet survives physically but faces environmental Armageddon - twice.

* There are more, but we’ll meet those properly at longer ranges where they aren’t be swamped by the direct effects.

Twenty to fifty light years:

Here the supernova’s light will be ‘only’ a thousand of times brighter than a full moon, and sheer radiation levels aren’t enough to kill - but their secondary effects can: The planet’s ozone layer will be skinned like a grape in a sandstorm, until being outside during the day would mean severe sunburn within twenty minutes. UV sensitive organisms, especially the ocean algae and plankton that form the base of many food chains, would be devastated, causing a ripple effect of starvation. There would be stranger effects as well, including massive lightning storms: High energy particles…
 
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Robert Zwilling

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#2
That's not encouraging. Suppose a large planet somewhat far from the event had an orbit that was at a right angle to the direction of the oncoming radiation and it's axis was in the horizontal plane facing the oncoming radiation and the system it was in was on a long enough arc so it seemingly continued to face the oncoming radiation. Would the polar area that was facing away from the radiation be a safe place or would the radiation wrap around the planet? How much shielding could a large planet provide?
 

StilLearning

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#3
Fair question - I'll do some more reading as that sounds like a good scenario to address. The first thought that comes to my mind is 'a lot', but the second is that some of the supernova's effects will produce stuff - like radioactive particles or smog - that can be carried by the atmosphere, so not total protection. And the downside is that the other hemisphere is getting a double, non stop, dose of the direct effects. You also still have the possibility of being engulfed by the expanding nebula cloud, which will just flow around the planet (if it's close enough for that to happen). If you're going for shielding then a big, airless, rock like Mercury might be a better bet than an earth like world - I've restricted the scenario I'm looking at to Earth like worlds as that seems most likely to be relevant to story telling scenarios, and to keep things to a reasonable length - but outside of the 'everything fries' zone of the supernova's own solar system a spaceship could look for such a planet and put down in an appropriate spot to ride things out.
 
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Brian G Turner

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#6
Going back to the piece for Critique - I think the set-up of a factsheet, followed by a longer explanation, works great as a format.

Honestly, if you put a whole series like this into a book, called it something like "Science for Science Fiction Writers", I can see it selling well. I'd definitely buy a copy for reference. :)
 

Joshua Jones

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#7
I would buy it as well, and agree that there would be a pretty good market for it. I think many SF writers want their stories to be at least plausible, but don't know where to start in making that happen, or struggle with the science part.

I also love your format; it gives a good summary and then a breakdown in a senario, which is also well written. This also confirms, in my mind, the previous critique that you didn't need the fictionalized portion with the science. Your descriptions inspire the imagination enough that, at least for me, I am already filling in the gaps with characters, tech, and events.

So, all that to say, exceptional job with this! Please put out a press release on here when you have a book of these together; I'll be your first customer.
 

StilLearning

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#8
Thanks for the feedback everyone, that's a great reaction to recieve. Thanks also to whoever added the image to the post! OK, you'll have to excuse me then - I have another twenty chapers that are at the first or second draft stage, so I need to get working...

John F
 

StilLearning

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#10
Have you been reading 'What If...?' by the author of XKCD, Al Jackson? That's the only place I've ever seen the numbers for lethality of neutrino radiation come up :D ! [EDIT: I just followed you link and realised you did, sorry for not doing that sooner Al Jackson - but I can still recommend XKCD and 'what if...?' as a Christmas present, it's got even stranger stuff than that in! END EDIT] It's worth noting that if you were that close to a supernova progenator star, even if it was healthy and not exploding, you'd still be vaporised - they are big, hot stars. I used the research you've linked as one of my sources, so I can thouroughly recommend it to anyone researching this topic - as it mentions the 50 ly kill zone is still something of a 'best guess' and isn't a hard edge, so don't think you're safe at 51 light years. or even 61. It also mentions some of the weirder effects at greater ranges, like a huge jump in lightening storms that trigger wildfires.

One thing it does skip over a bit is how the gamma rays are damaging within that approx 50 ly distance. It's not, generally*, the direct effects of gamma rays on living things but on the atmosphere of the planet - the ozone layer is totally converted into a toxic nitrous oxide smog, allowing lethal amounts of UV in. The direct effects on large mammals like humans are very bad - I think I mentioned the effects of exposure to unfiltered UV on human skin in the 2 to 5 light year section and it's also true that ozone loss would be total much further out - but many UV vulnerable species that make up the bases of various food chains are much more sensitve. Where smarter, more mobile, creatures might hope to adapt somehow (e.g. by changing their behavoir to become nocturnal) many simpler life cannot and just gets wiped out, causing a ripple effect of starvation through the food webs. If anyone wants to investigate a bit further here're some links on how the radiation from a nearby supernova would (and, it's thought, has in the deep past) damaged Earth's atmosphere and led to mass extinctions. They're a bit older, so take the ranges they give with a pinch of salt, but they give a good idea of the basic processes:

Ozone Depletion from Nearby Supernovae - IOPscience

[hep-ph/9303206] Could a nearby supernova explosion have caused a mass extinction? (publicly available preprint version) and Could a nearby supernova explosion have caused a mass extinction? (final harvard version, for those with access.

*There are rarer types of supernova that have greater radiation intensity, or radiation that is focussed unevenly, and they will kill via direct effects on life out to hundreds of light years. And there is one star, predicted to possibly die in such a way, that may just be close enough to catch Earth. Isn't astronomy relaxing?
 
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Al Jackson

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#11
Have you been reading 'What If...?' by the author of XKCD, Al Jackson? That's the only place I've ever seen the numbers for lethality of neutrino radiation come up :D ! [EDIT: I just followed you link and realised you did, sorry for not doing that sooner
Yeah I have been following XKCD for years. Actually there is a calculation of the lethal dose of neutrinos that Munroe must have read , it was on the web probably 25 years ago , I used to have but don't know where it is now.
There is an interesting paper about the probability of sterilization of the Earth , seems it is low:

The Resilience of Life to Astrophysical Events

Neutrinos and supernova are a fascinating story, it was not known until the early 1960's that it is the absorption of neutrinos in stellar collapse that blew the contracting envelope off!
 

StilLearning

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#12
'Death by whisper' :D
I think Munroe asked someone who'd read that original calculation then, I'm fairly sure in the book he mentions asking an astrophysicist who specialises in supernova. From the perspective of writing, the neutrino's given off by the core collapse are interesting as they (mostly) pass straight through the stars outer layers almost instantly , while the pressure/shock wave is two or three hours working its to the surface, so in effect they give you a few meagre hours of warning. You're well read on this Sir, I salute a fellow astronomy fan! :D
 
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#14
Sorry for the thread necromancy, but i thought folks might find this interesting: A new paper suggests that a delayed-action pulse of muon radiation may be able to kill by causing an epidemic of cancers in larger animals (they literally make a better target for the radiation), even at 150 light years. The delayed muon pulse would hit about 100 years after the main effects of the supernova, and could have been deadly even through tens of meters of water, wiping out large ocean mammals. Definitely getting a paragraph.
Paper: [1712.09367] Muon Radiation Dose and Marine Megafaunal Extinction at the end-Pliocene Supernova
Press release: Did supernovae kill off marine life at dawn of Pleistocene?
 

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