Deadly fireworks

I've always thought it would be amazingly cool to witness a supernova.

Imagine it.  Within a few hours, a dim, ordinary-looking star increases in luminosity until it outshines every other astronomical object in the sky except the Sun and Moon.  It's visible during the day and you can read by its light at night.  It's not a blink-and-you'll-miss-it phenomenon, either; the light from the massive explosion peaks rapidly but declines slowly.  Most supernovae will be visible for months, before dimming to near-invisibility, ending as neutron stars or black holes.

There are lots of candidates for what could be the next supernova, although don't get your hopes up; most of these fall into the "some time in the next million years" category.  Yeah, it could happen tomorrow, but I wouldn't put money on it.  Still, the list is sizable, and here are five of the best possibilities:

• Betelgeuse (720 light years away, in the constellation Orion).  This one got some serious press a few months ago because it suddenly started to decrease in brightness, and astronomers wondered if this was a prelude to an explosion.  What appears to have happened is that there was turbulence in the star's core that blew a cloud of dust from its surface, obscuring the star and making it appear to dim.  So we're still waiting for this red supergiant to explode, and probably will be for a while.
• IK Pegasi (154 light years away, in the constellation Pegasus).  IK Pegasi isn't well known because at an apparent magnitude of 6, it's not visible to the naked eye, but it bears mention as the nearest serious supernova candidate.  It's a double star -- a main-sequence star and a massive white dwarf orbiting a common center of mass.  As the main-sequence star evolves, it will become a red giant, with a radius large enough that its white dwarf companion will start suctioning matter from its surface.  When the white dwarf reaches what's called the Chandrasekhar Limit -- 1.4 solar masses -- it will explode cataclysmically as a Type 1a supernova.  This will not only be spectacular but potentially dangerous -- a topic we will revisit shortly.
• VY Canis Majoris (3,820 light years away, in the constellation Canis Major).  Another star not visible to the naked eye, VY Canis Majoris is a lot more spectacular than you'd think to look at it.  It's the largest star known, with a mass fifteen times that of the Sun, and a radius so large that if you put it where the Sun is, its surface would be about at the orbit of Jupiter (so we'd be inside the star).  This "hypergiant" is one of the most luminous stars in the Milky Way, and is only dim because it's so far away.  This one is certain to go supernova, probably some time in the next 100,000 years, and the remnants will collapse into a black hole.
• Eta Carinae (7,500 light years away, in the constellation Carina).  Eta Carinae is another huge star, with a radius twenty times that of the Sun, but what makes this one stand out is its bizarre behavior.  In 1837 it suddenly brightened to being one of the five brightest stars in the night sky, then over the next sixty years faded to the point that it was only visible in binoculars.  Detailed observations have shown that it blew out a huge cloud of material in "The Great Eruption," which is now the Homunculus Nebula.  It's a unique object, which makes it hard to predict its future behavior.  What seems certain is that it'll eventually explode, but there's no telling when that might occur.

The consensus amongst astronomers, however, is that the next likely supernova probably isn't on the list -- that it will be a previously-unknown white dwarf or an unremarkable-looking red giant.  We know so little about supernovas that it's impossible to predict them with any kind of accuracy.  And while this is an exciting prospect, we'd better hope that the next supernova isn't too close.

The Homunculus Nebula with Eta Carinae at the center [Image licensed under the Creative Commons ESA/Hubble, Cosmic Fireworks in Ultraviolet Eta Carinae Nebula, CC BY 4.0]

Not only do supernovas produce a lot of light, they generate a tremendous amount of radiation of other kinds, including cosmic rays.  A close supernova could produce enough cosmic rays to wipe out the ozone layer -- leading to a huge influx of ultraviolet light from the Sun, with devastating effects.

Scarily, this may have already happened in Earth's history.  One of the lesser-known mass extinctions occurred at the end of the Devonian Period, 359 million years ago.  Because it is poorly understood, and was dwarfed by the cataclysmic Permian-Triassic Extinction a little over a hundred million years later, it's not one you tend to read about in the paleontology-for-the-layperson books.  Even so, it was pretty significant, wiping out 19% of known families and 50% of known genera, including placoderms (armored fish), cystoids (a relative of the starfish), and graptolites (colonial animals not closely related to any living species).  Most striking were the collapse of reef-forming corals -- reefs didn't begin to form again on any significant scale until the Mesozoic Era, almost two hundred million years later -- and the near-complete wipeout of vertebrates.  The latter left no vertebrate species over a meter long (most of them were under ten centimeters), and again, it was millions of years before any kind of recovery took place.

Fortunately for us, it eventually did, because we're talking about our ancestors, here.

The cause of this catastrophe has been a matter of speculation, but a team led by Brian Fields, astrophysicist at the University of Illinois, may have found a smoking gun.  In a paper this week in Proceedings of the National Academy of Sciences, we find out that the most likely cause for the End-Devonian Extinction is a nearby supernova that caused the collapse of the ozone layer, leading to the Earth's surface being scorched by ultraviolet light.  This triggered a massive die-off of plants -- which had only recently colonized the land -- and worldwide anoxia.  

The result?  A mass extinction that hit just about every taxon known.

The idea that a supernova might have been to blame for the End-Devonian Extinction came from the presence of hundreds of thousands of plant spores in sedimentary rock layers that showed evidence of what appeared to be radiation damage.  This isn't conclusive, of course; the Fields et al. team is up front that this is only a working hypothesis.  What they'll be looking for next is isotopes of elements in those same rock layers that are only produced by bombardment with radiation, such as plutonium-244 and samarium-146.  "When you see green bananas in Illinois, you know they are fresh, and you know they did not grow here," Fields said, in an interview in Science Daily.  "Like bananas, Pu-244 and Sm-146 decay over time.  So if we find these radioisotopes on Earth today, we know they are fresh and not from here -- the green bananas of the isotope world -- and thus the smoking guns of a nearby supernova."

So as much as I'd love to witness a supernova in my lifetime, it'd be nice if it was one well outside of the terrifyingly-named "kill zone" (thought to be about 25 light years or so).  And chances are, there's nothing inside that radius we need to worry about.  If any of the known supernova candidates explode, we'll almost certainly be able to enjoy the fireworks from a safe distance.

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Fan of true crime stories?  This week's Skeptophilia book recommendation of the week is for you.

In The Poisoner's Handbook:Murder and the Birth of Forensic Medicine in Jazz Age New York, by Deborah Blum, you'll find out about how forensic science got off the ground -- through the efforts of two scientists, Charles Norris and Alexander Gettler, who took on the corruption-ridden law enforcement offices of Tammany Hall in order to stop people from literally getting away with murder.

In a book that reads more like a crime thriller than it does history, Blum takes us along with Norris and Gettler as they turned crime detection into a true science, resulting in hundreds of people being brought to justice for what would otherwise have been unsolved murders.  In Blum's hands, it's a fast, brilliant read -- if you're a fan of CSI, Forensics Files, and Bones, get a copy of The Poisoner's Handbook, you won't be able to put it down.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Listening to Cassandra

I like to think of myself as basically an optimistic person, and someone who looks for the best in my fellow humans.  But there are times that I think that a gigantic meteor strike might, all things considered, be the best option at this point.

Those times usually occur when people persist in a behavior that is known, for absolute certain, to be self-destructive.  And surprisingly enough, I'm not talking about climate change here, and our determination to keep burning fossil fuels despite the near-universal consensus amongst climatologists that this practice is drastically altering the Earth's climate.  What I'm referring to is two stories that both broke day before yesterday, and that leave me shaking my head and feeling like whatever happens to our species, we kind of deserve it.

The first, and more local, example of this phenomenon was described in an article in NPR Online, the title of which sums up the problem succinctly: "Levees Make Mississippi River Floods Worse, But We Keep Building Them."  The article, written by Rebecca Hersher, describes the ongoing catastrophe along the Mississippi River, wherein every single year there are destructive, often deadly, floods.

Here's a capsule summary of the problem.

Before the 20th century, the Mississippi had a habit shared by many large rivers; overflowing its banks during the rainy season.  This phenomenon had a couple of effects.  First, it brought the silt picked up along the way out of the river basin, depositing it on land.  Second, it meant that regular, minor floods -- the sort of thing one can prepare for and cope with -- were kind of a way of life.  (Why, for example, my uncle's fishing cabin in Henderson, Louisiana was built on stilts.)

But when the population started both to grow and urbanize, these floods were "mitigated" -- by installing a system of levees and spillways to "tame the river."  Mostly constructed in the 1930s and 1940s by the Army Corps of Engineers, the (well-meant) attempt to stop people from being flooded out every year had two unexpected effects.

One is that the silt that would have been deposited to either side of the river now was kept in the river itself.  This left only two places it could go -- deposited onto the river bottom, or flushed out into the Gulf at the delta.  The first raised the riverbed, and the second raised the mouth of the river; both of these had the effect of pushing the level of the river upwards.  Simultaneously, the silt that was in the river didn't end up on land, and the land itself started to subside.

Rising river + sinking land = a need for bigger levees.  So the levees were raised, making the problem worse -- and so on and so forth.  I still vividly remember being in New Orleans and walking along a footpath at the base of a levee along the Mississippi -- and looking up to see the top of a shrimp boat going past, about thirty feet above my head.

The 17th Street Canal in Metairie, Louisiana [Image licensed under the Creative Commons No machine-readable author provided. Infrogmation assumed (based on copyright claims)., MetOutletCanalDogwalkerBreechBkgrd, CC BY 2.5]

The second unexpected effect follows directly from the first.  If you build higher levees, the water level rises, so when the levees break, you don't have a minor flood, you have a catastrophic one.  This, of course, is what happened in New Orleans in 2005 during Hurricane Katrina, but it's inevitable that it'll happen again in the near future.

The kicker?  We've known about this problem for ages.  In 1989 John McPhee wrote an incredible book on the topic, called The Control of Nature, in which he laid out the problem clearly.  And what have we done differently since then?

Nada.  Build more levees.  Pretend we know what we're doing, and that nature won't ultimately have the last word.

The other example of humans doing idiotic self-destructive stuff revolves around something I always mention in my biology classes as the time our species did something right; the 1989 Montreal Protocol that banned the production or use of chlorofluorocarbons, a class of chemicals used as coolants and propellants that were thought to be harmless but turned out to destroy the atmosphere's protective ozone layer.  Almost all the nations on Earth signed on -- surely one of the only times in humanity's history where damn near everyone has agreed on something.

Or so we thought.  Since 2012, there's been a sudden and mysterious uptick in the amount of CFCs in the atmosphere -- up, at one estimate, by 25%.  As of the time of this writing, no one's quite sure where it's coming from.  Up until now, the CFC levels have been gradually falling (and ozone hole gradually diminishing) as the CFCs from before 1989 have broken down -- but it appears that we're not done with this problem yet.

"It is not clear why any country would want to start to produce, and inadvertently release, CFC-11, when cost-effective substitutes have been available for a long while," said NASA scientist Robert Watson, who led the studies thirty years ago that led to CFCs being banned.  "It is therefore imperative that this finding be discussed at the next Ministerial meeting of Governments given recovery of the ozone layer is dependent on all countries complying with the Montreal Protocol (and its adjustments and amendments) with emissions globally dropping to zero."

Durwood Zaelke, founder of the Institute for Governance and Sustainable Development and an expert on the Montreal Protocol, was more unequivocal still.  "Somebody's cheating.  There’s some slight possibility there’s an unintentional release, but… they make it clear there’s strong evidence this is actually being produced...  This treaty cannot afford not to follow its tradition and keep its compliance record...  They’re going to find the culprits.  This insults everybody who’s worked on this for the last 30 years.  That’s a tough group of people."

So at least we have some folks who are on the case.  What kind of power to compel they will turn out to have, once the culprits are identified, remains to be seen.  And here in the United States, we've seen in the past year a weakening of damn near every environmental regulation we have, in favor of corporate profit and short-term expediency.  So how much help our government will be is questionable.

I'm holding out some hope that at least by publicizing these issues, people are beginning to wise up.  However, our inaction on climate change -- a phenomenon we've known about since the 1890s -- doesn't bode well.  Mostly what has happened is that the people who are brave enough to sound the warning have turned into Cassandras -- prophets who are cursed to be correct, but no one believes them.

As for me, I'm trying to maintain my optimism, but after reading these two articles, right now mostly what I'm doing is scanning the skies looking for the incoming meteor.

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This week's book recommendation is a brilliant overview of cognitive biases and logical fallacies, Rolf Dobelli's The Art of Thinking Clearly.  If you're interested in critical thinking, it's a must-read; and even folks well-versed in the ins and outs of skepticism will learn something from Dobelli's crystal-clear prose.