Requiem for a dead planet

If I had to pick my favorite episode of Star Trek: The Next Generation, the clear winner would be "The Inner Light."  Some classic episodes like "Darmok," "Frames of Mind," "Yesterday's Enterprise," "The Offspring," "Cause and Effect," "Remember Me," "Time's Arrow," "The Chase," and "Best of Both Worlds" would be some stiff competition, but "The Inner Light" not only has a beautiful story, but a deep, heartwrenching bittersweetness, made even more poignant by a tour-de-force performance by Patrick Stewart as Captain Jean-Luc Picard.

If you've not seen it, the plot revolves around the Enterprise encountering a huge space station of some kind, of apparent antiquity, and in the course of examining it, it zaps Captain Picard and renders him unconscious.  What his crew doesn't know is that it's dropped him into a dream where he's not a spaceship captain but an ordinary guy named Kamin, who has a wife and children and a job as a scientist trying to figure out what to do about the effect of his planet's sun, which has increased in intensity and is threatening devastating drought and famine.

As Kamin, he lives for forty years, watching his children grow up, living through the grief of his wife's death and the death of a dear friend, and ultimately grows old without ever finding a solution to his planet's dire circumstances.  All the while, the real Captain Picard is being subjected to ongoing interventions by Dr. Crusher to determine what's keeping him unconscious, and ultimately unsuccessful attempts to bring him out of it.  In the end, which makes me ugly cry every damn time I watch it, Kamin lives to watch the launch of an archive of his race's combined knowledge, realizing that the sun's increase in intensity is leading up to a nova that will destroy the planet, and that their civilization is doomed.  It is, in fact, the same archive that the Enterprise happened upon, and which captured Picard's consciousness, so that someone at least would understand what the civilization was like before it was wiped out tens of thousands of years earlier.

"Live now," Kamin says to his daughter, Maribol.  "Make now always the most precious time.  Now will never come again."

And with that, Picard awakens, to find he has accumulated four decades of memories in the space of about a half-hour, an experience that leaves a permanent mark not only on his mind, but his heart.

*brief pause to stop bawling into my handkerchief*

I was immediately reminded of "The Inner Light" by a paper I stumbled across in Nature Astronomy, called, "Alkali Metals in White Dwarf Atmospheres as Tracers of Ancient Planetary Crusts."  This study, led by astrophysicist Mark Hollands of the University of Warwick, did spectroscopic analysis of the light from four white dwarf stars, which are the remnants of stellar cores left behind when Sun-like stars go nova as their hydrogen fuel runs out at the end of their lives.  In the process, they vaporize any planets that were in orbit around them, and the dust and debris from those planets accretes into the white dwarf's atmosphere, where it's detectable by its specific spectral lines.

In other words: the four white dwarfs in the study had rocky, Earth-like planets at some point in their past.

"In one case, we are looking at planet formation around a star that was formed in the Galactic halo, 11-12.5 billion years ago, hence it must be one of the oldest planetary systems known so far," said study co-author Pier-Emmanuel Tremblay, in an interview in Science Daily.  "Another of these systems formed around a short-lived star that was initially more than four times the mass of the Sun, a record-breaking discovery delivering important constraints on how fast planets can form around their host stars."

This brings up a few considerations, one of which has to do with the number of Earth-like planets out there.  (Nota bene: by "Earth-like" I'm not referring to temperature and surface conditions, but simply that they're relatively small, with a rocky crust and a metallic core.  Whether they have Earth-like conditions is another consideration entirely, which has to do with the host star's intrinsic luminosity and the distance at which the planet revolves around it.)  In the famous Drake equation, which is a way to come up with an estimate of the number of intelligent civilizations in the universe, one of the big unknowns until recently was how many stars hosted Earth-like planets; in the last fifteen years, we've come to understand that the answer seems to be "most of them."  Planets are the rule, not the exception, and as we've become better and better at detecting exoplanets, we find them pretty much everywhere we look.

When I read the Hollands et al. paper, I immediately began wondering what the planets around the white dwarfs had been like before they got flash-fried as their suns went nova.  Did they harbor life?  It's possible, although considering that these started out as larger stars than our Sun, they had shorter lives and therefore less time for life to form, much less to develop into a complex and intelligent civilization.  And, of course, at this point there's no way to tell.  Any living thing on one of those planets is long since vaporized along with most of the planet it resided on, lost forever to the ongoing evolution of the cosmos.

If that's not gloomy enough, it bears mention that this is the Earth's ultimate fate, as well.  It's not anything to worry about (not that worry would help in any case) -- this eventuality is billions of years in the future.  But once the Sun exhausts its supply of hydrogen, it will balloon out into a red giant, engulfing the inner three planets and possibly Mars as well, then blow off its outer atmosphere (that explosion is the "nova" part), leaving its exposed core as a white dwarf, slowly cooling as it radiates its heat out into space.

Whether by that time we'll have decided to send our collective knowledge out into space as an interstellar archive, I don't know.  In a way, we already have, albeit on a smaller scale than Kamin's people did; Voyager 2 carries the famous "golden record" that contains information about humanity, our scientific knowledge, and recordings of human voices, languages, and music, there to be decoded by any technological civilization that stumbles upon it.  (It's a little mind-boggling to realize that in the 48 years since Voyager 2 was launched, it has traveled about 20,000,000,000 kilometers, so is well outside the perimeter of the Solar System; and that sounds impressive until you realize that's only 16.6 light hours away, and the nearest star is 4.3 light years from us.)

So anyhow, those are my elegiac thoughts on this August morning.  Dead planets, dying stars, and the remnants of lost civilizations.  Sorry to be a downer. If all this makes you feel low, watch "The Inner Light" and have yourself a good cry.  It'll make you feel better.

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Advance notice

Today's science news involves something called the Chandrasekhar Limit.

Stars live for most of their lives in an equilibrium between two forces; the inward pull of their own gravity, and the outward pressure from the heat generated by fusion in their cores.  As long as there is plenty of hydrogen left to power fusion, those forces are equal and opposing, and the star is stable.

When the hydrogen is depleted, though, the balance shifts.  The core cools, and the gravitational collapse resumes.  This, however, heats things up -- recall the "ideal gas law" from high school chemistry, and that temperature and pressure are inversely proportional -- and the star begins to fuse the helium "ash" left over from hydrogen burning into carbon.  Eventually that runs out, too, and the process repeats -- carbon to oxygen and silicon, and on up the scale until finally it gets to iron.  At that point, there's nowhere to go; after iron, fusion begins to be an endothermic (energy-requiring) reaction, and the star is pretty much out of gas.

What happens at this point depends on one thing: the star's initial mass.  For a star the size of the Sun, the later stages liberate enough energy to balloon the outer atmosphere into a red giant, and when the final collapse happens, it blows off that atmosphere into a wispy bubble called a planetary nebula.  

The Cat's Eye Nebula (NGC 6543) [Image is in the Public Domain courtesy of NASA]

What's left at the center is the exposed core of the star -- a white dwarf, still glowing from its residual heat.  It doesn't collapse further because its mass is held up by electron degeneracy pressure -- the resistance of electrons to occupying the same quantum state, something known as the Pauli Exclusion Principle.  But it's no longer capable of fusion, so it will simply cool and darken over the next few billion years.

For heavier stars -- between two and ten times the mass of the Sun -- electron degeneracy is not sufficient to halt the collapse.  The electrons are forced into the nuclei of the atoms, and what's left is a densely-packed glob of neutrons called, appropriately enough, a neutron star.  So much energy is liberated by this process that the result is a supernova; the atmosphere is blown away completely, and the collapsed core, which is made of matter dense enough that a teaspoonful would weigh as much as Mount Everest, spins faster and faster because of the Law of Conservation of Angular Momentum, in some cases reaching speeds of thirty rotations per second.  This whirling stellar core is called a pulsar.

For stars even larger than that, though, the pressure of neutron star matter isn't enough to stop the gravitational collapse.  In fact, nothing is.  The supernova and subsequent collapse lead to the formation of a singularity -- a black hole.

So that's the general scheme of things, but keep in mind that this is the simplest case.  Like just about everything in science, reality is more complex.

Suppose you had an ordinary star like the Sun, but it was in a binary system.  The Sun-like star reaches the end of its life as a white dwarf, as per the above description.  Its partner, though, is still in stable middle age.  If it's close enough, the dense, compact white dwarf will begin to funnel material away from its partner, siphoning off the outer atmosphere, and -- this is the significant part -- gaining mass in the process.

Artist's conception of the white dwarf/main sequence binary AE Aquarii [Image is in the Public Domain courtesy of NASA]

The brilliant Indian physicist Subrahmanyan Chandrasekhar figured out that this process can only go on so long -- eventually the white dwarf gains enough mass that its gravity exceeds the outward pressure from electron degeneracy.  At a mass of 1.4 times that of the Sun -- the Chandrasekhar Limit -- the threshold is reached, and the result is a sudden and extremely violent collapse and explosion called a type 1a supernova.  This is one of the most energetic events known -- in a few seconds, it liberates 10^44 Joules of energy (that's 1, followed by 44 zeroes).

So this is why I got kind of excited when I read a paper in Nature Astronomy about a binary star system only 150 light years away made of two white dwarf stars, which are spiraling inward and will eventually collide.

Because that would be the type 1a supernova to end all type 1a supernovas, wouldn't it?  No gradual addition of little bits of mass at a time until you pass the Chandrasekhar Limit; just a horrific, violent collision.  And 150 light years is close enough that it will be a hell of a fireworks show.  Estimates are that it will be ten times brighter than the full Moon.  But at that distance, it won't endanger life on Earth, so it'll be the ideal situation -- a safe, but spectacular, event.

The two stars are currently orbiting their common center of mass at a distance of about one-sixtieth of that between the Earth and the Sun, completing an orbit every fourteen hours.  Immediately before collision, that orbital period will have dropped to the frantic pace of one revolution every thirty seconds.  After that...

... BOOM.

But this was the point where I started thinking, "Hang on a moment."  Conservation of energy laws suggest that to go from a fourteen-hour orbit with a radius of around 2.5 million kilometers, to a thirty-second orbit with a radius of close to zero, would require an enormous loss of energy from the system.  That kind of energy loss doesn't happen quickly.  So how long will this process take?

And there, in the paper, I found it.

This spectacular supernova isn't going to happen for another 23 billion years.

This was my expression upon reading this:

I don't know about you, but even in my most optimistic moments I don't think I'm going to live for another 23 billion years.  So this whole thing gives new meaning to the phrase "advance notice."

You know, I really think y'all astrophysicists need to step up your game, here.  You get our hopes up, and then say, "Well, of course, you know, astronomical time scales..."  Hell, I've been waiting for Betelgeuse to blow up since I was like fifteen years old.  Isn't fifty years astronomical enough for you?

And now, I find out that this amazing new discovery of two madly-whirling white dwarf stars on an unavoidable collision course is going to take even longer.  To which I say: phooey.

I know your priority isn't to entertain laypeople, but c'mon, have a heart.  Down here all we have to keep our attention is the ongoing fall of civilization, and that only gets you so far.  Back in the day, stuff like comets and supernovas and whatnot were considered signs and portents, and were a wonderful diversion from our ancestors' other occupations, such as starving, dying of the plague, and being tortured to death by the Inquisition.  Don't you think we deserve a reason to look up, too?  In every sense of the phrase?

So let's get a move on, astrophysicists.  Find us some imminent stellar hijinks to watch.  I'll allow for some time in the next few months.  A year at most.  I think that's quite generous, really.

And if you come up with something good, I might even forgive you for getting my hopes up about something amazing that won't happen for another 23 billion years.

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Requiem for a dead planet

If I had to pick my favorite episode of Star Trek: The Next Generation, the clear winner would be "The Inner Light."  Some classic episodes like "Darmok," "Frames of Mind," "Remember Me," "Time's Arrow," "The Chase," and "Best of Both Worlds" would be up there in the top ten, but "The Inner Light" not only has a beautiful story, but a deep, heartwrenching bittersweetness, made even more poignant by a tour-de-force performance by Patrick Stewart as Captain Jean-Luc Picard.

If you've not seen it, the plot revolves around the Enterprise encountering a huge space station of some kind, of apparent antiquity, and in the course of examining it, it zaps Captain Picard and renders him unconscious.  What his crew doesn't know is that it's dropped him into a dream where he's not a spaceship captain but an ordinary guy named Kamin, who has a wife and children and a job as a scientist trying to figure out what to do about the effect of his planet's sun, which has increased in intensity and is threatening devastating drought and famine.

As Kamin, he lives for forty years, watching his children grow up, living through the grief of his wife's death and the death of a dear friend, and ultimately grows old without ever finding a solution to his planet's dire circumstances.  All the while, the real Captain Picard is being subjected to ongoing interventions by Dr. Crusher to determine what's keeping him unconscious, and ultimately unsuccessful attempts to bring him out of it.  In the end, which makes me ugly cry every damn time I watch it, Kamin lives to watch the launch of an archive of his race's combined knowledge, realizing that the sun's increase in intensity is leading up to a nova that will destroy the planet, and that their civilization is doomed.  It is, in fact, the same archive that the Enterprise happened upon, and which captured Picard's consciousness, so that someone at least would understand what the civilization was like before it was wiped out tens of thousands of years earlier.

"Live now," Kamin says.  "Make now always the most precious time.  Now will never come again."

And with that, Picard awakens, to find he has accumulated four decades of memories in the space of about a half-hour, an experience that leaves a permanent mark not only on his mind, but his heart.

*brief pause to stop bawling into my handkerchief*

I was immediately reminded of "The Inner Light" by a paper this week in Nature Astronomy, called, "Alkali Metals in White Dwarf Atmospheres as Tracers of Ancient Planetary Crusts."  This study, led by astrophysicist Mark Hollands of the University of Warwick, did spectroscopic analysis of the light from four white dwarf stars, which are the remnants of stellar cores left behind when Sun-like stars go nova as their hydrogen fuel runs out at the end of their lives.  In the process, they vaporize any planets that were in orbit around them, and the dust and debris from those planets accretes into the white dwarf's atmosphere, where it's detectable by its specific spectral lines.

In other words: the four white dwarfs in the study had rocky, Earth-like planets at some point in their past.

"In one case, we are looking at planet formation around a star that was formed in the Galactic halo, 11-12.5 billion years ago, hence it must be one of the oldest planetary systems known so far," said study co-author Pier-Emmanuel Tremblay, in an interview in Science Daily.  "Another of these systems formed around a short-lived star that was initially more than four times the mass of the Sun, a record-breaking discovery delivering important constraints on how fast planets can form around their host stars."

This brings up a few considerations, one of which has to do with the number of Earth-like planets out there.  (Nota bene: by "Earth-like" I'm not referring to temperature and surface conditions, but simply that they're relatively small, with a rocky crust and a metallic core.  Whether they have Earth-like conditions is another consideration entirely, which has to do with the host star's intrinsic luminosity and the distance at which the planet revolves around it.)  In the famous Drake equation, which is a way to come up with an estimate of the number of intelligent civilizations in the universe, one of the big unknowns until recently was how many stars hosted Earth-like planets; in the last ten years, we've come to understand that the answer seems to be "most of them."  Planets are the rule, not the exception, and as we've become better and better at detecting exoplanets, we find them pretty much everywhere we look.

When I read the Hollands et al. paper, I immediately began wondering what the planets around the white dwarfs had been like before they got flash-fried as their suns went nova.  Did they harbor life?  It's possible, although considering that these started out as larger stars than our Sun, they had shorter lives and therefore less time for life to form, much less to develop into a complex and intelligent civilization.  And, of course, at this point there's no way to tell.  Any living thing on one of those planets is long since vaporized along with most of the planet it resided on, lost forever to the ongoing evolution of the cosmos.

If that's not gloomy enough, it bears mention that this is the Earth's ultimate fate, as well.  It's not anything to worry about (not that worry would help in any case) -- this eventuality is billions of years in the future.  But once the Sun exhausts its supply of hydrogen, it will balloon out into a red giant, engulfing the inner three planets and possibly Mars as well, then blow off its outer atmosphere (that explosion is the "nova" part), leaving its exposed core as a white dwarf, slowly cooling as it radiates its heat out into space.

Whether by that time we'll have decided to send our collective knowledge out into space as an interstellar archive, I don't know.  In a way, we already have, albeit on a smaller scale than Kamin's people did; Voyager 2 carries the famous "golden record" that contains information about humanity, our scientific knowledge, and recordings of human voices, languages, and music, there to be decoded by any technological civilization that stumbles upon it.  (It's a little mind-boggling to realize that in the 43 years since Voyager 2 was launched, it has traveled about 20,000,000,000 kilometers, so is well outside the perimeter of the Solar System; and that sounds impressive until you realize that's only 16.6 light hours away, and the nearest star is 4.3 light years from us.)

So anyhow, those are my elegiac thoughts on this February morning.  Dead planets, dying stars, and the remnants of lost civilizations.  Sorry to be a downer.  If all this makes you feel low, watch "The Inner Light" and have yourself a good cry.  It'll make you feel better.

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Science writer Elizabeth Kolbert established her reputation as a cutting-edge observer of the human global impact in her wonderful book The Sixth Extinction (which was a Skeptophilia Book of the Week a while back).  This week's book recommendation is her latest, which looks forward to where humanity might be going.

Under a White Sky: The Nature of the Future is an analysis of what Kolbert calls "our ten-thousand-year-long exercise in defying nature," something that immediately made me think of another book I've recommended -- the amazing The Control of Nature by John McPhee, the message of which was generally "when humans pit themselves against nature, nature always wins."  Kolbert takes a more nuanced view, and considers some of the efforts scientists are making to reverse the damage we've done, from conservation of severely endangered species to dealing with anthropogenic climate change.

It's a book that's always engaging and occasionally alarming, but overall, deeply optimistic about humanity's potential for making good choices.  Whether we turn that potential into reality is largely a function of educating ourselves regarding the precarious position into which we've placed ourselves -- and Kolbert's latest book is an excellent place to start.

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

Strange places

I remember when I took Quantum Physics as an undergraduate, many, many (many) years ago, my professor, Dr. John Matese, was fairly disparaging about the naming of the (then newly-discovered) quarks.  Up, down, top, bottom, strange, and charm, he said, were (1) misleading, because the names sound like they tell you something about the particle but don't, and (2) were cutesie, giving laypeople an impression of scientists as being "whimsical."

He said the last word in tones that left us in no doubt about his opinion of whimsy.

At least one of those names is apt, though, and that's "strange."  There's a hypothesis going around -- among serious physicists, I hasten to state, not among the whimsical -- that under sufficient pressure, matter can form which contains strange quarks.  (Ordinary matter is formed entirely of the two lightest-mass quarks, up and down.)  This "strange matter" has the property of being able to convert surrounding matter to strange matter, a little like "Ice-Nine" in Kurt Vonnegut's Cat's Cradle.  And if that's not weird enough, if a hypothesis pieced together from papers by A. R. Bodmer in 1971 and Edward Witten in 1984 is correct, it might be that the ordinary matter you see around us is the fluke; it's "metastable," meaning given the right conditions it could convert to the more stable strange matter, and our regular old atoms and molecules would condense into droplets...

... called "strangelets."

Speaking of cutesie names.

[Image licensed under the Creative Commons Brianzero, Quark wiki, CC BY-SA 3.0]

A paper published in the Journal of Astrophysics last week pushes the "strange matter hypothesis" a step further by suggesting that some of the astronomical objects we see may be strange, rather than ordinary, matter.  One possible place this stuff could live is the interior of neutron stars -- up till now thought to be extremely dense stuff, but the usual sort.  A team made up of physicists Abudushataer Kuerban, Jin-Jun Geng, Yong-Feng Huang, Hong-Shi Zong, and Hang Gong, of Nanjing University, has suggested that such bizarre matter may not just be confined to the cores of neutron stars -- it may be that there are whole planets of the stuff orbiting pulsars and even white dwarfs.

The authors write:

Since the true ground state of the hadrons may be strange quark matter (SQM), pulsars may actually be strange stars rather than neutron stars.  According to this SQM hypothesis, strange planets can also stably exist.  The density of normal matter planets can hardly be higher than 30 g cm−3. As a result, they will be tidally disrupted when its orbital radius is less than ∼5.6×10^10 cm, or when the orbital period (Porb) is less than ∼6100s.  On the contrary, a strange planet can safely survive even when it is very close to the host, due to its high density.  The feature can help us identify SQM objects.  In this study, we have tried to search for SQM objects among close-in exoplanets orbiting around pulsars. Encouragingly, it is found that four pulsar planets completely meet the criteria... and are thus good candidates for SQM planets.  The orbital periods of two other planets are only slightly higher than the criteria.  They could be regarded as potential candidates.  Additionally, we find that the periods of five white dwarf planets are less than 0.1 days.  We argue that they might also be SQM planets.  It is further found that the persistent gravitational wave emissions from at least three of these close-in planetary systems are detectable to LISA [the Laser Interferometer Space Antenna].  More encouragingly, the advanced LIGO [the Laser Interferometer Gravitational-Wave Observatory] and Einstein Telescope are able to detect the gravitational wave bursts produced by the merger events of such SQM planetary systems, which will provide a unique test for the SQM hypothesis.

 These planets would be, in a word, strange.  Their densities aren't just "high," as the authors state; they're "really fucking high."  (I realize that descriptor might not pass the editors for the Journal of Astrophysics, but I maintain that it's more accurate.)  For purposes of comparison, gold -- one of the densest familiar substances -- has a density of 19.3 grams per cubic centimeter.  The material making up a strange planet is predicted to be on the order of 400 trillion grams per cubic centimeter.

A planet with this density would have a gravitational pull so intense that taking one step up onto a hill a centimeter high would require more energy than leaping from sea level to the top of Mount Everest in one bound.

Suffice it to say that walking about on a strange planet would be pretty much out of the question.

Of course, the idea that the planets analyzed by Kuerban et al. are made of strange matter may not turn out to bear up under further scrutiny.  But the fact that it's even possible we've located some large chunks of such an exotic material is pretty fantastic.  Whether it pans out or no, I think we can all agree on one thing:

The universe is a very strange place.

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I am not someone who generally buys things impulsively after seeing online ads, so the targeted ad software that seems sometimes to be listening to our conversations is mostly lost on me.  But when I saw an ad for the new book by physicist James Trefil and astronomer Michael Summers, Imagined Life, it took me about five seconds to hit "purchase."

The book is about exobiology -- the possibility of life outside of Earth.  Trefil and Summers look at the conditions and events that led to life here on the home planet (after all, the only test case we have), then extrapolate to consider what life elsewhere might be like.  They look not only at "Goldilocks" worlds like our own -- so-called because they're "juuuuust right" in terms of temperature -- but ice worlds, gas giants, water worlds, and even "rogue planets" that are roaming around in the darkness of space without orbiting a star.  As far as the possible life forms, they imagine "life like us," "life not like us," and "life that's really not like us," always being careful to stay within the known laws of physics and chemistry to keep our imaginations in check and retain a touchstone for what's possible.

It's brilliant reading, designed for anyone with an interest in science, science fiction, or simply looking up at the night sky with astonishment.  It doesn't require any particular background in science, so don't worry about getting lost in the technical details.  Their lucid and entertaining prose will keep you reading -- and puzzling over what strange creatures might be out there looking at us from their own home worlds and wondering if there's any life down there on that little green-and-blue planet orbiting the Sun.

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

Tales from a white dwarf

This week we've focused on some cool scientific discoveries, which is, honestly, my happy place.  So we'll round out the week with a new piece of research that is kind of a double-edged sword.  It is (1) fascinating, but (2) tells us about how the Earth is going to be destroyed.  So while it's interesting, cheerful it isn't.

Of course, the upside is that the Earth isn't going to be destroyed for another few billion years.  So even in the best-case scenario, I won't be around when it happens.

The research was led by Christopher Manser of the University of Warwick, and is based on observations done of a white dwarf star at the 10.4-meter Gran Telescopio Canarias on La Palma in the Canary Islands.  White dwarfs are the remnants of stellar cores for stars smaller than about 10 times the mass of the Sun.  At the end of their lives, stars in this range exhaust the hydrogen fuel in their cores, and switch to burning helium -- this gives an added kick to the core temperature, and the outer atmosphere balloons out into what's called a red giant.  But eventually, it becomes a nova -- it exhausts the helium as well, the core collapses and heats up (dramatically), and that blows the outer atmosphere away (forming what's called a planetary nebula), in an expanding cloud of gas and dust surrounding the exposed core -- the white dwarf star.

[Image licensed under the Creative Commons, ESA/Hubble, Artist’s impression of debris around a white dwarf star, CC BY 4.0]

It was long thought that a star that becomes a white dwarf will in the process completely destroy any planets that happen to be orbiting around it.  When the Sun becomes a red giant, for example, it's believed that its outer edges will be somewhere between the orbits of Mars and Jupiter.  So where you are sitting right now will be inside the Sun.

I like it warm, but that's a bit toasty even my my standards.

So it was quite a shock when Manser et al. found that the white dwarf they were studying, the euphoniously named SDSS J122859.93+104032.9, had a planet orbiting it.

The fact that they could even tell that is pretty extraordinary.  As I explained in a previous post, the two most common ways of detecting planets are by occlusion (the star dimming because the planet has passed in front of it) or by Doppler spectroscopy (seeing shifts in the frequency of light from the star because it's being pulled around by the planet as it orbits).  Both of these work better when the planet is massive -- so for a little planet around a littler star, it's kind of amazing they even figured out it was there.

What they found was that there was light coming from the star system that was consistent with the emission spectrum of calcium, but oddly, the calcium spectral lines were split in two -- and the two lines oscillated back and forth with a period of almost exactly two hours.  The best explanation, say Manser et al, is that there is a planetesimal -- probably the iron-rich core of a planet that once orbited the star prior to its demise -- that is dragging around a cloud of calcium-rich gas that is being Doppler shifted first one way and then the other every time the planet circles the star.

As Luca Fossati, writing for Science magazine, describes the research:

The method of Manser et al. has revealed the presence of planetesimals without the need for the particular orbital geometry that is required by the transit method.  It could therefore be used to identify the presence of planetesimals orbiting other polluted white dwarfs and advance the study of the planetary systems evolution.  Furthermore, because planetesimals orbiting white dwarfs are believed to be the remnant cores of shattered planets, studying the spectra of polluted white dwarfs known to be surrounded by planetesimals enables one to gain information about the chemical composition and metal abundances of the infalling material—that is, planetary cores.

The most awe-inspiring part of this research is that this will be the likely fate of the Earth -- assuming that the red giant and nova phases of the Sun don't destroy it completely.  All that will be left is the remnant core of the Sun and the remnant core of the Earth, circling each other and gradually cooling, becoming a whirling pair of cinders forever spinning in the infinite dark, cold vacuum of space.

Have a nice day.

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This week's Skeptophilia book recommendation combines science with biography and high drama.  It's the story of the discovery of oxygen, through the work of the sometimes friends, sometimes bitter rivals Joseph Priestley and Antoine Lavoisier.   A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen is a fascinating read, both for the science and for the very different personalities of the two men involved.  Priestley was determined, serious, and a bit of a recluse; Lavoisier a pampered nobleman who was as often making the rounds of the social upper-crust in 18th century Paris as he was in his laboratory.  But despite their differences, their contributions were both essential -- and each of them ended up running afoul of the conventional powers-that-be, with tragic results.

The story of how their combined efforts led to a complete overturning of our understanding of that most ubiquitous of substances -- air -- will keep you engaged until the very last page.

[Note:  If you purchase this book by clicking on the image/link below, part of the proceeds will go to support Skeptophilia!]

Explosions in Andromeda

We've learned a lot about our own galaxy by studying our "sister galaxy," Messier-31, better known as the Andromeda Galaxy.  It's situated about 2.5 million light years away, so from our perspective looks to the naked eye like little more than a smudge of light in the night sky.

[Image is in the Public Domain, courtesy of NASA/JPL]

I remember when I was a kid and first grasped how far away Andromeda is.  Like many people of my generation, I was captivated by the original Star Trek.  In the episode "By Any Other Name," Kirk et al. are confronted by some aliens called Kelvans who come from the Andromeda Galaxy, and want to hijack the Enterprise to get back home.  Now, recall that because of warp drive, the intrepid space-farers of the United Federation of Planets are tooling about on a weekly basis, zipping from planet to planet, covering light-years of distance in mere hours.  So it was a bit of a shock -- to me, at least -- that at maximum warp, it would take three hundred years to reach the Andromeda Galaxy.

So far, in fact, that the Kelvans propose to reduce most of the crew to little geometric solids to save on food, lessen the likelihood of rebellion, have at least some of them still alive upon arrival, and also to reduce the number of extras the show's producers had to hire.

Of course, Kirk saves the day and they end up returning to our galaxy, kindly offering to leave the Kelvans on an uninhabited planet all their own.  Who could resist that?

In any case, I was blown away by how far away the Andromeda Galaxy is, not to mention the fact that the writers of Star Trek got that bit right given their extensive history of playing fast-and-loose with physics, despite Scotty's repeated admonition that ye canna change the laws thereof.  Everyone knows the stars in our own galaxy are far away; but this is an entirely different order of magnitude of distance.

Considering how far away we are from it, if you have a good enough telescope, it's surprising how spectacular it is.  Like our own, it's a spiral galaxy, so the disadvantage of being situated inside the thing we're trying to study has been ameliorated by the fact that there's a similar one right next door.  It's home to a trillion stars.

And there are some interesting ones.  Just last month, there was a paper in Nature about the discovery of a peculiar object called a recurrent nova that I had never heard of before.   A team of researchers found that this object, with the euphonious name M31N 2008-12a, is a white dwarf being circled by a small, dim star.  This pairing is resulting in some seriously cool behavior, which I'm glad we're observing from a safe 2.5 million light years away.

What's happening is this.  The white dwarf, which is the core of a collapsed star about the size of our Sun, has such a high gravitational pull that it's siphoning off material from its companion.  When the gas and dust approach the surface of the white dwarf, it's heated and compressed so much that the hydrogen component fuses into helium.  This releases so much energy that it causes an explosion, blowing away the top layer of the dust into space.

What's amazing is that these explosions are happening about once a year, and have been going on for a million years.  This has left a shell of dust 400 light years across.   But what's more fascinating still is that it can't go on forever.  Despite the explosions, the white dwarf is gradually gaining mass at the expense of its companion.  Once its mass gets to about 1.4 times the mass of the Sun -- the Chandrasekhar Limit -- the gravitational pull will exceed the outward pressure exerted by the atoms in the star, and it will collapse.  That collapse will trigger further fusion, of helium into carbon, carbon into oxygen, and so forth, and the energy produced by that will trigger one of the brightest events in the universe, a Type 1a Supernova.

Cool enough already, but wait till you hear the rest.  The fusion triggered by the explosion is what creates virtually all the heavier elements in the periodic table.  So a sizable fraction of the atoms in your body were formed during the first few seconds of a colossal stellar explosion.  We are, as Carl Sagan trenchantly remarked, truly made of star-stuff.

Oh, and the parts of the exploding white dwarf not blown away into space, to seed future planets and stars and life forms, are blown inward so hard that the electrons are forced into the atomic nuclei, resulting in, basically, a big ball o' neutrons.  This takes the remaining mass of the star and compresses it into a sphere about ten kilometers across, generating a substance so dense that a matchbox-sized piece of it would weigh three billion tons.

Like I said.  Good thing we're out here at a safe distance.  Sucks for the Kelvans, though.

The one disappointing thing is that the paper in Nature says that although the recurrent nova is still firing off once a year, the cataclysmic final explosion isn't going to happen for another forty thousand years, give or take a year or two.  So unfortunately, we won't be around to see it.  Unless some alien race shows up and turns us into geometric solids and sits us on a shelf, reawakening us just before the cosmic show starts.

But I suppose that's too much to hope for.

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You can't get on social media without running into those "What Star Trek character are you?" and "Click on the color you like best and find out about your personality!" tests, which purport to give you insight into yourself and your unconscious or subconscious traits.  While few of us look at these as any more than the games they are, there's one personality test -- the Myers-Briggs Type Indicator, which boils you down to where you fall on four scales -- extrovert/introvert, sensing/intuition, thinking/feeling, and judging/perceiving -- that a great many people, including a lot of counselors and psychologists, take seriously.

In The Personality Brokers, author Merve Emre looks not only at the test but how it originated.  It's a fascinating and twisty story of marketing, competing interests, praise, and scathing criticism that led to the mother/daughter team of Katharine Briggs and Isabel Myers developing what is now the most familiar personality inventory in the world.

Emre doesn't shy away from the criticisms, but she is fair and even-handed in her approach.  The Personality Brokers is a fantastic read, especially for anyone interested in psychology, the brain, and the complexity of the human personality.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Examining the Cow

Today's intriguing mystery comes from the realm of astronomy, with a colossal explosion in a distant galaxy that has scientists scratching their heads with puzzlement.

Nicknamed "the Cow" -- after its official name, AT2018cow -- it was so bright that initially astronomers thought it must be a nearer (and dimmer) phenomenon, possibly a flare-up of a white dwarf star after having engulfed material from a nearby companion star.  But analysis of the red shift of the light coming from the explosion shows that it's 200 million light years away -- so lies in a distant galaxy that at first was thought to be behind it.

This means that it was phenomenally bright.  Its peak luminosity was equivalent to a hundred billion Suns -- a good ten times brighter than the brightest supernova ever observed.

"The Cow" -- initial appearance (left), peak brightness (middle), and waning (right)

The Cow first appeared on June 16, 2018, and literally was not there one day and shining like a beacon the next.  Astronomers say this rules out a supernova, the most common cause of sudden increases in brightness, because supernovae -- contrary to how they're depicted in science fiction movies -- show a more gradual increase in brightness.  More puzzling still, the Cow continued to increase in brightness over a period of three weeks following its appearance.  This meant that there was something continuing to power the explosion after the initial kaboom, but what that something is, no one has been able to figure out.

This is despite intensive study.  "When we saw that, we thought, 'let's get on with it,'" said Daniel Perley, astronomer at Liverpool John Moores University in the United Kingdom.  "We dropped everything in the first two weeks, observing it seven times a night."

Even more curious is that the phenomenon, whatever it is, produced radiation across the electromagnetic spectrum, including a strong signal in the ultraviolet and x-ray regions.  But after three weeks, the x-ray emissions started to fluctuate wildly, and the intensity across the entire spectrum started to weaken.  Within six weeks, it was back to being entirely invisible.

One possibility is that it was a supernova surrounded by a thick gas cloud.  The initial brightening after the supernova's first burst of emissions was augmented when the shock wave hit the gas cloud, warming it up and causing it to glow.  The brightening continued as the shock wave plunged through, only diminishing when it reached the outer edges.

But that's only a speculative solution.  Other possibilities include the birth of a black hole or a white dwarf being swallowed by a neutron star.  But none of these align perfectly with the data.  "All of our explanations have problems," said Liliana Rivera Sandoval, astronomer at Texas Tech University.  "It's super weird."

The problem, of course, is these one-off phenomena -- events that occur so rarely that the chance of another one happening in our lifetime is small indeed -- give scientists scanty information at best, and no repeated data set with which to compare the initial measurements.  "I hope there are more Cows," Sandoval said, but the likelihood of that is pretty slim.  So now what we have is one six-week data set, with no way to test any theories against subsequent observations.

"The bright transient AT2018cow has been unlike any other known type of transient," write the research team in a paper published in arXiv last August.  "Its large brightness, rapid rise and decay and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources."

Frustrating, but that's the way science is, especially with the realms of science that do not allow for replication, such as astronomy, paleontology, and geology.  All you can do is use what information you have to generate hypotheses about what is going on, and see which one fits best.  After that, nothing much can be done except for waiting and hoping for more data.

So that's this week's puzzle.  A colossal explosion in a distant galaxy that is proving to have no easy explanation.  I don't know about you, but when I read stuff like this, it makes me feel awfully small and insignificant.  Not that this is necessarily a bad thing; there's nothing wrong with a good dose of humility.  But the idea that we have observed a mysterious unexplained phenomenon shining with the light of a hundred billion Suns, from a distance of two hundred million light years, boggles my mind with the sheer scale.

Such a big universe, and so much still to learn.

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This week's Skeptophilia book recommendation is a little on the dark side.

The Radium Girls, by Kate Moore, tells the story of how the element radium -- discovered in 1898 by Pierre and Marie Curie -- went from being the early 20th century's miracle cure, put in everything from jockstraps to toothpaste, to being recognized as a deadly poison and carcinogen.  At first, it was innocent enough, if scarily unscientific.  The stuff gives off a beautiful greenish glow in the dark; how could that be dangerous?  But then the girls who worked in the factories of Radium Luminous Materials Corporation, which processed most of the radium-laced paints and dyes that were used not only in the crazy commodities I mentioned but in glow-in-the-dark clock and watch dials, started falling ill.  Their hair fell out, their bones ached... and they died.

But capitalism being what it is, the owners of the company couldn't, or wouldn't, consider the possibility that their precious element was what was causing the problem.  It didn't help that the girls themselves were mostly poor, not to mention the fact that back then, women's voices were routinely ignored in just about every realm.  Eventually it was stopped, and radium only processed by people using significant protective equipment,  but only after the deaths of hundreds of young women.

The story is fascinating and horrifying.  Moore's prose is captivating -- and if you don't feel enraged while you're reading it, you have a heart of stone.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]