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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The stellar forges

A criticism sometimes aimed at us science types is that our obsession with naming, classifying, and explaining everything in the universe robs us of its wonder.  Why, they ask, do we have to get so damn technical about everything?  Why can't we just look at the stars, or the flowers, or a bird in flight, and appreciate their beauty?

Well, needless to say, I disagree with that pretty strenuously.  My understanding of science -- which, admittedly, is that of a reasonably well-read layperson's -- only adds to my sense of wonder.  For me, it's a case of the more you know, the more amazing it gets.

Let me give you an example of that -- a piece of research out of the University of Arizona that used the James Webb Space Telescope to peer far out into space (and thus, far back in time), and found something astonishing.  Something, in fact, that would appear quite mundane, meriting only a "So what?', if you didn't know some science.

Here's a capsule summary of the research -- then an explanation of why it's way cooler, and more surprising, than it appears at first.

The JWST just released a spectral analysis of a galaxy called JADES-GS-z14-0, which is about 13.5 billion light years away.  That's a pretty impressive feat; this means the light from it left on its journey to us when the universe was only two percent of its current age.  This, in fact, means the galaxy itself formed not long (in astronomical terms) after the cosmic microwave background radiation, the earliest remnants of radiation released when the universe settled down enough to allow photons to travel unimpeded.

Just seeing JADES is amazing enough.  "Imagine a grain of sand at the end of your arm," said Jakob Helton, who led the research.  "You see how large it is on the sky -- that's the size of the region we looked at."

The shocker came when they did an analysis of its spectrum, and found that it had high amounts of oxygen.  But why this is surprising -- why, in fact, it's going to force a rethinking of our understanding of how stars and galaxies form -- is where you have to know some background.

When heated or otherwise energized, each element emits a characteristic fingerprint of frequencies of light known as its emission spectrum.  The fact that these specific frequencies and no others are emitted was key to the development of quantum theory; energy levels in atoms are quantized, or exist in discrete steps, and an atom can no more emit a different frequency of light than you could go down a step-and-three-quarters on your staircase.  Because of these spectral fingerprints, it's now possible to determine the composition of distant stars by looking for the characteristic spectral lines of common elements in the star's spectrum.  This is how Helton et al. figured out that JADES contains large amounts of oxygen.

The emission spectrum of oxygen [Image is in the Public Domain]

Thing is, it shouldn't.  We have lots of oxygen here on Earth because the primordial cloud from which the Solar System condensed had a bunch of it; so, in fact, does the Sun, since it formed from the same cloud.  Alien astronomers could look at the Sun through their telescopes and figure that out the same way that we do.  But oxygen, it turns out, doesn't form all that readily.  The Solar System is oxygen-enriched because the Sun is (at least) a third-generation star.  In the very early universe, when there was nothing much around but hydrogen, helium, and trace amounts of lithium -- the atoms that were formed during the Big Bang itself -- stars had vanishingly small "metal content."  (To astrophysicists, "metals" are any elements heavier than helium.)  As those first stars underwent fusion in their cores, hydrogen was converted to helium, then helium to lithium and carbon; at the end of their lives, those stars that were heavy enough went supernova, and the pressures and temperatures of those colossal explosions not only generated "metals" but distributed them back into space.

Second-generation stars formed from the debris left behind by the explosion of first-generation stars.  Those second-generation stars, during the course of their lives and deaths, would have produced more "metals," and the cycle repeated, ultimately leading to the richness of composition we see in our own Solar System.

But it takes a while.  The amount of oxygen even in early third-generation stars is pretty small.  So where did all the oxygen in an extremely early galaxy like JADES come from?

We don't know.  "It's a very complicated cycle to get as much oxygen as this galaxy has," said study senior author George Rieke.  "So, it is genuinely mind boggling."

So there's evidently something about star formation and galaxy evolution we're missing.  Stars forming only three hundred million years after the Big Bang should be just about entirely hydrogen and helium.  And chances are, JADES is almost certainly not the only anomalous early object.  "The fact that we found this galaxy in a tiny region of the sky means that there should be more of these out there," Helton said. "If we looked at the whole sky, which we can't do with JWST, we would eventually find more of these extreme objects."

For me, it's lovely to look up into the sky on a clear night, but my enjoyment is much enhanced by the fact that I know a little bit about what I'm looking at.  The stars are stellar forges, creating all the matter around us -- we are truly, as Carl Sagan famously said, "made of star stuff."

In short: science itself is beautiful.  Understanding how the world works should do nothing but increase our sense of wonder.  If scientific inquiry isn't accompanied by a sense of "Wow, this is amazing!", you're doing it wrong.  I'll end with a quote from Nobel Prize winning physicist Richard Feynman, who in his 1988 book What Do You Care What Other People Think? had the following to say:

I have a friend who's an artist, and he sometimes takes a view which I don't agree with.  He'll hold up a flower and say, "Look how beautiful it is," and I'll agree.  But then he'll say, "I, as an artist, can see how beautiful a flower is.  But you, as a scientist, take it all apart and it becomes dull."  I think he's kind of nutty. …  There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower.  It only adds.  I don't understand how it subtracts.

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Off the chart

Way back around 1910, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell independently found a curious pattern when they did a scatterplot correlation between stars' luminosities and temperatures.

The graph, now called the Hertzsprung-Russell Diagram in their honor, looks like this:

[Image licensed under the Creative Commons Richard Powell, HRDiagram, CC BY-SA 2.5]

Most stars fall on the bright swatch running from the hot, bright stars in the upper left to the cool, dim stars in the lower right; the overall trend for these stars is that the lower the temperature, the lower the luminosity.  Stars like this are called main-sequence stars.  (If you're curious, the letter designations along the top -- O, B, A, F, G, K, and M -- refer to the spectral class the star belongs to.  These classifications were the invention of the brilliant astronomer Antonia Maury, whose work in spectrography revolutionized our understanding of stellar evolution.)

There is also a sizable cluster of stars off to the upper right -- relatively low temperatures but very high luminosities.  These are giants and supergiants.  In the other corner are white dwarfs, the exposed cores of dead stars, with very high temperatures but low luminosity, which as they gradually cool slip downward to the left and finally go dark.

So there you have it; just about every star in the universe is either a main-sequence star, in the cluster with the giants and supergiants, or in the curved streak of dwarf stars at the bottom of the diagram.

Emphasis on the words "just about."

One star that challenges what we know about how stars evolve is the bizarre Stephenson 2-18, which is in the small, dim constellation Scutum ("the shield"), between Aquila and Sagittarius.  At an apparent magnitude of +15, it is only visible through a powerful telescope; it was only discovered in 1990 by American astronomer Charles Bruce Stephenson, after whom it is named.

Its appearance, a dim red point of light, hides how weird this thing actually is.

When Stephenson first analyzed it, he initially thought what he was coming up with couldn't possibly be correct.  For one thing, it is insanely bright, estimated at a hundred thousand times the Sun's luminosity.  Only its distance (19,000 light years) and some intervening dust clouds make it look dim.  Secondly, it's enormous.  No, really, you have no idea how big it is.  If you put Stephenson 2-18 where the Sun is, its outer edge would be somewhere near the orbit of Saturn.  You, right now, would be inside the star.  Ten billion Suns would fit inside Stephenson 2-18. 

If a photon of light circumnavigated the surface of the Sun, it would take a bit less than fifteen seconds.  To circle Stephenson 2-18 would take nine hours.

This puts Stephenson 2-18 almost off the Hertzsprung-Russell Diagram -- it's in the extreme upper right corner.  In fact, it's larger than what what stellar evolution says should be possible; the current model predicts the largest stars to have radii of no more than 1,500 times that of the Sun, and this behemoth is over 2,000 times larger.

Astronomers admit that this could have a simple explanation -- it's possible that the measurements of Stephenson 2-18 are overestimates.  But if not, there's something significant about stellar evolution we're not understanding.

Either way, this is one interesting object.

There's also a question about what Stephenson 2-18 will do next.  Astrophysicists suspect it might be about to blow off its outer layers and turn either into a luminous blue variable or a Wolf-Rayet star (the latter are so weird and violent I wrote about them here a while back).  So it may not be done astonishing us.

Puts me in mind of the quote from Richard Dawkins: "The feeling of awed wonder that science can give us is one of the highest experiences of which the human psyche is capable."

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The stellar whirlpool

In today's installment of "The Universe Is A Really Weird Place," we have: a piece of our own galaxy that we didn't even know existed until now.

It's called the "Cepheus Spur" after the constellation Cepheus, in which (from the Earth perspective) the structure seems to reside.  It's a spiral of stars lying above the galactic plane, and at the moment, astronomers don't know how it got there.   "Possibly these are oscillations of the galactic disk resulting from the convulsive evolution of the galaxy," said co-discoverer Michelangelo Pantaleoni González, of the Spanish Astrobiology Center.  "Perhaps they are the echoes of collisions with other galaxies billions of years ago, or maybe it’s something else."

The befuddlement of the experts is indicative that this structure has some seriously odd characteristics.  One of the strangest is that it seems to be mostly composed of type-OB blue supergiant stars, which are amongst the rarest star types known; from observations of the Milky Way, only one star in a million is a type-OB blue supergiant.

That's even taking into account the fact that the ones we know about are visible from a long way off.  They have masses between twenty and fifty times that of the Sun, and luminosities on the order of a hundred thousand times higher.  One familiar example is Rigel, in Orion, which is the brightest star in the constellation despite being 860 light years away.

The constellation Orion, with Rigel at the lower right [Image licensed under the Creative Commons Rogelio Bernal Andreo, Orion Head to Toe, CC BY-SA 3.0]

Their rarity isn't just because it's unusual to have such a huge clump of matter form; they're also exceedingly short-lived.  Because of their mass, they burn through their hydrogen fuel quickly, which makes them the hottest stars -- with surface temperatures of between 10,000 and 50,000 K (the Sun's surface is on the order of 5770 K).  It's estimated that a typical type-OB blue supergiant goes from formation to supernova in something between a few hundred thousand and thirty million years; again, by contrast, the Sun is estimated at 4.6 billion years in age, and is only about halfway through its life.

So to have a swirl of these rare and short-lived stars whirling above the plane of the galaxy is a significant puzzle.

"When we discovered the spur, there was no explosive revelation, but something inside me was transformed.  That’s what draws you in and gives meaning to so much effort," said Pantaleoni González.  "We were in front of [astrophysicist] Jesús [Apellániz]’s computer when he began to inspect this density of dots on the map. I ran to make a special diagram to see if it was consistent with the idea that there was a structure there, and it appeared."

The presence of these stars outside of the galactic plane has yet to be explained, and it's still unknown if the Cepheus Spur really is composed primarily of rare type-OB blue supergiants, or if we're overestimating their frequency because they're so luminous.  It could be that there are a lot of other, dimmer stars in the Spur that we're not seeing because of its distance (estimated at an average of 100,000 light years).  In any case, what seems certain is that this discovery will keep the astrophysicists working for a long while -- and illustrates that once again, the universe is full of surprises.

Which is one of the reasons that science is so endlessly fascinating.

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When people think of mass extinctions, the one that usually comes to mind first is the Cretaceous-Tertiary Extinction of 66 million years ago, the one that wiped out all the non-avian dinosaurs and a good many species of other types.  It certainly was massive -- current estimates are that it killed between fifty and sixty percent of the species alive at the time -- but it was far from the biggest.

The largest mass extinction ever took place 251 million years ago, and it destroyed over ninety percent of life on Earth, taking out whole taxa and changing the direction of evolution permanently.  But what could cause a disaster on this scale?

In When Life Nearly Died: The Greatest Mass Extinction of All Time, University of Bristol paleontologist Michael Benton describes an event so catastrophic that it beggars the imagination.  Following researchers to outcrops of rock from the time of the extinction, he looks at what was lost -- trilobites, horn corals, sea scorpions, and blastoids (a starfish relative) vanished completely, but no group was without losses.  Even terrestrial vertebrates, who made it through the bottleneck and proceeded to kind of take over, had losses on the order of seventy percent.

He goes through the possible causes for the extinction, along with the evidence for each, along the way painting a terrifying picture of a world that very nearly became uninhabited.  It's a grim but fascinating story, and Benton's expertise and clarity of writing makes it a brilliant read.

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

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!]

World enough and time

Because I'm writing this in the last hours of the Trump presidency, and my other alternative is to become so anxious about what his followers might still do to fuck things up that I chew my fingernails till they bleed, today I'm going to focus on things that are very, very far from planet Earth.

Let's begin with the closest-to-home, three thousand light years away, which seems like it might be almost far enough for safety.

A new study of planetary nebulae -- gas and dust clouds that are what's left of stars that went supernova -- was the subject of a talk at the meeting of the American Astronomical Society last Friday.  Using the Hubble Space Telescope's Wide Field Camera, astronomers were able to photograph these amazing stellar remnants panchromatically (across the frequency spectrum of light).  And what they're learning is changing a lot of what we thought we understood.

Take, for example, NGC 6302, better known as the Butterfly Nebula.  It got its name because of symmetrical "wings" of debris that were thrown out when the central star blew up.  Why it has this strange symmetry is probably due to the magnetic field of the central star, but what's most surprising is that what astronomers thought was the central star doesn't seem to be, but is simply a white dwarf much closer to the Earth that happens to lie between us and the nebula.  Wherever the actual central star is, it's a doozy; from the spectral lines of the nebula, created when light from the star is absorbed and then re-emitted by the dust plumes, its surface is one of the hottest known, at a staggering 250,000 C.  (By comparison, the surface of our own Sun is a paltry 6,000 C or so.)

The Butterfly Nebula [Image is in the Public Domain courtesy of the Hubble Space Telescope and NASA/JPL]

Then there's NGC 7027, the Jewel Bug Nebula, which is also remarkable because of its symmetry -- depending on what feature you're looking at, it shows spherical symmetry (symmetry around the center, like a basketball), axis symmetry (symmetry around a line, like the letter T), or point symmetry (symmetry across a central point, like the letter N).  It's simultaneously one of the brightest planetary nebulae and one of the smallest, and the new study confirms that it's a recently-formed object -- it's only six hundred years old.  (Of course, since it's three thousand light years away, the structure is actually 3,600 years old; but what we're seeing is what it looked like when it was a mere six hundred.)

"We're dissecting [planetary nebulae]," said Joel Kastner, a professor in the Rochester Institute of Technology's Chester F. Carlson Center for Imaging Science and School of Physics and Astronomy.  "We're able to see the effect of the dying central star in how it's shedding and shredding its ejected material.  We're able to see that material that the central star has tossed away is being dominated by ionized gas, where it's dominated by cooler dust, and even how the hot gas is being ionized, whether by the star's UV or by collisions caused by its present, fast winds."

Moving farther afield, another paper presented at the AAS meeting is about a weird object in NGC 253, the Sculptor Galaxy, which is 11.4 million light years away.  It's called a magnetar, and is another stellar remnant, but this one of a supergiant star.  The Fermi Gamma-ray Space Telescope and the Mars Odyssey orbiter both picked up a 140-millisecond-long pulse of gamma rays which seems to have been caused by a starquake on the surface of this object, a cosmic shudder that in one burst released one thousand trillion trillion (10 followed by 27 zeroes) times more energy than the largest recorded earthquake Earth has experienced.  The quake ejected a blob of plasma at nearly the speed of light, and the acceleration is what caused the gamma rays.

The new study gives us a lens into the behavior of some of the oddest structures in the universe, and one that may also be responsible for "fast radio bursts" -- quick pulses of radio waves whose source has been a mystery up until now.  "The apparent frequency of magnetar flares in other galaxies is similar to the frequency of fast radio bursts," said astrophysicist Victoria Kaspi of McGill Space Institute.  "That argues that actually, most or all fast radio bursts could be magnetars."

Last, we go out an astonishing thirteen billion light years, which is only seven hundred million light years shy of the radius of the observable universe.  Another paper at the AAS meeting describes a quasar -- an ancient supermassive black hole that is radiating energy from infalling material, and is one of the brightest objects known -- that lies at the center of a galaxy, and now holds the record for the oldest black hole ever observed.

Like all good scientific discoveries, this one raises almost as many questions as it solves, especially about how such a massive object could have formed so early in the life of the universe.  "A gargantuan seed black hole may have formed through the direct collapse of vast amounts of primordial hydrogen gas," said study co-author Xiaohui Fan, of the University of Arizona in Tucson.  "Or perhaps J0313-1806’s seed started out small, forming through stellar collapse, and black holes can grow a lot faster than scientists think.  Both possibilities exist, but neither is proven.  We have to look much earlier [in the universe] and look for much less massive black holes to see how these things grow."

So that leaves us all the way across the universe, which is a nice comfortable distance to put between myself and the Proud Boys.  It'd be better still to have me stay here and send the Proud Boys out to the farthest reaches of interstellar space, so that their inevitable tweets about what a god-figure Trump is and what a libtard snowflake I am will take thirteen billion years to get here.

But I guess that's not gonna happen.  We all have to stay here and solve our own problems, quasars and magnetars and nebulae notwithstanding.  I'll end with a quote from Doctor Who, which seems apt somehow given the voyage through time and space we just took: "I do think there’s always a way to put things right.  If I didn’t believe that I wouldn’t get out of bed in the morning,  I wouldn’t eat breakfast; I wouldn’t leave the TARDIS ever.  I would never have left home.  There is always something we can do."

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I'm always amazed by the resilience we humans can sometimes show.  Knocked down again and again, in circumstances that "adverse" doesn't even begin to describe, we rise above and move beyond, sometimes accomplishing great things despite catastrophic setbacks.

In Why Fish Don't Exist: A Story of Love, Loss, and the Hidden Order of Life, journalist Lulu Miller looks at the life of David Starr Jordan, a taxonomist whose fascination with aquatic life led him to the discovery of a fifth of the species of fish known in his day.  But to say the man had bad luck is a ridiculous understatement.  He lost his collections, drawings, and notes repeatedly, first to lightning, then to fire, and finally and catastrophically to the 1906 San Francisco Earthquake, which shattered just about every specimen bottle he had.

But Jordan refused to give up.  After the earthquake he set about rebuilding one more time, becoming the founding president of Stanford University and living and working until his death in 1931 at the age of eighty.  Miller's biography of Jordan looks at his scientific achievements and incredible tenacity -- but doesn't shy away from his darker side as an early proponent of eugenics, and the allegations that he might have been complicit in the coverup of a murder.

She paints a picture of a complex, fascinating man, and her vivid writing style brings him and the world he lived in to life.  If you are looking for a wonderful biography, give Why Fish Don't Exist a read.  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!]

After the collapse

When you start looking into black holes, there's a lot to be fascinated by.

As you probably know, a black hole is one type of collapsed star.  The ultimate fate of a star depends on its initial mass.  When the collapse begins at the end of a star's life, it continues until it meets a force strong enough to counteract the gravitational pull of its mass.  In low-mass stars like the Sun, that oppositional force is the mutual repulsion of the negatively-charged electrons in its constituent atoms.  This leaves a dense, white-hot blob called a white dwarf, slowly radiating its heat away and cooling.  More massive stars -- between ten and twenty-five solar masses -- have such a high gravitational pull that once they start collapsing the electrostatic repulsion is insufficient to stop it.  The electrons are forced into the nuclei, resulting in a neutron star, a stellar core so dense that a matchbox-sized chunk of its matter would weigh three billion tons.

Above twenty-five solar masses, however, even the neutron degeneracy pressure isn't enough to halt the collapse.  Supergiant stars continue to collapse, warping space into a closed form that even light can't escape.

This is the origin of a black hole.

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

Black holes are seriously odd beasts.  Let's start with what we can infer from the upshot of Einstein's General Theory of Relativity, that gravitational fields and accelerated frames of reference are indistinguishable.  (To clarify with an easy example; if you were in a box with no windows, and were being accelerated at a rate of 9.8 m/s^2, you would have no way of knowing you weren't simply in Earth's gravitational field.)  So as weird as it sounds, the same relativistic weirdness would occur in a powerful gravitational field as occurs when you move at a high velocity; time would slow down, mass increase, and so on.  You might recall this from the movie Interstellar.  The crew of a spaceship stranded on a planet orbiting a black hole experiences time dilation -- while a year passes for them, a hundred years passes for people out in the more ordinary reaches of the universe.

This is only the start of the weirdness, though.  You may have heard about spaghettification -- yes, that's really what it's called -- when an object falls into a black hole.  Usually the example given is an astronaut, but that kind of seems cruel; spaghettification would be as unpleasant as it sounds.  What happens is that the falling object would be ripped apart by tidal forces.  A tidal force occurs when one part of an object experiences a different gravitational pull than another part of the same object, and the result is that the object is stretched.

There actually is a tidal force on your own body right now; assuming you're not doing a headstand, your feet are closer to the Earth's center of mass, so they're being pulled a little harder than your head is.  The difference is so small that we're unaware of it.  But with an object near a black hole, the gradient of gravitational pull is so large that when the object gets close -- how close depends on the black hole's mass -- the tidal forces rip it apart, stretching it in a thin filament of matter (thus the "spaghetti" in "spaghettification").

The reason all this comes up is a paper published this week in Monthly Notices of the Royal Astronomical Society that contains observational data of a star getting sucked into a black hole and spaghettified.  "When an unlucky star wanders too close to a supermassive black hole in the centre of a galaxy, the extreme gravitational pull of the black hole shreds the star into thin streams of material," said study co-author Thomas Wevers, a European Southern Observatory Fellow in Santiago, Chile, in an interview with Science Daily.  "As some of the thin strands of stellar material fall into the black hole during this spaghettification process, a bright flare of energy is released, which we can detect."

That's not the only reason that black holes were in the news last week.  In a paper in Nature Communications Physics, scientists describe their observations of a rare event -- the merger of two black holes.  When this happens, the coalescence causes such a powerful shift in the warped gravitational field surrounding it that it sends ripples out through the fabric of space.  These gravitational waves travel outward from their source at the speed of light, and the ones from something as cataclysmic as a black hole merger are so powerful they can be detected here on Earth, thousands of light years away.

"The pitch and amplitude of the signal increases as the two black holes orbit around their mutual center of mass, faster and faster as they approach each other," said Juan Calderón Bustillo, of the University of Hong Kong.  "After the collision, the final remnant black hole emits a signal with a constant pitch and decaying amplitude -- like the sound of a bell being struck."

So that's our excursion into the bizarre and counterintuitive world of collapsed stars.  The whole thing makes me realize what a violent and hostile place much of the universe is, and glad we're relatively safe down here on our comfortable little planet orbiting an ordinary star in the outer spiral arms of an ordinary galaxy.

Boring as it can seem sometimes, it beats being spaghettified by a significant margin.

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This week's Skeptophilia book recommendation is brand new, and is as elegiac as it is inspiring -- David Attenborough's A Life on Our Planet: My Witness Statement and a Vision for the Future.

Attenborough is a familiar name, face, and (especially) voice to those of us who love nature documentaries.  Through series such as Our Planet, Life on Earth, and Planet Earth, he has brought into our homes the beauty of nature -- and its desperate fragility.

At 93, Attenborough's A Life on Our Planet is a fitting coda to his lifelong quest to spark wonder in our minds at the beauty that surrounds us, but at the same time wake us up to the perils of what we're doing to it.  His message isn't all doom and gloom; despite it all, he remains hopeful, and firm in his conviction that we can reverse our course and save what's left of the biodiversity of the Earth.  It's a poignant and evocative work -- something everyone who has been inspired by Attenborough for decades should put on their reading list.

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

The interstellar lighthouse

It's funny the questions you don't think to ask.  You find out something, accept it without any objections, and only later -- sometimes much later -- you stop and go, "Wait a moment."

That happened to me just yesterday, about a topic most of us don't ponder much, and that's the peculiar astronomical object called a neutron star.  It was on my mind not by random chance -- even I don't just sit around and say, "Hmm, how about those neutron stars, anyway?" -- but because of some interesting new research (about which I'll tell you in a bit).

I first learned about these odd beasts when I took a class called Introduction to Astronomy at the University of Louisiana.  The professor, Dr. Whitmire, explained them basically as follows.

Stars are stable when there's a balance between two forces -- the outward pressure from the heat generated in the core, and the inward pull because of the gravity exerted by the star's mass.  During most of a star's life, those two are in equilibrium, but when the core exhausts its fuel, the first force diminishes and the star begins to collapse.  With small stars like the Sun, the collapse continues until the mutual repulsion of the atoms' electrons becomes a sufficient force to halt it from shrinking further.  This generates a white dwarf. 

In a star between 10 and 29 times the mass of the Sun, however, the mutual electric repulsion isn't strong enough to stop the collapse.  The matter of the star continues to fall inward until it's only about ten kilometers across -- a star shrunk to the diameter of a small city.  This causes some pretty strange conditions.  The matter in the star becomes unimaginably dense; a teaspoon of it would have about the same mass as a mountain.  The pressure forces the electrons into the nuclei of the atoms, crushing out all the space, so that what you have is a giant electrically-neutral ball -- effectively, an enormous atomic nucleus made of an unimaginably huge number of neutrons.

The first neutron star ever discovered, at the center of the Crab Nebula [Image is in the Public Domain, courtesy of NASA/JPL]

The immense gravitational pull means that the surface of a neutron star is the smoothest surface known; any irregularities would be flattened out of existence.  (It's worth mentioning that even the Earth is way smoother than most people realize.  The distance between the top of Mount Everest and the bottom of the Marianas Trench is less, as compared to its size, than the topographic relief in a typical scratch on a billiard ball.)

So far, so good.  But it was the next thing Dr. Whitmire told us that should have made me pull up short, and didn't until now -- forty years later.  He said that as a neutron star forms, the inward collapse makes its rotational speed increase, just like a spinning figure skater as she pulls in her arms.  Because of the Conservation of Angular Momentum, this bumps up the rotation of a neutron star to something on the order of making a complete rotation thirty times per second.  A point on the surface of a typical neutron star is moving at a linear speed of about one-third of the speed of light.

Further, because neutron stars have a phenomenally large magnetic field, this creates two magnetic "funnels" on opposite sides of the star that spew out jets of electromagnetic radiation.  And if these jets aren't aligned with the star's spin axis, they whirl around like the beams of a lighthouse.  A neutron star that does this, and appears to flash on and off like a strobe light, is called a pulsar.

This was the point when the red flags should have started waving, especially since I majored in physics and had taken a class called "Electromagnetism."  One of the first things we learned is that Scottish physicist James Clerk Maxwell discovered that magnetic fields are generated when charged particles move.  So how can a neutron star -- composed of electrically-neutral particles -- have any magnetic field at all, much less one so huge?  (The magnetic field of a typical neutron star is on the order of ten million Tesla; by comparison, one of the largest magnetic fields ever generated in the laboratory is a paltry sixteen Tesla, but was still enough to levitate a frog.)

The answer is a matter of conjecture.  One possibility is that even though a neutron star is neutral overall, there is some separation of charges within the star's interior, so the whirling of the star still creates a magnetic field.  Another possibility is that since neutrons themselves are composed of three quarks, and those quarks are charged, neutrons still have a magnetic moment, and the alignment of these magnetic moments coupled with the star's rotation is sufficient to give it an overall enormous magnetic field.  (If you want to read more about the answer to this curious question, the site Medium did a nice overview of it a while back.)

So it turns out that neutron stars aren't the simple things they appeared to be at first.  Not that this is much of a surprise -- seems like every time we answer one question in science, it generates three new ones.  What brought this up in the first place was yet another anomalous observation about neutron stars, described in a series of papers this past week in Astrophysical Journal Letters.  The conventional wisdom was that a neutron star's magnetic field would be oriented along an axis (which, as noted above, may not coincide perfectly with the star's spin axis).  This means that it would behave a bit like an ordinary magnet, with a north pole and a south pole on geometrically opposite sides.

That's what astronomers thought, until they found a pulsar with the euphonious name J0030+0451, 1,100 light years away in the constellation of Pisces.  Using the x-ray jets from the pulsar -- which should be aligned with its magnetic field -- they mapped the field itself, and found something extremely strange.

Instead of two jets, aligned with the poles of the magnetic field, J0030+0451 has three -- and they're all in the southern hemisphere.  One is (unsurprisingly) at the southern magnetic pole,  but the other two are elongated crescents at about sixty degrees south latitude.

To say this is surprising is an understatement, and the astronomers are still struggling to explain it.

"From its perch on the space station, NICER [the Neutron star Interior Composition Explorer] is revolutionizing our understanding of pulsars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington.  "Pulsars were discovered more than fifty years ago as beacons of stars that have collapsed into dense cores, behaving unlike anything we see on Earth."

It appears that we still have a way to go to fully explain how they work.  But that's how it is with the entire universe, you know?  No matter where we look, we're confronted by mysteries.  Fortunately, we have a tool that has proven over and over to be the best way of finding answers -- the collection of protocols we call the scientific method.  I  have no doubt that the astrophysicists will eventually explain the odd magnetic properties of pulsars.  But the way things go, all that'll do is open up more fascinating questions -- which is why if you're interested in science, you'll never run out of things to learn.

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This week's Skeptophilia book recommendation is pure fun, and a perfect holiday gift for anyone you know who (1) is a science buff, and (2) has a sense of humor.  What If?, by Randall Munroe (creator of the brilliant comic strip xkcd) gives scientifically-sound answers to some very interesting hypothetical questions.  What if everyone aimed a laser pointer simultaneously at the same spot on the Moon?  Could you make a jetpack using a bunch of downward-pointing machine guns?  What would happen if everyone on the Earth jumped simultaneously?

Munroe's answers make for fascinating, and often hilarious, reading.  His scientific acumen, which shines through in xkcd, is on full display here, as is his sharp-edged and absurd sense of humor.  It's great reading for anyone who has sat up at night wondering... "what if?"

[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!]