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, "Okay, hang on 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 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 -- over 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; a recurring theme here at Skeptophilia is that nature always seems to turn out to be more complicated than we expected.  What brought this up in the first place was yet another anomalous observation about neutron stars, described in a series of papers I ran across 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 I've said many times that if you're interested in science, you'll never run out of things to learn.

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A wolf, a disk, and a lighthouse

Because here in the United States, many Americans are looking at tomorrow's election the way a man walking in a railway tunnel sees the headlights of an approaching train, today I'd like to direct your attention away from the Earth entirely, into the cold, desolate voids of outer space.

Which, all things considered, seem like a pretty congenial place by comparison.

In the past week we've had three cool astronomical discoveries announced, highlighting the exciting fact of how much more we have left to learn about the universe in which we live.  The first comes from the European Southern Observatory, which got some fantastic new images of a nebula in the constellation Scorpio called the Dark Wolf Nebula, which (fitting to its name) they released on Halloween:

[Image credit: European Southern Observatory]

The Dark Wolf, and other dark nebulae -- such as the famous Coalsack Nebula in the constellation Crux -- are aggregations of dust and gas that shroud stars behind them.  They're far from being passive light-blockers, however; dark nebulae are often the sites of rapid star formation, as the material collapses into clumps and fusion starts.  Once this occurs, the radiation pressure from the newly-formed stars blows away the extra dust, revealing the newborn star cluster, such as what we see now in the Orion Nebula and the Pleaides.

The second study is a bit of a puzzle, and involves the star Vega, a bright star in the constellation Lyra easily visible in the Northern Hemisphere at this time of year.  Vega is only 25 light years away, and was made famous as the origin of the alien signal in the movie Contact, which remains my all-time favorite movie.

Vega is a young A-class blue-white star about twice the Sun's mass, forty times brighter, and almost 4,000 C hotter (surface temperature).  Because of its luminosity and proximity, it's one of the most intensively-studied stars in the sky, and a recent announcement by NASA (based on data from the Hubble and James Webb Space Telescopes) indicate that it's got a feature that's peculiar by any standards -- and suggest that one scene in Contact was downright prescient.

In the movie, astronomer Ellie Arroway intercepts a transmission from an advanced technological species which contains instructions on how to build a device that warps space and time, allowing a passenger to cross interstellar distances and drop in for a visit.  When Arroway (after many twists and turns and setbacks) ends up taking a ride in the device, it brings her to Vega, where she sees a massive debris disk -- but no planets.

And that's exactly what Hubble and the JWST found.  Having a debris disk isn't at all unusual; after all, current models indicate that planet formation occurs by gravitational clumping from a flat disk surrounding the parent star (much as stars coalesce from dust and gas in dark nebulae).  But what's strange is that Vega's disk is almost entirely homogeneous, made up of a circular sheet of similar-sized particles.  No planets at all.

"Between the Hubble and Webb telescopes, you get this very clear view of Vega," said team member Andras Gáspár of the University of Arizona. " It's a mysterious system because it's unlike other circumstellar disks we've looked at.  The Vega disk is smooth, ridiculously smooth."

There appears to be a trend toward gradually decreasing size at the edges of the disk, thought to be because radiation pressure tends to blow small particles outward more efficiently than larger ones.  But other than that, the disk is relatively featureless, which is something not seen in other stars of similar ages and characteristics, such as Fomalhaut in the constellation Piscis Australis.

"Given the physical similarity between the stars of Vega and Fomalhaut, why does Fomalhaut seem to have been able to form planets and Vega didn't?" said team member George Rieke, also of the University of Arizona.  "What's the difference?  Did the circumstellar environment, or the star itself, create that difference?  What's puzzling is that the same physics is at work in both."

The last story will appeal to anyone who likes to think about the extremes which nature can sometimes achieve, and has to do with something that's pretty astonishing all by itself -- neutron stars.  Neutron stars form from the gravitational core collapse of a star greater than about 1.4 solar masses; the outer atmosphere gets blown away in a supernova, and the core falls inward, overcoming electrostatic repulsion and electron degeneracy pressure, which has the effect of crushing electrons into atomic nuclei, forming (in essence) a gigantic ball of neutrons.

This means neutron stars are some of the densest known objects.  A matchbox-sized chunk of a typical neutron star would weigh three billion tonnes.  But they have another wild characteristic, which is why the topic comes up today; most of them rotate like crazy.

The reason is conservation of angular momentum -- the same reason that a spinning figure skater increases her rotational speed as she brings her arms inward.  When a neutron star collapses, this reduces its effective radius (what physicists call the moment of inertia), and the rate of rotation increases to compensate.

When the neutron star is emitting jets of radiation, this creates an effect like the beams from a lighthouse -- which is how we get pulsars.

The nebula surrounding the pulsar PSR B1509-58, which glows because of the radiation jets from the neutron star [Image is in the Public Domain courtesy of NASA]

And now, a team at the Technological University of Denmark has found a neutron star with a spin rate of an almost unimaginable 716 rotations per second, putting it in a tie for the fastest spinning astronomical object known.

"We were studying thermonuclear explosions from this system and then found remarkable oscillations, suggesting a neutron star spinning around its centre axis at an astounding 716 times per second," said Gaurava K. Jaisawal, first author on the study, which was published last week in the Astrophysical Journal.  "If future observations confirm this, the 4U 1820-30 neutron star would be one of the fastest-spinning objects ever observed in the universe, matched only by another neutron star called PSR J1748-2446."

So those are our cool discoveries in outer space for today.  And now, I suppose that we should reluctantly turn our attention back to the planet we live on.  If you live in the United States, please please please vote tomorrow.  If you live elsewhere, you might direct a prayer to whatever deity you happen to favor.  I know I've been a disbeliever for a good long while, but hell, at this point we need all the help we can get.

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The celestial lighthouse

Last week I did a piece on three weird astrophysical phenomena -- odd radio circles, high-energy neutrino bursts, and fast blue optical transients -- all of which have thus far defied explanation.  And this week, a paper came out in Nature about a recent discovery adding one more to the list of unexplained celestial curiosities -- one which has the alien intelligence aficionados raising their Spock-like eyebrows in a meaningful manner (although I hasten to point out that there is no evidence that either this one, or the other three I mentioned, have anything to do with you-know-who).

However, the most recent discovery is downright bizarre.  To understand why, a bit of background.

There are many more-or-less understood phenomena in astrophysics that result in a sudden surge in electromagnetic output from an astronomical body.  Some are aperiodic, or at least infrequent, such as fast radio bursts, which were discovered back in 2007 by astrophysicists Duncan Lorimer and David Narkevic.  These are quick, transient pulses in the radio region of the spectrum, and are now thought to be due either to neutron star mergers or starquakes on the surface of magnetars.

Then there are the repeating ones, such as the fast blinking on-and-off of pulsars.  These are the rapidly whirling cores of collapsed massive stars, which funnel out beams of high-energy radiation aligned with the poles of their magnetic fields; because of the star's rotation, the beam appears to pulse, in some cases dozens of times a second.  They were discovered back in 1967 by the brilliant astronomer Jocelyn Bell Burnell, but because no one could figure out what might create a repeating signal that regular, and also because Burnell was a woman in a field almost entirely dominated by men, her discovery was derisively referred to as LGM ("Little Green Men"), and assumed to be from some sort of prosaic terrestrial source.  It was only when more of them were found that astronomers began to take her seriously.  In 1974, the Nobel Prize in Physics was awarded for the development of radio astronomy, and in particular, for the discovery of pulsars...

... to Antony Hewish and Martin Ryle.  Note who wasn't included.  Burnell has graciously stated that she "feels no bitterness toward the Nobel Committee," but in her place, I sure as hell would have.

The paper in Nature, however, describes an object that doesn't seem to fit any of the known types of electromagnetic pulses.  Called GPM J1839-10, it releases energy in the radio region of the spectrum.  But in terms of periodicity, it's somewhere between pulsars (which are so regular they've been proposed as celestial clocks) and fast radio bursts (which are apparently aperiodic).  GPM J1839-10 is slow -- its signal reaches a peak about every twenty-two minutes -- but it's not precisely regular.  The four hundred seconds centering on that twenty-two minute mark is when the peak is most likely to come, but sometimes the window will pass with no peak.  The length of the pulses is also variable, usually between thirty and three hundred seconds in length.  And unlike both fast radio bursts and pulsars, the amplitude of the peak is quite low in energy.

As science writer John Timmer put it in Ars Technica, "The list of known objects that can produce this sort of behavior... consists of precisely zero items."

What's weirdest is that going back through the records of astronomical observations, this object has been doing its thing for three decades, and only just now is attracting attention.  The astrophysicists thus far have no good explanation for what it might be.  It sits out there in space, slowly flashing on and off like some sort of interstellar lighthouse, and the the flat truth is that at the moment, no one has the slightest idea what it might be.

Of course, "We don't know" opens the door for a certain group of people to say "We do!"

As I've said before, no one would be more delighted than me if we did come across evidence of an extraterrestrial signal, but I strongly suspect this ain't it.  For one thing, the semi-regular blips it's putting out don't appear to contain any information; put a different way, the pattern isn't complex.  It could be a beacon, I suppose, but how you'd tell the difference between an alien-built celestial lighthouse and a star of some sort that is sending out pulses of radio waves is beyond me.  With nothing more to go on, by far the greater likelihood is that there is some natural explanation for this slowly-pulsing object -- we just haven't found it yet.

Even so, it's intriguing.  I've always loved a mystery, and this certainly is one.  It's possible that we've missed other objects of this type; the kind of detailed repeated scans of the sky in the radio region of the spectrum that it would take to detect a pulsation this slow have only begun to be done with any kind of thoroughness.  Like with Burnell's discovery of pulsars, it took finding others before astronomers had enough data to start putting together an explanation.

But if no others are found, what then?  It'll be added to the list of astronomical mysteries, of which there are plenty.  It's a big old universe, and filled with wonders, many of which we are only just beginning to understand.

And those are cool enough without the aliens.  Although, of course, I wouldn't object to the aliens as well.

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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.

*****************************

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!]

The view from afar

One of the strangest phenomena in the universe -- and there's a lot of competition in that regard -- is the neutron star.

This is the ultimate fate of stars of mid-range mass -- between 10 and 29 solar masses.  With stars this size, when they exhaust their hydrogen fuel, the outward pressure from fusion of hydrogen into helium stops, and the core collapses, heating it up catastrophically.  The result is a supernova, in which the outer atmosphere of the star is blown away completely.  The remnant of the core is crushed inward, forcing the electrons into the nuclei of the atoms -- literally squeezing all the space out of the matter inside.  The electrons and protons, presumably present in roughly equal numbers, are smashed together, canceling out their net charge and resulting in a great big ball o' neutrons.

I remember learning about this when I took an astronomy class in college, and asking the professor in some astonishment, "So, neutron stars are basically enormous atomic nuclei?"

He said, "Essentially, yes. They're degenerate matter -- made up entirely of neutrons pushed as close together as possible."

There are a couple of mind-blowing results from this.  One is that because ordinary matter is largely empty space and the degenerate matter in neutron stars isn't, neutron stars are dense beyond what you can imagine.  The estimate is that a matchbox-sized chunk of a neutron star would weigh three billion metric tons.  The other thing that is bizarre about them is that because most -- probably all -- stars spin, as the core collapses into a neutron star, reducing a spinning ball that was on the order of two million kilometers in diameter to one that is ten kilometers across, its spin rate increases.  A lot.  The Law of Conservation of Angular Momentum implies that if a spinning body decreases in radius, it has to increase in rotational rate -- something seen when figure skaters bring in their arms, making them spin faster and faster.

But that increase is peanuts compared to what happens here.  One of the first neutron stars discovered, at the center of the Crab Nebula, is spinning thirty times a second.  This makes it seem to flash off and on at that rate as beams of radiation aligned with its magnetic field sweep across the Earth like the beam from a lighthouse.  This is so hard to imagine that when they were first identified by Jocelyn Bell Burnell in 1967, pulsars -- the name she gave to these flashing stars -- were thought to be signals from an extraterrestrial intelligence, and went by the code name LGM (Little Green Men).

[Image licensed under the Creative Commons ESA/Hubble, Moving heart of the Crab Nebula, CC BY 4.0]

All of this is by way of background for a news story that astronomers have observed, for the second time ever, the merger of two neutron stars.

The first time, you might recall, was almost two years ago, when two neutron stars in tight orbit finally coalesced, resulting in a pulse of gravitational waves that gave powerful support to Einstein's General Theory of Relativity.  This time, the merger was caught on x-ray camera -- as the collision occurred, it caused a shower of x-rays and left behind a single larger neutron star with an unimaginably huge magnetic field -- called a magnetar.

"We’ve found a completely new way to spot a neutron star merger," said Yongquan Xue, astronomer at University of Science and Technology of China and lead author of a paper on the subject that appeared two weeks ago in Nature.  "The behavior of this X-ray source matches what one of our team members predicted for these events."

I haven't told you what's the coolest thing about this.  The colliding neutron stars Xue et al. are studying aren't even in our own galaxy.  What they've done is develop a way to study the collision of two blobs of highly peculiar matter from a distance of six billion light years.

Which is not only an unimaginable distance, but means that the collision happened six billion years ago.  At that point, the Earth hadn't even completely coalesced from the primordial ring of dust and debris that formed it.  Six billion years is just shy of half the time between the Big Bang and now.

So I think you can label my mind blown.

Despite some of the stupid things humans do sometimes, you have to admire our ingenuity.  Sitting on this little speck of rock orbiting an ordinary star in the edge of one arm of an ordinary galaxy, we've found a way to probe the deepest secrets of the cosmos.  Or, as Carl Sagan put it:  "We are a way for the universe to know itself."

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This week's Skeptophilia book recommendation is a classic, and is pure fun: Man Meets Dog by the eminent Austrian zoologist and ethologist Konrad Lorenz.  In it, he looks at every facet of the human/canine relationship, and -- if you're like me -- you'll more than once burst out laughing and say, "Yeah, my dog does that all the time!"

It must be said that (as the book was originally written in 1949) some of what he says about the origins of dogs has been superseded by better information from genetic analysis that was unavailable in Lorenz's time, but most of the rest of his Doggy Psychological Treatise still stands.  And in any case, you'll learn something about how and why your pooches behave the way they do -- and along the way, a bit about human behavior, too.

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