Surf's up

One thing that never fails to leave me feeling awestruck is when I consider that astronomers figured out the shape and size of the Milky Way Galaxy while residing inside it.

I mean, think about it.  Imagine you're a tiny being (with a telescope) sitting on a raindrop near one edge of a huge cloud, and your task is to try to measure the distances and positions of enough other raindrops to make a good guess about the size and shape of the entire cloud.  That's what the astronomers have accomplished -- enough to state with reasonable confidence that we're in one of the arms of a barred spiral galaxy.

If ever there was an image you need to study in detail, this is it.  Take a look at the original, close up.  The Solar System is in the Orion Arm, directly down from the center of the galaxy.  The thing that blew me away is the circle marked "Naked Eye Limit" -- literally every star you have ever seen without the use of a telescope is in that little circle.  [Image licensed under the Creative Commons Pablo Carlos Budassi, Milky Way map, CC BY-SA 4.0]

What's even more astonishing is that the stars making up the Milky Way (and every other galaxy) are moving.  Not fast enough, on that kind of a size scale, that the map will be inaccurate any time soon; but fast enough to be measurable from here on Earth.  In fact, it was anomalies in galactic rotation curves -- the plot of the orbital speed of stars around the center of the galaxy, as a function of their distance from the center -- that clued in the brilliant astrophysicist Vera Rubin that there was (far) more matter in galaxies than could be seen, leading to the bizarre discovery that there is five times more dark matter (matter that only interacts via gravity) than there is the ordinary matter that makes up you, me, the Earth, the Sun, and the stars.

All of this makes the new study out of the European Space Agency even more incredible.  New data from the Gaia Telescope has found that the entire Milky Way is rippling as it rotates, a little like the fluttering of a Spanish dancer's frilly skirt.  The period of this wave-like motion is on the order of ten thousand light years, and it appears to affect the entire galaxy.

The astrophysicists are still trying to figure out what's causing it.

"What makes this even more compelling is our ability, thanks to Gaia, to also measure the motions of stars within the galactic disc," said lead author Eloisa Poggio, an astronomer at the Istituto Nazionale di Astrofisica (INAF) in Italy.  "The intriguing part is not only the visual appearance of the wave structure in 3D space, but also its wave-like behavior when we analyze the motions of the stars within it."

The discovery hinged on the use of standard candles, something you may be familiar with if you've read any cosmology.  Calculating distances of astronomical objects is tricky, for the same reason that it's difficult to tell how far away a single light is at night.  If the light seems bright, is it intrinsically bright (and perhaps quite distant), or are you looking at something that is dimmer, but close to you?  The only way to calculate astronomical distances is to use the small number of objects for which we know the intrinsic brightness.  The two most common are Cepheid variables, stars for which the oscillation period of luminosity is directly related to their brightness, and type 1a supernovas, which always have about the same peak luminosity.  Between these two, astrophysicists have been able to measure the changing positions of stars as the ripple of the wave passes them.

So the stars in our galaxy are riding the cosmic surf, and at the moment no one knows why.  One possibility is that this is a leftover gravitational effect from a collision with a dwarf galaxy some time in the distant past -- a little like the ripples from dropping a pebble into a pond lasting long after the pebble has come to rest on the bottom.  But the truth is, it will take further study to figure out for sure what's causing the wave.

Me, I find the whole thing staggering.  To think that only a little over a hundred years ago, there were still astronomers arguing (vehemently) that the only galaxy in the universe was the Milky Way, and all of the other galaxies were merely small local nebulae.  The last century has placed us into a universe vaster than the ancients could ever have conceived -- and I have no doubt that the next century will astonish us further, and in ways we never could have imagined.

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The lure of the unknown

Carl Sagan once said, "Somewhere, something incredible is waiting to be known."

I think that's one of the main things that attracted me to science as a child; its capacity to astonish.  I still remember reading the kids' books on various scientific stuff and being astounded to find out things like:

• dinosaurs, far from being the "failed experiment" they're often characterized as, "ruled the Earth" (as it were) for about five hundred times longer than humans have even existed.  (I only much later found out that dinosaurs still exist; we call 'em birds.)
• when supergiant stars end their lives, they detonate in a colossal explosion called a supernova that gives off in a few seconds as much energy as the Sun will emit in its entire lifetime.  What's left is called a black hole, where the gravitational pull is so powerful even light can't escape.
• bats can hear in a frequency range far above humans, and are so sensitive to their own vocalizations that they can hear the echoes of their own voices and distinguish them from the cacophony their friends and relatives are making.
• when an object moves, its vertical and horizontal velocities are completely independent of each other.  If you shoot a gun horizontally on a level surface, and simultaneously drop a bullet from the gun's muzzle height, the shot bullet and the dropped bullet will hit the ground at the same time.

And that's all stuff we've known for years, because (not to put too fine a point on it) I'm so old that when I was a kid, the Dead Sea was just sick.  In the intervening fifty years since I found out all of the above (and lots of other similar tidbits) the scientists have discovered tons of new, and equally amazing, information about our universe and how it works.  We've even found out that some of what we thought we understood was wrong, or at least incomplete; a good example is photoperiodism, the ability of flowering plants to keep track of day length and thus flower at the right time of year.  It was initially thought that they had a system that worked a bit like a chemical teeter-totter.  A protein called phytochrome has a "dark form" and a "light form" -- the dark form changes to the light form during the day, and the reverse happens at night, so the relative amounts of the two might allow plants to keep track of day length.  But it turns out that all it takes is a flash of red light in the middle of the night to completely upend the plant's biological clock -- so whatever is going on is more complex that we'd understood.

This sudden sense of "wow, we don't know as much as we thought!", far from being upsetting, is positively thrilling to scientists.  Scientists are some of the only people in the world who love saying, "I don't understand."  Mostly because they always follow it up with "... yet."  Take, for example, the discovery announced this week by the National Radio Astronomy Observatory of a huge cloud of gas and dust in our own Milky Way Galaxy that prior to this we hadn't even known was there.

It's been named the Midpoint Cloud, and it's about two hundred light years across.  It's an enormous whirlpool centered on Sagittarius A*, the supermassive black hole at the galaxy's center, and seems to act like a giant funnel drawing material inward toward the accretion disk.

"One of the big discoveries of the paper was the giant molecular cloud," said Natalie Butterfield, lead author of the paper on the phenomenon, which appeared this week in The Astrophysical Journal.  "No one had any idea this cloud existed until we looked at this location in the sky and found the dense gas.  Through measurements of the size, mass, and density, we confirmed this was a giant molecular cloud.  These dust lanes are like hidden rivers of gas and dust that are carrying material into the center of our galaxy.  The Midpoint Cloud is a place where material from the galaxy's disk is transitioning into the more extreme environment of the galactic center and provides a unique opportunity to study the initial gas conditions before accumulating in the center of our galaxy."

[Image credit: NSF/AUI/NSF NRAO/P.Vosteen]

Among the amazing features of this discovery is that it contains a maser -- an intense, focused microwave source, in this case thought to be caused by compression and turbulence in the ammonia-rich gas of the cloud.  Additionally, there are several sites that seem to be undergoing collapse; we might be witnessing the birth of new stars.

What's astonishing to me is that this cloud is (1) humongous, (2) in our own galaxy, and (3) glowing like crazy in the microwave region of the spectrum, yet no one had any idea it was there until now.  How much more are we overlooking because we haven't tuned into the right frequency or turned our telescopes to the right coordinates?

The universe is a big place.  And, I suspect, it's absolutely full of surprises.  Hell, there are enough surprises lying in wait right here on the Earth; to give just one example, I've heard it said that we know more about the near side of the Moon than we do about the deep oceans.

How could anyone not find science fascinating?

This is also why I've never understood how people think that science's progress could be turned into a criticism -- I used to hear it from students phrased as, "why do we have to learn all this stuff when it could all be proven wrong tomorrow?"  Far from being a downside, science's capacity to update and self-correct is its most powerful strength.  How is it somehow better to cling to your previous understanding in the face of evidence to the contrary?

That, I don't think I'll ever come close to comprehending.

I'll end with another quote from a scientific luminary -- the brilliant physicist Richard Feynman -- that I think sums it all up succinctly: "I'd much rather questions that cannot be answered than answers that cannot be questioned."

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The glowing death spiral

One of the things that always blows my mind about astronomy is how good we've gotten at using indirect evidence to figure out what's going on up there.

In a way, of course, it's all indirect, at least in the sense that everything we're seeing is (1) wicked far away, and (2) in the past.  I remember how weirded out I was when I first ran into the latter concept, back when I was maybe twelve years old.  My first inkling of it happened when I was out on a walk with my dad, and down the street there was a guy using a sledgehammer to pound in a fence post.  The strange thing was, I saw the hammer's head strike the post, and then, a second or two later I heard the bang of the strike.  I asked my dad why that was.

"Well," he said, after a moment's thought, "the sound takes a moment to get to your ears.  It's why we always see the lightning before we hear the thunder.  And the farther away it is, the longer the delay.  So as we get closer to the guy, the delay should get smaller."

Which, of course, it did.

After I'd had a minute to process that, I said, "But light takes time to get to your eyes, too.  A very short amount of time, but still, some time.  So does that mean you're not seeing things as they are, but as they were in the past?"

My dad agreed that must be so.

Upon learning some more physics, I found out that the Sun is far enough away from the Earth that it takes a bit over eight minutes for light to travel the distance in between.  So if the Sun suddenly vanished -- an unlikely eventuality, fortunately -- we not only wouldn't know it for eight minutes, there is no possible way to know it.  Einstein showed that information can't travel any faster than the speed of light -- it really is the ultimate speed limit.

The nearest star, Proxima Centauri, is 4.25 light years, so we're seeing it as it was 4.25 years ago, and have no way of seeing what it looks like right now.  Given that it seems to be a fairly stable star, it probably looks much the same; but the fact remains that we can't know what its current appearance is.  The most distant objects we've seen through our most powerful telescopes are some of the quasars, at thirteen billion light years distant (and thus, what they looked like thirteen billion years ago).  So what those quasars look like right now -- where they are, if they even exist any more -- is impossible to know.  We're seeing them as they looked shortly after the universe began; what they are today is anyone's guess.

Impressively far away, but at least still in our own galaxy, is Sagittarius A*, the supermassive black hole at the center of the Milky Way.  It's 26,000 light years distant.  But despite how far away it is -- and the fact that massive dust clouds lie between it and us, obscuring what light it does emit -- we've been able to find out an astonishing amount about it.

Sagittarius A*, as imaged by NASA's Chandra X-Ray Observatory (Image is in the Public Domain]

This, in fact, is why the topic comes up today -- some research out of the Université de Strasbourg that found evidence of a sudden flare-up of Sagittarius A*, around two hundred years ago.  For such a behemoth, it's been relatively quiet since its discovery in 1990.  But astrophysicist Frédéric Marin has found a cosmic glow that resulted from a brief, powerful flare of x-rays, during which Sagittarius A* was radiating a million times brighter than it is now.

The x-rays caused the clouds of dust surrounding the black hole to fluoresce; from the distance of those clouds from the event horizon of the black hole, Marin and his team determined that they must have been hit by a strong blast of x-rays about two hundred years ago.  (Keep in mind that because of the time-lag effect I described earlier, these times are all as seen from Earth; the actual flare-up occurred 26,200 years ago, or thereabouts.)

What caused the burst isn't known, but is surmised to be the sudden swallowing by the black hole of a denser blob of cosmic dust and gas.  As material goes into a death spiral toward the event horizon of a black hole, it speeds up, and electrons are stripped from atoms, leaving a whirling funnel cloud of charged particles.  These particles radiate away some of that energy in the form of x-rays -- the "smoking gun" that allows us to see black holes, which otherwise would be entirely invisible.

If you get a little nervous about such astronomical violence, there's no cause for alarm; neither Sagittarius A* nor any of its radiation blasts pose any sort of danger to us.  We'd only be in trouble if we were a great deal closer to the galactic center.

So we can just sit back and appreciate the amazing capacity the astrophysicists have for sifting through data and painting us a picture of what the universe looks like.  In this case, the last blaze of glory for a dust cloud that got sucked into a supermassive black hole 26,000 light years away.

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Blowing bubbles

After Monday's post, about the bizarre hypergiant star Stephenson 2-18, a reader commented, "If you think that's weird, look up 'Fermi bubbles.'"

So I did.  And... yeah.

Discovered back in 2010, the Fermi bubbles -- so named because they were discovered by NASA's Fermi Gamma-ray Telescope -- are a pair of nearly perfectly symmetrical bubbles of high-intensity gamma rays positioned above and below the galactic plane of the Milky Way.  They're huge; each one has a diameter of about 23,000 light years.

False-color image of the Fermi bubbles.  The Milky Way is seen edge-on, running across the middle of the photograph.  [Image is in the Public Domain courtesy of NASA/Goddard Space Flight Center]

Back in 2015, the Fermi bubbles were still completely unexplained, and in fact made #1 in Astronomy magazine's list of "The Fifty Weirdest Objects in the Universe."  That they had something to do with Sagittarius A*, the enormous black hole at the center of the galaxy, seemed like a reasonable guess; but what could create something with such a peculiar figure-eight shape was unknown.

A team led by astrophysicist Rongmon Bordoloi of the Massachusetts Institute of Technology, however, has a model to explain them.  Something around nine million years ago -- not really that far back, in the grand scheme of things -- Sagittarius A* pulled in an enormous cloud of gas and dust.  The origin of that dust cloud is uncertain, but what happened after it got caught is all too clear.  Most of it undoubtedly took the one way trip past the event horizon, but some of it was spun so fast by the black hole's rotation and the resultant twisting of space-time that it gained enough momentum to escape along Sagittarius A*'s spin axis -- i.e., perpendicular to the galactic plane.

This not only accelerated the gas to an unimaginable two million miles an hour, it heated it -- at its edges to just shy of ten thousand degrees C, and near the point of outflow to almost ten million degrees.  It's this heating that caused it to produce gamma rays, which is how the structure was detected.

Not a phenomenon you'd want to be standing in the way of.

"We have traced the outflows of other galaxies, but we have never been able to actually map the motion of the gas," Bordoloi said, somehow resisting adding, and holy shit, this thing is amazing.  "The only reason we could do it here is because we are inside the Milky Way.  This vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow."

And, along the way, to figure out what's going on with the number one Weirdest Object in the Universe.  Having an explanation doesn't make it any less impressive, of course.  Gas at a temperature of ten million degrees being flung about at two million miles per hour by a ginormous black hole isn't exactly a cause for a shoulder-shrug.

Besides, there are forty-nine more weird objects (at least) left to explain.  If you're into science, it means you'll never be bored.

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Continental bombardment

One of the reasons science is so useful is that our intuition about how things work is so often wrong.

A good example is the classic physics thought-experiment about taking two bullets -- one loaded in a gun that has the barrel perfectly horizontal, the other one held in your hand at the same height.  You fire the gun over level ground, and simultaneously let go of the bullet.  Which hits the ground first?

It seems like they should take different amounts of time; the one shot from the gun is traveling much farther, for one thing.  Most people think because of that, the dropped bullet would hit the ground first.  In fact, you undoubtedly know that (omitting the effects of air resistance or uneven terrain), the two bullets hit the ground at precisely the same time; Isaac Newton showed that the horizontal and vertical components of velocity are completely independent of one another.  It doesn't matter that the shot bullet is traveling rapidly in the horizontal direction; it and the dropped bullet have exactly the same vertical acceleration, namely 9.8 meters per second per second downward, starting from rest.  Thus they take exactly the same amount of time to hit the ground.

I was reminded of another example of this by some cool new research (which I will get to presently) I ran across yesterday.  It has to do with geology, namely, what the crust and mantle of the Earth are like.  It seems common-sensical that the surface of the Earth is uniformly cool and rocky, and the interior (judging by volcanoes) is molten; and while that isn't wrong in a broad-brush sort of way, what it misses is that there's a big difference between the rocks currently under your feet and the rocks at the bottom of the deep ocean.  Continental crust is thick, and extends both upwards into the air and downward into the mantle, a little like an iceberg; the rocks that make up the continents are, on the whole, lighter than oceanic crust, which is thin, brittle, and dense.  So the continents are literally floating in the liquid rock of the upper mantle.

This, of course, is what gives rise to plate tectonics; those iceberg-like blobs of floating rock we call continents, and the thin, heavy slabs of deep oceanic crust, jostle around on the magma of the upper mantle, colliding, pulling apart, shifting, and subducting (one piece going underneath another), and that gives rise to most of the geologic processes you've heard about.

But here's where we run into a fascinating question; why is the chemistry of continental rock (and thus its density) so different than oceanic rock?

[Image licensed under the Creative Commons Eric Gaba (Sting - fr:Sting), Tectonic plates boundaries detailed-en, CC BY-SA 2.5]

A piece of research out of Curtin University (Australia), published this week in Geology, suggests a surprising answer: the material that makes up the cratons -- the large, stable blocks of rock that form the nuclei of continents -- is extraterrestrial in origin.

Chris Kirkland, lead author of the study, was looking at the age of rocks in cratons around the world, and found something curious; their production seemed to occur at (roughly) two hundred million year intervals.  The formation of these blocks of rock coincide with the points at which the Solar System was passing through an area of dense stars in the spiral arm of the Milky Way as it orbited the Galactic Center.

"From looking at the age and isotopic signature of minerals from both the Pilbara Craton in Western Australia and North Atlantic Craton in Greenland, we see a similar rhythm of crust production, which coincides with periods during which the Solar System journeyed through areas of the galaxy most heavily populated by stars," Kirkland said.  "When passing through regions of higher star density, comets would have been dislodged from the most distant reaches of the Solar System, some of which impacted Earth.  Increased comet impact on Earth would have led to greater melting of the Earth’s surface to produce the buoyant nuclei of the early continents... Linking the formation of continents, the landmasses on which we all live and where we find the majority of our mineral resources, to the passage of the Solar System through the Milky Way casts a whole new light on the formative history of our planet and its place in the cosmos."

Of course, we've known for a while that all of the rock on Earth ultimately came from the coalescence of asteroids as the Solar System formed; but it's weird to think that the rock we're currently sitting atop may have been thrown at us by the near passage of other stars to our Sun as the entire Solar System hurtled its way around its host galaxy.  Whether Kirkland's claim will bear out under scrutiny, I don't know; but what's certain is that the methods of science has opened our eyes to a myriad processes that would have been entirely opaque to our so-called common sense.  Yes, scientists do get it wrong sometimes; they're fallible, and can misinterpret data or get hung up on their biases just like anyone.  But only science provides a protocol for catching and fixing those mistakes.

So it may not be perfect -- but for getting near to the truth, science really is the only game in town.

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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!]

The galactic shredder

One of the beliefs of our ancestors that has taken the hardest hit from science is that the heavens are static.

The (apparent) movement of the stars and planets against the backdrop of the night sky seemed so orderly that early astronomers like Ptolemy thought they moved in circles -- the perfect symmetry of the circle seemed appropriate for the divine reaches of the heavens.  It's one of the reasons that comets and supernovas upset everyone so much.  They were unpredictable, coming and going with no warning and no apparent cause, so they had to be portents of evil.

Then along came Tycho Brahe and Kepler and Newton, and science demonstrated that even if the movement of the planets wasn't in perfect circles, they did obey fixed mathematical rules that allowed the religious to breathe a sigh of relief (once they stopped putting scientists under house arrest or burning them at the stake).  Orderliness returned, even if it wasn't the order Ptolemy envisioned.  As Galileo put it, "Mathematics is the language in which God wrote the universe."

But even that didn't hold.  Edmond Halley (of Halley's Comet fame) discovered that the stars' positions were changing, that the "eternal heavens" weren't so eternal after all.  Einstein and Schrödinger showed us that Newton's vision of the cosmic rule book was wrong, or at least incomplete.  Heisenberg demonstrated that on some level, reality is fuzzy, that there's an inherent uncertainty that isn't an analytical flaw or poor experimental technique, it's built into the system.  If we gain precision in one measurement, we lose precision in another, and there's no way to get rid of the blur because the fundamental stuff of the universe is itself blurry.

Spooky action at a distance.  Quantum entanglement.  Bell's inequality.  Dark matter.  Dark energy.  All topics I've dealt with here before, and all of which emphasize that however far we've come in our understanding of the universe, we still have a deeply incomplete picture of things.

And still the stars turn in their courses, leading us to see permanence where there is none.

All of this disquieting stuff comes up because of a paper that appeared two weeks ago in Nature Astronomy called, "Detection of the Milky Way Reflex Motion Due to the Large Magellanic Cloud Infall."  In it, astrophysicists Michael S. Petersen and Jorge Peñarrubia of the University of Edinburgh have demonstrated that the Milky Way galaxy itself, which we picture as serenely turning in space like some kind of slow, tranquil whirlpool, is actually being torn apart.

The culprit is the Large Magellanic Cloud, an elliptical "satellite" galaxy named for Ferdinand Magellan, the Portuguese explorer who was the first white European to describe it.  The reason something so (relatively) small can have such a large effect is not only its proximity, but its dark matter content, which seems to be disproportionally high.  The authors write:

The Large Magellanic Cloud is the most massive satellite galaxy of the Milky Way, with an estimated mass exceeding a tenth of the mass of the Milky Way.  Just past its closest approach of about 50 kpc, and flying past the Milky Way at an astonishing speed of 327 km s−1 (ref. 6), the Large Magellanic Cloud can affect our Galaxy in a number of ways, including dislodging the Milky Way disk from the Galactic centre of mass.  Here, we report evidence that the Milky Way disk is moving with respect to stellar tracers in the outer halo in a direction that points at an earlier location on the Large Magellanic Cloud trajectory.  The resulting reflex motion is detected in the kinematics of outer halo stars and Milky Way satellite galaxies with accurate distances, proper motions and line-of-sight velocities.  Our results indicate that dynamical models of our Galaxy cannot neglect gravitational perturbations induced by the Large Magellanic Cloud infall, nor can observations of the stellar halo be treated in a reference frame that does not correct for disk reflex motion.

Did you catch that bit about "dislodging the Milky Way disk from the Galactic centre of mass?"

That's scientific-ese for "ripping it to shreds."

[Image licensed under the Creative Commons 

ESO/VMC Survey, The Large Magellanic Cloud revealed by VISTA, CC BY 4.0

So if anyone thought the Milky Way was a more-or-less permanent structure, this study killed that idea.  "This discovery definitely breaks the spell that our galaxy is in some sort of equilibrium state," said co-author Jorge Peñarrubia, in a press release from the University of Edinburgh.  "Actually, the recent infall of the LMC is causing violent perturbations onto the Milky Way.  Understanding these may give us an unparalleled view on the distribution of dark matter in both galaxies."

As with many studies, this one brings up more questions than it answers.  Why is the LMC moving at such an "astonishing" rate?  (As cautious as most scientists are in their word choice, the fact that they called its speed "astonishing" in a major scientific journal is eye-opening indeed.)  Why does it have enough dark matter to perturb the motions of a galaxy ten times larger, both in mass and in diameter, from a distance of 160,000 light years away?  What ultimate effect will the LMC's swift passage have on the shape of our own galaxy?

For me, it just reinforces something that has come up in Skeptophilia many times; we are very, very, very small in an absolutely enormous universe.  It's both awe-inspiring and a little frightening.  A good thing, probably, that we humans can't stay focused for long on our cosmic insignificance; our day-to-day needs and demands take over pretty quickly, and after all, even the astrophysicists have to fix lunch and renew their drivers' licenses and sleep at night.

But pondering this kind of thing even for a little while is kind of overwhelming, isn't it?  I like to take a quick look, but I don't think our brains are built to stare into the void for any extended period of time.  So if you're looking for me, I'll be huddled under my blankie for the rest of the day.

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I've always had a fascination with how our brains work, part of which comes from the fact that we've only begun to understand it.  My dear friend and mentor, Dr. Rita Calvo, professor emeritus of human genetics at Cornell University, put it this way.  "If I were going into biology now, I'd study neuroscience.  We're at the point in neuroscience now that we were in genetics in 1900 -- we know it works, we can see some of how it works, but we know very little in detail and almost nothing about the underlying mechanisms involved.  The twentieth century was the century of the gene; the twenty-first will be the century of the brain."

We've made some progress in recent years toward comprehending the inner workings of the organ that allows us to comprehend anything at all.  And if, like me, you are captivated by the idea, you have to read this week's Skeptophilia book recommendation: neuroscientist Lisa Feldman Barrett's brilliant Seven and a Half Lessons About the Brain.

In laypersons' terms, Barrett explains what we currently know about how we think, feel, remember, learn, and experience the world.  It's a wonderful, surprising, and sometimes funny exploration of our own inner workings, and is sure to interest anyone who would like to know more about the mysterious, wonderful blob between our ears.

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

Collision of galaxies

When I was an undergraduate at the University of Louisiana, I and several of my friends were blown away by the original series Cosmos, written and narrated by Carl Sagan.

Monday mornings, we gathered in the student lounge, eagerly discussing whatever mind-blowing filigree of physics had been the subject of that week's episode.  I still recall one of the ones that made the biggest impression on me -- the tenth episode, "The Edge of Forever," which included, among many other things, wonderful simulations of the motion of stars within a galaxy, and what happens when two galaxies collide.  (You can watch a clip of it here.)  The simulations were (at the time) state-of-the-art, and certainly enough to blow the mind of a sophomore physics student like myself; what struck me most was that galaxies aren't rigid, and their constituent stars don't "hang together," but move independently around the massive black hole at the galactic core.  This can settle down into a shape that seems pretty stable -- such as the spiral pattern of the Milky Way -- or it can destabilize, flinging stars out into space, exploding the galaxy and scattering its pieces across hundreds of thousands of light years.

Sagan, of course, put it best: "A galaxy is a fluid made of a billion suns, all bound together by gravity."

When galaxies collide, it disrupts both completely; at the same time, collisions between the stars themselves are extremely uncommon.  However big the stars are, they're still minuscule with respect to the galaxies that contain them.  It's like the atoms writ large, isn't it?  The seemingly solid matter around you is made up of tiny charged particles interacting through the force of electromagnetism, but in between those particles is... nothing.  Matter is mostly empty space, and only seems solid because you're feeling the mutual repulsion of the electrons in your fingers and the electrons on the surface of whatever you're touching.  Likewise, most of interstellar space is very close to nothing, and the galaxies themselves are made up of particles (stars) interacting through a different force (gravity), and separated by vast, empty voids.

Makes you almost think that the pagans might have been on to something with their dictum of "As above, so below."

Map of the Milky Way, as it would look from above the galactic disk [Image licensed under the Creative Commons 鄭興武和馬克 裡德（Mark J. Reid）銀河系棒和旋臂結構遺產性巡天(BeSSeL)項目組/南京大學/哈佛-斯密松天體物理中心., Milky Way large, CC BY-SA 4.0]

This topic, and my reminiscences of Cosmos, come up because of a paper in Nature Astronomy last week called "Evidence for a Vast Prograde Stellar Stream in the Solar Vicinity," by a team led by astronomer Lina Necib of the California Institute of Technology.  What this paper tells us is something stunning; there is a streamer of stars in the Milky Way that started out somewhere else, and collided with our galaxy.  Rather fortunately, apparently the angle and velocity with which the streamer hit were more or less the same direction the original galaxy was turning, so these stars simply got sucked in, like some bits of debris going down a whirlpool.

The streamer has been named Nyx, after the Greek goddess of the night.  250 stars have been identified as being part of Nyx.  "The two possible explanations here are that they are the remnants of a [galactic] merger, or that they are disk stars that got shaken into their new orbits because of a collision with the disk of the Milky Way," said study lead author Lina Necib, in an interview with CNN.  The likelihood, though, is the former, something that is expected to be confirmed by chemical analysis of the constituent stars.  "Galaxies form by swallowing other galaxies," Necib said. "We've assumed that the Milky Way had a quiet merger history, and for a while it was concerning how quiet it was because our simulations show a lot of mergers.  Now, we understand it wasn't as quiet as it seemed.  We're at the beginning stages of being able to really understand the formation of the Milky Way."

I think it's stunning that we can figure out this sort of thing at all -- that 250 out of the estimated 250 billion stars in the Milky Way started out somewhere else in the universe.  I think that's pretty damn impressive.  "This particular structure is very interesting because it would have been very difficult to see without machine learning," Necib said.  "I think we reached a point in astronomy where we are not data limited anymore.  This project is an example of something that would have not been possible a few years ago, the culmination of developments in data with Gaia, high resolution simulations, and machine learning methods."

How pleased and amazed Carl Sagan would have been.  He went a long way toward bringing the wonders of the universe, from the largest scales to the smallest, to laypeople.  He certainly blew the minds of me and my friends, and that was back in 1980.  Necib's comment, that we're still at the beginning of being able to understand the formation of galaxies, tells us that we have a long way still to go -- and that many, many more eye-opening discoveries are sure to come our way in the next years.

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This week's Skeptophilia book of the week is for anyone fascinated with astronomy and the possibility of extraterrestrial life: The Sirens of Mars: Searching for Life on Another World, by Sarah Stewart Johnson.

Johnson is a planetary scientist at Georgetown University, and is also a hell of a writer.  In this book, she describes her personal path to becoming a respected scientist, and the broader search for life on Mars -- starting with simulations in the most hostile environments on Earth, such as the dry valleys of central Antarctica and the salt flats of Australia, and eventually leading to analysis of data from the Mars rovers, looking for any trace of living things past or present.

It's a beautifully-told story, and the whole endeavor is tremendously exciting.  If, like me, you look up at the night sky with awe, and wonder if there's anyone up there looking back your way, then Johnson's book should be on your reading list.

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

Ripples in the cosmic pond

I know I've said this before, so at the risk of ringing the changes on this once too many times: I find it endlessly fascinating how much we can figure out about the universe, sitting here on this little speck of rock circling a mediocre star in the arm of an average galaxy.

Three papers came out last week in Nature Astronomy that each individually might bowl you over with the scale of things; put together, they're kind of staggering. First we have a paper by a team led by Tiantian Yuan, of Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).  Entitled "A Giant Galaxy in the Young Universe with a Massive Ring," this research looks at a very unusual object -- a collisional ring -- that is eleven billion light years away.

Meaning we're seeing it as it was eleven billion years ago.

"It is a very curious object that we’ve never seen before," Yuan said, in a press release.  "It looks strange and familiar at the same time.  It is making stars at a rate fifty times greater than the Milky Way.  Most of that activity is taking place on its ring – so it truly is a ring of fire."

"The collisional formation of ring galaxies requires a thin disk to be present in the ‘victim’ galaxy before the collision occurs," added Kenneth Freeman of the Australian National University, who co-authored the paper.  "The thin disk is the defining component of spiral galaxies: before it assembled, the galaxies were in a disorderly state, not yet recognizable as spiral galaxies.  In the case of this ring galaxy, we are looking back into the early universe by eleven billion years, into a time when thin disks were only just assembling.  For comparison, the thin disk of our Milky Way began to come together only about nine billion years ago.  This discovery is an indication that disk assembly in spiral galaxies occurred over a more extended period than previously thought."

Yes, you read that right.  The images of this object are pictures of something that existed two billion years before the Milky Way formed.

The second paper is about an object that is even older and father away than the ring galaxy.  Titled "A Cold, Massive, Rotating Disk Galaxy 1.5 Billion Years After the Big Bang," by a team led by Marcel Neeleman of the Max Planck Institute for Astronomy, is estimated to be 12.3 billion light years away -- so this structure is not only the oldest disk galaxy ever observed, it also gives us incredible new data on the way galaxies in general form.

The authors write:

Massive disk galaxies like the Milky Way are expected to form at late times in traditional models of galaxy formation, but recent numerical simulations suggest that such galaxies could form as early as a billion years after the Big Bang through the accretion of cold material and mergers.  Observationally, it has been difficult to identify disk galaxies in emission at high redshift in order to discern between competing models of galaxy formation...  The detection of emission from carbon monoxide in the galaxy yields a molecular mass that is consistent with the estimate [that the galaxy's mass is] about 72 billion solar masses.  The existence of such a massive, rotationally supported, cold disk galaxy when the Universe was only 1.5 billion years old favours formation through either cold-mode accretion or mergers, although its large rotational velocity and large content of cold gas remain challenging to reproduce with most numerical simulations.

So the astrophysicists are going to be sifting through that data for quite some time.

The third, "The Recurrent Impact of the Sagittarius Dwarf on the Star Formation History of the Milky Way," by a team led by Tomás Ruiz-Lara of the Instituto de Astrofísica de Canarias, describes something pretty amazing about our own galaxy; the main disc is orbited by a dwarf galaxy (the Sagittarius Dwarf in the title) which has an elliptical orbit, so it at regular intervals pierces the disc of the Milky Way -- causing eddies that trigger a huge spike in star production.

"You have the Milky Way in equilibrium, mostly calm, and then when Sagittarius passed it was like throwing a stone in a lake," said Ruiz-Lara, in an interview with New Scientist.  "It created these ripples in the galaxy’s density, so some areas became more dense and started forming stars more efficiently...  Maybe without Sagittarius the solar system wouldn’t exist.  The timing works out, but there is no way for us to know for sure."

[Image is in the Public Domain courtesy of NASA, ESA, and The Hubble Heritage Team STScI/AURA]

Gradually the dwarf galaxy is losing energy and its orbit is pulled in tighter and tighter, making these collisions and bursts of star formation more frequent.  "It’s getting closer and closer, little by little over time, and in the end it will merge with the Milky Way," Ruiz-Lara said.

Not to worry, that won't happen for another billion-odd years.  So no need to run and see if your stellar collision insurance is paid up.

It's kind of mind-boggling when you think about it, that a bunch of primates who were not so long ago loping around on the African savanna trying not to get eaten by lions have found a way to see into the farthest reaches of the universe.  Not to get cocky about it, but that's pretty spectacular.  Only a hundred years ago we didn't even know for sure how big or how old the universe is; today we're looking into the depths of space, and back in time almost as far is is physically possible.

It brings to mind the wonderful quote by Carl Sagan: "We are a way for the cosmos to know itself."

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This week's Skeptophilia book recommendation of the week is a fun one: acclaimed science writer Jennifer Ackerman's The Bird Way: A New Look at how Birds Talk, Work, Play, Parent, and Think.

It's been known for some years that a lot of birds are a great deal more intelligent than we'd thought.  Crows and other corvids are capable of reasoning and problem-solving, and actually play, seemingly for no reason other than "it's fun."  Parrots are capable of learning language and simple categorization.  A group of birds called babblers understand reciprocity -- and females are attracted to males who share their food the most ostentatiously.

So "bird brain" should actually be a compliment.

Here, Ackerman looks at the hugely diverse world of birds and gives us fascinating information about all facets of their behavior -- not only the "positive" ones (to put an human-based judgment on it) but "negative" ones like deception, manipulating, and cheating.  The result is one of the best science books I've read in recent years, written in Ackerman's signature sparkling prose.  Birder or not, this is a must-read for anyone with more than a passing interest in biology or animal behavior.

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

News from overhead

Seems like I've been writing a lot about the skies lately.

My general opinion is that what's going on up there is not only interesting, it's useful in taking my mind off the shitshow that's going on down here.  Be that as it may, in the last few weeks we've seen new discoveries about dark energy, a likely nearby supernova candidate, neutron stars, and the possibility of extraterrestrial life in unlikely places.  The astronomers and astrophysicists have been kept on their toes lately by the number of new discoveries and surprising observations -- in fact, in today's post, we'll take a look at not one, but two more pieces of news from above.

In the first, a team at the European Space Agency was working on mapping stellar positions in the "Gould's Belt," a ring of stars surrounding the Milky Way but tilted at about twenty degrees away from the galactic plane.  And what the team found was that within the Gould's Belt, there is a huge structure (from our perspective here on the Earth, it extends across half the sky) that shows regular up-and-down periodicity -- an enormous wave with a wavelength of about six thousand light years.

What could have created this structure is unknown, but waves are usually created when something gravitationally perturbs the pre-existing structure, so astronomers are trying to find something massive enough to cause a pattern change on this scale.  There don't seem to be any good candidates, so the current guess is that (once again) we may be talking about a clump of dark matter.

Whatever the hell that is.

"But this is very speculative at the moment, and other scenarios are as plausible, as an accretion of gas either from the halo of the Milky Way, stretched by the tidal forces of the galaxy (hence its narrowness)," said study lead author João Alves of the University of Vienna.  "Or maybe this is what spiral arms look like up close.  In summary, we have many ideas that we will be testing with future releases of Gaia data but we don't have a favorite scenario at the moment, and that is pretty exciting."

Another odd feature is the the wave is "damped' -- its amplitude decreases along its length.  This suggests that whatever created the disturbance interacted with the stars in the Belt and then passed on -- much like the waves from a rock dropped into a pond decrease in amplitude as they move outward.  It turns out that the Sun was passing through the belt about thirteen million years ago, but if it caused anything untoward here on Earth, it's left few traces.

"There was no obvious mass extinction event thirteen million years ago, so although we were crossing a sort of minefield back then, it did not leave an obvious mark," Alves said.  "Still, with the advent of more sensitive mass spectrometers, it is likely we will find some sort of mark left on the planet."

The second story is about another upcoming stellar explosion, this one more predictable (although less spectacular) than the Betelgeuse supernova about which I wrote two weeks ago.  The star in question is V Sagittae -- which, actually, is a binary system, a white dwarf (a collapsed stellar core) and a larger main-sequence companion.  Because of the white dwarf's gravitational pull, it is siphoning off matter from the surface of its partner, and the interaction is slowing down their rotation around their barycenter, so they're getting closer -- and will ultimately collide.

When that happens, it will cause a colossal explosion which will -- even at our position, 7,800 light years away -- release so much energy that for a short while, V Sagittae will be the brightest star in the sky.  And because we know a good bit about its rotational period and the rate at which the matter is being pulled from the main-sequence star, the astrophysicists also have a good idea of when this will happen: 2083, give or take a few years in either direction.

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

So there are people alive today who will see this happen.  Sadly, I'm probably not going to be one of them, because in 2083 I'd be 123 years old.  And even though I fully intend to live forever (so far, so good), I must grudgingly admit that the chances of my making it to 123 aren't that high.

Still, there's always the possibility of some advance in genetic engineering extending our life spans.  I'm not exactly optimistic about the likelihood of this, but hope springs eternal and all that nonsense.  And if I'm not going to get to see Betelgeuse go kablooie, then V Sagittae sounds like a decent second-best.

So that's the news from overhead for today.  It's hard not to be impressed by the strides we're making in figuring out how the universe works.  Even though we've got a lot more questions still to answer -- which, after all, is how science works -- the idea that sitting here, on a little planet around an average star in an average galaxy, we can figure all this out is pretty damned impressive.

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This week's Skeptophilia book of the week is scarily appropriate reading material in today's political climate: Robert Bartholomew and Peter Hassall's wonderful A Colorful History of Popular Delusions.  In this brilliant and engaging book, the authors take a look at the phenomenon of crowd behavior, and how it has led to some of the most irrational behaviors humans are prone to -- fads, mobs, cults, crazes, manias, urban legends, and riots.

Sometimes amusing, sometimes shocking, this book looks at how our evolutionary background as a tribal animal has made us prone all too often to getting caught up in groupthink, where we leave behind logic and reason for the scary territory of making decisions based purely on emotion.  It's unsettling reading, but if you want to understand why humans all too often behave in ways that make the rational ones amongst us want to do repeated headdesks, this book should be on your list.

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