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!]

The galactic river

I was an amateur stargazer as a kid.  I had a small refracting telescope and spent many hours out in my parents' front yard, looking at stars and planets and whatever else I could find.  My favorite astronomical object was (and, in fact, still is) the Pleiades, a star cluster and "stellar nursery" in the constellation Taurus:

[Image courtesy of NASA/JPL]

I pondered many times whether the stars I looked at hosted planets, and those planets intelligent life -- and whether there might be a little alien boy looking back at me through his telescope.  I also sometimes liked to stand on my head (I was a bit of a strange kid, a fact that should shock no one) and I remember thinking that when I did that at night, I had the stars beneath my feet.  And if I started falling upward, I would fall forever.

Such are the musings of a whimsical ten-year-old wannabe science nerd.

I still have a sense of wonder whenever I look up into the sky.  The sheer scale of it leaves me breathless.  And with every new discovery made about the universe we live in, the awe I feel becomes that much stronger.  Take, for example, the bit of research published last week in the journal Astronomy & Astrophysics, that many of the stars in the Southern Hemisphere of the sky are part of a stellar cluster that is in the process of being torn apart by tidal forces from the Milky Way.

The paper is entitled, "Extended Stellar Systems in the Solar Neighborhood: Discovery of a Nearby 120° Stellar Stream in Gaia DR2," by Stefan Meingast and Verena Fürnkranz of the University of Vienna and João Alves of Harvard University, and describes a startling finding -- an estimated 4,000 of the stars visible from southern latitudes are part of a "river of stars" produced when what was a compact cluster is stretched out into a long stellar stream.

These things aren't common, so to find one only (only!) 326 light years away is pretty phenomenal.  "Identifying nearby disc streams is like looking for the proverbial needle in a haystack," Alves said in an interview with Science Alert.  "Astronomers have been looking at, and through, this new stream for a long time, as it covers most of the night sky, but only now realise it is there, and it is huge, and shockingly close to the Sun.  Finding things close to home is very useful, it means they are not too faint nor too blurred for further detailed exploration, as astronomers dream."

The southern stellar stream -- stars that are part of it are highlighted in red [Image from Gaia DR2 Skymap]

The researchers think that the stars in the stream (and therefore the cluster in which they originated) is about a billion years old, meaning it's had time for about four complete revolutions around the galactic center.  This is time enough for tidal forces exerted by the Milky Way to stretch the cluster out from its original shape -- which was possibly something like the Pleaides -- into a streamer going nearly halfway around the night sky.

I wish I could see those stars, but none of them are visible from my perspective here in the frozen North.  I know they don't look any different from the stars I see at night, but still, the idea that I'd be looking at a stellar river that came from a billion-year-old cluster is pretty awe-inspiring.  But since I don't have any trips to the Southern Hemisphere planned, I'll just have to stick with the ones in my own neighborhood, which are wonderful enough.

Maybe they'll even inspire me to stand on my head.

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

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

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

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