Rough neighborhood

Most likely all of you know about Sagittarius A*, the supermassive black hole that sits at the center of the Milky Way Galaxy.

It's hard to talk about it without lapsing into superlatives.  It has a mass about 4.3 million times that of the Sun.  It's event horizon -- the "point of no return," the closest you can get to a black hole without being trapped by its gravitational pull -- has a radius of 11.3 million kilometers.  It sits at the center of a fifteen-light-year-wide whirlpool of gas and dust called the accretion disk, which we know about because the material in it is moving so fast it has heated up to as high as ten million degrees Celsius, resulting in a steady emission of high-frequency x-rays.

[Image licensed under the Creative Commons EHT Collaboration, EHT Sagittarius A black hole, CC BY 4.0]

It's curious that something this luminous wasn't immediately obvious to astronomers.  First, it doesn't emit a lot of visible light; we didn't have telescopes capable of detecting the x-rays that are its fingerprint until 1933.  By the 1970s, more precise observations showed that whatever the x-ray source was, it was extremely compact.  It wasn't until 1994 that Charles H. Townes and Reinhard Genzel showed that its mass and diameter were consistent with its being a black hole.  Another reason it took that long is that between us and the center of the galaxy there are massive dust clouds, so any visible light it does emit (or which is emitted by the dense clouds of glowing gas near it) mostly gets blocked.  (Even so, looking toward the center of the Milky Way in the constellation Sagittarius, visible where I am in late summer, is pretty damn spectacular.)

The third reason that we don't get the full luminosity of whatever electromagnetic radiation is emitted from Sagittarius A* is a fortunate one for us; because of the black hole's immense magnetic field, any bursts of light tend to get funneled away along the axis of its spin, creating jets moving perpendicularly to the galactic plane.  We, luckily, are comfortably out in the stellar suburbs, in one of the Milky Way's spiral arms.  Our central black hole is fairly quiet, for the most part, but even so, looking down the gun barrel of its magnetic field axis would not be a comfortable position to reside.

The reason this comes up is some new research out of the University of Colorado - Boulder, which used data from the James Webb Space Telescope to solve a long-standing question about why, given the high density of hydrogen and helium gas near the galactic center, the rate of star formation there is anomalously low.  This region, called Sagittarius C, extends about two hundred light years from the central black hole (by comparison, the Solar System is twenty-six thousand light years away).  And what the team of researchers found is that threading the entire region are filaments of hot, bright plasma, some of them up to several light years in length.

The reason for both the filaments and the low star formation rate is almost certainly the black hole's magnetic field, which acts to compress any gas that's present along the field lines, heating it up dramatically.  This, in turn, creates an outward pressure that makes the gas resist collapsing and forming stars.

"It's in a part of the galaxy with the highest density of stars and massive, dense clouds of hydrogen, helium and organic molecules," said Samuel Crowe, who co-authored the paper, which appeared this week in The Astrophysical Journal.  "It's one of the closest regions we know of that has extreme conditions similar to those in the young universe...  Because of these magnetic fields, Sagittarius C has a fundamentally different shape, a different look than any other star forming region in the galaxy away from the galactic center."

It is, to put it mildly, a rough neighborhood.

It's staggering how far we've come in our understanding of what our ancestors called the "fixed stars" -- far from being eternal and unchanging, the night sky is a dynamic and ever-evolving place, and with new tools like the JWST we're finding out how much more we still have to learn.  Something to think about the next time you look up on a clear, starry night.  The peaceful, silent flickering, set against the velvet black background, is an illusion; the reality is far wilder -- and far more interesting.

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Biggest and brightest

If you're the kind of person who likes having your mind blown by superlatives, astrophysics is the science for you.

I ran into two really good examples of that last week.  In the first, a paper in the journal Monthly Notices of the Royal Astronomical Society, from research led by astrophysicist Ruth Daly of Pennsylvania State University, found that the massive black hole at the center of the Milky Way -- Sagittarius A* -- is spinning so fast it's actually warping the fabric of space time around it, flattening it into the shape of a football.

The "no-hair theorem" of the physics of black holes states that they are rather simple beasts.  They can be completely characterized using only three parameters: their mass, charge, and angular momentum.  The name comes from the quip by physicist John Archibald Wheeler that "black holes have no hair," by which he meant that there are no other adornments you need to describe to get a full picture of what they're doing.  However, I've always been puzzled by what exactly it means to say that a black hole has angular momentum; objects with mass and spin, such as a twirling top or the rotating Earth, have angular momentum, but since the mass in a black hole has (at least as far as we understand them) collapsed into a singularity, what exactly is spinning, and how could you tell?

Last week's paper at least answers the second half of the question.  Using data from x-ray and radio wave collimation and material outflow from Sagittarius A*, astrophysicists can determine how much spacetime is being deformed by the angular momentum of the black hole, and from that determine its rate of spin.

And it's spinning fast -- an estimated sixty percent of the maximum possible rate, which is set by the universal speed limit that matter can't travel at or faster than the speed of light.  The deformation is so great that the fabric of spacetime is compressed along the spin axis, so it appears spherical from above but flattened from the side.

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

The second piece of research comes from a study at the European Southern Observatory, and was published in Nature Astronomy.  It looks at the recent discovery of the brightest object known, a quasar (an active galactic nucleus containing a supermassive black hole) that -- get ready for the superlatives -- is five hundred trillion times more luminous than the Sun, contains a black hole that has seventeen billion times the mass of the Sun, and is consuming one Sun's worth of mass a day.  This object, given the unassuming name of J0529-4351, is twelve billion light years away, making it also one of the most distant objects ever studied.

"All this light comes from a hot accretion disk that measures seven light-years in diameter -- this must be the largest accretion disk in the Universe," said study co-author Samuel Lai, of Australian National University.  If he sounds a little blown away by this -- well, so are we all.  A seven-light-year accretion disk means that if it were placed where the Sun is, not only would its accretion disk engulf the entire Solar System, it would extend outward past the five nearest stars -- the triple-star system of Alpha/Proxima Centauri, Barnard's Star, and Luhman 16.

I don't know about you, but something on that scale boggles my mind.

And that's not a bad thing, really.  I think we need to be reminded periodically that in the grand scheme of things, the problems we lose so much sleep over down here are pretty minuscule.  Also, it's good to have our brains overwhelmed by the grandeur of the universe we live in, to be able to look up into the night sky and think, "Wow.  How fortunate I am to be able to witness -- and in some small way, understand -- such wonders."

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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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Chewed up and spat out

Seems like I've featured a lot of research about astrophysics here at Skeptophilia lately, and that's not only because I'm really interested in it, but because the astrophysicists keep discovering stuff that is downright amazing.

Consider two papers last week highlighting different bizarre behaviors of one of the weirdest beasts in the cosmic zoo -- black holes. 

Since the first serious proposal of their existence, by German physicist Karl Schwarzschild in 1916, they've captivated the imagination.  Not only are they created in supernovas -- surely the most spectacular events in the universe -- their intense gravitational warping of space makes it impossible for anything, even light, to escape.  If you were falling into one (not recommended), time would slow down, at least as perceived by someone watching you from a safe distance.  From your perspective, though, your own watch would continue to run normally, until it (and you) succumbed to spaghettification -- yes, that's actually what the astrophysicists call it -- the point where the tidal forces across even such a short distance as the one between your head and your feet became sufficient to stretch you into the universe's most horrifying pasta.

As strange and terrifying as they are, they were thought for a long time to be physically quite simple; physicist John Archibald Wheeler said that "black holes have no hair," by which he meant that they have no arbitrary differences between each other that cannot be accounted for by three externally-observable parameters: their mass, angular momentum, and electric charge.  It took no less a luminary than Stephen Hawking to demonstrate that this wasn't true.  In 1974 he showed that (contrary to the picture of a black hole as a one-way-only object) they slowly evaporate through a phenomenon now called Hawking radiation in his honor.  The general idea here is that the extremely warped space near the event horizon generates sufficient energy to facilitate significant pair production -- creation of particle/antiparticle pairs.  Almost always, those pairs recombine and mutually annihilate in a fraction of a second after creation, so they're called "virtual particles" that have a measurable effect on ordinary matter but no long-term reality.  However, in the vicinity of a black hole, things are different.  Because of the extraordinary gravitational field at the event horizon, sometimes there's enough time for the two particles in the pair to separate sufficiently that one of them crosses the event horizon and the other doesn't.  At that point, the one that's fallen in is doomed; the other one just keeps moving away -- and that's the Hawking radiation.  

But what this does is robs a small bit of the mass/energy from the black hole, so its volume decreases.  What Hawking showed is that black holes actually evaporate.  It's on a huge time scale; a massive black hole has a life span many times longer than the current age of the universe.  But it suggests that everything -- even something as seemingly permanent as a black hole -- has a finite life span.

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

Even that, though, doesn't begin to plumb the depths of the weirdness of these things.  Take for example the two papers I referenced earlier, each of which shows an only partially-explained behavior of black holes.

In the first, that appeared in The Astrophysical Journal, researchers looked at the odd behavior of an object called X-7 that is close to Sagittarius A*, the massive black hole at the center of the Milky Way galaxy.  X-7 is a cloud of gas and dust about fifty times the mass of the Earth, and is so close to Sagittarius A* that it orbits it once every 170 years.  The tidal forces are spaghettifying X-7 -- fast enough to observe in real time.

"No other object in this region has shown such an extreme evolution," said Anna Ciurlo of UCLA, who is the paper’s lead author.  "It started off comet-shaped and people thought maybe it got that shape from stellar winds or jets of particles from the black hole.  But as we followed it for twenty years we saw it becoming more elongated.  Something must have put this cloud on its particular path with its particular orientation."

From its current trajectory, the researchers think that it will get close enough to the black hole by 2036 that it will be torn apart completely.

If X-7 is being chewed up, there's another place in the universe where a black hole has been spat out.  The galaxy RCP 28, 7.5 billion light years from Earth, appears to be undergoing something cataclysmic; its central black hole, with an estimated mass of twenty million times that of the Sun, has been ejected from the middle and is moving away at a speed of 5.6 million kilometers per hour, pulling along a streamer of stars behind it like the tail of a comet.

What could possibly slingshot an object that massive at such high velocities remains to be seen; the researchers think it was in some kind of unstable orbit with two or more massive bodies.  (As I described in a post a couple of years ago, the three-body problem -- the mathematics of three or more objects of similar masses orbiting a common center of gravity -- is one of the most famous unsolved problems in classical mechanics, and models show that most of the time, these sorts of configurations are unstable.)  But the authors are clear that more study is needed to confirm the analysis, and then, to come up with an explanation for what exactly is going on.

In any case, what's obvious is that we've only scratched the surface of these strange objects.  Every time we look up into the star-spangled sky, we find new and amazing things to wonder at.  The astrophysicists, I think, are in for a long and exciting ride.

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An encounter with Charybdis

At the center of our seemingly tranquil galaxy, there's a black hole massive enough that it significantly warps spacetime, swallows any matter that gets close enough, and in the process emits truly colossal amounts of radiation.  Named Sagittarius A*, it was discovered in 1954 because of its enormous output in the radio region of the spectrum.  [N. B.  Throughout this post, when I refer to the black hole's radiation output, I am not of course talking about anything coming from inside its event horizon; that's physically impossible.  But the infalling matter that gets eaten by it does emit electromagnetic radiation before it takes its final plunge and disappears forever.  Lots of it.]

This thing is a real behemoth, at an estimated four million times the mass of the Sun.  There is a lot of interstellar dust between it and us -- after all, when you're looking at the constellation of Sagittarius, you're looking down a line going directly along the plane of the galaxy toward its center -- but even without the dust, it wouldn't be all that bright.  Most of its output isn't in the visible light region of the spectrum.  This doesn't mean it's dim in the larger sense; not only are there the radio waves that were the first part of its signal detected, but it has enormous peaks in the gamma and x-ray part of the spectrum as well.

Earlier this month, the European Southern Observatory released the first actual photograph of Sagittarius A*:

[Image licensed under the Creative Commons EHT Collaboration, EHT Sagittarius A black hole, CC BY 4.0]

How could something that enormous form?  We have a pretty good idea about how massive stars (over ten times the mass of the Sun) become black holes; when their cores run out of fuel, the gravitational pull of its mass collapses it to the point that the escape velocity at its surface exceeds the speed of light.  At that point everything that falls within its event horizon is there to stay.

But we're not talking about ten times more massive than the Sun; this thing is four million times more massive.  Where did all that matter come from -- and how did it end up at the center of not only our galaxy, but every spiral galaxy studied?

A step was taken in our understanding of galactic black hole formation by a team of astronomers at the University of North Carolina - Chapel Hill, in a paper that appeared this week in The Astrophysical Journal.  It's long been known that most large galaxies are attended by an array of dwarf galaxies, such as the Milky Way's Small and Large Magellanic Clouds.  (Which, unfortunately, are only visible in the Southern Hemisphere.  This is why they're named after Magellan.  Typical of the Eurocentric approach to naming stuff; clearly indigenous people knew about the Magellanic Clouds long before Magellan ever saw them.)  It's also known that because of the gravitational pull of the larger galaxies, the smaller ones eventually collide with them and merge into a single galaxy.  In fact, that even happens to big galaxies; gravity has a way of winning, given enough time.  The Milky Way and the Andromeda Galaxy, which are about the same size, will eventually come together into a single blob of stars, but what its final shape will be is impossible to predict.

As an aside, there's no need to worry about this.  First, it's not going to happen for another four and a half billion years.  Second, when galaxies (of any size) collide, there are relatively few actual stellar collisions.  Galaxies are mostly empty space, and when they merge the stars that comprise them mostly just pass each other without incident.

But not the black holes at their centers.  Those, being the center of mass of the entire aggregation, eventually slam together in a collision with a magnitude that's impossible to imagine.  And the team at UNC found out that this is one of the ways that galactic black holes become so large; they discovered that even dwarf galaxies have central black holes, and when they get swallowed up, that mass gets added to the central black hole of the larger galaxy.

Sagittarius A* sits in the middle of the whirling vortex of stars, like the sea monster Charybdis in Greek mythology, sucking down anything that comes close enough -- including, apparently, other black holes.  The celestial fireworks with a collision between two large black holes, such as the ones in the Milky Way and Andromeda, must release a fantastic amount of energy.

Wouldn't that be something to see?

From a safe distance, of course.

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A black hole's strange glow

I think part of my enjoyment of science is that I love a good mystery.

The universe is endlessly fascinating and also endlessly complicated, and if you get into science you'll never want for new things to learn about.  You'll also be pushing the edges of what we can explain.  Some fairly simple-to-ask questions that we still haven't solved:

• Why do we dream?  It's ubiquitous amongst mammals, but its purpose is still uncertain.
• Why does space have three spatial dimensions?  There's nothing particularly special about having three dimensions, at least from what we know.  There's a conjecture that (if string theory is correct) there are eleven spatial dimensions, but if so, why are eight of them essentially undetectable?
• Is life common in the universe, or are we alone?
• Where does consciousness come from?
• What caused the Big Bang?
• What causes aging... and can it be slowed or stopped entirely?
• What causes the flow of time?  Most processes in physics are time-reversible -- they make equal sense if you watch them by running the clock backwards.  Why do we have an unshakeable sense of time's arrow only pointing one way?
• Could human cognition and personality theoretically be emulated in a machine?
• What are dark matter and dark energy?  And why can't we detect them except by their gravitational signature?

So if you like to wonder about stuff, immerse yourself in science.  I can promise you you'll never be bored.

This comes up because of some weird behavior by one of the oddest things in the universe: black holes.  You probably know that a black hole is a collapsed supergiant star, an object that is so massive that it warps space into a closed shape.  Even light can't escape (thus the name).  Around the border of a black hole is the event horizon, which is the point of no return -- when you cross it, you'll never escape, and will ultimately fall into the singularity at the center.  But you'll be dead long before then, torn to shreds by the tidal forces as you approach (a process astrophysicists have nicknamed, no lie, spaghettification.)

Black holes, though, aren't necessarily produced by the collapse of a single star.  It's thought that most galaxies have massive black holes at their center.  The Milky Way has one with the unprepossessing name Sagittarius A*, which becomes a little more impressive when you find out that it has four million times the mass of the Sun.

You might wonder how (being black) it was detected.  As matter falls into a black hole, it accelerates, and in the process emits radiation.  (Sort of an electromagnetic death scream, is how I think of it.)  Being as massive as it is, Sagittarius A* has quite a signature in the radio region of the spectrum, which is how it was first detected way back in 1931.

Sagittarius A* [Image is in the Public Domain, courtesy of NASA]

What got me thinking about this is that Sagittarius A* has been acting rather strangely of late.  Like most black holes studied, it does fluctuate in its energy output, presumably as the amount of matter falling into it varies.  But back in May of this year, its luminosity in the near-infrared region of the spectrum increased by a factor of 75...

... in a period of two hours.

"The brightness of Sgr A* varies all the time, getting brighter and fainter on the timescale of minutes to hours—it basically flickers like a candle," said study leader, UCLA astronomer Tuan Do.  "We think that something unusual might be happening this year because the black hole seems to vary in brightness more, reaching brighter levels than we've ever seen in the past...  Many astronomers are observing Sgr A* this summer.  I'm hoping we can get as much data as we can this year before the region of the sky with Sgr A* gets behind the Sun and we won't be able to observe it again until next year...  Maybe the black hole is waking up—there's a lot we don't know at this point so we need more data to understand if what we are seeing is a big change in what is feeding the black hole or this is a brief event."

Whatever it is, it certainly is intriguing.  Such a rapid and massive increase in luminosity from such an enormous object is hard even to wrap your brain around.  All of which just goes to show that even when you have a pretty good idea of how the universe works, it can turn around an astonish you.

Which, after all, is what science is all about.

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This week's Skeptophilia book recommendation is a must-read for anyone interested in astronomy -- Finding Our Place in the Universe by French astrophysicist Hélène Courtois.  Courtois gives us a thrilling tour of the universe on the largest scales, particularly Laniakea, the galactic supercluster to which the Milky Way belongs, and the vast and completely empty void between Laniakea and the next supercluster.  (These voids are so empty that if the Earth were at the middle of one, there would be no astronomical objects near enough or bright enough to see without a powerful telescope, and the night sky would be completely dark.)

Courtois's book is eye-opening and engaging, and (as it was just published this year) brings the reader up to date with the latest information from astronomy.  And it will give you new appreciation when you look up at night -- and realize how little of the universe you're actually seeing.

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