Blink of an eye

I know I often write about strange and unexpected discoveries out there in the universe in the context of how much more we have to learn, but even by those standards, the discovery announced by astrophysicists at the Massachusetts Institute of Technology this week was bizarre.

Most everyone knows about black holes -- stellar remnants that have collapsed to a density that they warp space/time into a closed surface.  The usual way this is put is that their gravitational pull is so strong even light isn't fast enough to escape, but that's not really that accurate; light is massless and therefore photons exert (and feel) no gravitational pull.  However, they are constrained to follow the lines of space/time they're traveling through, just as cars can take whatever road their drivers choose, but are still constrained to stay on the surface of the Earth's sphere.

Around a black hole, the fabric of space is so distorted that it's a bit like an infinitely-deep well.  Once inside the black hole's event horizon, there's no escape.  Weirder still, since not only space but time is affected by such a mass, to an outside observer watching an object falling into a black hole, it would seem to take an infinite amount of time.  The closer it got, the slower it would move, until it finally paused, forever, on the surface of the event horizon.  (Due to the vagaries of general relativity, this wouldn't help the hapless space traveler falling into a black hole.  Time would run at the regular speed for him/her, and in a very finite amount of time, the spaceship and everything and everyone in it would get ripped to shreds by the tidal forces exerted by the black hole's mass.)

[Image licensed under the Creative Commons User:Alain r, BH LMC, CC BY-SA 2.5]

It's this last bit that's germane to this week's announcement.  Black holes are black (duh), even light can't escape, so how do we see them?  It's because of material that's falling toward them.  Black holes tend to form accretion disks of stuff circling the central singularity at a high rate of speed, and the acceleration of this disk causes it to emit x-rays.  (In fact, the first black hole ever observed, Cygnus X-1, was given that name because it was the first x-ray source found in the constellation Cygnus.)

So we see the black hole by its brilliant x-ray "corona."  Generally, the larger the black hole, the bigger the accretion disk and the brighter it is; the center of the Milky Way, the object called Sagittarius A*, has a radius of 22 million kilometers, and parts of its accretion disk are being whirled about at thirty percent of the speed of light.

1ES 1927+654 is another such supermassive galactic nucleus, but its behavior is even weirder than our own.  In March 2018 it flashed -- its luminosity suddenly jumped by forty percent.  Keep in mind that these things are already phenomenally luminous, so such a jump is stupendous by anyone's estimate.  "This was an AGN [active galactic nucleus] that we sort of knew about, but it wasn't very special," said MIT astronomer Erin Kara.  "Then they noticed that this run-of-the-mill AGN became suddenly bright, which got our attention, and we started pointing lots of other telescopes in lots of other wavelengths to look at it."

That's why Kara and her team were watching when 1ES 1927+654 suddenly -- and completely -- disappeared.

Put more accurately, it became undetectable.  Something had apparently vaporized its corona completely, causing the x-ray emissions to stop.  The most amazing thing is how fast it happened -- an astronomical blink of an eye.  "We expect that luminosity changes this big should vary on timescales of many thousands to millions of years," said Kara.  "But in this object, we saw it change by 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling."

Here's what they think happened.

Something disrupted the accretion disk, possibly a large star that got caught in the black hole's gravitational well and was shredded by tidal forces as it approached.  That's a lot of material to throw into the accretion disk at once, and the star's own gravity destabilized the disk.  As an analogy, imagine a small whirlpool, like water going down a drain.  If you pour something like a dye into it slowly, it gets pulled in and incorporated smoothly.  But drop a gallon of dye into the whirlpool suddenly, and it disrupts the whirlpool completely, turning it into turbulent chaos.

That's what is thought to have happened here.  The shredding of the star is what created the flash we detected two years ago, then as the remnants plunged into the accretion disk, it blew the disk apart, and a lot of the material simply dropped into the black hole.  The acceleration of the material around the black hole is what causes the corona -- so when that's gone, the x-rays stop, and the black hole becomes undetectable.

The astronomers believe that the black hole's luminosity will "turn back on" as material around it begins to whirl around again, but the honest truth is that no one knows what it'll do next.  "We want to keep an eye on it," Kara said.  "It's still in this unusual high-flux state, and maybe it'll do something crazy again, so we don't want to miss that."

So that's our "you thought outer space was weird before" story for today.  Once again illustrating that we really are only on the beginning of our journey toward understanding the universe we live in.  If you keep your eyes on the stars, you will never lack for something to fascinate and startle you.

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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!]

The second biggest bang

There are times in science where -- if you're going to describe something accurately -- you rapidly become lost in superlatives.

That was my reaction to a paper this week in Astrophysical Journal titled, "Discovery of a Giant Radio Fossil in the Ophiuchus Galaxy Cluster," by a team led by Simona Giacintucci of the Naval Research Laboratory.  Here's what the researchers had to say about it:

The Ophiuchus galaxy cluster exhibits a curious concave gas density discontinuity at the edge of its cool core...  Using low-frequency (72-240 MHz) radio data from MWA GLEAM and GMRT, we found that the X-ray structure is, in fact, a giant cavity in the X-ray gas filled with diffuse radio emission with an extraordinarily steep radio spectrum.  It thus appears to be a very aged fossil of the most powerful AGN [active galactic nucleus] outburst seen in any galaxy cluster (pV∼5×10^61 erg for this cavity).  There is no apparent diametrically opposite counterpart either in X-ray or in the radio.  It may have aged out of the observable radio band because of the cluster asymmetry.  At present, the central AGN exhibits only a weak radio source, so it should have been much more powerful in the past to have produced such a bubble.  The AGN is currently starved of accreting cool gas because the gas density peak is displaced by core sloshing.  The sloshing itself could have been set off by this extraordinary explosion if it had occurred in an asymmetric gas core.  This dinosaur may be an early example of a new class of sources to be uncovered by low-frequency surveys of galaxy clusters.

To say that this explosion was huge doesn't even begin to describe it.  The energy output of this outburst puts it in second place ever -- the only event we know of that was more energetic than this was the Big Bang itself.

Its size isn't the only odd thing about it.  "We've seen outbursts in the centers of galaxies before but this one is really, really massive," said Melanie Johnston-Hollitt of Curtin University's International Centre for Radio Astronomy Research, in an interview at Phys.Org.  "And we don't know why it's so big.  But it happened very slowly—like an explosion in slow motion that took place over hundreds of millions of years."

However slow it was, the explosion blew a hole in the sphere of superhot plasma surrounding the massive black hole at the center of the galaxy.  Study lead author Simona Giacintucci compares it to the pressure from the eruption of Mount Saint Helens blowing off the entire top of the mountain, leaving a crater behind.  "The difference," she said, "is that you could fit fifteen Milky Way galaxies in a row into the crater this eruption punched into the cluster's hot gas."

[Image licensed under the Creative Commons Rogelio Bernal Andreo, Rho Ophiuchus Widefield, CC BY-SA 3.0]

Johnston-Hollitt, who directs the Murchison Widefield Array in Western Australia, said that despite the enormity of the relic explosion, it was only recently observed because of a drastic improvement in astronomers' ability to observe the skies in the very-low-frequency end of the spectrum.  "It's a bit like archaeology," she said.  "We've been given the tools to dig deeper with low frequency radio telescopes so we should be able to find more outbursts like this now."

So there might be other colossal explosion remnants out there just waiting to be found.

What it brings up for me, non-researcher that I am, is to wonder what on earth could have caused a detonation on this scale.  To my knowledge, the explanation is still uncertain, and in fact can't be accounted for by any known natural process.  The lack of a mechanism and the size of the outburst led scientists at first to doubt the measurements were correct.  "People were skeptical because of the size of outburst," Johnston-Hollitt said.  "But it really is that."

And improvements to the Murchison Widefield Array is improving its sensitivity by a factor of ten, which means we're only seeing the beginning of discoveries like this, and who knows what else.  "The Universe is a weird place," Johnston-Hollitt said.

Indeed it is.  Awe-inspiring to the point of bowling over your brain, at times.  Look around you at your house, town, and region, your friends, family, and pets, even the bigger concerns of politics and global conflict -- and realize that on the grand scheme of things, we are minuscule, hardly even a blip on the surface of cosmic space-time.  Humbling and a little scary, isn't it?

But the human brain isn't built to conceptualize such enormities, and it's best not to dwell on it.  On the whole, it's probably better to have another cup of coffee and think about something else for a while.

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One of my favorite people is the indefatigable British science historian James Burke.  First gaining fame from his immensely entertaining book and television series Connections, in which he showed the links between various historical events that (seen as a whole) play out like a centuries-long game of telephone, he went on to wow his fans with The Day the Universe Changed and a terrifyingly prescient analysis of where global climate change was headed, filmed in 1989, called After the Warming.

One of my favorites of his is the brilliant book The Pinball Effect.  It's dedicated to the role of chaos in scientific discovery, and shows the interconnections between twenty different threads of inquiry.  He's posted page-number links at various points in his book that you can jump to, where the different threads cross -- so if you like, you can read this as a scientific Choose Your Own Adventure, leaping from one point in the web to another, in the process truly gaining a sense of how interconnected and complex the history of science has been.

However you choose to approach it -- in a straight line, or following a pinball course through the book -- it's a fantastic read.  So pick up a copy of this week's Skeptophilia book of the week.  You won't be able to put it down.

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

Blazing a trail

What I find the most stunning about scientific research is the breadth and scope of what it uncovers about the universe.

Think about it.  In the last hundred years, we have gone all the way from quarks -- particles a third the size of a neutron, or an average of 4 x 10^-27 kilograms -- to the largest known structure in the universe, the Virgo Supercluster, which is 110 million light years across.  We have a decent picture of what happened at each stage in the development of the cosmos, all the way back to the Big Bang, 13.6 billion years ago.  We have found out about how our DNA guides our development from a single fertilized egg, how evolution has generated the biodiversity of the nine-million-odd species on Earth, and how the thoughts you're having as you read this are encoded and modulated by tiny electrochemical signals amongst the 100 billion neurons in your brain.

It is beyond me how anyone could consider these things and not be entirely overawed by the grandeur of it all.

It's why I get a little impatient with people who say that looking for scientific explanations cheapens our sense of beauty and wonder.  "Why can't you just look at the flowers and appreciate them?" I've heard people say.  "You have to classify and name and dissect instead."  Well, all I can say is my love for flowers is only deepened by the fact that I know how photosynthesis is working to convert sunlight to chemical energy in their leaves, that the daylilies in my garden have specialized structures for attracting pollinators so they can reproduce, and that the tomatoes currently laden with fruit in my wife's veggie garden are close cousins to peppers, potatoes... and deadly nightshade.

So that's why it was with an almost visceral sense of wonder that I read a paper last week about the detection of a neutrino that originated four billion years ago in one of the most powerful energy sources in the universe -- a blazar.

Artist's depiction of a blazar [Image is in the Public Domain, courtesy of NASA/JPL]

A blazar is an active galactic nucleus, powered by a supermassive black hole, which spews out a jet of particles propelled at very nearly the speed of light.  It'd be significantly unfortunate for any planetary systems that the jet is aimed toward; that's why the ones we know about are really far away, so we can analyze the jet and its source without being fried to a rich crispy golden-brown.

This all comes up because of a paper that appeared in the journal Science last week.  A team of scientists analyzing data from the IceCube particle detector, buried a kilometer deep underneath an ice sheet in Antarctica, detected a neutrino with an energy of nearly 300 trillion electron volts.  Naturally, a particle that energetic immediately attracted attention, leading to the question of where it had come from and what had given it that hard a kick.  Tracing its origin from the angle at which it hit the detector, they determined that it had started as part of a jet of gamma rays and other particles from a blazar with the euphonious name TXS 0506+056, 3.7 billion light years away in the constellation Orion.

The IceCube collaborative team write:

Neutrinos interact only very weakly with matter, but giant detectors have succeeded in detecting small numbers of astrophysical neutrinos.  Aside from a diffuse background, only two individual sources have been identified: the Sun and a nearby supernova in 1987.  A multiteam collaboration detected a high-energy neutrino event whose arrival direction was consistent with a known blazar—a type of quasar with a relativistic jet oriented directly along our line of sight.  The blazar, TXS 0506+056, was found to be undergoing a gamma-ray flare, prompting an extensive multiwavelength campaign.  Motivated by this discovery, the IceCube collaboration examined lower-energy neutrinos detected over the previous several years, finding an excess emission at the location of the blazar.

Astronomer Regina Caputo, of NASA's Goddard Space Flight Center in Maryland, was less measured in her response, but what she said illustrates the fact that understanding deeply what's going on doesn't decrease your wonder or enjoyment.  "This is crazy, the sky is erupting," Caputo said to reporters.  "I almost couldn’t believe it; the universe is revealing itself in ways we have never imagined before."

So the whole thing is kind of stunning.  It leaves me yearning for more.  I mean, think of it; a hundred years ago, we didn't know about any of this stuff.  Five hundred years ago, we had no idea what the brain did, what matter was made of, and we still believed that the stars were pinpricks of light all equidistant from the Earth (which was, of course, at the center of the universe).

Considering what we could do in the next hundred years absolutely boggles the mind.

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This week's Skeptophilia book recommendation is a must-read for anyone concerned about the current state of the world's environment.  The Sixth Extinction, by Elizabeth Kolbert, is a retrospective of the five great extinction events the Earth has experienced -- the largest of which, the Permian-Triassic extinction of 252 million years ago, wiped out 95% of the species on Earth.  Kolbert makes a persuasive, if devastating, argument; that we are currently in the middle of a sixth mass extinction -- this one caused exclusively by the activities of humans.  It's a fascinating, alarming, and absolutely essential read.  [If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]