Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.
An ordinary, Sun-like star called Gaia20ehk -- eleven thousand light years away in the constellation Puppis -- had, up until 2016, a nearly flat energy output. This is more or less what our Sun would look like from that distance; yes, there are minor fluctuations, but (fortunately for us) it's pretty stable over short time intervals.
Then... well, here it is in Tsanidakis's words: "The star's light output was nice and flat, but starting in 2016 it had these three dips in brightness," he said. "And then, right around 2021, it went completely bonkers. I can't emphasize enough that stars like our Sun don't do that. So when we saw this one, we were like 'Hello, what's going on here?'"
The chaotic fluctuations in energy output were across the electromagnetic spectrum, but strongest in the infrared region. And stranger still, a more detailed analysis showed that the peculiar behavior was not from the star itself, but because there was -- suddenly -- a huge, irregular debris cloud surrounding it. This rock and dust eclipsed the star's light, but some of it was apparently radiating itself, accounting for the wild yo-yoing in the infrared. "The infrared light curve was the complete opposite of the visible light," Tzanidakis said. "As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot -- so hot that it's glowing in the infrared."
Tsanidakis and his team figured out that there was only one phenomenon that fit all the observations; two of Gaia20ehk's planets had collided with each other.
"It's incredible that various telescopes caught this impact in real time," Tzanidakis said. "There are only a few other planetary collisions of any kind on record, and none that bear so many similarities to the impact that created the Earth and Moon. If we can observe more moments like this elsewhere in the galaxy, it will teach us lots about the formation of our world."
Artist's rendition of the collision of the two planets in the Gaia20ehk system [Image credit: A. Tsanidakis et al.]
Tsandiakis and his colleagues are particularly interested in watching how this all plays out, because -- as he mentioned -- it is very similar to the process that is thought to have formed the Moon. The collision between the proto-Earth and a Mars-sized planet astronomers call Theia, something like 4.5 billion years ago, triggered the remelting of the entire combined mass; the energy of the collision sheared off a chunk of Theia, which collapsed into what would eventually become the Moon. Now that we've actually seen something similar happening in another star system, astronomers will be on the lookout for more events like this.
"How rare is the event that created the Earth and Moon? That question is fundamental to astrobiology," said James Davenport, senior author of the paper, which was published three days ago in Astrophysical Journal Letters. "It seems like the Moon is one of the magical ingredients that makes the Earth a good place for life. It can help shield Earth from some asteroids, it produces ocean tides and weather that allow chemistry and biology to mix globally, and it may even play a role in driving tectonic plate activity. Right now, we don't know how common these dynamics are. But if we catch more of these collisions, we'll start to figure it out."
Tsanidakis explains that while collisions are probably common in the early history of a stellar system, they can still occur in systems with stable, middle-aged stars like Gaia20ehk. Near passes by other stars, or by rogue exoplanets, could destabilize planetary orbits, causing one of the system's planets either to be ejected, or (in this case) gradually to spiral inward. This could explain the three dips in brightness that was his first clue something odd was happening -- they represent grazing passes as the two planets' orbits overlapped more and more. But eventually, they got close enough that there was a head-on impact, and all hell broke loose.
Considering the quantity of data that missions like Gaia produce, I find it astonishing that Tsanidakis and his colleagues even picked up on it. You have to wonder what other wonders might be hidden in the enormous hauls from JWST, Hubble, and (soon) the Vera Rubin Telescope. Fortunately, a sharp-eyed astronomer caught this one, and as a result we've learned a huge amount about exoplanetary collisions.
It's staggering to think about. The awe-inspiring vistas we're seeing through our best telescopes are only now being studied and analyzed, and who knows what else the astronomers will find?
All from following astrophysicist Neil deGrasse Tyson's adjuration -- "Keep looking up."
Coming right on the heels of yesterday's post about a star so large the astrophysicists are at a loss to explain how it even exists, today we have...
... a supermassive black hole moving so fast it seems to be exceeding the escape velocity of the entire galactic cluster.
The paper about the discovery, by Yale University astronomer Pieter van Dokkum et al., appeared last week in Astrophysical Journal Letters, and its findings are hard to summarize without lapsing into superlatives. Data from the James Webb Space Telescope identified a large, rapidly-moving object from its bow shock -- the compression waves surrounding a projectile as it moves through a medium (picture the pile-up of water and resulting waves preceding a boat as it moves across the surface of a lake). But an analysis of this particular bow shock demonstrated something incredible; the object creating it was ten million times the mass of the Sun -- thus, a supermassive black hole -- and it was moving at an estimated three hundred kilometers a second.
For reference, this is over two hundred times faster than the muzzle velocity of a rifle bullet.
A map of the JWST data that led to the discovery [Image credit van Dokkum et al.]
Amongst the many cool things about this discovery is that there is a higher-than-expected number of very young stars in the wake of this thing. Apparently, the compression caused by the black hole is triggering gas cloud collapse and star formation as it passes.
What could give something this massive that much momentum? The quick answer is "no one knows for sure," but a good candidate is a galactic merger. Two colliding galaxies represent a quantity known to astrophysicists as "a shitload of kinetic energy," and the slingshot effect -- where two moving objects pass close enough to each other that there's a transfer of momentum, causing one to slow down and the other to accelerate -- could be responsible. It might be that this was once the black hole at the center of a galaxy, but the collision caused it to swing around an even more massive black hole from the other galaxy, resulting in its being jettisoned -- not just from the combined mass of the merger, but from the entire galactic cluster.
The question that naturally comes up is "what if it was headed toward us?" Well, to start with, it's not; just a glance at the map of the bow shock should tell you that. Second, its light has a red shift of 0.96, putting it at about a billion light years away, so even if it was, it wouldn't be anything you or I would have to fret about in our lifetimes.
On the other hand, what if there was a black hole like this headed our way? Being black (as advertised), would we see it coming before the Earth was messily devoured? The answer is "almost certainly;" not only would there be the effects of the compression waves heating up the gas ahead of it, causing it to emit radiation, there'd be the fact that massive black holes cause gravitational lensing -- they bend and distort the light of objects behind them. If we were looking down the barrel of a black hole headed our way, we'd see this as an optical effect called an Einstein-Chwolson ring:
[Nota bene: black holes that are not moving toward us also cause gravitational lensing and Einstein-Chwolson rings; it'd be the combination of the lensing effect and the heating of the gas in front of the black hole that would tell us it was heading in our direction.]
Given astronomical distances, though, we still wouldn't have to worry about anything in our lifetimes. It might be bad news for our possible descendants a hundred million years from now, but there are way worse problems to concern ourselves with in the interim. And in any case, even if there was a supermassive black hole headed our way that was due to arrive either a hundred million years from now or a week from next Tuesday, there'd be absolutely nothing we could do about it. Altering the trajectory of a something with ten million times the mass of the Sun, traveling at three hundred kilometers per second, gives new meaning to the word "unfeasible." The only option, really, would be to stick your head between your legs and kiss your ass goodbye.
But like I said, the one van Dokkum et al. discovered isn't going to be a problem, even millions of years from now. It's something we can goggle at from a safe distance. A massive bullet flying through space, leaving a spangle of new stars in its wake. Yet another example of how endlessly awe-inspiring the universe is -- and the more we find out about it, the more wonderful it gets.
Way back around 1910, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell independently found a curious pattern when they did a scatterplot correlation between stars' luminosities and temperatures.
The graph, now called the Hertzsprung-Russell Diagram in their honor, looks like this:
Most stars fall on the bright swatch running from the hot, bright stars in the upper left to the cool, dim stars in the lower right; the overall trend for these stars is that the lower the temperature, the lower the luminosity. Stars like this are called main-sequence stars. (If you're curious, the letter designations along the top -- O, B, A, F, G, K, and M -- refer to the spectral class the star belongs to. These classifications were the invention of the brilliant astronomer Antonia Maury, whose work in spectrography revolutionized our understanding of stellar evolution.)
There is also a sizable cluster of stars off to the upper right -- relatively low temperatures but very high luminosities. These are giants and supergiants. In the other corner are white dwarfs, the exposed cores of dead stars, with very high temperatures but low luminosity, which as they gradually cool slip downward to the right and finally go dark.
So there you have it; just about every star in the universe is either a main-sequence star, in the cluster with the giants and supergiants, or in the curved streak of dwarf stars at the bottom of the diagram.
Emphasis on the words "just about."
One star that challenges what we know about how stars evolve is the bizarre Stephenson 2-18, which is in the small, dim constellation Scutum ("the shield"), between Aquila and Sagittarius. At an apparent magnitude of +15, it is only visible through a powerful telescope; it wasn't even discovered until 1990, by American astronomer Charles Bruce Stephenson, after whom it is named.
Its appearance, a dim red point of light, hides how weird this thing actually is.
When Stephenson first analyzed it, he initially thought what he was coming up with couldn't possibly be correct. For one thing, it is insanely bright, estimated at a hundred thousand times the Sun's luminosity. Only its distance (19,000 light years) and some intervening dust clouds make it look dim. Secondly, it's enormous. No, really, you have no idea how big it is. If you put Stephenson 2-18 where the Sun is, its outer edge would be somewhere near the orbit of Saturn. You, right now, would be inside the star. Ten billion Suns would fit inside Stephenson 2-18.
If a photon of light circumnavigated the surface of the Sun, it would take a bit less than fifteen seconds. To circle Stephenson 2-18 would take nine hours.
This puts Stephenson 2-18 almost off the Hertzsprung-Russell Diagram -- it's in the extreme upper right corner. In fact, it's larger than what what stellar evolution says should be possible; the current model predicts the largest stars to have radii of no more than 1,500 times that of the Sun, and this behemoth is over 2,000 times larger.
Astronomers admit that this could have a simple explanation -- it's possible that the measurements of Stephenson 2-18 are overestimates. But if not, there's something significant about stellar evolution we're not understanding.
Either way, this is one interesting object.
There's also a question about what Stephenson 2-18 will do next. Astrophysicists suspect it might be about to blow off its outer layers and turn either into a luminous blue variable or a Wolf-Rayet star (the latter are so weird and violent I wrote about them here a while back). So it may not be done astonishing us.
As far as the scientists, they love peculiar puzzles like this. Contrary to the picture many people have, of scientists being stick-in-the-mud conservatives who do nothing but prop up the current dominant paradigm, the vast majority of scientists absolutely live for having their prior notions being challenged, because that's when new avenues for understanding open up.
As the brilliant polymath Isaac Asimov put it, "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!', but '... that's funny.'"
The death of massive stars, ten or more times the mass of the Sun, is thought to have a predictable -- if violent -- trajectory.
During most of their lifetimes, stars are in a relative balance between two forces. Fusion of hydrogen into helium in the core releases heat energy, which increases the pressure in the core and generates an outward-pointing force. At the same time, the inexorable pull of gravity generates an inward-pointing force. For the majority of the star's life, the two are in equilibrium; if something makes the core cool a little bit, gravity wins for a while and the star shrinks, increasing the pressure and thus the rate of fusion. This heats the core up, increasing the outward force and stopping the collapse.
Nice little example of negative feedback and homeostasis, that. Stars in this long, relatively quiescent phase are on the "Main Sequence" of the famous Hertzsprung-Russell Diagram:
Once the hydrogen fuel starts to deplete, though, the situation shifts. Gravity wins once again, but this time there's not enough hydrogen-to-helium fusion to counteract the collapse. The core shrinks, raising the temperature to hundreds of millions of degrees Kelvin -- enough to fuse helium to carbon. This release of energy causes the outer atmosphere to balloon outward, and the star becomes a red supergiant -- the surface is cool (and thus reddish), but the interior is far hotter than the core of our Sun.
Two famous stars -- Betelgeuse (in Orion) and Antares (in Scorpio) are in this final stage of their lives.
Here's where things get interesting, because the helium fuel doesn't last forever, either. The carbon "ash" left behind needs an even higher temperature to fuse into oxygen, nitrogen, and heavier elements, which happens when the previous process repeats itself -- further core collapse, followed by further heating. But this can't go on indefinitely. When the fusion reaction starts to generate iron, the game is up. Iron represents the turnaround point on the curve of binding energy, where fusion stops being an exothermic (energy-releasing) reaction and becomes endothermic (energy-consuming). At that point, the core can't respond with anything to support the pull of gravity, and the entire star collapses. The outer atmosphere rebounds off the collapsing core, creating a shockwave called a core-collapse (type II) supernova, releasing in a few seconds as much energy as the star did during its entire life on the main sequence. What's left afterward is a super-dense remnant -- either a neutron star or a black hole, depending on its mass.
Well, that's what we thought happened. But now a paper in Science describing the collapse of a supergiant star in the Andromeda Galaxy has suggested there may be a different fate for at least some massive stars -- that they may go out not with a bang, but with a whimper.
The occurrence that spurred this discovery was so underwhelming that it took astronomers a while to realize it had happened. A star began to glow intensely in the infrared region of the spectrum, and then suddenly -- it didn't anymore. It seemed to vanish, leaving behind a faintly glowing shell of dust. Kishalay De, lead author of the paper, says what happened is that we just witnessed a black hole forming without a supernova preceding it. The core ran out of fuel, the outer atmosphere collapsed, and the star itself just kind of... winked out.
"This has probably been the most surprising discovery of my life," De said. "The evidence of the disappearance of the star was lying in public archival data and nobody noticed for years until we picked it out... The dramatic and sustained fading of this star is very unusual, and suggests a supernova failed to occur, leading to the collapse of the star’s core directly into a black hole. Stars with this mass have long been assumed to always explode as supernovae. The fact that it didn’t suggests that stars with the same mass may or may not successfully explode, possibly due to how gravity, gas pressure, and powerful shock waves interact in chaotic ways with each other inside the dying star."
It's honestly unsurprising that we don't have the mechanisms of supernovae and black hole formation figured out completely. They're not frequent occurrences. The most recent easily visible supernova in the Milky Way was all the way back in 1604 -- "Kepler's Supernova," as it's often called. Since then we've seen them occur in other galaxies, but that means from here they're invisible to the naked eye, and often difficult to study even with powerful telescopes.
But I will say that the whole thing has me worried. Betelgeuse is predicted to run out of fuel soon, and all my life I've been waiting for it to explode violently (yes, yes, I know that "soon" to an astrophysicist means "some time in the next hundred thousand years). If it just decides to go pfft and vanish one night, I'm gonna be pissed.
Oh, well, as my grandma used to tell me, wishin' don't make it so. But still. Life down here on Earth has been pretty damn distressing lately, can't we have just one nice thing?
The list of confirmed exoplanets now exceeds six thousand. Considering the fact that the three main ways they're detected -- direct measure of stellar wobbles, transit photometry, and Doppler spectroscopy -- all require either that the host star be close, that the planets be massive, or that the planetary orbit be aligned just right from our perspective, or all three, it's almost certain that there are vast numbers of exoplanets going undetected.
All of which bodes well for those of us who would love for there to be extraterrestrial life out there somewhere.
On the other hand, of the exoplanets we've found, a great many of them are inhospitable to say the least, and some of them are downright bizarre. Here are a few of the weirder ones:
TrES-2b, which holds the record as the least-reflective planet yet discovered. It's darker than a charcoal briquet. This led some people to conclude that it's made of dark matter, something I dealt with here at Skeptophilia a while back. (tl:dr -- it's not.)
CoRoT-7b, one of the hottest exoplanets known. Its composition and size are thought to be fairly Earth-like, but it orbits its star so closely that it has a twenty-day orbital period and surface temperatures around 3000 C. This means that it is likely to be completely liquid, and experience rain made of molten iron and magnesium.
PSR J1719−1438, a planet orbiting a pulsar (the collapsed, rapidly rotating core of a giant star), and therefore somehow survived its host star going supernova. It has one of the fastest rates of revolution of any orbiting object known, circling in only 2.17 hours.
V1400 Centauri, a planet with rings that are two hundred times wider than the rings of Saturn. In fact, they dwarf the planet itself -- the whole thing looks a bit like a pea in the middle of a dinner plate.
BD+05 4868 Ab, in the constellation of Pegasus. Only 140 light years away, this exoplanet is orbiting so close to its parent star -- twenty times closer than Mercury is to the Sun -- that its year is only 30.5 hours long. This proximity roasts the surface, melting and then vaporizing the rock it's made of. That material is then blasted off the surface by the stellar wind, so the planet is literally evaporating, leaving a long, comet-like trail in its wake.
Today, though, we're going to look at some recent research about a planet that should be near the top of the "Weirdest Exoplanets Known" list. It's 55 Cancri Ae, the innermost of four (possibly six; two additional ones are suspected but unconfirmed) planets around the star 55 Cancri A, a K-type orange star a little over forty light years away. 55 Cancri Ae orbits its host star twice as close as Mercury does the Sun, making a complete ellipse around it in only a bit under three days. This means that like CoRoT-7b and BD+05 4868 Ab, it's crazy hot.
This is where some new research comes in. A presentation at an exoplanet conference in Groningen, Netherlands last week considered a puzzling feature of 55 Cancri Ae -- a measure of its heat output shows odd, non-cyclic fluctuations that don't seem to be in sync with its orbital period (or anything else). The fluctuations aren't small; some of them have approached a 1,000 C difference from peak to trough. They were first detected ten years ago, and physicists have been at a loss to account for the mechanism responsible.
But now, we might have an explanation -- and it's a doozy. Models developed by exoplanet astrophysicist Mohammed Farhat of the University of California - Berkeley found that the anomalous temperature surges could be explained as moving hotspots.
Which sounds pretty tame until you read Farhat's description of what this means. We're talking about a planet close in to a star not much smaller than the Sun, being whirled around at dizzying speeds. This means it's experiencing enormous tidal forces. The planet itself is so hot it's probably liquid down to its core. Result: tidal waves of lava several hundred meters high, moving at the speed of a human sprinter.
The presentation definitely got the attendees' attention. "This is right in the sweet spot of something that is interesting, novel, and potentially testable," said planetary astronomer Laura Kreidberg, of the Max Planck Institute for Astronomy. "I had this naïve idea that lava flows were too slow-moving to have an observable impact, but this new work is pointing otherwise."
The whole thing reminds me of the planet Excalbia from Star Trek, from the episode "The Savage Curtain," which was completely covered by churning seas of lava -- except for the spot made hospitable by some superpowerful aliens so Captain Kirk could have a battle involving Abraham Lincoln, Genghis Khan, and various other historical and not-so-historical figures to find out whether good was actually stronger than evil.
Put that way, I know the plot sounds pretty fucking ridiculous, but don't yell at me. I didn't write the script.
In any case, I doubt even the Excalbians would find 55 Cancri Ae hospitable. But it is fascinating. It pushes the definition of what we even consider a planet to be -- a sloshing blob of liquid rock with lava waves taller than a skyscraper. Makes me thankful for the calm, temperate climes of Earth.
I'll start today with a quote (often misquoted) from William Shakespeare -- more specifically, Hamlet, Act I, Scene 5:
Horatio:
O day and night, but this is wondrous strange!
Hamlet:
And therefore as a stranger give it welcome. There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.
Horatio and Hamlet, of course, are talking about ghosts and the supernatural, but it could equally well be applied to science. It's tempting sometimes, when reading about new scientific discoveries, for the layperson to say, "This can't possibly be true, it's too weird." But there are far too many truly bizarre theories that have been rigorously verified over and over -- quantum mechanics and the General Theory of Relativity jump to mind immediately -- to rule anything out based upon our common-sense ideas about how the universe works.
That was my reaction while watching a YouTube video about an astronomical object I'd never heard of -- Przybylski's Star, named after its discoverer, Polish-born Australian astronomer Antoni Przybylski. The video comes from astronomer David Kipping's channel Cool Worlds Lab, which looks at cutting-edge science -- and tantalizing new data about the universe we live in. (You should subscribe to it -- you won't be sorry.) Przybylski's Star is 355 light years from Earth, in the constellation of Centaurus, and is weird in so many ways that it kind of boggles the mind.
It's classified as a Type Ap star. Type A stars are young, compact, luminous, and very hot; the brightest star in the night sky, Sirius, is in this class.
Przybylski's Star rotates slowly. I mean, really slowly. Compared to the Sun, which rotates about once every 27 days, Przybylski's Star rotates once every two hundred years. Most type A stars rotate even faster than the Sun; in fact, a lot of them rotate so quickly that the light from their receding hemisphere and that from their approaching hemisphere experience enough red-shift and blue-shift (respectively) to smear out their spectral lines, making it impossible for us to tell exactly what they're made of.
You probably know that most ordinary stars are primarily composed of hydrogen, and of the bit that's not hydrogen, most of it is helium. Hydrogen is the fuel for the fusion in the core of the star, and helium is the product formed by that fusion. Late in their life, many stars undergo core collapse, in which the temperatures heat up enough to fuse helium into heavier elements like carbon and oxygen. Most of the rest of the elements on the periodic table are generated in supernovas and in neutron stars, a topic I dealt with in detail in a post I did about six years ago.
My point here is that if you look at the emission spectra of your average star, the spectral lines you see should mostly be the familiar ones from hydrogen and helium, with minuscule traces of the spectra of other elements. The heaviest element that should be reasonably abundant, even in the burned-out cores of stars, is iron -- it represents the turnaround point on the curve of binding energy, the point where fusion into heavier elements starts consuming more energy than it releases.
So elements that are low in abundance pretty much everywhere, such as the aptly-named rare earth elements (known to chemists as the lanthanides), should be so uncommon as to be effectively undetectable. Short-lived radioactive elements like thorium and radium shouldn't be there at all, because they don't form in the core of your ordinary star, and therefore any traces present had to have formed prior to the star in question's formation -- almost always, enough time that they should have long since decayed away.
The composition of Przybylski's Star, on the other hand, is so skewed toward heavy elements that it elicits more in the way of frustrated shrugs than it does in viable models that could account for it. It's ridiculously high in lanthanides like cerium, dysprosium, europium, and gadolinium -- not elements you hear about on a daily basis. There's more praseodymium in the spectrum of its upper atmosphere than there is iron. Even stranger is the presence of very short-lived radioactive elements such as plutonium -- and actinium, americium, and neptunium, elements for which we don't even know a naturally-occuring nuclide synthesis pathway capable of creating them.
So where did they come from?
"What we’d like to know... is how the heavy elements observed here have come about," said astronomy blogger Paul Gilster. "A neutron star is one solution, a companion object whose outflow of particles could create heavy elements in Przybylski’s Star, and keep them replenished. The solution seems to work theoretically, but no neutron star is found anywhere near the star."
"[T]hat star doesn’t just have weird abundance patterns; it has apparently impossible abundance patterns," said Pennsylvania State University astrophysicist Jason Wright, in his wonderful blog AstroWright. "In 2008 Gopka et al. reported the identification of short-lived actinides in the spectrum. This means radioactive elements with half-lives on the order of thousands of years (or in the case of actinium, decades) are in the atmosphere... The only way that could be true is if these products of nuclear reactions are being replenished on that timescale, which means… what exactly? What sorts of nuclear reactions could be going on near the surface of this star?"
All the explanations I've seen require so many ad-hoc assumptions that they're complete non-starters. One possibility astrophysicists have floated is that the replenishment is because it was massively enriched by a nearby supernova, and not just with familiar heavy elements like gold and uranium, but with superheavy elements that thus far, we've only seen produced in high-energy particle accelerators -- elements like flerovium (atomic number 114) and oganesson (atomic number 118). These elements are so unstable that they have half-lives measured in fractions of a second, but it's theorized that certain isotopes might exist in an island of stability, where they have much longer lives, long enough to build up in a star's atmosphere and then decay into the lighter, but still rare, elements seen in Przybylski's Star.
There are several problems with this idea, the first being that every attempt to find where the island of stability lies hasn't succeeded. Physicists thought that flerovium might have the "magic number" of protons and neutrons to make it more stable, but a paper released not long ago seems to dash that hope.
The second, and worse, problem is that there's no supernova remnant anywhere near Przybylski's Star.
The third, and worst, problem is that it's hard to imagine any natural process, supernova-related or not, that could produce the enormous quantity of superheavy elements required to account for the amount of lanthanides and actinides found in this star's upper atmosphere.
Which brings me to the wildest speculation about the weird abundances of heavy elements. You'll never guess who's responsible.
Go ahead, guess.
There is a serious suggestion out there -- and David Kipping does take it seriously -- that an advanced technological civilization might have struck on the solution for nuclear waste of dumping it into the nearest star. This explanation (called "salting"), bizarre as it sounds, would explain not only why the elements are there, but why they're way more concentrated in the upper atmosphere of the star than in the core.
"Here on Earth... people sometimes propose to dispose of our nuclear waste by throwing it into the Sun,” Wright writes. “Seven years before Superman thought of the idea, Whitmire & Wright (not me, I was only 3 in 1980) proposed that alien civilizations might use their stars as depositories for their fissile waste. They even pointed out that the most likely stars we would find such pollution in would be… [type] A stars! (And not just any A stars, late A stars, which is what Przybylski’s Star is). In fact, back in 1966, Sagan and Shklovskii in their book Intelligent Life in the Universe proposed aliens might 'salt' their stars with obviously artificial elements to attract attention."
A curious side note is that I've met (Daniel) Whitmire, of Whitmire & Wright -- he was a professor in the physics department of the University of Louisiana when I was an undergraduate, and I took a couple of classes with him (including Astronomy). He was known for his outside-of-the-box ideas, including that a Jupiter-sized planet beyond the orbit of Pluto was responsible for disturbing the Oort Cloud as it passed through every hundred million years or so (being so far out, it would have a super-long rate of revolution). This would cause comets, asteroids, and other debris to rain in on the inner Solar System, resulting in a higher rate of impacts with the Earth -- and explaining the odd cyclic nature of mass extinctions.
So I'm not all that surprised about Whitmire's suggestion, although it bears mention that he was talking about the concept in the purely theoretical sense; the weird spectrum of Przybylski's Star was discovered after Whitmire & Wright's paper on the topic.
Curiouser and curiouser.
So we're left with a mystery. The "it's aliens" explanation is hardly going to be accepted by the scientific establishment without a hell of a lot more evidence, and thus far, there is none. The problem is, the peculiar abundance of heavy elements in this very odd star remains unaccounted for by any science we currently understand. The fact that Kipping (and others) are saying "we can't rule out the alien salting hypothesis" is very, very significant.
I'll end with another quote, this one from eminent biologist J. B. S. Haldane: "The universe is not only queerer than we imagine, it is queerer than we can imagine."
There are specific solutions for objects of a particular mass starting out with a particular set of coordinates and velocities, and lots of them result in highly unstable orbits. But despite the fact that there are computer models that can predict the movements of three objects in a gravitational dance -- such as the members of a triple-star system -- the overarching mathematical framework has proven intractable.
How, then, can we predict the orbits of the eight planets (and countless dwarf planets, asteroids, and comets) around the Sun to such high precision? Some of the great names of physics and astronomy in the sixteenth and seventeenth centuries -- Galileo Galilei, Tycho Brahe, Johannes Kepler, and Isaac Newton, especially -- used highly accurate data on planetary positions to conclude that the planets in the Solar System go around the Sun in elliptical orbits, all powered by the Universal Law of Gravitation. The mathematical model they came up with worked to a high degree of accuracy, allowing earthbound astronomers to predict where the planets were in the sky, and also such phenomena as eclipses.
The reason it works, and doesn't fall prey to the three-body problem chaos, is that the Sun is so massive in comparison to the objects orbiting it. Because the Sun is huge -- it has a thousand times more mass than the largest planet, Jupiter -- its gravitational pull is big enough that it swamps the pull the planets exert on each other. For most purposes, you can treat each orbit as independent two-body problems; you can (for example) look at the masses, velocities, and distances between the Sun and Saturn and ignore everything else for the time being. (Interestingly, it's the slight deviation of the orbit of Uranus from the predictions of its position using the two-body solution that led astronomers to deduce that there must be another massive planet out there pulling on it -- and in 1846 Neptune was observed for the first time, right where the deviations suggested it would be.)
I said it was "lucky" that the mass imbalance is so large, but I haven't told you how lucky. It turns out that all you have to do is add one more object of close to the same size, and you now have the three-body problem, and the resulting orbit becomes unpredictable, chaotic, and -- very likely -- unstable.
It's what I always think about when I hear woo-woos burbling on about Nibiru, a huge extrasolar planet that has been (repeatedly) predicted to come zooming through the Solar System. We better hope like hell this doesn't happen, and not because there could be collisions. A huge additional mass coming near the Earth would destabilize the Earth's orbit, and could cause it to change -- very likely making it more elliptical (meaning we'd get fried at perigee and frozen at apogee). Interestingly, this is one thing that even the writers of Lost in Space got right, at least temporarily. The planet John Robinson et al. were on had a highly elliptical orbit, leading to wild climatic fluctuations. The "temporarily" part, though, came about because apparently the writers found it inconvenient to have the Robinson Family deal with the alternating icebox/oven climate, and after a short but dramatic story arc where they were contending with it, it never happened again.
Or maybe the planet just decided to settle down and behave. I dunno.
An unstable orbit can also have one other, even more dire outcome; it can cause a planet to get ejected from its star system entirely. This would be seriously bad news if it happened here, because very quickly we'd exit the habitable zone and be frozen solid. This is likely the origin of rogue planets -- planets that started out orbiting a star, but somehow have lost their gravitational lock, and end up floating in the vast dark of interstellar space.
This does bring up an interesting question, though; if they're out in outer space, but emit no light, how do we know they're there? Well, they were conjectured for decades, based on the argument above, about orbital instability; but as far as detection goes, that's proven harder. But now, we have actually detected one, and how we did it is absolutely staggering.
One of the outcomes of Einstein's General Theory of Relativity is that the presence of matter warps space. A common two-dimensional analogy is a bowling ball sitting on a trampoline, deflecting the membrane downward. If you roll a marble on the trampoline, it'll curve around the bowling ball, not because the bowling ball is magically attracting the marble, but because its presence has changed the shape of the space the marble is moving through. Scale that up by one dimension, and you've got the idea.
What's cool about this is that because it's the shape of spacetime that has warped, everything passing through that region is affected -- including light. This is called gravitational lensing, and has been used to infer the positions and masses of black holes, which (duh) are black and therefore hard to see. But by detecting the distortion of light emitted by objects behind the black hole, we can see its effects.
And now, that's been done with a rogue exoplanet. Judging by the lensing effect it created, it's about the mass of Saturn, and the conclusion based on its mass and velocity was that it was indeed once part of a planetary system -- and then got ejected, probably because of a close encounter with another massive object, or perhaps because it was part of a multiple star system and was in an unstable orbit from the get-go.
Now, though, it's lost -- a lonely wanderer tracking its way through the vastness of interstellar space. How many of these rogue planets there are is unknown; as you probably concluded, detection isn't easy, relying on having a powerful telescope aimed in the right direction at the moment the planet passes in front of a distant star. But given how easy it is to destabilize an orbit, there are likely to be millions.
Which, we have to hope, will all stay the hell away from us. Nibiru notwithstanding, having a rogue planet pass through the Solar System would make even Donald Trump drop to number two on the List Of The Biggest Current Threats To Humanity. Fortunately, it's unlikely; space is big. We'd also likely have a decent amount of warning, because as soon as it got near enough (right around the orbit of Pluto), it'd reflect enough of the Sun's light that it'd become visible to astronomers.
Unfortunately, though, there's probably nothing much we could do about it. We've just begun to experiment with the possibility of deflecting small asteroids; deflecting an entire planet, especially one the size of Saturn, would be a case where the best strategy would be to stick your head between your legs and kiss your ass goodbye.
I mean, not to end on a pessimistic note. Let's all focus on the "unlikely" part. And continue working on the next biggest threat, which frankly is occupying more of my anxiety at the moment.
If you own anything made of gold, take a look at it now.
I'm looking at my wedding ring, made of three narrow interlocked gold bands. It's a little scratched up after twenty-three years, but still shines.
Have you ever wondered where gold comes from? Not just "a gold mine," but before that. If you know a little bit of physics, it's kind of weird that the periodic table doesn't end at 26. The reason is a subtle but fascinating one, and has to do with the binding energy curve.
The vertical axis is a measure of how tightly the atom's nucleus is held together. More specifically, it's the amount of energy (in millions of electron-volts) that it would take to completely disassemble the nucleus into its component protons and neutrons. From hydrogen (atomic number = 1) up to iron (atomic number = 26), there is a relatively steady increase in binding energy. So in that part of the graph, fusion is an energy-releasing process (moves upward on the graph) and fission is an energy-consuming process (moves downward on the graph). This, in fact, is what powers the Sun; going from hydrogen to helium is a jump of seven million electron-volts per proton or neutron, and that energy release is what produces the light and heat that keeps us all alive.
After iron, though -- specifically after an isotope of iron, Fe-56, with 26 protons and 30 neutrons -- there's a slow downward slope in the graph. So after iron, the situation is reversed; fusion would consume energy, and fission would release it. This is why the fission of uranium-235 generates energy, which is how a nuclear power plant works.
It does generate a question, though. If fusion in stars is energetically favorable, increasing stability and releasing energy, up to but not past iron -- how do the heavier elements form in the first place? Going from iron to anywhere would require a consumption of energy, meaning those will not be spontaneous reactions. They need a (powerful) energy driver. And yet, some higher-atomic-number elements are quite common -- zinc, iodine, and lead come to mind.
Well, it turns out that there are two ways this can happen, and they both require a humongous energy source. Like, one that makes the core of the Sun look like a wet firecracker. Those are supernova explosions, and neutron star collisions. And two astrophysicists -- Szabolcs Marka of Columbia University and Imre Bartos of the University of Florida -- have found evidence that the heavy elements on the Earth were produced in a collision between two neutron stars, on the order of a hundred million years before the Solar System formed.
This is an event of staggering magnitude. "If you look up at the sky and you see a neutron-star merger a thousand light-years away," Marka said, "it would outshine the entire night sky."
What apparently happens is when two neutron stars -- the ridiculously dense remnants of massive stellar cores -- run into each other, it is such a high-energy event that even thermodynamically unfavorable (energy-consuming) reactions can pick up enough energy from the surroundings to occur. Then some of the debris blasted away from the collision gets incorporated into forming stars and planets -- and here we are, with tons of lightweight elements, but a surprisingly high amount of heavier ones, too.
But how do they know it wasn't a nearby supernova? Those are far more common in the universe than neutron star collisions. Well, the theoretical yield of heavy elements is known for each, and the composition of the Solar System is far more consistent with a neutron star collision than with a supernova. And as for the timing, a chunk of the heavy isotopes produced are naturally unstable, so decaying into lighter nuclei is favored (which is why heavy elements are often radioactive; the products of decay are higher on the binding energy curve than the original element was). Since this happens at a set rate -- most often calculated as a half-life -- radioactive isotopes act like a nuclear stopwatch, analogous to the way radioisotope decay is used to calculate the ages of artifacts, fossils, and rocks. Backtracking that stopwatch to t = 0 gives an origin of about 4.7 billion years ago, or a hundred million years before the Solar System coalesced.
So next time you look at anything made of heavier elements -- gold or silver or platinum, or (more prosaically) the zinc plating on a galvanized steel pipe -- ponder for a moment that it was formed in a catastrophically huge collision between two neutron stars, an event that released more energy in a few seconds than the Sun will produce over its entire lifetime. Sometimes the most ordinary things have a truly extraordinary origin -- something that never fails to fascinate me.
Today I'm going to focus on outer space, because if I don't I'll be forced to deal with events down here on Earth, and it's a little early to start drinking.
The James Webb Space Telescope just posted information on a structure called the Saraswati Supercluster, which at a diameter of 650 million light years and a mass of twenty quadrillion times the mass of the Sun, is one of the largest gravitationally-bound structures known. If you look toward the constellation Pisces, visible in the Northern Hemisphere from August to early January, you're staring right at the Saraswati Supercluster.
Not that you can see it with the naked eye. Its center is about four billion light years away, meaning not only that it's extremely faint, the light from it has taken about a third of the age of the universe to get here, so it's really red-shifted. Here's the rather mind-blowing image the JWST team just posted on their site:
On this diagram, the Sun and Solar System are at the center, and as you move outward the scale increases exponentially, allowing us to visualize -- or at least imagine -- the astonishing vastness of the universe. (Saraswati is just slightly to the left of top center on the diagram.)
The name of the supercluster is from a Sanskrit word meaning "ever-flowing stream with many pools," which is appropriate. It's made of forty-three galaxy clusters -- not galaxies, mind you, but galaxy clusters -- of which the largest, Abell 2631, is thought to be made up of over a thousand galaxies (and something on the order of a hundred trillion stars).
If your mind is not boggling yet, you're made of sterner stuff than I am.
Because of its distance and faintness, we haven't known about Saraswati for all that long. It was discovered in 2017 by a team of Indian astronomers led by Joydeep Bagchi from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, India, and since has been the object of intense study by astrophysicists for two main reasons. First -- although it's phenomenally massive, its vast diameter makes it remarkable that it hangs together gravitationally. (Remember that gravitational attraction falls off as the square of the distance; it never goes to zero, but it does get really weak.) The fact that it does seem to be acting as a single structure could give us valuable information about the role of the elusive dark matter in making large objects stick together over time.
Second, it might provide some insight into solving another mystery, the question of how (or if) dark energy, the strange force that seems to be making the expansion of the universe speed up, is changing over time. You may recall that just this past August, a pair of papers came out suggesting that the strength of this peculiar phenomenon might be decreasing; that instead of heading toward the rather ghastly prospect of a "Big Rip," where dark energy overpowers every other known force and tears matter apart into a soup of subatomic particles, the expansion might eventually stop or even reverse. The old "oscillating universe" idea, that the universe goes through an endless series of expansions and collapses -- popularized by such brilliant luminaries of physics as Paul Steinhardt and Roger Penrose -- might have legs after all. Studying Saraswati might give us more information about how the strength of dark energy has changed in the four-billion-odd years it's taken the light from the supercluster to arrive here.
So next time you look up into a clear night sky, think of what lies beyond the bit you can actually see. Every individual star visible to the naked eye lives in a (relatively) tiny sphere in the Orion Arm of the Milky Way. The few bits that visible but are farther away -- the smear of light that is all we can discern of the rest of our own galaxy, as well as the few other galaxies we can see without a telescope (like Andromeda and the two Magellanic Clouds) are so distant that individual stars can't be resolved without magnification. What we think of as the impressive grandeur of the night sky is, basically, like thinking you're a world traveler because you drove around your own neighborhood once or twice.
But I guess I need to come back down to Earth. Unfortunately. On the whole, I'm much happier looking up. It makes the current horror show we're living through at least seem a little less overwhelming, and puts our own place in the universe into perspective.
Maybe if our so-called leaders spent more time stargazing, it might provide them with some much-needed humility.
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