Flash in the pan

"There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy."

So wrote William Shakespeare in Hamlet, and if anything, it's a significant understatement.  If Shakespeare were writing today, considering recent discoveries in science, he might phrase it as, "Horatio, you seriously have no idea how weird it is out there.  I mean, literally," which gains in accuracy but does lose something in poetic diction.

To take just one example, consider the paper that appeared in Astrophysical Journal Letters this week, about a gamma ray burst that was discovered by the amusingly-named Very Large Telescope (they're currently building a bigger one down in Chile which will be called, I shit you not, the Extremely Large Telescope).  Gamma ray bursts are already pretty astonishing; NASA describes them as "second only to the Big Bang as the most energetic and luminous phenomena known."  There are several possible causes of these enormous releases of high-frequency electromagnetic radiation -- supernovae, the catastrophic merger of neutron stars, and flares from magnetars amongst them.  (You would not want to be looking down the gun barrel of one of these when it went off.  There is some suspicion that the Late Ordovician Mass Extinction -- one of the "Big Five" mass extinctions, and second only to the Permian-Triassic "Great Dying" event in terms of magnitude -- was caused by a nearby gamma ray burst.)

Most of these events are one-offs, and considering the energy they involve (most of them release more energy in a few seconds than the Sun will in its entire lifetime) you can understand why.  After one flare-up of that size, it's unsurprising that it wouldn't do it again any time soon.  So the astrophysicists were puzzled when they found a gamma-ray burster (GRB 250702B) that seems to recur -- it produced a sequence of five flares, and did that entire sequence three times.  Weirdest still, each time, the interval between the second and third flare in the sequence was an integer multiple of the interval between the first two!

What in the hell could cause that?

The gamma-ray burst seems to be extragalactic -- to be coming from a source outside the Milky Way.  The source is near a known galaxy, but whether the burst is coming from within the galaxy, or simply from a source that happens to be lined up with it, hasn't been determined yet.  The galaxy is one of the thousands that have been located by the Hubble and James Webb Space Telescopes but have yet to be studied; they don't even know what its red shift is (which would tell you how far away it is).  But because the red shift of gamma ray bursts is impossible to determine -- to calculate red shift, you need identifiable spectral lines, and those don't occur in something as massive and chaotic as a burst -- this still wouldn't tell you whether the source was actually inside the galaxy or not.

In fact, there's more that's unknown than known about this phenomena.  The periodicity led the researchers to suggest one possibility, that it was some unfortunate massive star in an elliptical orbit around a massive black hole, and having pieces torn off it every time it gets to perihelion.  Another possibility is an "atypical stellar core collapse," which is astrophysics-speak for "a collapsing star where we really have no idea why it's acting like it does."  A third is that the detected periodicity is an artifact caused by "dust echoes" -- reflection of the original gamma-ray burst from concentric shells of dust surrounding the remains of an exploded star.  The final possibility -- at least of the ones the authors came up with -- is that it's an example of gravitational lensing, where light emitted by a star (or other astronomical object) travels close to a black hole, the curved space around the black hole causes the light beam to split along more than one path, and different parts of it arrive at different times.

The paths of light traveling through a gravitational lens [Image is in the Public Domain courtesy of NASA/JPL]

The upshot is that we simply don't know what's going on here.  The authors write:

We have... new, multiwavelength observations of a superlative series of associated GRB triggers, GRB 250702B.  Our observations reveal a rapidly fading, multiwavelength counterpart likely to be embedded in a galaxy with a complex and asymmetric morphology.  We... conclude that GRB 250702B is an extragalactic event.  The relatively bright and extended host suggest the redshift is moderate (z < 1).

GRB 250702B is observationally unprecedented in its timescale, morphology, and the onset of X-ray photons prior to the initial GRB trigger.  In addition, we find a striking, near-integer time step between the GRB outbursts, suggesting (although not proving) possible periodicity in the events.

All of this is absolutely fascinating to the astronomers, because it opens up the perennial question of "Is this a phenomenon we've already seen and know how to explain, or is it actually new physics?"  At present, there's no way to answer this with any certainty.  All that's known is something really weird is going on out there, and we're going to have to do a lot more observation before we'll be able to figure out what the explanation is.

So like I said, Shakespeare was spot-on.  And the more we look out into the skies, the more we find that is Not Dreamt Of In Our Philosophy.  Only now we have astrophysicists working on actually explaining these phenomena -- so perhaps this very peculiar flash-in-the-pan won't remain a mystery forever.

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Twinkle, twinkle, little antistar

It's a big mystery why anything exists.

I'm not just being philosophical, here.  According to the current most widely-accepted cosmological model, when the Big Bang occurred, matter and antimatter would have formed in equal quantities.  As anyone who has watched Star Trek knows, when matter and antimatter come into contact, they mutually annihilate and all of the mass therein is converted to a huge amount energy in the form of gamma rays, the exact quantity of which is determined by Einstein's law of E = mc^2.

So if we started out with equal amounts of matter and antimatter, why didn't it all eventually go kablooie, leaving a universe filled with nothing but gamma rays?  Why was there any matter left over?

The answer is: we don't know.  Some cosmologists and astrophysicists think that there may have been a slight asymmetry in favor of matter, driven by random quantum fluctuations early on, so while most of the matter and antimatter were destroyed by collisions, there was a little bit of matter left, and that's what's around today.  (And "a little bit" is honestly not an exaggeration; the vast majority of the universe is completely empty.  An average cubic meter of space is very unlikely to have much more than an atom or two in it.)

One question this sometimes brings up is whether the stars and galaxies we see in the night sky are matter; if, perhaps, some entire galaxies are made of antimatter, and there really are equal amounts of the two.  After all, antimatter is predicted to act exactly like matter except that its fundamental particles have the opposite charges -- its protons are negative, its electrons positive, and so forth.  So a planet entirely formed of antimatter would look (from a safe distance) exactly like an ordinary planet.

And just to throw this out there, an antiplanet wouldn't have copies of all of us except for having the opposite personalities, for example some people who are good guys being evil and/or having beards, as outlined in the highly scientific Lost in Space episode "The Antimatter Man:"

Nor would there be a creepy bridge between the two universes, covered with fog and backed by eerie music:

Which is a shame, because I always kinda liked that episode.

Considerations of evil Major Don West with a beard notwithstanding, here are two arguments why most physicists believe that the stars we see, even the most distant, are made of ordinary matter.  The first is that there is no known process that would have sorted out the matter from the antimatter early in the universe's life, leaving isolated clumps of each to form their respective stars and galaxies.  Secondly, if there were antistars and antigalaxies, then there'd be an interface between them and the nearest clump of ordinary stars and galaxies, and at that interface matter and antimatter would be constantly meeting and mutually annihilating.  This would produce a hell of a gamma ray source -- and we haven't seen anything out there that looks like a matter/antimatter interface (although I will return to this topic in a moment with an interesting caveat).

A paper last year found that the key to understanding why matter prevailed might lie in the mysterious "ghost particles" called neutrinos.  There are three kinds of neutrinos -- electron neutrinos, muon neutrinos and tau neutrinos -- and one curious property they have is that they oscillate, meaning they can convert from one type to another.  The rate at which they do this is predicted from current theories, and it's thought that antineutrinos do exactly the same thing at exactly the same rate.

The experiment described in the paper took place in Japan, and found that there is an unexpected asymmetry between neutrinos and antineutrinos.  Beams of muon neutrinos and muon antineutrinos were sent on a six-hundred-kilometer journey across Japan, and upon arriving at a detector, were analyzed to see how many had converted to one of the other two "flavors."  The surprising result was that the neutrinos had oscillated a lot more than predicted, and the antineutrinos a lot less -- something called a "CP (charge-parity) violation" that shows antimatter doesn't, in fact, behave exactly like matter.  This asymmetry could lie at the heart of why the balance tipped in favor of matter.

But now a new analysis of data from the Fermi Gamma-ray Space Telescope has thrown another monkey wrench into the works.  The study was undertaken because of a recent puzzling detection by an instrument on the International Space Station of nuclei of antihelium, which (if current models are correct) should be so rare in the vicinity of ordinary matter that they'd be entirely undetectable.  But what if the arguments against antistars and antigalaxies I described earlier aren't true, and there are such odd things out there?  Antistars would be undergoing fusion just like the Sun does, and producing antihelium (and other heavier antielements), which then would be shed from the surface just like our Sun sheds helium.  And some of it might arrive here, only to fall into one of our detectors.

But what about the whole gamma-rays-at-the-interface thing?  Turns out, the study in question, the subject of a paper last week in the journal Physical Review D, found that there are some suspicious gamma-ray sources out there.

Fourteen of them, in fact.

These gamma-ray sources are producing photons with an energy that's hard to explain from known sources of gamma rays -- pulsars and black holes, for example.  In fact, the energy of these gamma rays is perfectly consistent with the source being ordinary matter coming into contact with an antistar.

Curiouser and curiouser.

It doesn't eliminate the problem of why the universe is biased toward matter; even if these are antistars, their frequency in the universe suggests that only one in every 400,000 stars is an antistar.  So we still have the imbalance to explain.

But it's a strange and fascinating finding.  Astrophysicists are currently re-analyzing the data from every angle they can think of to try and account for the odd gamma-ray sources in any way other than it being evidence of antistars, so it may be that the whole thing will fizzle.  But for now, it's a tantalizing discovery.  It brings to mind the famous quote from J. B. S. Haldane -- "The universe is not only queerer than we imagine, it's queerer than we can imagine."

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When people think of mass extinctions, the one that usually comes to mind first is the Cretaceous-Tertiary Extinction of 66 million years ago, the one that wiped out all the non-avian dinosaurs and a good many species of other types.  It certainly was massive -- current estimates are that it killed between fifty and sixty percent of the species alive at the time -- but it was far from the biggest.

The largest mass extinction ever took place 251 million years ago, and it destroyed over ninety percent of life on Earth, taking out whole taxa and changing the direction of evolution permanently.  But what could cause a disaster on this scale?

In When Life Nearly Died: The Greatest Mass Extinction of All Time, University of Bristol paleontologist Michael Benton describes an event so catastrophic that it beggars the imagination.  Following researchers to outcrops of rock from the time of the extinction, he looks at what was lost -- trilobites, horn corals, sea scorpions, and blastoids (a starfish relative) vanished completely, but no group was without losses.  Even terrestrial vertebrates, who made it through the bottleneck and proceeded to kind of take over, had losses on the order of seventy percent.

He goes through the possible causes for the extinction, along with the evidence for each, along the way painting a terrifying picture of a world that very nearly became uninhabited.  It's a grim but fascinating story, and Benton's expertise and clarity of writing makes it a brilliant read.

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