Brighter than the Sun

A frequent (and maddening) thing in science journalism is when they lead news stories with clickbait-y headlines like "This Will Rewrite All Of The Science Textbooks!"  When, in fact, the story turns out to be no more than mildly interesting, and will at best generate a footnote in chapter 23 of the science textbooks.

Likewise for stories headed by "Researchers Dumbfounded" or "Scientists Are Back To The Drawing Board."

Sometimes, though, there really are discoveries that leave scientists baffled, and one of these was the subject of a paper last week in Science (although the event it analyzes happened in May of 2021).  And despite intensive research during the intervening two and a half years, physicists are still unsure of how to explain what happened -- especially since it isn't the first time.

The discovery was made by the Telescope Array in Utah, which doesn't follow the usual pattern of astronomers giving new telescopes clever names (like MeerKAT in South Africa and IceCube in Antarctica).  Did they just give up during the naming process?  You have to wonder if the conversation went like this:

Astronomer 1: I'm completely out of ideas.  All the cool names for observatories are already taken.

Astronomer 2: Plus, don't you think it's time we do some actual research rather than spending all our time trying to name this damn telescope array?

Astronomer 1 and Astronomer 2: *look at each other*

Astronomer 1 and Astronomer 2 (simultaneously):  I have an idea.

In any case, the Telescope Array was studying cosmic rays, high-energy particles that constantly bombard the Earth's upper atmosphere.  Most of them come from the Sun, but some originate outside the Solar System (or even outside the Milky Way).  They're a pretty well understood phenomenon -- but every once in a while, there's one that makes astrophysicists sit up and take notice, like the one recorded on 27 May 2021.

This one had an energy of 244 exa-electron-volts.  If you're not familiar with the prefix exa-, you're not alone; I used to teach science and I had to look it up.  It means 10^18 -- 10 followed by 18 zeroes.  So this cosmic ray had an energy of 244,000,000,000,000,000,000 electron volts, or -- as the brilliant science writer Jennifer Ouellette described it, the energy of a bowling ball dropped from shoulder height compressed into a volume smaller than a hydrogen atom.

Researchers nicknamed the event Amaterasu, after the Shinto goddess of the Sun.

[Image is in the Public Domain]

It's an evocative choice for a name but inaccurate in one respect -- the particle didn't come from the Sun.  In fact, where exactly it came from is a significant mystery.  There is an astrophysical principle called the GZK cutoff (named for the three scientists who proposed it, Kenneth Greisen, Georgiy Zatsepin, and Vadim Kuzmin), which showed that there is a theoretical limit for the energy of a cosmic ray -- it can carry no more than 50 EeV, and come from no farther away than three hundred million light years.  Amaterasu is one of two events that exceeded that -- the other is the aptly-named "Oh-My-God particle," which carried an estimated 320 EeV (equivalent to the kinetic energy of a hundred-mile-an-hour baseball).

Most baffling of all, when astrophysicists traced the trajectory of both Amaterasu and the OMG particle backwards, they led into different parts of an area called the Local Void -- a vast region of empty space.

So not only is there nothing there that looks capable of being able to produce such a high-energy particle, there's... nothing there.

But whatever's doing this, there are at least two of them.

"These events seem like they're coming from completely different places in the sky,” said study co-author John Belz, of the University of Utah. "It’s not like there's one mysterious source.  It could be defects in the structure of spacetime, colliding cosmic strings.  I mean, I’m just spit-balling crazy ideas that people are coming up with because there's not a conventional explanation.  Maybe magnetic fields are stronger than we thought, but that disagrees with other observations that show they’re not strong enough to produce significant curvature at these ten-to-the-twentieth electron volt energies.  It’s a real mystery."

So thanks to my eagle-eyed writer friend Gil Miller, who alerted me to this story.  I guess this is a discovery that may "rewrite the textbooks," or at least add an interesting new chapter.

Once they figure out what the hell it actually is.

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