Fish star

Fomalhaut is the brightest star in the southern constellation of Piscis Austrinus, the Southern Fish.  At a declination (stellar latitude) of −29° 37′, it's seldom visible where I live, but I did get a good look at it when I was in Ecuador a few years ago.  It's bright -- a first-magnitude star -- but looked brighter because of the elevation; when you're up in the mountains, on a clear night it's hard to recognize constellations because there are so many visible stars.

The star's odd moniker comes directly from the Arabic Fom al-Haut, "the mouth of the whale."  As always, though, other cultures saw it differently.  The Chinese gave it the fanciful name Běiluòshīmén, meaning "the north gate of the military camp."  To the Persians it was Hastorang, one of the "Four Royal Stars."  (The other three were Aldebaran, Regulus, and Antares.)  It seems to have had some significance to indigenous Americans; the two-thousand-year-old Earthwork B, in Mounds State Park in Indiana, seems to line up with the rising of Fomalhaut, but the reason is unknown.  To the Moporr, an indigenous people in South Australia, it was a powerful male deity named Buunjill.  Not to be outdone, in the Lovecraftian mythos Fomalhaut is the home of the Great Old One Cthugha, who appeareth unto mankind as a fiery sphere and basically scareth the absolute shit out of everyone who seeeth him.

More prosaically, though, Fomalhaut is interesting to astronomers as the eighteenth brightest star in the sky overall, and the third brightest star known (or thought) to have a planetary system (after the Sun and Pollux).  It's young, something on the order of four hundred million years old.  (I know that seems pretty damn old, but keep in mind that the Sun is over ten times older than that.)  It's a Type A star, which doesn't mean that it's hard-working and tightly-wound, but that it's blue-white in color and has strong emission lines from hydrogen and ionized metals.  (Another, better known, Type A star is Vega, made famous as the home system of the aliens in the wonderful movie Contact.)

What's coolest about this star, though -- and the reason it comes up today -- is its ring of dust and debris, which was photographed directly in 2012 by ALMA (the Atacama Large Millimeter/submillimeter Array):

[Image licensed under the Creative Commons LMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope ; Acknowledgement: A.C. Boley et al., ALMA observes a ring around the bright star Fomalhaut, CC BY 4.0]

The James Webb Space Telescope just got even more detail; it was able to discern not only the outer ring of debris but an inner ring, comparable to the Sun's Kuiper Belt and Asteroid Belt, respectively. which suggests to astrophysicists that there are planets gravitationally "herding" the debris into rings, just as Neptune and Jupiter do for our two belts.

"I would describe Fomalhaut as the archetype of debris disks found elsewhere in our galaxy, because it has components similar to those we have in our own planetary system," said András Gáspár of the University of Arizona in Tucson, lead author of the paper, which appeared in Nature Astronomy last week.  "By looking at the patterns in these rings, we can actually start to make a little sketch of what a planetary system ought to look like -- if we could actually take a deep enough picture to see the suspected planets."

"Where Webb really excels is that we're able to physically resolve the thermal glow from dust in those inner regions," said Schuyler Wolff, also of the University of Arizona in Tucson, who co-authored the paper.  "So you can see inner belts that we could never see before.  We definitely didn't expect the more complex structure with the second intermediate belt and then the broader asteroid belt.  That structure is very exciting because any time an astronomer sees a gap and rings in a disk, they say, 'There could be an embedded planet shaping the rings!'"

Or, you know, a Lovecraftian Elder God creating a fire vortex in the eldritch nether regions of the void.  You know how it goes.

In any case, it's incredibly cool to see what's coming in from the JWST.  Here, we're seeing a system that might be a little like what the Solar System looked like four billion years ago, as the planets were coalescing from the rocky debris of the protoplanetary disk.  The astronomers, of course, are going to give it a much closer look.  "The belts around Fomalhaut are kind of a mystery novel: Where are the planets?" said George Rieke, of the JWST's Mid-Infrared Instrument (MIRI) team, who also co-authored.  "I think it's not a very big leap to say there's probably a really interesting planetary system around this star."

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