The Eye of Sauron Reveals a Forming Solar System!

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Today's episode is supported by CuriosityStream. It's well known that after his defeat at the end of the Third Age, the Dark Lord Sauron fled Mordor into the sky and traveled about 25 light years towards the constellation Pisces Estrinus.

We still see his terrible flaming eye gazing down at us, biding his time.

The incredible Hubble Space Telescope picture of the star Fomalhaut does excite the imagination, doesn't it?

Today, I want to set your mind at ease. This isn't really the eye of Sauron. Probably.

Fomalhaut is an A-type star about twice as massive and much hotter and brighter than the sun. At only 25 light years away, it's the 18th brightest star on the sky.

But even as a non-Dark Lord, it's a fascinating object. Let's look at some pictures.

That dot in the middle marks the location of the star. But you can't actually see Fomalhaut in this picture because the mask was placed directly in front of it, for the picture. Such a mask is called a coronagraph. And its purpose is to block the bright light of Fomalhaut so that its faint surrounding structures can be studied. The slittered pupil is the shadow of that coronagraph. Sadly, it's not a real part of the structure, but the surrounding ring is very real. Fomalhaut itself is brightest in the ultraviolet. To our eyes, it twinkles bluish-white on the night sky. But the ring is brightest in the infrared. Here are some infrared pics from the Herschel Space Telescope and from ALMA. In the Herschel image, the star doesn't even need to be masked. We're seeing the heat glow of a giant ring of ice and dust, 40 billion kilometers in diameter. It's the remnant of Fomalhaut's protoplanetary disk, the whirlpool of debris left over after the star formed and from which a planetary system may now be forming. That makes Fomalhaut an incredible laboratory for us to study our own solar system and how it may have formed. Here's how we think that goes. Start with a dense core in a giant molecular cloud. Cold and adrift, the mostly hydrogen gas yields to gravity once it reaches the critical gene's mass. As the gas collapses, it builds up heat and density until the pressure of the gas dramatically slows collapse, and you have a hot protostar surrounded by a great cloud of dust and gas. The protostar continues to collapse more slowly until eventually the core gets hot and dense enough to ignite infusion. The star is born, and outflowing energy resists any further collapse. Conservation of angular momentum has the central star spinning rapidly. The surrounding debris also rotates, and that rotation allows it to resist falling towards the central axis. But gravity can still pull the debris together in the up-down direction, so it flattens into a disk.

Eventually, winds from the newborn star in the center disperse this extra gas and dust, revealing whatever planets manage to form from the debris in that time. The formation of planets itself is a fascinating process.

The leading formation model is core accretion, in which tiny granules are drawn together and clump by static electricity. They grow in size until they're large enough that they can start collecting more material through collisions. These collisions must be very gentle, or else pieces will shatter on impact. Eventually, the growing rock has enough mass to attract material through its own gravity. At this point, it's a planetesimal, at about a kilometer in diameter. By the time it's at least 10% of the Earth's mass, it will have cleared its orbit of other planetesimals and will have rounded out into a planet. Our own solar system went through this process four and a half billion years ago, and the solar wind has long since dispersed what was left of our own protoplanetary disk. This is believed to have happened some tens of millions of years after the sun first formed. Fomalhaut is a strange case. It's going through an unusually long puberty. The star is 440 million years old. That's still very young, but it's surprising that it's holding onto part of its protoplanetary disk for so long. The Herschel and Elmer images show very clearly that the ring has sharp edges, particularly that inner edge. The leading idea is that newly formed planets carved out that ring with their gravity. Check out Saturn's F ring. Its clean lines are carved by what we call shepherd moons. In Fomalhaut's case, it may be shepherd planets.