Fomalhaut, case of disappearing planet

Stargazing can be a lonely preoccupation. Often, it’s challenging to convince your loved ones to travel to the middle of nowhere in the dark to see a bunch of sparkly things, as beautiful as they may be.

Take heart, solitary stargazers. This time of year, the patron star of lonely astronerds sits low and forlorn in the south.

Generations of stargazers have referred to Fomalhaut as the “Solitary One” or the “Lonely One.” It is easy to see why.

Look south just after midnight, and you’ll see a single star surrounded by a large patch of darkness.

The other stars in Piscis Austrinus are too faint to see from all but the darkest rural locations. Thus, Fomalhaut seems isolated from a late-summer sky otherwise filled with stars.

Because it never gets very high above the horizon, it frequently takes on a dim orange cast as the thick layer of air close to the horizon filters its light.

It is traditionally associated with the coming autumn and summer end. Add to that its isolated location, and you have one depressing star.

Don’t let appearances fool you. Fomalhaut is a hot, young star that burns with an almost pure, white flame.

A recent study of the star estimates its age at 440 million years. Our sun has reached a respectable middle age at about five billion years old.

Like most youngsters, Fomalhaut burns hot. Its surface temperature is about 15,000 degrees Fahrenheit. Compare that with the sun’s tranquil 10,000 degrees.

Fomalhaut has a mass about twice as great as the sun and a diameter just under twice as large. But those figures don’t capture Fomalhaut’s ferocity. It produces over 16 times the energy of old Sol.

It is one of the brightest stars in the nighttime sky, partly because of its luminosity and relative proximity at only about 25 light-years away. (One light year is equivalent to 5.9 trillion miles.)

Fomalhaut is one of the first stars around which astronomers discovered a disk of cold dust and gas. Astronomers believe that such disks eventually form into planets like those in our solar system.

Fomalhaut’s dusty disk was discovered in 1983 by IRAS, the Infra-Red Astronomical Satellite, sent into orbit by NASA to examine the infrared light emanating from the stars.

In 2008, astronomers announced the existence of a planet orbiting inside the outer debris ring. They based their findings on data collected in 2004 and 2006.

The planet was massive, at least as big as Neptune and perhaps three times the size of our most massive planet, Jupiter. Fomalhaut b, as astronomers officially called it, was apparently the first-ever extra-solar planet photographed in visible light by the Hubble Space Telescope.

In 2014, the International Astronomical Union (IAU) began public voting to give some extra-solar planets informal names. In December 2016, they announced that Fomalhaut’s planet would be forever known as Dagon.

Most people have heard the story of Sampson, the great Israelite hero and strong man seduced by the Philistine woman Delilah. However, they don’t know that the story has an astronomical connection.

Sampson derived his strength from his body hair, and men of his clan were not permitted to shave or cut it. Delilah learned his secret and had his hair shaved off. The weakened Sampson was at the mercy of his Philistine enemies, who had his eyes gouged out.

The Philistines decided to offer a sacrifice to the fish-god Dagon in honor of their triumph. It’s hard to blame them. Sampson had slain more than a few Philistines in his time.

So the Philistines had an enormous debauch in Dagon’s temple, located in the town of Gaza. To add insult to injury, they paraded the blinded and weakened Sampson before the assembled multitude.

Summoning his last reserve of strength, Sampson pushed on the temple’s pillars. He managed to take thousands more Philistines with him as the falling temple debris crushed them.

Dagon is none other than the star Fomalhaut. The Philistines worshiped the starry representation of the god at their temple at Gaza.

The IAU voters couldn’t rename the star, so they restored its Biblical connection by naming its planet Dagon.

As it turned out, the IAU’s decision was premature. In 2020, astronomers looked at data collected from 2008 to 2014. They discovered that the planet had slowly dissipated by the time of the IAU naming decision in 2016.

Fomalhaut b, which had been so bright in visible light in 2008, was undetectable to the Hubble Space Telescope, based on data the telescope collected in 2014. The object that was so visible in 2008 had utterly disappeared by 2014.

Analysis of images taken between those dates shows a bright dot slowly spreading out in space. Astronomers speculate the collision of two small, rocky objects, each about 125 miles wide, caused a quickly expanding cloud of dust and debris.

The cloud has grown to about 200 million miles wide, about the same diameter as Earth’s orbit around the sun.

There’s a lesson in all this. Science sometimes comes to incorrect conclusions from the data it collects. However, scientists are not afraid to admit that it is wrong when new data suggests new conclusions.

Certain politicians and, I am pained to say, certain religious groups have a lot to learn from the example of science.

Like the supposed planet, the temple’s rubble has long since turned to dust, but the star remains a symbol of Sampson’s power. Sampson was as alone and isolated as the star at the time of his death. Surrounded by his enemies, he summoned the strength to triumph.

More than a few times, my friends and relatives have gently made fun of my fascination with the lore and science of the night. I tell them that such knowledge adds an ineffable depth to the pleasure of observing even a single star.

As summer turns to fall, I’ll find a night to stare long and hard at Piscis Austrinus and its lonely star Fomalhaut. And I will reflect upon the hero Sampson and a grand temple reduced to dust and scattered in the wind.

I will think about the ephemerality of human accomplishment and the slow, sometimes halting, but steady growth of our knowledge about the universe of which we are so tiny a part.

By Tom Burns


Tom Burns is the former director of the Perkins Observatory in Delaware.