The Birth of a Solar System
On one of my favorite astronomy pictures
Author’s note: This is a selection from a series of short essays about some of my favorite astronomy pictures of all time. Today, ALMA’s 2014 image of the protostar HL Tau.
No, it’s not the eye of Sauron. While I admit sometimes babies can look like evil ringless dark lords, this particular cherub is one of the most beautiful I’ve ever seen. The culmination of thousands of hours of effort by over a thousand people, this is the first ever resolved picture of a solar system as it is born.
Astronomers think that solar systems form out of collapsing clouds of dust and gas. Gravity pulls the particles into a great spinning pancake with the fledgling star a toad-in-the-hole yoke at its center. As the cloud cools tiny pebbles begin to precipitate from it like rain, rocky droplets which begin to combine under the influence of gravity: great orbiting rubble piles that soon grow into rocks, boulders, objects big enough to attract the surrounding gas and dust to form surfaces and atmospheres.
The bright yellows and oranges in this image come from cold microwaves emitted by the great pancake cloud, pregnant with planetary material. The dark rings — this is the best part — these are areas swept free of planet batter by the emerging baby worlds: gaps carved by planets as they form. A cosmic birth in all its glory.
The planets of HL Tau aren’t the only births we see in this image. Released in 2014, this was one of the first images taken with the complete ALMA Telescope, a project specially designed to detect the invisible light emitted by that pebble producing batter. ALMA isn’t just one telescope, but an array of sixty-six radio dishes, each nearly 40 feet across.1 The dishes are spread over 10 miles in the Atacama Desert in Chile, collectively turning like a great clone army from one target in space to another. The data moves through fibers at near light speed back to a central supercomputer more computationally powerful than the collective laptop power in the city of Chicago. After being combined in the supercomputer, the data gets shipped to astronomers around the world, who spend weeks processing the data to produce images like the one above.
First envisioned over three decades before its first light, building this telescope was a feat of human ingenuity, and by that I mean craziness. The Atacama Desert is located nearly 17,000 feet above sea level, over 2000 feet higher than the tallest Colorado Rockies. Constructing an instrument this ambitious required the combined efforts of countries from around the world and development of completely new technologies. The transporters that delivered the dishes to the site had to be specially designed to accommodate oxygen tanks for the drivers. Engines, tools, and computers had to work in a low oxygen, dry, earthquake prone environment, and workers required not only specialized training, but the fitness of the world’s best mountain climbers as they positioned telescopes to fractions of millimeters.
And yet, insanity yields results: a baby star and its planets blinking down on us from on high. This image dropped during my third year of graduate school, a time when I was climbing the intellectual mountains required to learn to use telescope arrays like ALMA. Many of my friends and colleagues were using this new baby instrument, and working with it through its growing pains. So to see this success was something special. The birth of a new scientific instrument unveiling the birth of a new solar system yielding the birth of new heights of scientific understanding.
As with any new life, this picture gave astronomy something new: not just what people expected, it presented as many questions as it answered. For example, HL Tau, astronomers think, is only 1 million years old, mere minutes by stellar standards. And yet its planets were already forming, carving out rings clear as day. The astonishing speed of planet growth here clashed with computer simulations, leading to new puzzles, improved models, and a push to understand even more of the mysterious and awesome mechanisms that give birth to solar systems, planets, and by extension, life as we know it.
Well, a few at the middle are smaller: “just” 23 feet across. While bigger telescopes are usually better, having a few smaller dishes is intentional in this case. Due to the way arrays of telescopes work, smaller dishes actually can see larger areas of the sky all at once, so they provide a compliment to the more powerful, but more narrowly focused larger dishes.