Humans have now witnessed the birth of a solar system in greater detail than ever before.
Until now, astronomers have only theorized about the way planets develop in solar systems—they’ve had no concrete visual evidence to back up their claims, and they’ve relied mostly on computer-generated images or artists’ renditions to illustrate their theories.
But with its new high-resolution capabilities, the ALMA radio telescope has captured fledgling planets in the midst of their early formation around the sun-like star HL Tau, which lives in the constellation Taurus 450 light years from Earth.
HL Tau itself is masked behind dust and gas, making it difficult to observe using visible light. But ALMA takes pictures using longer wavelengths, enabling it to penetrate through dust to get at the more detailed activity going on in the core of this protoplanetary disk. The result is an astonishingly clear picture of what a planetary system looks like when it is just barely coming into existence.
Here’s Ian O’Neill, writing for Discovery News:
In short, this is the mother of all embryonic star system ultrasounds. But this dazzling new observation is so much more—it’s a portal into our solar system’s past, showing us what our system of planets around a young sun may have looked like over 4 billion years ago. And this is awesome, because it proves that our theoretical understanding about the evolution of planetary systems is correct.
Nevertheless, there were some surprises. The astronomers working with ALMA saw features of this particular system’s development that distinguished it from what they thought was physically possible. Here’s O’Neill again:
“These features are almost certainly the result of young planet-like bodies that are being formed in the disc. This is surprising since such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image,” said Stuartt Corder, ALMA Deputy Director.
Despite its unexpected maturity, the HL Tau system does confirm astronomers’ theories about planetary formation. They suspected that after a star forms from the gravitational collapse of a nebula, leftover gas and dust coagulate, creating a disk around the star. Then small particles come together to form asteroids, planetesimals—rocky objects anywhere from several meters to hundreds of kilometers wide—and finally, planets. The planetary objects then attract remaining debris as they circle the star, forming clear rings that trace the objects’ orbit. This process, though sped-up, is exactly what astronomers are seeing in the HL Tau system—and that could be a revolutionary finding for the future of astronomy.