Welcome to HL Tauri — a star system that is just being born and the target of one of the most mind-blowing astronomical observations ever made.
Observed by the powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, this is the most detailed view of the proto-planetary disk surrounding a young star 450 light-years away. And those concentric rings cutting through the glowing gas and dust? Those, my friends, are tracks etched out by planets being spawned inside the disk.
HL Tau's surroundings, as seen by Hubble. HL Tau is a sun-like star around 450 light-years from Earth
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.
However, there are some surprises.
“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.
The protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system
“When we first saw this image we were astounded at the spectacular level of detail,” said Catherine Vlahakis, ALMA Deputy Program Scientist. “HL Tauri is no more than a million years old, yet already its disc appears to be full of forming planets. This one image alone will revolutionize theories of planet formation.”
After a star sparks to life from the gravitational collapse of a star-forming nebula, the leftover gas and dust will collect around the star, creating a disk. Conventional theory suggests that, over time, the disk cools and small particles begin to accrete, forming small pebbles, then asteroids, then planetesimals and, eventually, planets.
The antennas that make up Alma are separated by up to 15km, high in Chile's
Atacama Desert
As these embryonic planetary bodies orbit the star, they clear a track in the remaining disk of dust, ‘vacuuming’ up the remaining debris with their increasing gravitational dominance, continuing to bulk up their mass.
And this is exactly what we are seeing here. HL Tauri has a protoplanetary disk that is being populated with planets carving out their individual orbital paths. Eventually, the majority of the dust in HL Tauri will be consumed by the growing population of asteroids and planets, maturing into a stable star system like ours. However, the star system seems to be growing up fast, a puzzle that astronomers will no doubt be trying to understand for some time to come.
ALMA is nearing completion and this is the first precision observation in it’s near-fully commissioned configuration. Using the technique of long-baseline interferometry, ALMA is composed of many individual antennae spread over a large area. The distance between the antennae mimics one large antenna spread over a huge area. ALMA can therefore beat the precision of any other observatory on Earth or even in space, including Hubble.
Artist's impression of the HL Tauri protoplanetary disk
“The logistics and infrastructure required to place antennas at such distant locations required an unprecedented coordinated effort by an expert international team of engineers and scientists,” said ALMA Director Pierre Cox. “These long baselines fulfill one of ALMA’s major objectives and mark an impressive technological, scientific and engineering milestone.”
“Most of what we know about planet formation today is based on theory,” added Tim de Zeeuw, Director General of the European Southern Observatory. “Images with this level of detail have up to now been relegated to computer simulations or artist’s impressions. This high resolution image of HL Tauri demonstrates what ALMA can achieve when it operates in its largest configuration and starts a new era in our exploration of the formation of stars and planets.”
A peek inside a cavern of roiling dust and gas in the Great Orion Nebula shows where thousands of stars are forming
