Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have captured an image of a protoplanetary disk around a young Sun-like star known as HL Tauri. This revolutionary new image reveals extraordinarily fine detail that has never been seen before in the planet-forming disc around an infant star.
HL Tauri is thought to be less than 100,000 years old. It lies in the direction of the constellation Taurus at a distance of 450 light years.
The protoplanetary disk around this star is unusually massive and bright, which makes it an excellent place to search for signs of forming planets.
HL Tauri is hidden in visible light behind a massive envelope of dust and gas. But ALMA observes at much longer wavelengths and is able to peer through the intervening dust to study the processes right at the core of this cloud.
The new ALMA image reveals never-before-seen features in this system, including multiple concentric rings separated by clearly defined gaps.
These structures suggest that planet formation is already well underway around HL Tauri.
“These features are almost certainly the result of young planet-like bodies that are being formed in the disk,” said ALMA Deputy Director Dr Stuartt Corder.
“When we first saw this image we were astounded at the spectacular level of detail,” said Dr Catherine Vlahakis, ALMA deputy program scientist.
Young stars like HL Tauri are born in clouds of gas and fine dust, in regions that have collapsed under the effects of gravitation, forming dense hot cores that eventually ignite to become young stars.
These stars are initially cocooned in the remaining gas and dust, which eventually settles into a disc, known as a protoplanetary disc.
Through many collisions the dust particles will stick together, growing into clumps the size of sand grains and pebbles. Ultimately, asteroids, comets and even planets can form in the disc. Young planets will disrupt the disc and create rings, gaps and holes such as those seen in the structures now observed by ALMA.
The investigation of these protoplanetary discs is essential to our understanding of how Earth formed in the Solar System.
This image shows the protoplanetary disc surrounding the young star HL Tauri; it reveals 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. Image credit: ALMA / ESO / NAOJ / NRAO.
Observing the first stages of planet formation around HL Tauri may show us how our own planetary system may have looked more than 4 billion years ago, when it formed.
“Most of what we know about planet formation today is based on theory,” said 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.”
Dr Crystal Brogan of the National Radio Astronomy Observatory added: “this is truly one of the most remarkable images ever seen at these wavelengths. The level of detail is so exquisite that it’s even more impressive than many optical images. The fact that we can see planets being born will help us understand not only how planets form around other stars but also the origin of our own Solar System.”