Space

ALMA Uncovers Planet Formation Around Binary Star

Using the largest, most sensitive radio telescope in existence, the Atacama Large Millimeter-submillimeter Array (ALMA), astronomers have uncovered new details about the early stages of planet formation around a binary star named HD 142527.

Scientists discovered a massive crescent region of dust that is unusually devoid of gas in the outer reaches of the systems protoplanetary disk. The results provide new insights into planet formation around binary stars, an area that is not well understood in the field.

binary-star-system

Astronomers struggle to understand how planets form in binary systems. Image credit: Casey Reed

HD 142527 is a binary star system approximately 450 light years away consisting of two stars – its main star is more than twice as massive as the Sun, while its companion is about a third the mass of the Sun. The system had been previously studied by ALMA so it was a good opportunity to compare observations from now to the past.

“This binary system has long been known to harbor a planet-forming corona of dust and gas,” said Andrea Isella, team member and astronomer at Rice University in Texas. “The new ALMA images reveal previously unseen details about the physical processes that regulate the formation of planets around this and perhaps many other binary systems.”

ALMA is the largest astronomical project in existence and the most sensitive radio telescope in the world. It consists of 66 radio antennas, each weighing more than 100 tonnes, perched atop the Chajnantor Plateau 5000 meters above sea level in northern Chile. It’s one of the only surface telescopes capable of revealing finer detail in young protoplanetary disks.

ALMA-protoplanetary

An artist impression of binary system HD 142527. The dotted red orbit is the orbit of the smaller star. The red dust above highlights the area where gas has “frozen out” likely providing a jolt to planet formation. Image credit: B. Saxton/ NRAO

The AMLA observations revealed a broad expansive disk of material surrounding HD 142527 – the radius of the disk being about 50 times the Sun to Earth distance. Most of the environment consists of gases, but there is a noticeable void of gas that extends about a third of the system in a massive arch.

Could this be the very early stages of planet formation? Researchers think it’s possible.

“The temperature is so low that the gas turns into ice and sticks to the grains,” Isella explains. “This process is thought to increase the capacity for dust grains to stick together, making it a strong catalyst for the formation of planetesimals, and, down the line, of planets.”

ALMA-protoplanetary-2

The actual ALMA composite image of HD 142527. Image credit: B. Saxton/ NRAO

“We’ve been studying protoplanetary disks for at least 20 years,” Isella said. “There are between a few hundred and a few thousands we can look at again with ALMA to find new and surprising details. That’s the beauty of ALMA. Every time you get new data, it’s like opening a present – you don’t know what’s inside.”

Andrea Isella is part of a group, led by Rice University’s Yann Boehler, that will publish an upcoming paper on the ALMA observations of HD 142527. The research was funded by the National Radio Astronomy Observatory, a division of the National Science Foundation.

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