Binary stars cause different planetary formation

Nearly half of all Sun-like stars are in a binary, or multiple, system: two or more stars orbiting each other. While we know planets can form around these stars, it’s possible there are major differences between these planets and those in our Solar System.

An international team of astronomers has found that a binary star system is dramatically affecting the formation of planets around it.

“The result is exciting, since the search for extraterrestrial life will be equipped with several new, extremely powerful instruments within the coming years,” says Professor Jes Kristian Jørgensen, a researcher at the University of Copenhagen, Denmark, and lead author of a paper describing the research, which has been published in Nature.

“This enhances the significance of understanding how planets are formed around different types of stars. Such results may pinpoint places which would be especially interesting to probe for the existence of life.”

The researchers used the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile to observe the binary star system NGC 1333-IRAS2A.

This star system is still surrounded by a protoplanetary disc, the dust and gas of which will eventually coalesce into planets.

They then used computer simulations to model the star system’s behavior both backwards, and forwards, in time.

“The observations allow us to zoom in on the stars and study how dust and gas move towards the disc. The simulations will tell us which physics are at play and how the stars have evolved up till the snapshot we observe, and their future evolution,” says co-author Dr Rajika Kuruwita, also from the University of Copenhagen.

According to their observations and simulations, this protoplanetary disc occasionally moves much faster and becomes much brighter, before returning to normal. The researchers believe this is because of the motion of the two stars. At certain points, their joint gravity sucks in huge amounts of protoplanetary material.

“The falling material will trigger a significant heating. The heat will make the star much brighter than usual,” says Kuruwita.

“These bursts will tear the gas and dust disc apart. While the disc will build up again, the bursts may still influence the structure of the later planetary system.”

Both the physical and chemical structures of planets are likely to be different with this sort of formation.

Jørgensen says: “The heating caused by the bursts will trigger evaporation of dust grains and the ice surrounding them. This may alter the chemical composition of the material from which planets are formed.”

Dishes of alma telescope at night
ALMA at night. Credit: ESO/B. Tafreshi (twanight.org)

The researchers hope to use ALMA to examine other binary systems which have forming or formed planets.

“The wavelengths covered by ALMA allow us to see quite complex organic molecules, so molecules with nine to 12 atoms and containing carbon. Such molecules can be building blocks for more complex molecules which are key to life as we know it. For example, amino acids which have been found in comets,” says Jørgensen.

Other new telescopes, like the James Webb Space Telescope and the Square Kilometer Array (SKA), are likely to assist with this as well.

“The SKA will allow for observing large organic molecules directly. The James Webb Space Telescope operates in the infrared which is especially well suited for observing molecules in ice,” says Jørgensen.



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