Planets of a Binary Star as Possible Homes for Alien Life

The ALMA telescopes at night with a full moon.

The ALMA telescope array in Chile. (Image: S. Guisard via ESO)

Nearly half of the Sun-size stars are binary. According to University of Copenhagen research, planetary systems around a binary star may be very different from those around single stars. This points to new targets in the search for extraterrestrial life forms.

Since the only known planet with life, the Earth, orbits the Sun, planetary systems around stars of similar size are obvious targets for astronomers trying to locate extraterrestrial life. Nearly every second star in that category is a binary star. A new result from research at the University of Copenhagen indicates that planetary systems are formed in a very different way around binary stars than around single stars such as the Sun. Professor Jes Kristian Jørgensen, Niels Bohr Institute, University of Copenhagen, heading the project, said:

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“The result is exciting since the search for extraterrestrial life will be equipped with several new, extremely powerful instruments within the coming years. 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 results from the project, which also has the participation of astronomers from Taiwan and the U.S., are published in the journal Nature.

Bursts shape the planetary system of a binary star

The new discovery has been made based on observations made by the ALMA telescopes in Chile of a young binary star about 1,000 lightyears from Earth. The binary star system NGC 1333-IRAS2A is surrounded by a disc consisting of gas and dust. The observations can only provide researchers with a snapshot from a point in the evolution of the binary star system. However, the team has complemented the observations with computer simulations reaching both backward and forward in time. Postdoc Rajika L. Kuruwita, Niels Bohr Institute, second author of the Nature article, explained:

“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.”

Simulation of a binary star.
Simulation of a binary star. (Image: via Jørgensen, Kuruwita et al.)

Notably, the movement of gas and dust does not follow a continuous pattern. At some points in time – typically for relatively short periods of ten to one hundred years every thousand years – the movement becomes very strong. The binary star becomes 10 to 100 times brighter until it returns to its regular state. Presumably, the cyclic pattern can be explained by the duality of the binary star. The two stars encircle each other, and at given intervals, their joint gravity will affect the surrounding gas and dust disc in a way that causes huge amounts of material to fall toward the star. Rajika L. Kuruwita said:

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

Comets carry building blocks for life

The observed stellar system is still too young for planets to have formed. The team hopes to obtain more observational time at ALMA, allowing them to investigate the formation of planetary systems. Jes Kristian Jørgensen said:

“Comets are likely to play a key role in creating possibilities for life to evolve. Comets often have a high content of ice with the presence of organic molecules. It can well be imagined that the organic molecules are preserved in comets during epochs where a planet is barren, and that later comet impacts will introduce the molecules to the planet’s surface.”

He added that understanding the role of the bursts is important in this context:

“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.”

Thus, chemistry is a part of the research scope:

“The wavelengths covered by ALMA allow us to see quite complex organic molecules, so molecules with 9-12 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.”

Powerful tools join the search for life in space

ALMA (Atacama Large Millimeter/submillimeter Array) is not a single instrument but 66 telescopes operating in coordination. This allows for a much better resolution than could have been obtained by a single telescope. Very soon, the new James Webb Space Telescope (JWST) will join the search for extraterrestrial life. Near the end of the decade, JWST will be complemented by the ELT (European Large Telescope) and the extremely powerful SKA (Square Kilometer Array) both planned to begin observing in 2027.

Video simulation of a binary star. The binary star system NGC 1333-IRAS2A is surrounded by a disc consisting of gas and dust. Notably, the movement of gas and dust does not follow a continuous pattern. For relatively short periods of 10 to 100 years every thousand years the movement becomes very strong. The binary star becomes 10 to 100 times brighter until it returns to its regular state. (Image: via Jørgensen, Kuruwita et al)

The ELT will with its 39-meter mirror be the biggest optical telescope in the world and will be poised to observe the atmospheric conditions of exoplanets (planets outside the Solar System, ed.). SKA will consist of thousands of telescopes in South Africa and in Australia working in coordination and will have longer wavelengths than ALMA, Jes Kristian Jørgensen concluded:

”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. Finally, we continue to have ALMA which is especially well suited for observing molecules in gas form. Combining the different sources will provide a wealth of exciting results.”

Provided by University of Copenhagen [Note: Materials may be edited for content and length.]

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