Science & Technology

Close binary stars may be more likely to harbour life

The effect of a passing star pushing together binary star pairs could increase the chances of life in that system, new research suggests.
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The effect of a passing star pushing together binary star pairs could increase the habitable zone and therefore chances of life in that system, new research suggests.

The early history of planetary systems is a tale of violent collisions and encounters. These young worlds orbit stars in stellar nurseries were upheaval and chaos hardly provide an ideal environment for life to develop — much less thrive. 

Astronomers at the University of Sheffield at found an unlikely ally to the development of life amid this tumultuous period. A model developed by undergraduate student Bethany Wootton and Royal Society Dorothy Hodgkin Fellow Dr Richard Parker looks at how the habitable zone — the region around a star where the temperature allows liquid water to exist — changes around pairs of stars, so-called binary systems.

A NASA graphic showing an Earth-sized planet inside, within, and outside of the habitable zone around a star (NASA)

The two discovered that an encounter with a third — passing star — could push the binary pair together. The effect of this is to expand the habitable zone — often referred to as the ‘Goldilocks zone’ for being not too hot and not too cold — which is essential for the development of life. Planets outside of this zone are unlikely to develop life as the development of complex molecules — needed for the development of life — is severely restricted. Thus, the more planets that can be included in this zone — the greater the chances of life in that system. 

Richard Parker / Bethany Wootton / University of Sheffield

Around one-third of stellar systems in our galaxy are thought to be made up of two or more stars, and this fraction is much higher when stars are young. If these stars are a relatively large distance apart, the size of the Goldilocks zone around each star is governed by the radiation from the individual star. If the two stars are closer, the size of the Goldilocks zone increases because each star feels additional warmth from the other and this increases the likelihood of a planet being located in the right place for life to develop.

As Wootton says: “The search for life elsewhere in the universe is one of the most fundamental questions in modern science, and we need every bit of evidence we can find to help answer it.

“Our model suggests that there are more binary systems where planets sit in Goldilocks zones than we thought, increasing the prospects for life. So those worlds beloved of science fiction writers — where two suns shine in their skies above alien life — look a lot more likely now.”

Planets with binary stars are often depicted in science-fiction- such as this famous image of Luke Skywalker stares at the twin suns of Tattooine (Lucasfilm) 

Wootton and Parker used computer simulations to model the interactions between young stars in these clusters, calculating how these encounters affected the binary pairs. In a typical stellar nursery with 350 binaries, the two researchers found that 20 would have their stars squeezed together, and their Goldilocks zones then expanded.

In a few cases, the habitable zones of widely separated stars actually overlapped, further increasing the prospect of any planets in orbit around one or both of the stars being in the right place for life to develop.

The next steps for this research are to use more computer models to understand whether the negative processes a young star experiences are outweighed by the positives. Parker and his research team are currently exploring whether internal heating within the Earth happens because our young Sun was born close to a supernova explosion of a massive star.

This explosion would be catastrophic for life on Earth today but may provide the necessary conditions for life to have developed on Earth in the first place.

Research available at https://academic.oup.com/mnrasl/advance-article/doi/10.1093/mnrasl/sly238/5368077

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