How multiple star systems evolve

November 1, 2017 by Nadia Murillo, Leiden University
Credit: Leiden University

Sirius is not a single star at all, but a binary system of two stars. Polaris, the north star, is actually a system of three stars. And Castor, in the constellation of Gemini, actually consists of a whopping six stars. Current models show stars forming by the fragmentation of massive interstellar gas clouds, spinning themselves by gravity into stardom, in isolation and unaffected by nearby stars. But the plethora of systems in our galaxy that consist of multiple stars now has astronomers wondering why stars so often come in groups.

At Leiden Observatory in the Huygens Laboratory building, PhD student Nadia Murillo is looking at data gathered by (among others) ALMA, an array of sixty-six 12 meter radio telescopes in the Chajnantor valley, Chile. She's observing the very early stages of star formation in a region of the galaxy known as the Gould belt. Positioned at some 325 light-years away, it's a prime location to find out what leads to gas clouds fragmenting into young star systems.

Murillo: "We know that fragmentation of occurs, and that clouds can fragment into systems of mutiple stars, because we can see the final result. But we're not sure yet what causes and influences the fragmentation of clouds. Why are there single stars forming in some places and multiples in others?"

This is the main question that Murillo wants to answer in her thesis. The answers are surprising. "Disc formation around stars has turned out to be important in the early stages of star formation, as discs can eventually fragment and form . Furthermore, what could have started as a binary star can end up with a disc that fragments and then turns into . This all affects how a given systems ends up looking."

"We analyse the of a given system, knowing that there are molecules that occur in cold regions and ones that occur in warm regions. Looking at their distribution allows us to the physical and chemical structure of young stars and their influence on the surrounding material, telling us what systems actually look like."

Murillo's thesis research has changed the way she sees astronomy, modeling, and chemistry. "I once had a somewhat black-box view of some parts of the field, but it quickly turned out not to be as difficult or as out of reach as I thought. I now work together with lab scientists, modelers and observers to find out what's causing star systems to form."

In her research, Murillo took a multidisciplinary approach. "Sometimes we rely too much on models, sometimes too much on observations, or theory. It is important to consider all three - to cast a broader gaze. Earlier models and simulations have suggested that temperature could be an important factor in star formation, making the difference between fragmenting and not fragmenting. We studied different molecules in cold and warm gas and compared their presence in single, binary and multiple young stars known as protostars. We didn't find any difference in the temperatures of the protostars, but we do find what seems to be a relation with mass."

"My thesis is a tiny piece of the big picture of . Right now, models show in isolation, forming in a vacuum - and that is rarely the case. Current theories and models need to be adapted to include multiplicity, and until we do so, the big picture is incomplete."

Explore further: The origin of binary stars

Related Stories

The origin of binary stars

August 21, 2017

The origin of binary stars has long been one of the central problems of astronomy. One of the main questions is how stellar mass affects the tendency to be multiple. There have been numerous studies of young stars in molecular ...

Star-forming filaments

May 22, 2017

Interstellar molecular clouds are often seen to be elongated and "filamentary" in shape, and come in a wide range of sizes. In molecular clouds, where stars form, the filamentary structure is thought to play an important ...

Most stars are born in clusters, some leave 'home'

September 24, 2014

New modeling studies from Carnegie's Alan Boss demonstrate that most of the stars we see were formed when unstable clusters of newly formed protostars broke up. These protostars are born out of rotating clouds of dust and ...

Image: Hubble's cosmic atlas

July 28, 2017

This beautiful clump of glowing gas, dark dust and glittering stars is the spiral galaxy NGC 4248, located about 24 million light-years away in the constellation of Canes Venatici (The Hunting Dogs).

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

NASA instruments image fireball over Bering Sea

March 22, 2019

On Dec. 18, 2018, a large "fireball—the term used for exceptionally bright meteors that are visible over a wide area—exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.