For the first time, astronomers have caught a multiple-star system in the beginning stages of its formation.
Barnard 5 seen within its neighborhood, embedded in dust (blue) as seen with ESA’s Herschel Space Observatory, in infrared light. Image credit: Bill Saxton / NRAO / AUI / NSF.
“Understanding why and how multiple star systems form is essential for grasping phenomena such as star and planet formation, planet frequency and habitability,” said Dr Jaime Pineda from the Institute for Astronomy at ETH Zurich, Switzerland, the first author of a paper published in the journal Nature.
“The number of stars in a system is determined during the earliest stage of star formation but critical processes occurring then are usually hidden by dense clouds of dust and gas.”
“The new observations also help to explain why some pre-stellar gas condensations go on to form a system with only a single star like ours, while others form binary (two stars) or multi-star systems,” added co-author Dr Stella Offner of the University of Massachusetts Amherst.
The scientists used the Very Large Array (VLA) and the Green Bank Telescope (GBT), along with the James Clerk Maxwell Telescope (JCMT) in Hawaii, to study a dense core of gas called Barnard 5.
Barnard 5 is a molecular cloud located in the constellation Perseus, approximately 800 light-years away.
It contains one young protostar and three dense condensations that the astronomers say will collapse into stars in the astronomically-short period of 40,000 years.
Of the eventual four stars, they predict that three may become a stable triple-star system.
When the astronomers used the VLA to map radio emission from Barnard 5’s methane molecules, they discovered that filaments of gas in the cloud are fragmenting, and the fragments are beginning to form into additional stars that will become a multiple-star system.
“This is the first time we’ve been able to show that such a young system is gravitationally bound,” Dr Pineda said.
“This provides fantastic evidence that fragmentation of gas filaments is a process that can produce multiple-star systems.”
Barnard 5. Image credit: Bill Saxton / NRAO / AUI / NSF.
The condensations in Barnard 5 that will produce stars now range from 1/10 to 1/3 the mass of the Sun. Their separations will range from 3,000 to 11,000 times the Earth-Sun distance.
The scientists analyzed the dynamics of the gas condensations and predict that, when they form into stars, they will form a stable system of an inner binary, orbited by a more-distant third star.
The fourth star, they suggest, will not long remain part of the system.
According to the astronomers, the knowledge gained from witnessing this system as it is forming does not include signatures or characteristics to help them locate more like it.
“We would like to know how common this configuration is. Unfortunately, we couldn’t predict what was there from the initial GBT survey, so we don’t know what to look for in other places. It will take more survey work and more numerical modeling to be able to identify other very young systems like this one,” Dr Offner said.
“In terms of what this means for the formation of our Sun, it suggests that its early conditions did not look like this forming system.”
“Instead, the Sun likely formed from something that was more spherical than filamentary. The distribution of the planets in our Solar System also suggests that our Sun was never part of a multiple system like this one.”
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Jaime E. Pineda et al. 2015. The formation of a quadruple star system with wide separation. Nature 518, 213–215; doi: 10.1038/nature14166
