Space

Astronomers Reveal How Stellar Binaries Form

ALMA Reveals How Stellar Binaries Form

An ALMA millimeter-wavelength image of protostellar binary stars early in their formation. (The length scale and the size of the telescope’s beam are shown at the bottom.) Astronomers have studied seventeen multiple systems and found evidence supporting the model of multiple stars developing from disk fragmentation. Tobin et al.

Most stars with the mass of the sun or larger have one or more companion stars, but when and how these multiple stars form is one of the controversial central problems of astronomy. Gravity contracts the natal gas and dust in an interstellar cloud until clumps develop that are dense enough to coalesce into stars, but how are multiple stars fashioned? Because the shrinking cloud has a slight spin, a disk (possibly a preplanetary system) eventually forms. In one model of binary star formation, this disk fragments due to gravitational instabilities, producing a second star. The other model argues that turbulence in the contracting cloud itself fragments the clumps into multiple star systems. In the first case, simulations show that the two stars should be relatively close together, typically less than about 600 astronomical units (one AU is the average distance of the earth from the sun). If the second mechanism is correct, both close and wide binary pairs can form. A distinguishing feature of the turbulent fragmentation process, and one that facilitates an observational test, is that the seeds for multiplicity are produced early in the pre-stellar phases.

CfA astronomers Sarah Sadavoy and Mike Dunham were members of a team of astronomers that used the VLA and ALMA radio and millimeter-wave facilities to study seventeen protostellar systems of multiple stars in the nearby Perseus cloud. The sensitive observations were able to reveal the environments of the systems and determine the presence of any small-scale rotation or surrounding material. Twelve of the systems were spatially resolved, and eight showed dust emission structures surrounding the pair. The slightly more evolved systems in the set showed no evidence of circumbinary dust; they have probably reached the end point of their early evolution and finished accreting material. In summary, about two-thirds of the systems were consistent with the disk fragmentation theory and one-third were inconsistent with it. The results show that the disk fragmentation mechanism is an important one but probably not the whole story, and a larger sample should help constrain the processes even further.

Reference: “The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems,” John J. Tobin, Leslie W. Looney, Zhi-Yun Li, Sarah I. Sadavoy, Michael M. Dunham, Dominique Segura-Cox, Kaitlin Kratter, Claire J. Chandler, Carl Melis, Robert J. Harris, and Laura Perez, 29 October 2018, The Astrophysical Journal.
DOI: 10.3847/1538-4357/aae1f7

Share
By
Harvard-Smithsonian Center For Astrophysics

Recent Posts

Fatty Liver Disease: A Hidden Danger to Your Brain?

A study conducted by the Roger Williams Institute of Hepatology, affiliated with King's College London…

February 8, 2023

Space Mystery: Unexpected New Ring System Discovered in Our Own Solar System

ESA’s Cheops finds an unexpected ring around dwarf planet Quaoar During a break from looking…

February 8, 2023

Smart Energy Savings: Chameleon-Like Building Material Changes Its Infrared Color

To address the challenge of saving energy in the face of increasingly frequent extreme weather…

February 8, 2023

Cancer Conundrum Solved: Researchers Unravel a Population of ‘Cheating’ Cells

The study provides answers to multiple conundrums about cancer, while also uncovering new areas for…

February 8, 2023

Unlocking the Mystery of the Stellar Initial Mass Function: A New Breakthrough Discovery

The fate of galaxies is determined by the initial mass distribution at the birth of…

February 8, 2023

NASA Awards $11.7 Million to Historically Black Colleges and Universities

NASA is awarding $11.7 million to eight Historically Black Colleges and Universities (HBCUs) through the…

February 8, 2023