An
image taken at submillimeter wavelengths of a star-forming core,
showing that it contains two young stellar embryos. Astronomers have
concluded from a systematic study of very young cores that most
embryonic stars form in multiple systems, and later some of them
separate. Credit:Sadavoy and Stahler
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 clouds to look for variations in binary frequency
with stellar mass, but so many other effects can influence the result
that the results have been inconclusive. These complicating factors
include dynamical interactions between stars that can eject one member
of a multiple system, or on the other hand might capture a passing star
under the right circumstances.
Some studies, for example, found that
younger stars are more likely to be found in binary pairs. One issue
with much of the previous observational work, however, has been the
small sample sizes.
CfA astronomer Sarah Sadavoy and her colleague used combined
observations from a large radio wavelength survey of young stars in the
Perseus cloud with submillimeter observations of the natal dense core
material around these stars to identify twenty-four multiple systems.
The scientists then used a submillimeter study to identify and
characterize the dust cores in which the stars are buried.
They found
that most of the embedded binaries are located near the centers of their
dust cores, indicative of their still being young enough to have not
drifted away. About half of the binaries are in elongated core
structures, and they conclude that the initial cores were also elongated
structures.
After modeling their findings, they argue that the most
likely scenarios are the ones predicting that all stars, both single and
binaries, form in widely separated binary pair systems, but that most
of these break apart either due to ejection or to the core itself
breaking apart. A few systems become more tightly bound. Although
other studies have suggested this idea as well, this is the first study
to do so based on observations of very young, still embedded stars. One
of their most significant major conclusions is that each dusty core of
material is likely to be the birthplace of two stars, not the single
star usually modeled. This means that there are probably twice as many
stars being formed per core than is generally believed.
Reference(s):
"Embedded Binaries and Their Dense Cores," Sarah I. Sadavoy and Steven W. Stahler, MNRAS 469, 3881, 2017.
