ALMA'S IMAGE OF A NEW PLANET FORMATION IN A BINARY STARS SYSTEM

A composite image of the HD 142527 binary star system from data captured by ALMA shows a distinctive arc of dust (red) and a ring of carbon monoxide (blue and green). The red arc is free of gas, suggesting the carbon monoxide has "frozen out", forming a layer of frost on the dust grains in that region. Astronomers speculate this frost provides a boost to planet formation. The two dots in the center represent the two stars in the system.
Credit: Andrea Isella/Rice University; B. Saxton (NRAO/AUI/NSF); ALMA (NRAO/ESO/NAOJ)

The Atacama Large Millimeter/submillimeter Array (ALMA) has observed a new very early stage of planet formation around the binary star system HD 142527 (in the costellation of Lupus) and has provided fresh insights into the planet-forming potential of a binary system.


It is not clear how the planets form in a binary stars system. Observational evidence reveals that planets form and maintain surprisingly stable orbits around double stars disproving the theoretical models that suggest that the gravitational tug-of-war between two stellar bodies would send young planets into eccentric orbits, possibly ejecting them completely from their home system or sending them crashing into their stars.

ALMA's new, high-resolution images of HD 142527 show a broad elliptical ring around the double star (main star ~ 2 M_sun - companion star ~1/3 M_sun). The stars are separated by approximately one billion miles: a little more than the distance from the Sun to Saturn. The disk begins incredibly far from the central star - about 50 times the Sun-Earth distance. Most of it consists of gases, including two forms of carbon monoxide (13CO and C180), but there is a noticeable dearth of gases within a huge arc of dust that extends nearly a third of the way around the star system.

Image: Artist impression of the HD 142527 binary star system based on data from the Atacama Large Millimeter/submillimeter Array (ALMA). The rendition shows a distinctive arc of dust (red) embedded in the protoplanetary disk. The red arc is free of gas, suggesting the carbon monoxide has "frozen out", forming a layer of frost on the dust grains in that region. Astronomers speculate this frost provides a boost to planet formation. The two dots in the center represent the two stars in the system. Credit: B. Saxton (NRAO/AUI/NSF)

This crescent-shaped dust cloud may be the result of gravitational forces unique to binary stars and may also be the key to the formation of planets. The current theoretical models suggest that small dust grains and pockets of gas eventually come together under gravity, forming larger and larger agglomerations and eventually asteroids and planets. The fine points of this process are not well understood, however. By studying a wide range of protoplanetary disks with ALMA, astronomers hope to better understand the conditions that set the stage for planet formation across the Universe.

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▪ ALMA Unveils Details of Planet Formation around Binary Star