Surprising dissimilarities in a newly formed pair of 'identical twin' stars.

The mass and chemical composition of a star are the primary determinants of its basic physical properties-radius, temperature and luminosity-and how those properties evolve with time. Accordingly, two stars born at the same time, from the same natal material and with the same mass, are 'identical twins,' and as such might be expected to possess identical physical attributes. We have discovered in the Orion nebula a pair of stellar twins in a newborn binary star system. Each star in the binary has a mass of 0.41 +/- 0.01 solar masses, identical to within 2 per cent. Here we report that these twin stars have surface temperatures differing by approximately 300 K ( approximately 10 per cent) and luminosities differing by approximately 50 per cent, both at high confidence level. Preliminary results indicate that the stars' radii also differ, by 5-10 per cent. These surprising dissimilarities suggest that one of the twins may have been delayed by several hundred thousand years in its formation relative to its sibling. Such a delay could only have been detected in a very young, definitively equal-mass binary system. Our findings reveal cosmic limits on the age synchronization of young binary stars, often used as tests for the age calibrations of star-formation models.

A triple-star system with a misaligned and warped circumstellar disk shaped by disk tearing.

Young stars are surrounded by a circumstellar disk of gas and dust, within which planet formation can occur. Gravitational forces in multiple star systems can disrupt the disk. Theoretical models predict that if the disk is misaligned with the orbital plane of the stars, the disk should warp and break into precessing rings, a phenomenon known as disk tearing. We present observations of the triple-star system GW Orionis, finding evidence for disk tearing. Our images show an eccentric ring that is misaligned with the orbital planes and the outer disk. The ring casts shadows on a strongly warped intermediate region of the disk. If planets can form within the warped disk, disk tearing could provide a mechanism for forming wide-separation planets on oblique orbits.