January 20, 2002 | David F. Coppedge

Some Exoplanets May Be Exostars

A brown dwarf was measured with more precision, and was found to be more massive than expected.  Robert Roy Britt in Space.com says this may call into question some of the discoveries of bodies orbiting other stars that were assumed to be planets.  I. Neill Reid,1 writing in Nature where the measurement was announced,2 explained the implications:

Clearly, this is only one datum point, for one particular age and one particular mass.  Nonetheless, there are wide potential ramifications.  If this is a fair reflection of the theoretical models, then analyses of the luminosity distribution of low-mass stars and brown dwarfs in young clusters may be systematically underestimating their masses.  In consequence, the turnover in the mass function would be exaggerated (that is, there would be more brown dwarfs than currently estimated), but a lower-mass cut-off might lie at higher masses, because the supposed objects of 1-2 Jupiter masses might in fact exceed 15�20 Jupiter masses (0.015�0.02 solar masses).   (Emphasis added in all quotes.)

See also the report on EurekAlert.


1I. Neill Reid, “Astronomy: Weighing the baby,” Nature 433, 207 – 208 (20 January 2005); doi:10.1038/433207a.
2Close et al., “A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages,” Nature 433, 286 – 289 (20 January 2005); doi:10.1038/nature03225.

There could well be planets around other stars, but it’s one thing to find an exoplanet.  It’s another thing to find a privileged exoplanet.

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