19 August 2006

Mass Limit for Fusion

Astronomers may have found the lower limit on mass for nuclear fusion, and thus the upper limit for brown dwarfs, BBC reports. Unfortunately, they present some new misconceptions in the process - brown dwarfs aren't "dead" stars, they're stars that were never born, or perhaps overweight gas giants. But they never did have hydrogen fusion in the core, so they never stopped.

What Richer, et al., actually did was turn the HST towards a globular cluster in our Milky Way and take a 5-day exposure. (In reality they took multiple shorter exposures that were combined into one long one - no one takes a single exposure that long in case something goes wrong and because the tracking isn't perfect even on the HST.) In the image, the faintest stars they could see corresponded to 8.3% of the Sun's mass. If fainter stars existed Hubble would've been able to pick them up, but the article isn't on astro-ph and Science magazine restricts (free) access to the abstract only. If anyone has a subscription and can find the mass-equivalent detection limit of Hubble in the full article, I'd love to know.

No comments: