Exotic - "Exotic" Distance Indicators All of the...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
"Exotic" Distance Indicators All of the above methods rely on a straightforward application of the inverse-square law or the angular diameter-distance relation. There is also a range of techniques that use more involved or indirect combinations of observables. Some examples are: The Hubble time : for simple big-bang models, ages of objects (stars, radioactive nuclei) set bounds on H 0 . The age of the universe is of order the Hubble time τ H =1/ H 0 , to within a factor of order unity depending on the deceleration history of the expansion. For H 0 =50 km/s Mpc, τ H = 2 x10 10 years; for 100 km/s Mpc, 10 10 years. This must be greater than the age determined from geological and stellar-evolutionary timescales, nuclear isotopic clocks like 235 U/ 238 U, and consistent with the dynamical status of galaxies and clusters. The small amount of evolution observed in elliptical galaxies to about z=1 favors smaller H 0 in simple models (Hamilton 1985 ApJ 297, 371). One should beware subtly circular arguments - globular-cluster ages were
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

Ask a homework question - tutors are online