By Ron Cowen
Using the sharp X-ray eye of an orbiting observatory, astronomers have employed a novel method to measure distance within the Milky Way. If they can extend the technique to objects far outside our galaxy, it could yield a new estimate of the age of the cosmos.
The technique relies on the halo of radiation that surrounds objects that emit intense X rays. The halo arises as the X rays bounce off tiny dust grains lying between the object and Earth. These scattered X rays take slightly longer to reach Earth than those traveling directly. The delay for radiation coming from different parts of the halo, along with their apparent separation, indicates the distance.