Active galactic nuclei measure the universe

Active galactic nuclei measure the universe
http://physicsworld.com/cws/article/news/47391

Darach Watson and colleagues at the University of Copenhagen, Denmark,
and the University of Queensland, Australia, have worked out a way of
using supermassive black holes – which power active galactic nuclei
(AGNs) – as "standard candles" for making accurate measurements of
cosmic distances. The work is important because AGNs can be found just
about everywhere in the universe, and unlike the supernovae currently
used as standard candles, the light from AGNs endures for long periods
of time.

See: http://physicsworld.com/cws/article/news/47391