Good morning from Belfast! I’m sitting inside the main lecture theatre here at Queen’s University listening to the two early morning plenary session talks. Dr Brian Schmidt from the Australian National University is first up and is giving a great talk on ‘Measuring cosmic acceleration’. It’s a fascinating story which begins, in some sense at least, in the mid to late nineties when astronomers found evidence that the rate at which the Universe was expanding is accelerating.

They had been studying cosmic events called Type Ia supernovae. These are violent thermonuclear events which can appear up to 100 times brighter than Type II supernovae in the night sky and “5 billion times brighter than our Sun”. Astronomers use this particular brand of supernovae as what they call a ‘standard candle’; essentially a cosmic distance marker*. That’s because the mechanisms and processes that form them (currently thought to be the dumping of matter (accretion) onto a white dwarf by a companion star) are fairly well understood. Since they are understood and are extremely bright, for a given distance, astronomers know how bright they should be; thus making them good standard candles.

Today much of what we know about dark energy and the expansion of the Universe has come from observations of distant Type Ia supernovae and the Cosmic Microwave Background. According to Dr Schmidt the whole discussion around the accelerating Universe has developed tremendously in the last ten years. That is primarily because of the discovery of the presence (or really the inference) of dark energy - a component of matter, in the Universe, which appears to be causing the rate of expansion to speed up.

Dr Schmidt has a website here and a great web-presentation on ‘The Accelerating Universe - an explanation for the interested non-scientist’ here.

*It’s worth noting, says Dr Schmidt, that not all Type Ia supernovae are the identical. It’s thanks to work done by several astronomers investigating the nature of different Type Ia events (and their light curves) that we can still use them as good standard candles.

Above: The result of a Type Ia supernova? - Tycho’s Supernova
Credit: NASA/ESA, CXO and P. Ruiz-Lapuente (University of Barcelona)