Coming soon to a sky near you a new telescope array – known as NuSTAR. This high energy X ray observatory should have been launched in March, but the software running the launch rocket was not quite ready. Instead, NuSTAR should be launched after mid -June.
Artist's concept of NuSTAR on orbit. Image credit: NASA/JPL-Caltech
Other missions have operated in the X ray part of the spectrum, but this telescope will be much more sensitive. X rays are produced by a wide variety of astronomical objects, from black holes to the Sun. X rays are very penetrating (that’s why they get used when looking for broken bones) – and this means that they can travel through clouds of dust and gas that would otherwise obscure objects. Of particular interest are black holes like the supermassive black hole at the centre of our milky way and those associated with the collapse of massive stars. Supernova remnants are another target – supernovae are responsible for many of the heavier elements in the universe, but the ways in which these elements are produced and dispersed is not well understood. Supernova remnants by their nature conceal their centres with material from the explosion that formed them, so an x-ray observatory might finally reveal details from the heart of the explosion.
A more exotic particle – an axion – will also be searched for. Axions are one of the possible dark matter particles. The dark matter problem was recently thrown a curve ball with results from the European Southern Observatory’s La Silla Observatory in Chile. A team of astronomers mapped the area of the galaxy around the Sun, out to 13,000 light years in places. They found enough visible matter to match the predicted mass of this region – but no dark matter. Dark matter is needed to explain the rotation of the galaxy (unless you want to go with one of the alternate theories, like modified Newtonian Dynamics or Variable speed of light). Dark Matter is matter that does gravity, but is not detectable by direct emitted light. It could be composed of fundamental particles that might have mass or much larger object like black holes or brown dwarfs. Nustar should be able to spot x-rays produced from axions escaping from the core of the sun and may be able to give an indication of their mass.
Axions are a theoretical particle, suggested in 1977 as a way to solve a problem in quantum chromodynamics. They could be 500 million times lighter than an electron. Nobody has ever seen an axion, despite quite a few international teams hunting for them. In particular, the CERN Axion Solar Telescope ran for six months in 2003 and failed to detect any axions arriving from the sun. With the dark matter seeming to be missing from near the Sun, good luck to NuSTAR team in finding any!
This episode of “What is the Stars?” was broadcast the week of June 4, 2012. Listen live on RTÉ’s lyricfm Mondays and Fridays at 22:45. 
