Fe Edge in Quasar APM 8279+5255
Credit: N. Schartel/ESA/MPE

The Edge at the Edge of the Universe

Sometimes astronomers are more interested in what they don't see than what they do see. Absorption of starlight by intervening clouds of gas and dust allow astronomers to measure the density and composition of this absorbing medium. In a recent study of the X-ray emission from a very distant quasar known as APM 8279+5255 using the XMM-Newton X-ray observatory's EPIC camera, astronomers at the European Space Agency (ESA) and the Max-Planck-Institut für extraterrestrische Physik (MPE) found a feature which they interpreted as absorption from iron atoms in a cloud of gas between the quasar and us. This absorption is called the iron (Fe) K edge, and it can be seen in the bottom part of the image above as a reduction in the amount of detected X-rays compared to a model of the emission. From the energy at which the edge was observed, astronomers determined that the absorbing material is near the quasar, i.e. about 13.5 billion light years from earth, so that this material existed when the universe was only a fraction of its present age. From the depth of the iron K edge astronomers deduced the abundance of iron in the absorbing medium and they were shocked to note that a huge amount of iron, about 3 times the abundance in the sun, must be present in the absorbing material. This is strange because iron is thought to be produced in the cores of massive stars, and according to conventional thinking there shouldn't have been enough massive stars to produce the observed amount of iron in the very early Universe. Either there were many more massive stars in the early universe than previously believed, or perhaps the Universe knows of another way to make iron - or maybe the Universe is actually much older than it appears.

Last Week * HEA Dictionary * Archive * Search HEAPOW * Education

Each week the HEASARC brings you new, exciting and beautiful images from X-ray and Gamma ray astronomy. Check back each week and be sure to check out the HEAPOW archive!

Page Author: Dr. Michael F. Corcoran
Last modified July 22, 2002