Public Lectures for the Session 2002-2003 held in Room E7 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

20 February 2003

''The Hidden X-ray Universe''

Dr. Omar Almaini
(Royal Observatory Edinburgh)

In the second of our cosmological series of lectures in 2003 Dr Almaini told us that X-rays are produced by the most energetic astronomical phenomena: supernovae, active galaxies and black holes. However only radio and optical wavelengths are able to reach the surface of the earth and so X-ray astronomy had to wait for orbiting satellites such as XMM and Chandra , observing from space-born platforms to investigate these exotic objects.

Dr. Almaini then gave a background to X-ray astronomy starting with the 1962 proposals by the 2002 Nobel Prize winner, Riccardo Giaconi to observe solar X-rays reflected from the moon. In this early experiment, many X-ray sources were discovered across the celestial sphere, including from strong emitters such as Scorpius X1, an X-ray binary star. But the experiment also showed background sources that we now know to be quasars at the birth of the universe.

X-ray imaging is difficult. It relies on superbly figured, nested, hyperbolic-parabolic Iridium coated reflecting surfaces that guide grazing-incidence X-rays to a reasonably tight focus. The technology is precise and difficult but is making progress. Research has shown that X-ray objects must be small and very energetic. They must also be only a few light-days across at most in the case of active galactic nuclei. In the case of Seyfert galaxies, long known to have nuclei that fluctuate in magnitude at visible wavelengths, they may be black holes feeding on in-falling stars. The core of the Andromeda galaxy is thought to contain a black hole that emits X-rays.

Our own Milky Way galaxy has now been shown, via radio investigations, to contain a very dense massive object that may be a dormant black hole and identified as Sag. A*. Time-lapse high-resolution radio images show that nearby stars are orbiting an invisible mass that is judged to be a 2.2 Million Solar Mass object, currently starved of fuel by solar winds generated by the central object.

X-ray astronomy is supporting models of the universe that a decade ago was only within the domain of mathematical cosmologists.

Synopsis by Kevin J. Kilburn (Secretary)

Maintained by Michael Oates
Page modified 28 October, 2006