A multiwavelength approach is needed to discover a quasars’ behaviour as a whole and uncover its structure. This means obtaining data from the long wavelength radio regime

through to high energy gamma rays.

From each observation we can extract:

V

As quasars are so luminous they can be seen out to great distances. This means we are seeing

things as they were billions of years ago which provides a rare probe of

conditions in the early Universe.

It is also important to understand the physical processes which contribute to a quasars’ emission in each

waveband and why enormous changes in output occur on several timescales. A

supermassive black hole feeding on a surrounding disk of accreting matter is widely

accepted as the central engine of a quasar. Accretion disks are found

elsewhere in the Universe, for example in accreting binary star systems, and less massive

black holes may exist in many (possibly all) galaxies including our own Milky Way.

The study of quasars is not only to unravel their mysteries, but also to

help put together the bigger picture of the dynamics and evolution of the Universe.

Quasars are the the highly luminous centres of galaxies, thought to be powered by accretion onto a supermassive black hole. These objects

are immensely powerful, often completely outshining the billions of stars in their host

galaxy. They emit at wavelengths spanning the entire electromagnetic spectrum and many

quasars are extremely variable on timescales ranging from hours to years. These incredible

objects show such a wide range of characteristics, many of which lack convincing

explanations.

A unified model describing a possible structure for all quasars

has been proposed but no two objects are identical and many

cannot be explained by this model. It is nicely summarized by the adjacent diagram, where the innermost layer is the accretion disk, surrounded by fast-moving

clouds enshrouded by a dusty ring (shown in orange) with a

low-velocity cloud region furthest from the central black hole.

Quasars - revealing the powerhouses of the distant Universe

Rhaana Starling (rlcs@mssl.ucl.ac.uk)Supervisor: Dr. E. M. Puchnarewicz Department: Space and Climate Physics, MSSL

Spectra – the light dispersed to show its intensity at each wavelength, much like splitting white light (optical) into the colours of the rainbow using a prism

Lightcurves – a plot of the light intensity over the duration of the observation. Multiple observations spanning months to years can be combined to find long-term trends.

Lightcurves provide evidence for variability and spectra reveal which chemical elements are

present in the emitting material, their abundances and the materials’ density and

velocity. The characteristic shape of the spectrum may help determine the physical

processes taking place.

I also have high resolution X-ray data from the latest X-ray telescope to be launched, XMM-Newton (left; artists impression). It also has an optical telescope on-board so simultaneous optical and X-ray data are available for each observation; this is very important since many quasars are extremely variable.

The particular objects I am studying have remained elusive since their discoveries many

years ago. This is perhaps not surprising since so many of the fundamental physical processes

underpinning quasar behaviour are yet to be fully understood. However, with better quality data now available these powerhouses of the distant

Universe may soon be revealed.

Images – some quasars have jets (top left;

Chandra X-ray telescope) or the host galaxies may

be visible as seen in these Hubble images.

I am looking at two very unusual objects, IRAS13349+2438 and REJ2248-511, both atypical

in different ways, aiming to determine their emission mechanisms and physical geometry. To do this I have infrared and optical observations I

obtained at the South African Astronomical Observatory plus some archival information at

other wavelengths.

NASA/CXC