Quasars - revealing the powerhouses of the distant
Rhaana Starling (email@example.com)
Supervisor: Dr. E. M. Puchnarewicz Department: Space and Climate Physics, MSSL
Quasars are the the highly luminous centres of galaxies, thought Spectra – the light
to be powered by accretion onto a supermassive black hole. dispersed to show its
These objects are immensely powerful, often completely intensity at each
outshining the billions of stars in their host galaxy. They emit at wavelength, much like
wavelengths spanning the entire electromagnetic spectrum and splitting white light
many quasars are extremely variable on timescales ranging from (optical) into the
hours to years. These incredible objects show such a wide range colours of the rainbow
of characteristics, many of which lack convincing explanations. using a prism
As quasars are so luminous they can be seen out to great Lightcurves provide evidence for variability and spectra reveal
distances. This means we are seeing things as they were billions which chemical elements are present in the emitting material,
of years ago which provides a rare probe of conditions in the their abundances and the materials’ density and velocity. The
early Universe. characteristic shape of the spectrum may help determine the
It is also important to understand the physical processes which physical processes taking place.
contribute to a quasars’ emission in each waveband and why
enormous changes in output occur on several timescales. A unified model describing a possible
A supermassive black hole feeding on a surrounding disk of structure for all quasars has been proposed
accreting matter is widely accepted as the central engine of but no two objects are identical and many
a quasar. Accretion disks are found elsewhere in the Universe, cannot be explained by this model. It is
for example in accreting binary star systems, and less massive nicely summarized by the adjacent diagram,
black holes may exist in many (possibly all) galaxies including where the innermost layer is the accretion
our own Milky Way. disk, surrounded by fast-moving clouds
The study of quasars is not only to unravel their mysteries, but enshrouded by a dusty ring (shown in
also to help put together the bigger picture of the dynamics and orange) with a low-velocity cloud region NASA/CXC
evolution of the Universe. furthest from the central black hole.
A multiwavelength approach is needed to discover a quasars’ I am looking at two very unusual objects, IRAS13349+2438 and
VREJ2248-511, both atypical in different ways, aiming to determine
behaviour as a whole and uncover its structure. This means their emission mechanisms and physical geometry. To do this I
obtaining data from the long wavelength radio regime through have infrared and optical observations I obtained at the South
to high energy gamma rays. African Astronomical Observatory plus some archival information
From each observation we can extract: at other wavelengths.
I also have high resolution X-ray data from the latest X-
Lightcurves – a plot of the light ray telescope to be launched, XMM-Newton (left; artists
intensity over the duration of the impression). It also has an optical telescope on-board so
observation. Multiple simultaneous optical and X-ray data are available for each
observations spanning months to observation; this is very important since many quasars are
years can be combined to find extremely variable.
The particular objects I am studying have remained elusive since
their discoveries many years ago. This is perhaps not surprising
Images – some quasars have jets since so many of the fundamental physical processes
(top left; Chandra X-ray telescope) underpinning quasar behaviour are yet to be fully understood.
or the host galaxies may be visible However, with better quality data now available these
powerhouses of the distant Universe may soon be revealed.
as seen in these Hubble images.