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					       Quasars - revealing the powerhouses of the distant
Rhaana Starling             (
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.
                               long-term trends.

                                                                         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.

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