BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-1502
DTSTART:20090410T170000Z
DTEND:20090410T180000Z
DTSTAMP:20260420T111925Z
LAST-MODIFIED:20090403T142952Z
LOCATION:6515 Sterling Hall
SUMMARY:Positron Annihilation Radiation from the Center of our Galaxy\
 , Special Astronomy Colloquium Talk\, Nidhal Guessoum\, American Unive
 rsity of Sharjah
DESCRIPTION:The staggering rate of positron production and annihilatio
 n in the<br>
\nGalaxy (1043 e+/s) has been established for three decad
 es now but has yet to find a convincing explanation\, especially after
  the INTEGRAL satellite (launched in 2002) produced a radiation map sh
 owing the emission to be mostly coming from the galactic bulge (Knodls
 eder et al. 2004\, Weidenspointner et al. 2008). While the physics of 
 the annihilation of positrons has now mostly been understood (Guessoum
 \, Jean\, Gillard 2005)\, the origin and propagation of those positron
 s remain an unsettled question\, although good progress has been made 
 lately with interesting models and constraints presented.<br><br>
\n<b
 r>
\nIn this seminar I first review the current knowledge of that<br>

 \npositron-electron annihilation radiation\, with what the spectroscop
 ic analysis and the spatial mapping tell us about the media of annihil
 ation (mainly) and to some extent about the sources of positrons. I ex
 plain the physical processes which the positrons undergo during their 
 long lives and highlight the role of the interstellar gas\, dust\, and
  organic molecules. I then focus on the Galactic Center (with its supe
 rmassive black hole) and its potential contribution to explaining part
 \, if not all\, of the annihilation radiation observed at least in the
  Galactic bulge. Several specific proposals have recently been made fo
 r the production of positrons by the GC?s SMBH\, and they will be crit
 ically reviewed on the basis of:a) the positrons? propagation away fro
 m the central compact source\, given their initial kinetic energy\; b)
  the constraint from direct annihilation emission in flight produced b
 y relativistic positrons\; c) estimates of the rates of positron produ
 ction and other plausibility considerations. Finally\, I briefly highl
 ight the important issue of positron propagation from their production
  site(s)\, for which the specific physical process is uncertain (colli
 sional or diffusional) and the conditions of the region (density\, tem
 perature\, and magneticfield distributions) are complex.<br>
\n<br><br
 >
\nI conclude with some pointers for near-future research on the prob
 lem.
URL:https://www.physics.wisc.edu/events/?id=1502
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