Dark energy

1
(No Transcript)
2
Dark energy

• What constitutes our Universe?
• Simply radiation and baryonic matter?
• Is there more than meets the eye?
• Up to 95 of its energy content is thought to be
  exotic.

3
Dark energy

• 2 leading DE models cosmological constant (?)
  and quintessence.
• ? has constant negative pressure, causing
  expansion of the Universe to accelerate.
• Quintessence is a dynamical field in which
  negative pressure DE varies in space and time.
• ? is the most economical solution to cosmic
  expansion.

4
Dark energy and the Universe

• DE has many implications for the history and fate
  of the Universe.
• The more DE, the older the Universe and the
  expansion increases with time.

5
Type Ia Supernovae

• SNIa are semi-detached
• binary systems.
• When the Chandrasekhar
• mass limit is reached,
• the white dwarf explodes violently.
• SNIa have a characteristic light curve.
• Important feature decay rate is related to peak
  intrinsic luminosity of SN.

6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
Evidence from SNIa of acceleration

• A SNIa survey in the late 1990s provided some of
  the 1st evidence of cosmic acceleration.
• SNIa were used as standard candles to measure the
  expansion history of the Universe.
• Results indicated acceleration , i.e. large DE
  content.

10
SDSS-II

• Aim Study structure of Milky Way
• and nature of dark energy.
• Expected to discover 200 new SNIa by 2008.
• Already over 100 new confirmed SNIa have been
  announced.
• After each nights observing, hand scanners work
  through 5000 objects to try identify SNIa
  candidates.

11
(No Transcript)
12
SDSS-II

• Performance of the scanners is continuously
  monitored.
• Spectroscopic follow up observations and
  multi-band light curve fitting are carried out on
  SNIa candidates.

13
South Africas Involvement

• SALT will study the Universe at very early times.
• The high res. Spectrograph could be used to
  obtain SNIa spectra.
• Multi-wavelength observations of SNIa will help
  determine extinction effects of galaxies.
• Significant results would yet again change out
  view of the Universe!

14
The end.