How to Calculate
the Expansion Rate of the Universe (in Ten Easy
Steps)...
1) Witness a supernova (SN) explosion
in a nearby galaxy
2) With ground-based telescope, measure lightcurve
of SN over several weeks and its spectral output
(Needs to be a Type 1A
supernova)
3) Propose for Hubble Space Telescope time using
Advanced Camera for Surveys to observe host galaxy
4) Win awarded time; observe over many months in
several filters
5) Measure light fluctuations from Cepheid
variables in the host galaxy
6) Compare host galaxy's Cepheids to Cepheids in
the Milky Way Galaxy
7) Determine an accurate distance to the host galaxy
8) Compare SN light curve in nearby host galaxy
to other galaxies much farther away
9) Get advanced degree in cosmology
10) Write peer-reviewed journal article with results
Supernova SN2002fk in NGC 1309
In 2002, NGC 1309 hosted a supernova,
a star that blew off its outer layers in a massive
explosion. This ground-based image of NGC 1309 was
taken in 2002 when SN2002fk was still visible. It
was observed with the Lick Observatory KAIT telescope.
The Hubble ACS image at right shows the location
of the supernova, well after its light has died
down.
Click
to enlarge
Lick Observatory image: W. Li and A. V.
Filippenko (University of California, Berkeley)
HST image: NASA, ESA, The Hubble Heritage
Team (STScI/AURA), and A. Riess (STScI)
|
Cepheid Variables in NGC 1309
NASA, ESA, The Hubble Heritage Team (STScI/AURA),
and A. Riess (STScI)
Supernovae, such as SN2002fk, can be used to calibrate
distance measurements in the universe, because other,
fainter stars of known brightness can be observed
in the same galaxy. These stellar "standard candles"
are the Cepheid variable stars, which vary regularly
in brightness with periods that are directly related
to their intrinsic brightness, and thus allow the
distance to the galaxy--and the supernova--to be
determined directly. However, only the Hubble Space
Telescope, equipped with the Advanced Camera for
Surveys, has the capability to resolve these individual
Cepheids in NGC 1309.
The below image shows a Hubble ACS observationsof
NGC 3370 which was also taken for its resolvable
Cepheid variables. It hosted a type Ia supernova
in 1994.
Click
to visit Heritage release of NGC 3370
NASA, ESA, The Hubble Heritage Team (STScI/AURA),
and A. Riess (STScI)
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