What
is TopHat?
TopHat
and Understanding the "Big Bang"
TopHat is an instrument that has been designed to collect
data on the CMBR. Its mission is to study light in the
microwave and infrared wavelengths.
The
TopHat experiment includes a spinning telescope and a
detector system. It will map a 48 degree diameter disk
of the sky above the Southern Polar Cap. To accomplish
this, the telescope will simply spin at a constant rate
about its vertical axis. As the Earth rotates, the entire
polar cap will be observed each day.
|
|
A
scale drawing of TopHat on top of the balloon together
with a blow-up image of the top package. |
A
wireframe drawing of the top of the TopHat test package,
showing the mirrors, the dewar and the rotation stage.
Click here for an animated view. (594K)
(47K) |
|
A
cutaway view of the indigo dewar.
|
The
detector system uses bolometers. These heat sensing detectors
are very sensitive and are ideal for making these measurements.
This is because the CMBR is a form of heat in the sky.
Using them, TopHat will be able to make observations of
cosmic microwave background anisotropy of unprecedented
sensitivity.
The
TopHat balloon flight from McMurdo Station, Antarctica
will last approximately 2 weeks.
TopHat
and Understanding the "Big Bang"
The
ability to understand the origin and evolution of our
universe is the driving force behind the TopHat project.
We can gain valuable insights into the characteristics
of our universe by making measurements of the Cosmic Microwave
Background Radiation (CMBR).
The
Big Bang is the generally accepted theory as to how the
Universe began. The idea is that the universe started
out very hot and very small. As time went on, the universe
expanded and cooled off. Eventually, it was large enough
and cool enough for helium and hydrogen (the lightest
elements) to form. This happened between 150,000 and 300,000
years after the Big Bang. It took yet another billion
years or so for the first stars and galaxies to form -
and nearly another 10 billion years for our sun and the
Earth to form. All this time the universe has continued
to expand and cool off. In fact, we can measure this expansion
in the stars and galaxies around us today!
The
Cosmic Microwave Background Radiation was produced at
the same time the first hydrogen were produced. Since
at the time the universe was very hot (over 3,000 degrees
Celsius!) the universe "glowed" - just like a fireplace
glows and keeps us warm. The CMBR is the leftover radiation
from that glow.
TopHat
measures the brightness of the CMBR in different parts
of the sky. This tells us which areas of the universe
were extra hot and which areas were extra cold when the
hydrogen and helium were produced. It turns out that many
characteristics of the universe can be inferred from the
distribution of these hot and cold spots on the sky. In
fact, with TopHat's measurements we can explore some very
fundamental questions, including:
How
fast is our universe expanding?
Will
it expand forever? Or will it eventually start contracting?
What's
making our universe expand?
How
much of our universe is made up of the same materials
that we're made of?
You
can learn more about the properties of our universe and
the CMBR at the following web sites:
Good
for beginners:
http://www.astro.ubc.ca/people/scott/cmb.html
http://map.gsfc.nasa.gov/
A
bit more advanced:
http://www.sns.ias.edu
http://www.hep.upenn.edu/~max/cmb/pipeline.html
http://astro.estec.esa.nl/Planck/report/redbook/redbook-science.htm