Saturday, November 7, 2009
Here a picture of the Telescope in the Mount.
BICEP 2 is a microwave telescope looking back at the Cosmic Microwave Background (CMB--The time about 400,000 years after the Big Bang, where the universe was cool enough for matter to form) for a certain signature indicative of an inflationary epoch in our early universe. It has been posited that after the Big Bang, the universe expand at an exponential rate. This explains some "strange" behavior that we see in our universe. Everything that happened between the Big Bang and the CMB is be imprinted on the CMB, thus this massive inflation would leave its mark on the CMB. We are looking for this mark with BICEP2, observing from the South Pole. The South Pole was chosen, as it is a very cold, dry, dark place. As water in the atmosphere absorbs microwave radiation (think of how a microwave oven works--the water in the food absorbs microwave radiation and heats up), we require an extremely dry environment. A space mission would be ideal, but the cost to put a telescope in space is extreme, and ground based experiments so far have been sensitive enough. There is a balloon borne experiment scheduled for next year as well, which takes the telescope and puts it extremely high in the atmosphere.
The Mount is the blue thing, which controls the movement of the telescope. The white thing is called the Cryostat, it's the part that keeps the telescope under vacuum and really really cold. It's filled with Liquid Helium (4K = -452 F), though the detectors are kept much colder than that, at around 0.250 K with a He10 dilution fridge. In this picture, you can see the window, which allows microwave radiation through. Inside the cryostat are the lenses, which focus the incoming light, filters to reject out of band radiation (ie not microwaves), and the detectors. There are 256 pixels, each sensitive to 2 orthogonal polarizations of light. They are made of a series of antennae coupled with a microstrip into Transition Edge Sensors (TES's). TES's are devices that are kept just on the transition of a material from its normal operating state to its superconducting state. This transition is a very steep curve in resistance, and thus a small signal on the antennae translates to a clear jump in the TES resistance. I won't bother with the rest of the circuitry right now, but I think that how the TES's work is really cool.
So the telescope scans across the sky, and we take these tiny changes in resistance and translate them into pretty pictures of the early universe!