Tag Archives: Dark Sector

SCIENCE! Part III

MAPO

http://www.astro.caltech.edu/~lgg/keck/keck_front

MAPO, or the Martin A. Pomerantz Observatory, is the first building one encounters upon crossing the skiway. The blue box-like building housing the telescopes Viper (now complete and waiting demolition) and SPUD, used to sit high above the snow surface to avoid drifting issues, but the stilts are now long buried.

SPUD is looking at a similar radiation spectrum as the South Pole 10m telescope (about 2mm wavelength) but at a much larger scale with far less resolution. The project is described in the Science Planning Summary USAP-2011-2012 as:
Small Polimeter Upgrade for DASI (SPUD) is the next generation instrument in the ongoing Background Imaging of Cosmic Extragalactic Polarization (BICEPT/BICEP2) program of experiments. It will place multiple receivers similar to BICEP2 on the telescope mount originally built for the Degree Angular Scale Interferometer (DASI) experiment. SPUD will increase sensitivity over BICEP2 by increasing the number of detectors and in future seasons by also expanding to other frequencies to mitigate possible foreground contamination. The scientific objective is the same as BICEP2 – to attempt to measure B-mode polarization caused by gravity waves spawned in the first tiny fraction of a second after the big bang by the process of “inflation.” Inflation is the favored cosmo-genic model and finding direct “smoking-gun” evidence for it is one of the highest priorities in cosmology today. SPUD will increase sensitivity over BICEP2 by increasing the number of detectors, and, in future seasons, by also expanding to other frequencies to mitigate possible foreground contamination.

The South Pole Telescope as seen through the SPUD telescope

As with the South Pole Telescope this is not an optical telescope. The image to the right is of the South Pole Telescope as seen through SPUD.

The telescope is extremely simple as far as telescopes go; inside each receiver two lenses focus the radiation on the primary sensor. Opaque Teflon and nylon disks, looking a bit like the plastic from a milk jug, help filter out unwanted wavelengths. The sensor is comprised of four silicon chips with extremely thin metal resistors imprinted upon the surface. Very slight changes in temperature from the incoming radiation induce resistance variations, producing a temperature map of the sky, of the Cosmic Microwave Background. Five receivers will be mounted inside the ground shield and can rotate 360 degrees as well as scan vertically. From the station the Ground Shield looks like a giant plywood flower or bowl, but inside it’s lined with mirror-like metal. The purpose is to limit radiation bouncing off the buildings and snow surrounding MAPO.

The SPUD telescope attached to the side of MAPO as seen from ground level

The commemoration plaque by the entrance to MAPO

The view from inside the receiver housing, looking down the ladder to MAPO

The walls inside the receiver housing

One of the new receivers before being mounted inside the housing

The silicone film inside the receiver itself

The door into the shield - the part of the telescope visible to the rest of the station

The receiver housing as seen from the outside - note the station seen just above the edge of the ground shield

The mirror lined ground shield reflecting the mottled cloudy sky

The Station as seen from MAPO

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SCIENCE! Part II

10-Meter South Pole Telescope
http://pole.uchicago.edu/

The South Pole Telescope looking at the ski directly above – the metal scaffolding is being added this year in an attempt to reduce “noise” from reflections off the snow surface.

The South Pole Telescope (often referred to as simply 10-meter or “SPT”) is an iconic feature here at Pole. Constructed during the Austral summer of 2006-2007, the impressive two dimensional rotating 10-meter dish located just across the skiway from the station is hard to miss.

In the Science Planning Summary USAP-2011-2012 the SPT project is described as:

Looking at the intensity and polarization anisotropy of the CMB. By surveying 4,000 square degrees of the sky with high sensitivity in three wavelength bands, the telescope can detect galaxy clusters through the spectral distortion they impart on the CMB. Researchers will use the resulting catalog of galaxy clusters to set constraints on the mysterious dark energy that dominates the mass-energy density of the universe and is causing the expansion of the universe to accelerate.

The telescope is looking primarily at the CMB (or cosmic microwave background) of the universe. In particular they’re interested in finding and cataloging very distant galaxy clusters and learning more about Dark Energy, the phenomena that would explain the accelerating expansion of our universe. With a 1 arc minute beam the telescope has a relatively high resolution. The WMAP satellite is also mapping the CMB in the same spectrum (95-250 Ghz) but with far less detail. Ultimately they’re looking at changes in temperature of the CMB radiation reaching us here at Earth – these variations are extremely subtle and the focal plane is cooled down to .25 degrees above zero Kelvin with liquid helium to increase sensitivity. Atmospheric water vapor acts as a barrier to this type of radiation, which makes South Pole the ideal place for millimeter and sub-millimeter astronomy.

This is all very good, but what is the CMB? This can be hard to explain, and harder to conceptualize, but here’s a try…The Big Bang theory states that in the very very early stages of the universe matter was so dense it was plasma, at some point there was an inflation event that caused the universe to expand at speeds faster than the speed of light. The CMB is essentially radiation from the boundary between space and this plasma – it’s the boundary between “empty space” with stars and suns and planets etc, and matter that’s so hot and dense light cannot pass through. This background glow is incredibly unifrom across the sky with a temperature of about 2.7 degrees Kelvin.
The CMB is not what that part of the universe looks like now, but what it looked like 300,000 years after the big bang, when the light we’re seeing today was transmitted. We’re seeing what the universe looked like everywhere before it expanded and cooled enough to have different particles separated by space. We know that light travels at a constant rate (2.9×10^8 m/s, or roughly 671 million miles per hour) – it takes ~8.3 minutes for light from the sun to reach earth, 4.24 years for light from the nearest star to reach our sun, and 100,000 years for light to travel across the Milky Way. So… Looking into space really is looking back in time.

An important fact to keep in mind is that there is no center of the universe. Though the Big Bang theory states that everything started in a condensed state and expanded rapidly from there, there’s no center and no matter where you are, everywhere in the universe will look like the center. No matter where in the sky you point the telescope it will see the CMB at the same distance – kind of like if you were in the middle of a giant bubble, no matter where you looked you would see that inside surface of the bubble the same distance away. To get much useful information from the CMB you need special telescopes, the size of which affects the resolution, but everyone has seen remnants of the CMB without even knowing it. The fuzzy static on TVs (before there was 24/7 digital broadcasting)…that is the TV picking up on this white noise penetrating the universe, this distant radiation from the birth of our universe.

Galaxy clusters are some of the largest physical pieces within the universe. They are so large they create something like a shadow against the backdrop of the CMB radiation. Because of its high resolution the SPT is able to locate, and thus catalogue, many previously undiscovered distant galaxy clusters. Part of their project is to create a database of such features to be analyzed with different types of telescopes in the future.

The second part is Dark Energy – our universe is still expanding, that’s fine, but it’s accelerating in rate of expansion! Theoretically with the amount of material and energy presently known to exist in our universe the effects of gravity should have slowed the expansion by now. It doesn’t make sense. To explain this acceleration there needs be far more matter and energy for the equations to work out. This unknown factor is termed Dark Matter and Dark Energy. NASA provides a much better explanation: http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/

The Dark Sector Lab and the SPT in it’s docked position where they can work on the receiver.

The hinge of the telescope and the doors to the receiver area – last year I got to help clean off the grease under and around this part. In the winter the grease freezes and cracks off as it gets pushed out of the hinge, in the summer it thaws and gets very messy.

The base of the telescope – the hole is an access point to the cables and interior of the telescope, the dark piece above is the bearing on which the telescope turns.

Many meters of fiber optic cables run inside the telescope allowing it to turn more than 360. As part of the bearing change last year I got to help unwind and carefully set aside all of these.

The Inside of the telescope – where the cables are usually coiled. This picture was taken last year when the telescope was lifted up to change out the bearing.

The telescope separated to remove the old bearing and slide in a new one. The raised part of the telescope weighed over 65,000lbs!!

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SCIENCE!

So many of you may be wondering by this point “working at the South Pole is cool and all, but…Why?”
Why are we here?
Why is there this giant station?
Why do we have US Air Force planes?
Why is there so much going on down here?

All of these questions, and more, can be answered with the one word: SCIENCE!Everything here is in support of research and for the most part funded through the US National Science Foundation (NSF).

The South Pole, with an elevation of nearly 10,000 feet, an average yearly temperature of -56.9F, and 6 months of darkness is an ideal site for astronomical observations. While there are numerous projects of both short and long term duration the two major ones are IceCube and the 10 meter South Pole Telescope.

NOAA (the National Oceanic and Atmospheric Administration) has a long term Earth Systems Research Laboratory monitoring site here. It’s part of several Global Monitoring Division sites – of which Summit Station, Greenland is also affiliated.

Over the next few posts I’ll highlight some of the primary research projects currently underway here at the South Pole.

ICECUBE
http://icecube.wisc.edu/

A good diagram showing the various parts of the IceCube detector

The IceCube project is a Neutrino detector. Sounds simple enough, but this detector is unlike any other in the world.
Neutrinos are sub-atomic particles of immense energy, but lacking an electric charge – so tiny and with so much energy that they pass through most matter without interaction. Neutrinos are a byproduct of radioactive decay and can be found many places here on earth, but IceCube is interested in a different scale. This project is focusing on neutrinos formed from extremely high energy events such as exploding stars, black holes, and gamma ray bursts. The project goals are to explain these events more thoroughly, shed light on dark matter in our universe, and study the more remote parts of the universe that previously have been too obscured to see. Neutrinos are not affected by magnetic fields, take an extremely long time to decay, and are rarely absorbed, putting them above neutrons or protons as useful particles to study the corners of the universe.

There are several detectors around the world, but the one here at Pole is particularly interesting as it is using the entire earth as a filter. Buried 1.5 kilometers beneath the ice surface the array spans a cubic kilometer! 5160 DOMs (digital optical module) were deployed on 86 vertical strings frozen within the ice sheet.
A hot water drill bored down to 2450m with 1000psi of near boiling water, leaving a tube of liquid water with a 24hr window before it began to freeze. A cable was lowered with the DOMs (61-64 per cable) attached at set intervals. Another part of the project is IceTop which deployed 324 DOMs in tanks on the surface. (http://icecube.wisc.edu/science/icetop) This is an immense project and took over 6 years to complete, the final string being deployed in December 2010. The detector has been collecting data since the first few strings were completed in 2006 and is expected to last another 20 years before the ice stretches and breaks the cables. An international collaboration, there are over 250 scientists around the world are analyzing the overwhelming amount of data being produced. With so many sensors in the ice and with such a large expense it’s good to know that there has been less than a 2% failure rate of the DOMs.

The idea behind having a three dimensional detector is that it is able to track the direction and speed of incoming particles. While many particles come from “above” here, they are noticed first by the IceTop array and can be weeded out, as muons or other various particles not necessarily neutrinos. Particles that come from “below” – or from the North Pole, travelling through the earth, are more likely to be actual neutrinos as most other things are essentially filtered out by the earth’s mass.

How many DOMs total are deployed within the ice here? 5484!
How many miles of copper wire are buried here to transfer data from the strings to the data center in the ICL (IceCube Lab)? 11,650 miles!
Some more fun facts can be found at: http://icecube.wisc.edu/about/facts
A fascinating article (with AMAZING pictures) by NPR about Neutrios and IceCube: http://www.npr.org/blogs/pictureshow/2011/02/24/133997980/cool-science-the-icecube-neutrino-observatory

The IceCube Lab or ICL – all the cables from the DOM strings come back to the ICL where the data is compiled and stored.

A few of the cables as they come together before entering the ICL

The hot water drill itself – the bowed out pieces are to keep the drill from spinning and oriented vertically

A hole over 2.5km deep!

A Digital Optical Module that us G.A.s got to sign last year

A few of the DOMs ready to be deployed on a cable

One of the last strings deployed last year

The DOMs are hung vertically and tensioned carefully so the cable bends around each sensor.

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