The Cylinder Radio Telescope:
Observing the CMB
Paul A. Fleiner
Ph 70 Popular Presentation
May 10, 2011
Outline
• Radio Astronomy
• 21cm Baryon Acoustic Oscillations (BAOs)
• Cylinder Telescope
– Prototype
– Possible Sites
– Challenges
• Looking Ahead
Radio Astronomy: The Beginning
• Early Attempts
– Nikola Tesla, Oliver Lodge
– Attempted to observe radio emissions from the
sun
– Unsuccessful
• Technical Limits
Radio Astronomy
• First RA observations
– Karl Jansky, 1930s
– Bell Labs
Jansky’s Discovery
• Investigating source
of interference in
short-wave transAtlantic
transmissions
• Initially thought
source was solar
– Happened every 23
hours, 56 minutes
• Actually Milky Way
Modern Radio Telescopes
• Very Large Array (VLA)
– New Mexico, 1980
– $78.5m, ~$10,000/m2
• Square Kilometer Array
(SKA)
– Australia, 2024
– >$2b, $1,000/m2 (Target)
How do they work?
What We “See”
• Hydrogen atom moving away from us is
redshifted:
– f=700MHz
– λ=42cm
• Hydrogen atom at rest:
– F=1420MHz
– λ=21cm
Baryon Acoustic Oscillation (BAO)
• Method of tracking expansion of universe
• About 400,000 years after Big Bang
– Universe expanded, temperature cooled
– Electrons and protons combine to form H
• Photons no longer Thompson scattered
• Observing these photons gives us a “ruler” for
measuring expansion
BAO
• Can use the ruler to
plot the redshift
– Can create a 3D
mapping of the
universe through
time
– Measure the
expansion
– Will help us quantify
“dark energy”
Cylinder Radio Telescope
• Popular from 1960-1980
• Abandoned in favor of devices with
cryogenically cooled pre-amps
• Illinois 400 ft
Telescope, circa
1960
CRT Enabling Technology
• Low Noise Amplifiers (LNAs) are much cheaper
• T<<300K
• Increased capabilities of Analog to Digital
Converters (ADCs)
• Better Digital Signal Processing
• GPUs, FPGAs
• More sophisticated FFTs (N log N)
• High speed, low power, low cost
• Reduces the cost to ~$100/m2
CRT Design
• Parabolic half-cylinders
• Focuses radio waves radially inward
– Strikes axial array of antennas
• Key Requirements
– High Resolution
• Overall array size, time observed
– Large Sky Coverage
• Number of channels
– Large Redshift Range
• Bandwidth
CMU Prototype
• Built by Prof. Peterson’s group in Pittsburgh
Goal Design
• Array of 10 cylinders
– 10m wide, 100m long
• Coverage
– 20,000 sq. degrees
• Frequency Range
– 300-1500MHz
• Bandwidth
– >200MHz
Challenges
• Synchrotron frequency, free-free emission
– Total 21cm signal is ~300µK
– 21cm BAO signal is only ~300nK
• Instrument Calibration
• Environment Calibration
– RF Interference
• Far from power lines, most electronics
Possible Sites
• Several in Morocco
Moving Forward
• Model removal of foreground noise
• Build 2 to 3 cylinders
– 10m wide, 50m long
• Set up larger prototypes in less noisy place
• Actually remove noise
Acknowledgements
• Professor Jeff Peterson, CMU
• Kevin Bandura, PhD Candidate
• Bruce Taylor, Communication and Facilities
Consultant