The Cylinder Radio Telescope:Observing the CMB

Paul A. FleinerPh 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 trans-Atlantic 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 throughtime

– 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 ftTelescope, circa1960

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