GRAA NEWSLETTER
P.O. Box 1184, Greenbelt, MD 20768-1184

IMPORTANT DATES

COMMENTS FROM TONY COMBERIATE, GRAA PRESIDENT: Our March luncheon speaker was Dr. Edward Wollack, an astrophysicist in GSFC’s Observational Cosmology Laboratory. His presentation is entitled “Postcards from the Edge: Developments in Infrared Astrophysics.” He specializes in the development and use of precision microwave and infrared imaging systems, cameras and detectors that map the structures and contents of the universe. He showed how maps of the Cosmic Microwave Background (CMB) radiation have become more defined as the sensitivity and observational strategies employing these instruments have evolved. The CMB is relic electromagnetic leftover from the formative stage of the universe. Today this glow is strongest in the microwave region of the spectrum. Tiny temperature variations imparted in the CMB 380,000 years after the Big Bang defined the age and composition of the universe. Two hundred million years later the first stars were formed. The age of the universe today is 13.7 billion years. Ed develops instruments (some using superconductive electronics operating as low as 100mK) that are able to make astronomical measurements accurate to a part per million. He explained how measurements are necessary because conditions are not always the way we expect them to be. Experiments enable scientific theories to be tested, confirmed, or refuted and thus expand our understanding of how things work.

Dr. Wollack traced the history of experiments that have observed the CMB. In the 1990s, NASA’s COBE (Cosmic Background Explorer) first mapped CMB temperatures and saw ‘bumps’ on angular scales of several degrees and demonstrated this background radiation had a black body spectrum. In 2003, WMAP (Wilkinson Microwave Anistropy Probe) measured the CMB temperature structure over the full sky with an angular resolution of 0.3 degrees. WMAP’s improved sensitivity, angular resolution, and systematic control enabled measurements which constrained the age and contents of the early universe. This is accomplished by comparing the amplitude of CMB variations on the sky as a function of angular scale (i.e., the so-called “angular power spectrum”) to theoretical prediction. The subsequent European Space Agency (ESA) Planck spacecraft, with a higher (0.1 degree) resolution and spectral coverage, refined the accuracy of this picture and expanded our understanding of astrophysical processes observed in the microwave and Terahertz.

Ed is now working on the next generation cameras with even higher sensitivity that will measure the polarization of the CMB. The scattering of light off of electrons in the plasma variations in the early universe (i.e., the so-called “last scattering surface” induces a linearly polarization signature. This scattered light encodes the conditions of the early universe through the patterns (i.e., compressional, vertical, and gravitational wave perturbations) present on the microwave sky today which can be contrasted with theoretical predictions. The gravity waves sensed in the CMB also help us understand the earliest structures and conditions in the early universe.

Ed’s detector development work has also contributed to measurements of the Milky Way galaxy. The HAWC+ (High-resolution Airborne Wideband Camera+) instrument on the SOFIA (Stratospheric Observatory for Infrared Astronomy) airborne telescope is a polarimeter that uses a focal plane with superconducting sensors to measure the polarization of dust at galactic center in the far infrared band. Similar detector systems will be used in the HR (High Resolution Mid-Infrared Spectrometer) to understand the kinematics of water vapor and oxygen in protoplanetary disks.

Ed concluded his presentation by discussing the WFIRST (Wide Field InfraRed Survey Telescope), a NASA astrophysics flagship mission in development which will measure the expansion history and growth of structure in the universe. This aspect of WFIRST science largely focuses on the period spanning 8 to 11 billion years in the past; however, the system’s imaging capabilities have more general utility for astronomical observations in the infrared by guest observers. WFIRST will look at over 38 million galaxies, covering a field of view 100 times greater than Hubble Space Telescope and with a higher resolution. It will investigate both Dark Energy, the repulsive force that affects the universe expansion speed, and Dark Matter, which is affected by the attractive force of gravity which causes objects to move toward each other. WFIRST, to be launched in late 2025, will also perform a statistical census of exoplanetary systems in the Milky Way galaxy. Dr. Wollack ended his talk by explaining how an adiabatic demagnetization refrigerator attains temperatures below one degree Kelvin, which is the operating temperature required by several of the instruments he designs.