Cornell researchers build telescopes to measure universe’s earliest light
By Rick Ryan
Teams of scientists, including researchers from the Cornell physics and astronomy departments, are collaborating on two of the largest telescopes ever built to take readings on the universe’s oldest light measurable, known as the Cosmic Microwave Background, or CMB.
These telescopes will be placed in the Atacama Desert of Northern Chile and will give scientists new tools to record the earliest signals from the universe.
“These telescopes will play a critical role in searching for signatures from gravitational waves in the early universe and measuring gravitational lensing of the CMB in coming decades,” said Mike Niemack, assistant professor of physics. “In addition to constraining models of the early universe, we will help measure the neutrino masses, because they affect how structures grow, and we could find evidence for alternative forms of dark matter in the early universe.”
The Simons Observatory, a collaborative effort of more than 40 institutions from around the world, including Cornell, recently announced it will be building one of these instruments; a new 6-meter aperture telescope in Chile in addition to multiple 0.5-meter aperture telescopes to measure the CMB polarization. These new telescopes will be built concurrently with the Cornell-led Cerro Chajnantor Atacama Telescope-prime (CCAT-prime), announced last year.
The CMB, which formed 380,000 years after the Big Bang, is flush with information about the exponential expansion of the universe a fraction of a second after the Big Bang. During this expansion, powerful gravitational waves propagated through space. Later, the gravitational waves left signatures on the CMB that have the potential to reveal vital information about the physics that drove the initial expansion.
With the Simons Observatory, scientists will search for these signatures by combining CMB measurements from both the 6- and 0.5-meter aperture telescopes, which could rule out a large number of theoretical models and point physicists toward an accurate description of the high-energy physics of the early universe.
Both the 6-meter Simons Observatory telescope and the CCAT-prime telescope are based on a configuration that was first proposed in the 1970s by Corrado Dragone of Bell Labs, and tailored by Niemack and colleagues for telescopes of this large scale. Each immense telescope will consist of two high-precision reflective mirrors with a 6-meter (nearly 20-foot) diameter. This design allows for an expanded field of view across the sky to enable ultra-precise CMB measurements, thereby reducing uncertainty in measurements of fluctuations in the temperature and polarization of CMB light, a benchmark in the field of cosmology.
The speed with which scientists can reduce this uncertainty is directly proportional to the number of detectors that they can deploy in each telescope. These two telescopes combined will be able to house 10 times more detectors than any current telescope.
Prior to this new design, collaborations were looking to simply build more telescopes with current technologies in order to capture the same amount of information as these two instruments.
“We are collecting about as much data as we can with current telescopes, while pushing the superconducting detector arrays we deploy on these telescopes to the fundamental noise limits,” Niemack said. “Our new telescopes will allow scaling up these detector arrays and measurements by an order of magnitude to achieve better precision.”
The Simons Observatory telescope is optimized for CMB polarization surveys. It is designed to observe wavelengths of 1 to 15 millimeters, where the far-off cosmic signals are most easily seen. In addition to the 6-meter aperture telescope, the Simons Observatory is building 0.5-meter (20-inch) aperture telescopes optimized to search for gravitational wave signatures. These measurements are complemented by CCAT-prime, which will pursue measurements at some overlapping wavelengths, even shorter submillimeter wavelengths, and spectroscopic measurements to study a variety of different astrophysical phenomena. Cornell graduate and undergraduate students are working with faculty on developing the science cases and instrumentation for both Simons Observatory and CCAT-prime.
The inventive “crossed-Dragone” optical design of each telescope will deliver a wide field of view capable of illuminating more than 100,000 millimeter-wavelength detectors, and many more at submillimeter wavelengths, so that large areas of the sky can be scanned rapidly.
Both instruments will be placed at high elevations in the Atacama Desert of northern Chile, the current home of the Atacama Cosmology Telescope (ACT) and the Simons Array. Here, the CMB can be observed with lower noise, due to the reduced oxygen and water in the atmosphere. The Simons Observatory telescope will be located next to the ACT at 17,000 feet above sea level, while CCAT-prime will be built near the top of Cerro Chajnantor, at 18,400 feet above sea level.
Both the Simons Observatory 6-meter telescope and CCAT-prime are being designed and built by Vertex Antennentechnik GmbH, furthering the efficiency of design and collaboration between the two projects. The construction phase is scheduled to start in late 2018 and is expected to lead to “first light” for both projects in 2021. Each has its role to play in CMB research while also serving as crucial test beds for further developments in astronomical instrumentation.
While Cornell is the lead institution of CCAT-prime and also a major collaborator in the Simons Observatory, Niemack explains that there is a conscious effort to minimize competition between the two projects.
“Early on we decided to build first light instruments that are complementary,” Niemack said. “We will eventually observe the same wavelengths in the same regions of the sky with both telescopes, which will allow us to focus on improving the CMB sensitivity and really see the benefits of the two projects. This cooperation is important.”
The Simons Observatory is primarily supported by the Simons Foundation, the Heising-Simons Foundation and other member institutions.
Rick Ryan is a science communicator for CLASSE.