HERA: Unveiling the Cosmic Dawn

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Humanity's quest to understand the Universe and our place in it has led to some of the hallmark scientific and technical achievements of our time. These include the discovery of the Cosmic Microwave Background, the discovery of the accelerating expansion of the Universe, and the use of a variety of observational techniques to characterize the cosmology of the Universe. Scientists have measured the six key cosmological parameters that govern the geometry of the Universe with great precision, but they have not yet connected the dots to understand how the seeds of early structure from the Big Bang evolved into the stars, galaxies, and black holes seen today in the local Universe. In particular, there are very few observations of a period known as the "Cosmic Dawn" when the Universe was approximately 100 to 1000 million years old. During the Cosmic Dawn, the first stars and galaxies formed out of a pristine hydrogen gas that was synthesized during the Big Bang. As stars lit up, burned, and exploded in supernovae, the energy they released started to heat and then ionize the hydrogen that was not yet trapped in galaxies. Today, astronomers observe that nearly all hydrogen between galaxies has been re-ionized into a plasma state. The time when this happened is called the Epoch of Reionization. This project will use the Hydrogen Epoch of Reionization Array (HERA), a purpose-built telescope, to measure and characterize the Universe from the Cosmic Dawn to the Epoch of Reionization, to fill in this critical gap. Astronomy has broad interest throughout society and serves as an excellent introduction to science and technology for young people. In order to bring this impact to under-served students HERA has instituted an undergraduate outreach program called CHAMP, which serves as a significant summer internship program for underrepresented minorities at HERA partner institutions. HERA is an international project with Partners in the US, UK, Canada, Italy and South Africa. The telescope is well under construction in the Karoo region of Northern Cape South Africa at the South African Radio Astrophysical Observatory's Karoo Astronomy Reserve. Starting in 2019, HERA will comprise 350 14-m antennas in close proximity to one another and operate from 50-250 MHz. The Karoo location has been established as a special "radio-quiet" zone, meaning that efforts are undertaken to minimize the impact of the radio frequency emission that humans generate through our technology. Currently operational, HERA is measuring the emission due to the red-shifted hyperfine transition of hydrogen gas, which has a rest frequency of 1420 MHz. The expansion of the Universe redshifts these frequencies down to 50-250 MHz at the age of the Universe expected for the Cosmic Dawn and Epoch of Reionization. Given the expected structure of the gas over these redshifts, the signal is expected to be spectroscopically distinguishable from the much brighter foreground, which is predominantly spectrally smooth emission from our Galaxy's synchrotron radiation. Given its sensitivity and special-purpose design, HERA is expected to accurately measure the reionization fraction over this span of epochs. This measurement will allow us to understand the cosmology and astrophysics of the Universe over this transitional portion of its history. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.