CAREER: Towards Dark Energy -- A High-precision Drone-based Calibrator for Next-Generation 21cm Cosmology Experiments

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Measurements of the Universe over the last two decades have shown that nearly 75% of the Universe is made of a mysterious component: Dark Energy. Unlike "regular matter", Dark Energy seems to act against gravity and is causing the expansion of the Universe to accelerate. This is very confusing, and to explain it, we may have to re-write particle physics or perhaps even the laws of gravity. The best way to answer the question "What is Dark Energy?" is to measure the expansion of the Universe farther back in time. Recently astronomers realized that radio telescopes have the potential to make this measurement better than any other type of telescope. This has never been attempted before, and we are now building telescopes to achieve this goal. However, to be successful we need to understand the telescope "beam" (like a beam of light, a telescope points at one place and focuses there, and we must know what that beam looks like on the sky). For this CAREER grant, the PI is building radio sources to put on quadcopter drones to fly above the telescope. Using the radio telescope data, the location of the drone (with special position sensors), and some new analysis techniques, we will make a map of our telescope beam. The end result will be an important measurement that helps us understand Dark Energy better. The accelerated expansion of the Universe was discovered from supernova measurements in 1998 and no fundamental theories for this acceleration have yet been experimentally verified. As a result, cosmologists inserted a new component ("Dark Energy") into our cosmological models, but the underlying theories to explain the accelerated expansion involve either (i) a modification to General Relativity or (ii) a new particle which would predict a unique time dependence of the expansion rate. Either would revolutionize our current models of fundamental theories of physics. To answer these questions we must measure the expansion history of the Universe across the past 11 billion years and pin down the influence of Dark Energy on the expansion. The most promising path for this comes from measurements of galaxies (measuring 100, 000 galaxies across a wide swath of the sky). Unfortunately, current and next-generation optical galaxy surveys are restricted in how far back in time they can see due to limitations in detector technology. Radio telescopes do not have these limitations, and offer a promising solution to make radio surveys of galaxies across most of cosmic time. This measurement has never been attempted before and we are now building radio telescopes designed to achieve this goal. However, we already know that to be successful we must understand our telescope characteristics extremely well, in particular the telescope "beam" (like a beam of light, a telescope points at one place and focuses there, and we must know what that beam looks like on the sky). For this CAREER grant, the PI is developing a beam mapper using a quadcopter drone. The PI's team will fly a radio source on the drone above the telescopes and use the radio data and drone position to make a map of the beam. This requires developing a stabilized noise source to be flown on the drone, improved sensors for better drone position accuracy, and new analysis techniques - particularly a mathematical transformation to use measurements made near the dish and infer what they look like on the sky. The end result will be an important measurement for cosmology radio telescopes and a beam mapping technique that is demonstrated to work at the high precision required for Dark Energy science goals.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.