Thursday, March 08, 2018 at 2:00 pm

JILA Auditorium

Raul Monsalve, CU Boulder

"Detecting the Fingerprints of the First Stars"

Abstract:

The first stars in the Universe formed before 100 million years after the Big Bang, which marks the transition from the "Dark Ages" into "Cosmic Dawn". They formed due to the gravitational collapse of primordial neutral hydrogen gas left over after the release of the cosmic microwave background (CMB). The UV radiation that these stars produced penetrated the atoms of the surrounding neutral hydrogen gas, which caused the gas to absorb photons from the CMB. This impact on the hydrogen gas should be observable today as an absorption feature in the radio spectrum at frequencies below 200 MHz. In this talk I will describe the detection by the EDGES experiment of an absorption feature centered at 78 MHz in the sky-averaged spectrum. This feature is compatible with the expected timing for the impact of the first stars on the hydrogen gas, approximately 180 millions after the Big Bang. However, the amplitude of the observed signal is ~0.5 K, twice as large as expected. New theories have already been proposed that could produce this deeper absorption. Two leading options correspond to a higher radiation background than previously thought during Cosmic Dawn, and a new form of interaction between the hydrogen gas with the colder dark matter. I will review the theory of this cosmological radio measurement and describe the EDGES experiment, including the instruments used for the detection and the data analysis. I will also present exciting developments at CU Boulder to measure this signal from the pristine environment of the lunar farside. From that environment, and with the technology and techniques under development, not only the signal from Cosmic Dawn will be precisely characterized, but new predictions indicate that the radio measurements could even access the Dark Ages themselves, which would represent a revolutionary step forward for cosmology.

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