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Increasing Accuracy in Measurements of the Hubble Constant:

Is There Evidence for New Physics?”

Date:

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Time:

Thursday, 10 Feb. 2022

Video-Recording for any system with MP4-support

- Video.mp4 (ca. 0 Mb)

15:15 – 16:15

Speaker today: Wendy Freedman (University of Chicago)

Abstract:

An important and unresolved question in cosmology today is whether there is

new physics that is missing from our current standard Lambda Cold Dark Matter

(LCDM) model. Recent measurements of the Hubble constant, Ho – based

on Cepheids and Type Ia supernovae (SNe) -- are discrepant at the 4-5-sigma level

with values of Ho inferred from measurements of fluctuations in the cosmic

microwave background (CMB). The latter assumes LCDM, and the former

assumes that systematics have been fully accounted for.

If real, the current discrepancy could be signaling a new physical property

of the universe. I will present new results based on an independent calibration

of SNe Ho based on measurements of the Tip of the Red Giant Branch (TRGB).

The TRGB marks the luminosity at which the core helium flash in low-mass stars

occurs, and provides an excellent standard candle. Moreover, the TRGB method

is less susceptible to extinction by dust, to metallicity effects, and to crowding

blending effects than Cepheid variable stars.

I will address the current uncertainties in both the TRGB and Cepheid distance

scales, the promise of upcoming James Webb Space Telescope data, as well as

discuss the current tension in Ho and whether there is need for additional physics

beyond the standard LCDM model.

Brief CV

Wendy Freedman is the John & Marion Sullivan University Professor of

Astronomy & Astrophysics at the University of Chicago.

She is a member of the National Academy of Sciences in the US and was elected

Legacy Fellow of the American Astronomical Society in 2020.

She has won numerous prizes, including the Gruber Cosmology Prize in 2009.