Project description
Variable stars could provide a cosmic yardstick for the accelerating Universe
New evidence shows that the Universe is expanding faster than expected as scientists cannot yet explain the discrepancy between their models and new measurements. It remains unclear whether this 'crisis in cosmology' should call for new physics to settle the controversy over the Hubble's constant or whether this value is subject to underestimated systematic errors. Many tools including variable stars, such as Cepheids, are used to calculate the expansion rate over time. The EU-funded H1PStars project will conduct research to mitigate biases that could shift the centre value of reported Hubble's constant measurements and quantify relevant systematic uncertainties. Project results could reinforce understanding of how solid the cosmic distance ladder is.
Objective
What's up with Hubble's constant (H0)? Recent H0 measurements have shown that the Universe is expanding faster than cosmology predicts, indicating a possible cosmological crisis. To wit, H0 measured to 1.9% precision in today's Universe using a cosmic distance ladder composed of classical Cepheids and type-Ia supernovae differs by 8.9% (4.2 sigma) from H0 predicted by cosmology based on observations of the Cosmic Microwave Background emitted 13.8 billion years ago. However, it remains unclear whether new physics must be invoked to reconcile cosmology with today's H0, or whether today's H0 is subject to as yet unknown or underestimated systematic errors. An unbiased 1% measurement of H0 is required to understand whether physics is on the brink of a major breakthrough.
So, how solid is our distance ladder? To answer this, my research seeks to a) mitigate biases that can shift the center value of reported H0 measurements, b) quantify relevant systematic uncertainties, and c) reinforce the foundation of the distance ladder through a solid astrophysical understanding of pulsating stars, in particular, classical Cepheids. These steps must be taken now to achieve an unbiased 1% H0 measurement and to ensure the legacy of today's distance ladder for future space-borne facilities and ground-based extremely large telescopes. Imminent data releases of the ESA mission Gaia and precise time series spectroscopy will provide unprecedented opportunity to calibrate the distance ladder and unravel the structure and evolution of Cepheids through their variability.
The H1PStars project will leverage my expertise in the astrophysics of classical Cepheids and the calibration of the distance ladder to support precision cosmology via accurate stellar physics, and vice versa. Thanks to this fresh perspective, my team and I will either reconcile the tension in H0 or confidently establish a need to revise cosmology.
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ERC-STG - Starting GrantHost institution
1015 Lausanne
Switzerland