ERC Grant for Sherry Suyu: Cosmic Fireworks Première

Unravelling Enigmas of Type Ia Supernova Progenitors and Cosmology through Strong Lensing

December 04, 2017

End of November, the European Research Council announced that Sherry Suyu, research group leader at the Max Planck Institute for Astrophysics and member of the Max-Planck@TUM programme, is one of the awardees of the 2017 ERC Consolidator Grants. With this funding, Suyu can expand her group to study gravitationally lensed supernovae and find out more about their progenitors. Strongly lensed supernovae also provide an independent way of measuring the Hubble constant, which tells scientists about the rate of expansion of the Universe.

The first and only spatially-resolved strongly lensed Type Ia Supernova, iPTF16geu, discovered by Goobar et al. (2017). Left: HST image taken on 28 October 2016, showing four images of the same source around the foreground galaxy. Middle and right: Two different reconstructions from lens mass models of the system by More, Suyu, Oguri et al. (2017). 

For decades, cosmologists have used a certain type of stellar explosion, Type Ia supernovae (SNe Ia) to measure the distance to far-away galaxies and thus the rate of the expansion of the universe. Only in the past 10 years or so, however, they have started to use an additional cosmic effect to gain even more information: strong gravitational lensing. This occurs if a substantial mass concentration, e.g. a galaxy or galaxy cluster, lies between the source in a far-away galaxy and the observer on Earth. The light rays passing on different sides of the lens will then be bent and lead to multiple images of the same source. Additionally, if the source is intrinsically variable, e.g. lighting up as in the case of a supernova explosion, the multiple images will appear at different times due to the different optical path lengths of their light paths and gravitational delay by the lens. This time delay contains valuable information on the geometry of the Universe.

Gravitational lensing of the Type Ia Supernova iPTF16geu. The spacetime between the supernova (marked with a star symbol) and the observer (on Earth) is disturbed by the gravity of the lensing galaxy (in orange). The observer will see the host galaxy of the supernova form a ring-like structure in the background, and the supernova split into four images. As Type Ia Supernovae have a distinct light-curve shape, the time delay between the four images can easily be determined (bottom image).

The LENSNOVA project proposed by Sherry Suyu plans to capitalize on her experience in the field of strong lensing time delays. With the aid of lensing, SNe can be observed in their entirety with unprecedented temporal sampling. Observations of the beginning of SN explosions are key to revealing SN progenitors that have been under debate for decades. Strongly lensed SNe Ia also allow an independent measurement of the Hubble constant (H0) that sets the cosmic expansion rate. The independent measurement is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tensions in current H0 measurements. Thus, the LENSNOVA project will shed light on the natures of SNe Ia progenitors and dark energy, two of the greatest puzzles in the present era.

The advent of new, powerful telescopes such as the Large Synoptic Survey Telescope and the Euclid mission makes LENSNOVA particularly timely for building the first sample of a handful of strongly lensed SNe Ia. The ERC grant now enables Sherry Suyu to recruit further researchers for her team and to acquire the computing resources needed to capitalise on the new data. Thus, the project could potentially revolutionise both the fields of stellar physics and cosmology.

The reconstructed surface brightness distribution of the supernova host galaxy in Fig 1 from the best lens model. The location of the supernova is indicated with a blue star.

The ERC Consolidator Grants are awarded to outstanding researchers of any nationality and age in any field of research, with at least seven and up to twelve years of experience after PhD, and a scientific track record showing great promise. Research must be conducted in a public or private research organisation located in one of the EU Member States or Associated Countries. The funding (maximum of €2 million per grant), is provided for up to five years and mostly covers the employment of researchers and other staff to consolidate the grantees' teams. Proposals are evaluated by selected international peer reviewers who assess them on the basis of excellence as the sole criterion.

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