We Timed a Cosmic Explosion. It Might Solve Dark Energy.

Quick Overview

The Time Delay Cosmography (TDCosmo) program using strongly lensed supernovae like SN Refsdal provides an independent measurement of the Hubble Constant (H0) that is inconsistent with, yet complementary to, measurements from the Cosmic Microwave Background (CMB), suggesting that new physics might be required to resolve the Hubble Tension if systematic errors are ruled out.

Key Points: The 2014 observation of the gravitationally lensed supernova SN Refsdal, magnified by the MACS J1149.5+2223 galaxy cluster, allowed astronomers to measure the time delay between its four images. The time delay measurement, combined with the geometry of the lens, yields a Hubble Constant (H0) value of 71.6+3.9-3.3 km/s/Mpc (using the full HOLiCOW analysis), which is high compared to the CMB-derived value. The technique of Time Delay Cosmography (TDCosmo) relies on observing the time difference between multiple images of a transient source (like a supernova or quasar) caused by gravitational lensing. Two main challenges exist for TDCosmo: the rarity of good strongly lensed quasars and the difficulty in accurately modeling the mass distribution (including dark matter) of the lensing galaxy. The Holy Cow collaboration's 2019 measurement using six strongly lensed quasars yielded H0 = 73.3+1.8-1.7 km/s/Mpc, which is inconsistent with the CMB result, suggesting a probability of less than 1 in 10 million that the discrepancy is due to random noise. New surveys like the Vera C. Rubin Observatory's LSST aim to find thousands of new lensed quasars, which will significantly reduce the uncertainty in H0 measurements derived from this method. The DESI survey is also measuring baryon acoustic oscillations to provide an independent, complementary measurement of the expansion history.

Context: This video explains the 'Hubble Tension'—the significant disagreement between measurements of the universe's expansion rate (the Hubble Constant, H0) derived from early universe data (like the Cosmic Microwave Background, CMB) and those derived from late universe measurements (like Type Ia supernovae). The video focuses on an alternative, independent method called Time Delay Cosmography (TDCosmo), which utilizes the time delays between multiple images of gravitationally lensed objects, specifically supernovae like SN Refsdal, to measure H0.