A Universe Speed Camera

The universe stretches beyond imagination. Even as you read these words, it continues to expand. However, this expansion isnt uniform. Objects farther from us drift away faster than those nearby. For every megaparsecroughly 3.3 million light-yearsthe recession speed increases by about 45 miles per second. This measurement is known as the Hubble Constant, named after Edwin Hubble, the astronomer who first identified the universes expansion in 1929.

Researchers at the University of Tokyo have introduced an innovative technique called time-delay cosmography to refine measurements of the Hubble Constant, with their results recently published in Astronomy & Astrophysics.

Traditionally, astronomers estimate the Hubble Constant using distance ladders. They start with a nearby cosmic objectsuch as a supernova or a starmeasure its properties, then examine progressively more distant objects to determine how fast they are receding from us.

Cosmic Distortion: Artificially colored illustrations show eight gravitational lens systems. Each image highlights a massive central galaxy, with surrounding bright spots representing quasars whose light is bent and magnified by the galaxys gravity. (Images by TDCOSMO Collaboration et al.)

Time-delay cosmography, on the other hand, leverages gravitational lensing. A massive galaxy acts as a natural lens, bending light from background quasars. By tracking changes in the distorted quasar images, astronomers can measure the difference in time it takes for light to reach Earth. Using this approach, the team obtained an expansion rate that aligns with the Hubble Constant.

This method may help address a longstanding puzzle known as the Hubble Tension. Observations with space telescopes typically yield a Hubble Constant of about 45 miles per second per megaparsec, while measurements based on the cosmic microwave background suggest a smaller value of roughly 42 miles per second per megaparsec. Scientists have debated whether this discrepancy is due to observational errors or reflects underlying cosmic physics.

Author: Grace Ellison