The JWST’s near-infrared camera (NIRCam) captured a mesmerizing sight in the galaxy cluster PLCK G165.7+67.0, located 3.6 billion light-years from Earth. Astronomers observed three distinct points of light originating from a single type Ia supernova. This cosmic illusion is the result of gravitational lensing, where the immense gravity of a foreground galaxy bends and magnifies the light from the distant supernova.
Type Ia supernovae occur when material from one star falls onto a white dwarf, triggering a massive thermonuclear explosion. These cosmic explosions are considered “standard candles” due to their consistent brightness, allowing astronomers to measure vast cosmic distances and calculate the Hubble constant.
The observed supernova, dating back 10.2 billion years, provides a unique opportunity to study the early universe and its expansion. By analyzing the time delays between the three lensed images and incorporating them into gravitational lensing models, researchers have obtained a new measurement of the Hubble constant.
The Hubble tension : A cosmic conundrum
The latest findings from the JWST add another layer to the ongoing debate surrounding the Hubble tension. This perplexing issue arises from conflicting measurements of the universe’s expansion rate, depending on which part of the cosmos is observed. The discrepancy threatens to undermine our current model of the universe.
There are two primary methods for determining the Hubble constant :
- Analyzing fluctuations in the cosmic microwave background
- Measuring distances using Cepheid variable stars
The cosmic microwave background method yields an expansion rate of approximately 67 kilometers per second per megaparsec (km/s/Mpc), aligning with predictions from the standard model of cosmology. However, measurements using Cepheid variables produce a significantly higher value of 73.2 km/s/Mpc.
The new study using the gravitationally-lensed supernova observed by JWST has yielded a Hubble constant value of 75.4 km/s/Mpc (with a margin of error of +8.1 or -5.5). This result further contradicts the standard model and deepens the Hubble tension mystery.
Implications for our understanding of the cosmos
The persistent Hubble tension has profound implications for our comprehension of the universe’s fundamental nature. According to the standard model, a mysterious force known as dark energy should be driving the universe’s expansion at a constant rate. However, the conflicting measurements challenge this understanding.
Dr. Brenda Frye, an associate professor of astronomy at the University of Arizona and co-author of the study, emphasized the significance of their findings : “Our team’s results are impactful : The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young.”
To illustrate the various Hubble constant measurements, consider the following table :
| Method | Hubble Constant (km/s/Mpc) |
|---|---|
| Cosmic Microwave Background | ~67 |
| Cepheid Variables | 73.2 |
| JWST Lensed Supernova | 75.4 (+8.1/-5.5) |
As astronomers continue to grapple with this cosmic puzzle, the James Webb Space Telescope’s advanced capabilities offer new avenues for exploration. Researchers plan to gather additional data from other exploding stars throughout the galaxy, hoping to shed more light on this perplexing discrepancy in our understanding of the universe’s expansion.
The quest to resolve the Hubble tension remains ongoing, with various research groups pursuing different investigative approaches. As we delve deeper into the mysteries of the cosmos, the James Webb telescope’s observations of ancient supernovae replaying through cosmic time warps may prove instrumental in unraveling the enigma of universal expansion.
The Webb result has such a large margin of error that it doesn’t really disagree with the cepheid or the microwave measurements.