13/09/2023
In the time you read this, the universe got a bit bigger.
One of the goals of NASA's Hubble Space Telescope was to determine how fast the universe is expanding. Webb has now corroborated 30 years of Hubble data, deepening a persistent mystery: Why is the universe expanding so fast?
Scientists predicted how fast the universe is expanding based on “baby pictures” of the universe in the aftermath of the big bang. But Hubble's measurements suggested a faster expansion rate than what was predicted — a discrepancy known as the Hubble Tension.
The image here is a composite of Webb and Hubble data. It shows spiral galaxy NGC 5584, one of the galaxies involved in the Webb research team’s calculations of the universe’s expansion rate.
Hubble and Webb both calculated how fast the universe is expanding with the help of extremely bright, pulsating stars called Cepheids. Due to their known properties, these stars often serve as cosmic yardsticks for measuring distances in space.
Using the stars within galaxies as markers, astronomers can stack measurements in a “cosmic distance ladder.” They start with measurements of actual distances to nearby galaxies, then move to galaxies farther and farther out. Then they use these values, along with measurements of the galaxies’ light, to ultimately determine how fast the cosmos expands over time.
Hubble has the ability to single out Cepheids in a crowded star field, but it primarily sees in visible light. This presents an issue when cosmic dust can absorb and scatter visible light, making distant objects look farther away than they actually are. Enter Webb. Its sharper infrared vision cuts through the dust, and it more clearly isolates Cepheid stars. While Webb’s data has less noise, the results match Hubble's — indicating that any potential Hubble inaccuracy was not the source of the Hubble Tension.
What could be causing the discrepancy instead? Learn more: https://go.nasa.gov/3r7tXVz
Credit: NASA, ESA, A. Riess (STScI), W. Yuan (STScI).
