How fast is the Universe expanding?
In the past two decades, scientists have measured the “Hubble constant”—the rate at which the Universe is expanding—in two different ways. They have come up with different answers, wondering if something is missing from our model of how the Universe works.
However, according to new measurements from the James Webb Space Telescope, there may not be a conflict, also known as the ‘Hubble tension,’ after all.
After analyzing Webb data, University of Chicago cosmologist Wendy Freedman and her colleagues measured the distance to ten nearby galaxies and a new value for the Hubble Constant. Their measurement—70 kilometers per second per megaparsec—overlaps the other major method for the Hubble constant.
Freedman, a renowned astronomer and the John and Marion Sullivan University Professor in Astronomy and Astrophysics at the University of Chicago said, “Based on these new JWST data and using three independent methods, we do not find strong evidence for a Hubble tension. To the contrary, it looks like our standard cosmological model for explaining the evolution of the Universe is holding up.”
“Confirming the reality of the Hubble constant tension would have significant consequences for fundamental physics and modern cosmology.”
When making these measurements, scientists test them with different methods to ensure they’re as accurate as possible.
Cosmic Microwave Background, or CMB, is one major approach to determining the remnant light from the aftermath of the Big Bang. This method’s current best estimate of the Hubble constant, which is very precise, is 67.4 kilometers per second per megaparsec.
Another approach involves using stars’ brightness to measure the expansion of galaxies in our local cosmic neighborhood. Measuring the distances and speeds at which the galaxies are moving away from us tells us how fast the Universe is expanding.
This method previously gave a higher Hubble constant value—around 74 kilometers per second per megaparsec.
This is a huge difference. According to scientists, something significant might be missing from our standard Universe evolution model. This apparent mismatch has become known as the ‘Hubble tension.’
Scientists used Webb’s data to measure ten nearby galaxies, which provided a foundation for measuring the Universe’s expansion rate.
They used three different methods to verify their results. The first method uses a type of star known as a Cepheid variable star, which varies predictably in brightness over time.
The second method, called the “Tip of the Red Giant Branch,” measures the brightness limits of low-mass stars. The third method uses carbon stars, which have stable colors and brightnesses in near-infrared light. The new analysis combines all three methods, using them within the same galaxies for the first time.
In each case, the values were close to the 67.4 kilometers per second per megaparsec result from the cosmic microwave background method, falling within its margin of error.
“Getting good agreement from three completely different types of stars to us, is a strong indicator that we’re on the right track,” said Freedman.
“Future observations with JWST will be critical for confirming or refuting the Hubble tension and assessing the implications for cosmology,” said study co-author Barry Madore of the Carnegie Institution for Science and visiting faculty at the University of Chicago.
Journal Reference:
- Wendy L. Freedman, Barry F. Madore, In Sung Jang, Taylor J. Hoyt, Abigail J. Lee, Kayla A. Owens. Status Report on the Chicago-Carnegie Hubble Program (CCHP): Three Independent Astrophysical Determinations of the Hubble Constant Using the James Webb Space Telescope. The Astrophysical Journal. DOI: 10.48550/arXiv.2408.06153
