New observations by the James Webb Space Telescope confirm the accuracy of the universe’s expansion rate measured by its predecessor, Hubble.
The rate of expansion of the universe, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the universe. However, a constant difference called “Hubble tension” is observed between the value of the constant measured by a wide range of independent distance gauges and its value predicted from the afterglow of the Big Bang.
Before Hubble’s launch in 1990, the rate of expansion of the universe was so uncertain that astronomers were unsure whether the universe had expanded in 10 billion or 20 billion years. This is because a faster expansion rate leads to a younger age of the universe, and a slower expansion rate leads to an older age of the universe.
Hubble has better visible wavelength resolution than any ground-based telescope because it overcomes the obscuring effects of Earth’s atmosphere. As a result, it can identify individual Cepheid variable stars — which have provided the most accurate distance measurements for more than a century because they are so bright — that are more than a hundred million light years apart and measures the time interval in which they change their brightness.
“However, we also need to observe Cepheids in the near-infrared part of the spectrum to see the light passing unharmed through the intervening dust. (Dust absorbs and scatters blue optical light, creating distant something that seems to weaken and deceive us.) they are further away than they are),” Adam Riess of John Hopkins University, who led the new research with Webb, explained in a statement.
Unfortunately, Hubble’s view of red light is not as sharp as blue, so the light from Cepheid stars mixes with other stars in its field of view.
“However, the sharp infrared vision is one of the superpowers of the James Webb Space Telescope. With its large mirror and sensitive optics, it can easily separate Cepheid light from neighboring stars with little that mix,” Riess explained.
In the first year of Webb’s operations, observations of Cepheids found by Hubble were collected in two steps along the so-called cosmic distance ladder: a series of different methods for making distance measurements- on to bigger things.
The Webb measurements greatly reduced the noise of the Cepheid measurements due to the observatory’s resolution at near-infrared wavelengths. Observing more than 320 Cepheids confirmed that earlier Hubble Space Telescope measurements were accurate, albeit noisier.
“Webb’s measurements provide the strongest evidence yet that systematic errors in Hubble’s Cepheid photometry do not play a significant role in Hubble’s current tension. As a result, the most interesting possibilities remains on the table and the mystery of the Hubble Strain deepens,” concluded Riess.
