James Webb in search of the Hubble constant

2023-09-23 06:00:03

The Universe, in perpetual expansion, keeps unsolved mysteries within it. One of the most intriguing is the “Hubble Tension”, a persistent mismatch between the theoretical and measured speed of the expansion of the Universe. New observations (Observation is the action of attentively following phenomena, without wanting to…) from the space telescope (A space telescope is a telescope placed beyond the atmosphere. The…) James Webb might, however, provide clarification.
This illustration shows how the Hubble and Webb space telescopes work to precisely measure the distances of certain special stars called “Cepheid stars.” These Cepheid stars are used to calibrate the speed of expansion of the Universe. They are often surrounded by other stars, which can make the measurement of their brightness less precise because of the light from neighboring stars.

Webb has sharper infrared vision which allows him to more clearly isolate a Cepheid star. 4 to 15 times more massive than the…) of other surrounding stars, as seen on the right side of the illustration. Webb’s data confirm the precision of Hubble’s 30-year observations of Cepheid stars. These observations are crucial to establishing the first step in measuring the rate of expansion of the universe, which is called the “cosmic distance scale”.

To the left of the illustration, NGC 5584 is seen in a composite image obtained using Webb’s NIRCam (near infrared camera) instrument and Hubble’s Wide Field Camera 3.

Crédit: NASA, ESA, A. Riess (STScI), W. Yuan (STScI).

The expansion rate of the Universe, called the Hubble constant, is a fundamental parameter for understanding its evolution and its ultimate fate. The “Hubble Voltage” manifests itself when the measured value of this constant differs from that predicted from the residual brightness of the Big Bang (The Big Bang is the dense and hot epoch that the universe experienced there is …).

Adam Riess, a Nobel laureate and researcher at Johns Hopkins University, used observations from the James Webb telescope to refine local measurements of the constant of Hubble. This space telescope is capable of separating the light of Cepheid-type variable stars from that of neighboring stars, which makes it possible to measure the distance of galaxies (Galaxies is a quarterly French magazine devoted to science fiction. With.. .) more precisely.

Cepheid variable stars have long served as the “standard candle” for measuring the distance of distant galaxies. These supergiants see their luminosity vary periodically, a phenomenon which is directly linked to their intrinsic luminosity.

With the Hubble Space Telescope, launched in 1990, astronomers were able to refine the measurements, but these data were still affected by various sources of uncertainty. The James Webb telescope, with its infrared vision, considerably improves the quality of measurements.

Comparison of Cepheid period-luminosity relationships used to measure distances. The red dots come from the Webb telescope, and the gray dots come from the Hubble telescope.
Crédit: NASA, ESA, A. Riess (STScI), et G. Anand (STScI).

However, even though Webb’s observations confirm previous Hubble measurements, they do not solve the mystery of the “Hubble Voltage.” Hypotheses are rife, from the presence of exotic dark energy to revisions in our understanding of gravity (Gravitation is one of the four fundamental interactions of physics.).
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