- 4571 - WEBB TELESCOPE MYSTERIES? - James Webb Space Telescope results have revealed that there may not be a “Hubble tension” after all. But contradictions within the findings point to a deeper mystery. New measurements taken with JWST have deepened the scientific controversy of the Hubble tension, suggesting it may not exist at all.
------------------------------ 4571
- WEBB TELESCOPE
MYSTERIES
-
- Astronomers have found that the universe
appears to be expanding at different speeds depending on where they look, a
conundrum they call the “Hubble tension”. Some of the measurements agree with
our best current understanding of the universe, while others threaten to break
it.
-
- JWST
results are consistent with the standard model. There are two gold-standard methods for
figuring out the “Hubble constant”, a value that describes the expansion rate
of the universe. The first involves poring over tiny fluctuations in the cosmic
microwave background, an ancient relic of the universe's first light produced
just 380,000 years after the Big Bang.
-
- After mapping out this microwave hiss using
the European Space Agency's Planck satellite, cosmologists inferred a Hubble
constant of roughly 46,200 mph per million light-years, or around 67 kilometers
per second per megaparsec ( 67 km/s/Mpc). This, alongside other measurements of
the early universe, aligned with theoretical predictions.
-
- The second method operates at closer
distances and in the universe's later life using pulsating stars called
“Cepheid variables”. Cepheid stars are slowly dying, and their outer layers of
helium gas grow and shrink as they absorb and release the star's radiation,
making them periodically flicker like distant signal lamps.
-
- As Cepheids get brighter, they pulsate more
slowly, enabling astronomers to measure the stars' intrinsic brightness. By
comparing this brightness to their observed brightness, astronomers can chain
Cepheids into a "cosmic distance ladder" to peer ever deeper into the
universe's past.
-
- They measured the Hubble constant using the
Hubble Space Telescope and JWST, they found a puzzlingly high value of 73.2
km/s/Mpc. Hence the tension, a significant discrepancy between methods
measuring the expansion rate in the early universe and those in the more modern
one.
-
- Astronomers suggested that dust, gas and
other stars could be throwing off the brightness measurements of the Cepheids,
creating the appearance of a discrepancy where there isn‘t one at all.
-
- In the new study, to tease out a possible
systematic error in Cepheid crowding, astronomers trained JWST on 11 nearby
galaxies containing Type Ia supernovae, measuring their distances and anchoring
them to three independent distance ladders with intrinsic brightnesses in
similar regions of the sky: the Cepheids; and two other standard candle red
giant stars known as "tip-of-the-red-giant-branch" (TRGB) stars and
J-region asymptotic giant branch (JAGB) stars.
-
- Their results were puzzling. The TRGB and
JAGB stars gave Hubble constant results of 69.85 km/s/Mpc and 67.96 km/s/Mpc,
respectively. But the Cepheids returned 72.04 km/s/Mpc, replicating the Hubble
tension.
-
- The answer is to make even more
measurements, potentially some with an additional type of star. This work to be completed in the next two
years. Yet whether additional measurements will resolve the problem or add to
it is debated. JWST is a marvelous
machine, and it's exactly what we need to get at some of these kinds of issues.
It's a good time to be working on this.
-
-
October 4, 2024 WEBB
TELESCOPE MYSTERIES 4571
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--------------------- --- Saturday, October 5,
2024
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