- 4576
- HUBBLE TENSION
- how fast is Universe
expanding? The “Hubble Tension' is the
dilemma that the expansion rate for the Universe seems to be different
depending on what direction you look or how you measure it. The 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.
-
------------------=-=---------- 4576
- HUBBLE TENSION
- how fast is Universe
expanding?
-
- New measurements taken with JWST have
deepened the scientific controversy of the “Hubble tension”, suggesting it may
not exist at all. For years,
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.
-
- When JWST came online in 2022, one team of
researchers used the space telescope's unprecedented accuracy to confirm the
tension exists. But according to the new results from a different team of
scientists, the Hubble tension may arise from measurement error and be an
illusion after all. Yet even these results are not definitive.
-
- Currently, there are two gold-standard
methods for figuring out the “Hubble constant of Universe expansion rate” a
value that describes this expansion rate. The first involves poring over tiny
fluctuations in the cosmic microwave background which is 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 “46,200 mph per million
light-years”, or around “67 kilometers per second per megaparsec (km/s/Mpc)”.
This, alongside other measurements of the early universe, aligned with many
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.
-
- Astronomer 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.
-
- But some previously 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, they 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.
-
- To make a measurement of Cepheid stars you
get the star colors wrong, you get the dust correction wrong, you get the
metallicity correction wrong. And, you get a different expansion rate.
-
- Astronomers believe 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.
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 15, 2024 HUBBLE
TENSION - how fast is Universe expanding? 4576
------------------------------------------------------------------------------------------
-------- Comments appreciated and Pass it on to
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--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for
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--- to:
------ jamesdetrick@comcast.net ------
“Jim Detrick” -----------
--------------------- --- Tuesday, October 15,
2024
---------------------------------
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