- 4397
- WEBB -
finds a strange Universe? - James Webb telescope confirms there is
something seriously wrong with our understanding of the universe. Depending on where we look, the universe is
expanding at different rates. Now, scientists have confirmed that the
observation is not down to a measurement error.
------------------------- 4397 -
WEBB - finds a strange Universe?
-
- Astronomers have confirmed one of the most
troubling conundrums in all of physics that the universe appears to be
expanding at bafflingly different speeds depending on where we look.
-
- This problem, known as the “Hubble Tension”,
has the potential to alter or even upend cosmology altogether. In 2019,
measurements by the Hubble Space Telescope confirmed the puzzle was real; in
2023, even more precise measurements from the James Webb Space Telescope (JWST)
cemented the discrepancy.
-
- There may be something seriously wrong with
our understanding of the universe. With
measurement errors negated, what remains is the real and exciting possibility
we have misunderstood the universe.
-
- Currently, 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 (CMB) which is
an ancient relic of the universe's first light produced just 380,000 years
after the Big Bang.
-
- Between 2009 and 2013, astronomers mapped
out this microwave fuzz using the European Space Agency's Planck satellite to
infer a Hubble constant of roughly 46,200 mph per million light-years, or
roughly 67 kilometers per second per megaparsec (km/s/Mpc).
-
- The second method uses pulsating stars
called Cepheid variables. Cepheid stars are 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, giving astronomers a means to measure their absolute 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. With this ladder in place, astronomers can find a precise
number for its expansion from how the Cepheids' light has been stretched out,
or red-shifted.
-
- But this is where the mystery begins.
According to Cepheid variable measurements taken the universe's expansion rate
is around 74 km/s/Mpc: an impossibly high value when compared to Planck's
measurements. Cosmology had been hurled into uncharted territory.
-
- Initially, some scientists thought that the
disparity could be a result of a measurement error caused by the blending of
Cepheids with other stars in Hubble's aperture. But in 2023, the researchers
used the more accurate JWST to confirm that, for the first few
"rungs" of the cosmic ladder, their Hubble measurements were right.
-
- To resolve this issue astronomers built on
their previous measurements, observing 1,000 more Cepheid stars in five host
galaxies as remote as 130 million light-years from Earth. After comparing their
data to Hubble's, the astronomers confirmed their past measurements of the
Hubble constant.
-
- Combining Webb and Hubble gives us the best
of both worlds. We find that the Hubble measurements remain reliable as we
climb farther along the cosmic distance ladder.
The tension at the heart of cosmology is here to stay.
-
- Webb continues to confirm that Universe is
behaving strangely. Over a century ago,
astronomers Edwin Hubble and Georges Lemaitre independently discovered that the
Universe was expanding. Since then, scientists have attempted to measure the
rate of expansion (known as the Hubble-Lemaitre Constant) to determine the
origin, age, and ultimate fate of the Universe.
-
- This has proved very daunting, as
ground-based telescopes yielded huge uncertainties, leading to age estimates of
anywhere between 10 and 20 billion years! This disparity between these
measurements, produced by different techniques, gave rise to what is known as
the “Hubble Tension”.
-
- It was hoped that the aptly named Hubble
Space Telescope (launched in 1990) would resolve this tension by providing the
deepest views of the Universe to date. After 34 years of continuous service,
Hubble has managed to shrink the level of uncertainty but not eliminate it.
-
- This led some in the scientific community
to suggest (as an Occam’s Razor solution) that Hubble‘s measurements were
incorrect. But according to the latest data from the James Webb Space Telescope
(JWST), Hubble’s successor, it appears that the venerable space telescope’s
measurements were right all along.
-
- The Hubble Tension arises from the fact
that different distance measurements ( the “Cosmic Distance Ladder“) result in
different values. For the calibration of short distances or the first “rung” on
the ladder, astronomers rely on parallax measurements of nearby stars. For the
next “rung,” they rely on Cepheid variables and Type Ia supernovae to measure
the distances to objects tens of millions of light-years away. Distance
measurements for these stars by Hubble yielded a value of 252,000 km/h per megaparsec
(Mpc).
-
- The final rung consists of using redshift
measurements of the Cosmic Microwave Background (CMB) to calibrate distances of
billions of light-years. The mapping of this background by the ESA’s Planck
satellite yielded an estimate of about 244,000 km/h per Mpc (or about 269 km/s
per light year).
-
- The simplest explanation for the
discrepancy was that Hubble‘s measurements were inaccurate, perhaps because of
uncertainties in the Cosmic Distance Ladder. Since it was launched in December
2021, the JWST has made its own measurements of Cepheid variables with its
advanced infrared optics.
-
- This has allowed astronomers to cross-check
the optical-light measurements made by Hubble. Webb’s observations in 2023
confirmed that Hubble’s measurements of the expanding Universe were accurate.
-
- Their latest analysis was based on Webb’s
observations of over 1,000 Cepheids used as “anchors” in the distance ladder,
eight Type Ia supernovae, and NGC 5468, the farthest galaxy where Cepheids have
been well measured, roughly 130 million light-years distant.
-
- With measurement errors negated, what
remains is the real and exciting possibility that we have misunderstood the
Universe. We’ve now spanned the whole range of what Hubble observed, and we can
rule out a measurement error as the cause of the Hubble Tension with very high
confidence.
-
- Thanks to Webb’s sharp imaging capabilities
at infrared wavelengths, astronomers can now see through the obscuring dust and
get a clearer look at distant Cepheids. Combined with Hubble’s observations,
the team determined that Hubble‘s observations were correct. As a result
scientists are left with only one explanation for the Hubble Tension, which is
that there is an unseen force responsible for how the cosmos is expanding.
-
- Combining Webb and Hubble gives us the best
of both worlds. We find that the Hubble measurements remain reliable as we
climb farther along the cosmic distance ladder. We need to find out if we are
missing something on how to connect the beginning of the Universe and the
present day.
-
-
March 21, 2023 WEBB -
finds a strange Universe? 4397
------------------------------------------------------------------------------------------
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--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for
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------ “Jim Detrick” -----------
--------------------- --- Thursday, March 21,
2024
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