- 4578 - JAMES WEBB - discoveries strange galaxies? 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. 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”.\
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- JAMES WEBB - discoveries strange galaxies?
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- 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.
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- 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. The CMB is an ancient relic of the universe's
first light produced just 380,000 years after the Big Bang.
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- 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 (km/s/Mpc). This, alongside other measurements of the
early universe, aligned with theoretical predictions.
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- 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.
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- 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.
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- The Hubble constant measured using the
Hubble Space Telescope and JWST 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.
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- It was 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.
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- In this study, to tease out a possible
systematic error in Cepheid crowding, astronomer 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.
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- 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.
-
- JWST confirms the earliest galaxy in the
universe is bursting with way more stars than we thought possible. Named JADES-GS-z14-0, the galaxy formed at
least 290 million years after the Big Bang, and contains stars that have been
bursting into life since an estimated 200 million years after our universe
began.
-
- These mysterious origins and rapid
development of the stars has opened up some fundamental questions about how our
universe came to be. The discovery by
JWST of an abundance of luminous galaxies in the very early Universe suggests
that galaxies developed rapidly, in apparent tension with many standard models.
-
- Astronomers aren't certain when the very
first globules of stars began to clump into the galaxies we see today, but
cosmologists previously estimated that the process began slowly within the
first few hundred million years after the Big Bang.
-
- Current theories suggest that halos of dark
matter (a mysterious and invisible substance believed to make up 85% of the
total matter in the universe) combined with gas to form the first seedlings of
galaxies. One billion to 2 billion years into the universe's life, these early
protogalaxies reached adolescence, forming into dwarf galaxies that began
devouring one another to grow into ones like our own.
-
- In February 2023, a group of astronomers
analyzing data from the telescope discovered a group of six gargantuan
galaxies, aged between 500 to 700 million years after the Big Bang, that were
so massive they were in tension with 99% of cosmological models.
-
- The light from JADES-GS-z14-0 is similarly
puzzling. The light detected by NIRSpec
finds its origins in an enormous halo of young stars surrounding the galaxy's
core, which have been burning for at least 90 million years before the point of
its observation. The galaxy is also crammed with unusually high quantities of
dust and oxygen, which suggests its history of star birth and death may be even
longer.
-
- This finding shows that ultra-bright
galaxies in the early universe are not just the product of active black holes
greedily gobbling up matter, as is often assumed to be the case. The new
observations show that runaway star formation is also a viable explanation for
the surprising brightness of these ancient galaxies.
-
- So how did galaxies like JADES-GS-z14-0
produce so many stars, so quickly? Answers to this cosmic mystery remain
elusive, but it's unlikely they will break our current understanding of
cosmology. Instead, astronomers are toying with explanations that include the
earlier-than-anticipated appearance of giant black holes; supernova feedback;
or even dark energy to understand why these ancient stars were able to form so
rapidly.
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-
October 17, 2024 JAMES
WEBB - discoveries strange galaxies? 4578
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