September 24, 2023

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The James Webb Space Telescope has just measured the expansion rate of the universe.  Astronomers are confused.  Science alert

The James Webb Space Telescope has just measured the expansion rate of the universe. Astronomers are confused. Science alert

The James Webb Space Telescope has measured the expansion rate of the universe, and the results are not great news for the biggest crisis in cosmology.

This result is consistent with measurements made by the Hubble Space Telescope. This means that there is nothing wrong with the Hubble data, and we are still at a dead end.

There’s still disagreement between different measurement methods known as Hubble tensor, so we’ll have to rely on another way to figure out how fast the universe is expanding.

The universe around us may appear to be stationary, unchanged, but everything we see is moving away at an enormous rate known as the Hubble Constant, or H0. It’s unclear exactly how fast H0 is, because different ways of measuring it give different results.

One way is to look at traces of the early universe, such as residual light in the cosmic microwave background, or sound waves frozen in time.

Another way is to measure distances to objects with known intrinsic brightness, such as type Ia supernovae, or Cepheid variable starswhose light fluctuates regularly, which is related to its intrinsic brightness.

Variable Cepheid distance measurements taken by Hubble (gray) and JWST (red). (NASA, European Space Agency, Canadian Space Agency, c. Kang/STScI; Science: A. Res/STScI)

The first method tends to return an expansion rate of about 67 kilometers per second per million parsecs. The second, about 73 kilometers per second per megaparsec. This discrepancy between the two is known as the Hubble tension.

These measurements were made repeatedly, greatly reducing the chances of error in each of the estimates. However, there remains the possibility that there is something misleading about at least some of the data – especially since some of the best data we have on Cepheid variables comes from a single source, the Hubble Space Telescope.

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“[Cepheid variables] It is the gold standard instrument for measuring distances between galaxies 100 million light-years or more away, and is a crucial step in determining the Hubble constant. “Unfortunately, stars in galaxies are clustered together in a small area from our distant viewpoint, so we often lack the resolution to separate them from their line-of-sight neighbors.” Astrophysicist Adam Ries explains Space Telescope Science Institute (STScI) and Johns Hopkins University.

“The main justification for building the Hubble Space Telescope was to solve this problem… Hubble has better visible wavelength resolution than any ground-based telescope because it lies above the hazy effects of Earth’s atmosphere. As a result, it can identify individual Cepheid variables in galaxies more than a hundred kilometers away.” million light-years and measuring the time interval over which its brightness changes.”

In order to cut off any light blocking dust near the light These observations must be made in the near infrared, a part of the electromagnetic spectrum in which Hubble is not particularly strong. This means that there is still some uncertainty about the data he obtained.

The James Webb Space Telescope, on the other hand, is a powerful infrared telescope, and any data it collects is not subject to the same limitations.

A diagram showing the difference between Hubble and JWST observations, and how combining them yields a more confident result. (NASA, European Space Agency, c. Kang/STScI; Science: A. Res/STScI)

Rees and his team first turned the James Webb Space Telescope into a galaxy of known distance, to calibrate the telescope for Cepheid variable illumination. Then they noticed Cepheids in other galaxies. In all, the James Webb Space Telescope collected observations of 320 cepheid stars, greatly reducing the noise present in the Hubble observations.

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Although the Hubble data is very noisyHowever, the distance data were still consistent with observations from the James Webb Space Telescope. This means that we cannot rule out H0 calculations based on the Hubble data; The current speed is 73 kilometers per second per megaparsec at the moment, and human error – at least in this case – cannot explain the Hubble jitter.

We still don’t know the cause of the tension. One prime candidate is dark energy, a mysterious and little-known but seemingly fundamental force Apply negative pressure This accelerates the expansion of the universe. With new James Webb Space Telescope measurements, we may be a little closer to the answer.

“With Webb confirming the measurements from Hubble, Webb’s measurements provide the strongest evidence to date that systematic errors in Hubble’s Cepheid photometry do not play a significant role in the current Hubble jitter.” says Reese.

“As a result, the most interesting possibilities remain on the table and the ambiguity of tension deepens.”

The results were accepted in Astrophysical Journaland is available on arXiv.