Astronomers are confused about why the universe is expanding

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

The universe around us may appear unchanging, but everything we see is moving away at a speed 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 observe remnants of the early universe, such as remnants of light in the cosmic microwave background radiation or sound waves frozen in time.

Another method is to measure distances to objects with known intrinsic brightness, such as type Ia supernovae, or Cepheid variable stars, whose light fluctuates with a regularity related to their intrinsic brightness.

Variable Cepheid distance measurements taken by Hubble (gray) and JWST (red). (NASA, ESA, CSA, J. Kang/STScI; Science: A. Rees/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. The discrepancy between the two is known as the Hubble effort.

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.

“[Variáveis ​​Cefeidas] It is the gold standard instrument for measuring the distances of galaxies 100 million light-years or more away, and is a crucial step in determining the Hubble constant. “Unfortunately, stars in galaxies are crowded into a small space from our distant view, so we often don’t have the resolution to separate them from their line-of-sight neighbors,” explains astrophysicist Adam Rees of Space Telescope Science. STScI and Johns Hopkins University.

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

To eliminate any dust blocking light near the visual field, these observations must be made in the near infrared, a part of the electromagnetic spectrum in which Hubble is not particularly strong.

The James Webb, 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 reliable result. (NASA, ESA, J. Kang/STScI; Science: A. Reiss/STScI)

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

Although the Hubble data were very noisy, the ranging data still agreed with the James Webb Space Telescope observations. This means that we cannot rule out H0 calculations based on the Hubble data; There are still 73 kilometers per second per megaparsec yet, and human error – at least in this case – cannot explain the Hubble lineage.

We still don’t know what causes stress. One prime candidate force is dark energy, a mysterious, unknown but seemingly fundamental force that appears to exert negative pressure that accelerates the expansion of the universe. And with James Webb’s new measurements, we may be a little closer to the answer.

“With Webb’s confirmation of the Hubble measurements, 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 lineage,” says Reiss.

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

Translated by Matthews Lineker from Science Alert