When you’re trying to solve one of the biggest puzzles in cosmology, you need to triple-check your homework. The mystery, called the Hubble tension, is that the universe is currently expanding faster than astronomers expect based on the initial conditions of the universe and our current understanding of its evolution. Astronomers using the NASA/ESA Hubble Space Telescope and many other telescopes are constantly discovering numbers that don’t match predictions based on observations from ESA’s Planck mission. Does this discrepancy require new physics to resolve, or is it a result of measurement errors between the two different methods used to determine the rate of expansion of space?
NGC 5468 is an image of a galaxy located approximately 142 million light-years away in the constellation Virgo, combining data from Hubble and Webb. Image credit: NASA / ESA / CSA / STScI / A. Riess, JHU & STScI.
One of the scientific justifications for building Hubble was to use its observational capabilities to provide accurate values for the rate of expansion of the universe.
Before Hubble’s launch in 1990, ground-based telescope observations were subject to large uncertainties. Depending on what we infer from the expansion rate, the age of the universe could be between 10 and 20 billion years old.
Over the past 34 years, Hubble has reduced this measurement to less than 1% accuracy, dividing the difference by an age value of 13.8 billion years.
This was achieved by improving the so-called “cosmic distance ladder” by measuring important milepost markers known as Cepheid variable stars.
However, the Hubble value does not match other measurements that suggest the universe expanded faster after the Big Bang.
These observations were made by mapping the Cosmic Microwave Background (CMB) radiation by ESA’s Planck satellite.
A simple solution to this dilemma would be that the Hubble observations are wrong as a result of some inaccuracy creeping into the measurements of the deep space yardstick.
Then the James Webb Space Telescope came along, allowing astronomers to cross-check Hubble’s results.
Webb’s infrared observations of Cepheids were consistent with Hubble’s optical data.
Webb confirmed that Hubble’s keen observations were correct all along and dispelled any lingering doubts about Hubble’s measurements.
The bottom line is that the Hubble tension between what’s happening in the nearby universe and the expansion of the early universe remains a perplexing puzzle for cosmologists.
“There may be something woven into the fabric of the universe that we don’t yet understand,” the astronomers said.
“Do we need new physics to resolve this contradiction? Or is it the result of measurement errors between the two different methods used to determine the rate of expansion of space?”
Hubble and Webb are now working together to make the final measurements, making it even more likely that something else, not measurement error, is influencing the rate of expansion.
Dr. Adam Rees, a physicist at Johns Hopkins University and leader of the SH0ES (Dark Energy Equation of State Supernova “This is a very real and interesting possibility.” ) Team.
As a cross-check, the first Webb observations in 2023 confirmed that Hubble’s measurements of the expanding universe were accurate.
But in hopes of softening the Hubble tension, some scientists have speculated that invisible measurement errors may grow and become visible as we look deeper into the universe.
In particular, star crowding can systematically affect measurements of the brightness of more distant stars.
The SH0ES team obtained additional observations by Webb of an object that is a Cepheid variable star, an important cosmic milepost marker. This can now be correlated with Hubble data.
“We now have the entire range observed by Hubble and can rule out measurement errors as a cause of the Hubble tension with very high confidence,” Dr. Rees said.
The team’s first few Webb observations in 2023 succeeded in showing that Hubble is on the right track in firmly establishing the fidelity of the first rung of the so-called cosmic distance ladder.
Astronomers use different methods to measure relative distances in space, depending on the object they are observing.
These techniques are collectively known as the space distance ladder. Each stage or measurement technique relies on previous steps for calibration.
But some astronomers believe that the cosmic distance ladder could become unstable as we move outward along the second rung, as Cepheid measurements become less accurate with distance. suggested.
Such inaccuracies can occur because the Cepheid’s light can mix with the light of neighboring stars. This effect can become more pronounced at greater distances, as stars become denser in the sky and harder to distinguish from each other.
The observational challenge is that past Hubble images of these more distant Cepheid variable stars show that as the distance between us and our host galaxy grows ever greater, they appear to overlap more closely with their neighbors. Therefore, this effect needs to be carefully considered.
Intervening dust makes reliable measurements in visible light even more difficult.
The web cuts through the dust, naturally isolating the Cepheid cluster from its neighboring stars. The reason is that its view is clearer at infrared wavelengths than the Hubble Cluster.
“Combining Webb and Hubble gives us the best of both worlds. We find that the reliability of Hubble measurements remains as we climb further along the cosmic distance ladder,” Dr. Rees said.
The new Webb observations include five host galaxies consisting of eight type Ia supernovae containing a total of 1,000 Cepheids, and are located 130 million light-years away, the most distant galaxy in which Cepheids have been sufficiently measured. NGC 5468 is also reached in the distance.
“This spans the entire range measured by Hubble, so we’ve reached the end of the second rung of the cosmic distance ladder,” said Dr. Gagandeep Anand, an astronomer at the Space Telescope Science Institute. Told.
of the team paper Published in Astrophysics Journal Letter.
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Adam G. Reese other. 2024. JWST observations refute unrecognized crowding of Cepheid photometry as an explanation for the Hubble tension with 8σ confidence. APJL 962, L17; doi: 10.3847/2041-8213/ad1ddd
