One of the U.S. Congress’s three scientific justifications for building the Hubble Space Telescope was that it would use the telescope’s observing power to accurately determine the rate of expansion of the universe. Before Hubble was launched in 1990, observations made with ground-based telescopes led to huge uncertainties. Depending on the expansion rate of the universe, this period could be between 10 and 20 billion years. Over the last 34 years, Hubble has narrowed this value down to an accuracy approaching one percent. This was achieved by improving the so-called “cosmic distance ladder” method by measuring the gold standard of cosmic column markers known as Cepheid variable stars.

But the results baffled cosmologists for a decade. Hubble’s best measurements show that the universe is now expanding faster than predicted based on observations of what it looked like shortly after the Big Bang. These observations were made using satellite mapping of the Planck cosmic microwave background, a kind of blueprint for how the structure of the universe would evolve as it cooled after the Big Bang.

A simple solution to this dilemma is to say that perhaps Hubble’s observations are flawed by some gradual inaccuracy in deep space measurements. Then came the James Webb Space Telescope to confirm Hubble’s results. Sharp infrared images of Webb Cepheids are consistent with Hubble data. Webb confirmed that the Hubble telescope’s sharp eye was accurate all along.

As a result, the so-called “Hubble tension” between what’s happening in the nearby universe and the expansion of the early universe remains a fascinating puzzle for cosmologists. Perhaps there is something woven into the fabric of space that we don’t yet understand.

NASA’s Webb and Hubble telescopes confirm the expansion rate of the universe, mystery continues

You should triple check your homework when trying to solve one of the biggest puzzles in cosmology. The puzzle, called the Hubble Stretch, is that the current expansion rate of the universe is faster than astronomers expected, based on our current understanding of the initial conditions of the universe and the evolution of the universe.

Scientists using NASA’s Hubble Space Telescope and many other telescopes consistently find a number that does not match predictions based on observations of ESA’s (European Space Agency) Planck mission. Does resolving this inconsistency require new physics? Or is it due to measurement errors between two different methods used to determine the expansion rate of space?

Hubble has been measuring the current expansion rate of the universe for 30 years, and astronomers want to clear up any doubts about its accuracy. Now Hubble and NASA’s James Webb Space Telescope have teamed up to make the final measurements, confirming that something other than measurement error is affecting the expansion rate.

“Once measurement error is eliminated, there is a real and exciting possibility that we are misunderstanding the universe,” said physicist Adam Riess of Johns Hopkins University in Baltimore. Riess won the Nobel Prize for discovering the fact that the expansion of the universe is being accelerated by a mysterious phenomenon now called “dark energy.”

As a cross-check, Webb’s first observation in 2023 confirmed that Hubble’s measurements of the expansion of the universe were accurate. But some scientists hoping to ease Hubble’s stress have suggested that as we look deeper into the universe, invisible errors in measurements may grow larger and become visible. In particular, clustering of stars can systematically affect brightness measurements of more distant stars.

The SH0ES (Supernova H0 for State of Dark Energy Equation) team, led by Riess and Webb, obtained additional observations of objects known as Cepheid variable stars, critical cosmic markers, that can now be correlated with Hubble data.

“We have now covered all Hubble observations and can exclude measurement error as the cause of the Hubble voltage with a very high degree of confidence,” Riess said.

The first few observations made by Webb’s team in 2023 showed that Hubble was on the right track and firmly established the accuracy of the first steps of the so-called cosmic distance ladder. (See chart below.)

Astronomers use different methods to measure relative distances in the universe depending on the object being observed. Collectively, these methods are known as cosmic distance ladders; Each step or measurement technique relies on the previous step for calibration.

But some astronomers have suggested that the cosmic distance ladder might wobble if measurements of the Cepheid become less accurate with distance as we move outward along the “second rung.” Such inaccuracies can occur because the Cepheid’s light can interfere with the light of a nearby star; This effect can become more pronounced with increasing distance as stars cluster together and become harder to distinguish from each other.

The observational problem is that past Hubble images of these more distant Cepheid variables appear to become more clustered and overlapped by nearby stars at increasing distances between us and our host galaxies, and careful accounting for this effect is necessary. The introduction of dust further complicates the accuracy of measurements in visible light. Webb cuts through the dust and naturally isolates the Cepheids from nearby stars because its view is sharper than Hubble’s in the infrared.

“The combination of Webb and Hubble gives us the best of both worlds. “We found that Hubble measurements continue to be reliable as we move up the cosmic distance ladder,” Riess said.

Webb’s new observations include five host galaxies with eight Type Ia supernovae containing a total of 1,000 Cepheids, reaching NGC 5468, the most distant galaxy where Cepheids have been well measured, at a distance of 130 million light-years. “This covers the entire range that we measured with Hubble. “So we’ve reached the end of the second rung of cosmic distance,” said co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, which operates the Webb and Hubble telescopes for NASA.

Further confirmation of the Hubble voltage by Hubble and Webb set up other observatories to possibly solve this mystery. Rome’s planned Nancy Grace Space Telescope will take broad surveys of the sky to study the effects of dark energy, the mysterious energy causing the expansion of the universe. ESA’s Euclid Observatory carries out a similar mission with the participation of NASA.

For now, the fulcrum of the distance ladder observed by Hubble and Webb appears to be firmly established on one side of the river, and the post-Big Bang glow observed by Planck’s measurements from the beginning of the universe appears to be firmly established on the other. . . How the expansion of the universe changes over the billions of years between these two extremes has not yet been directly observed. “We need to find out if we’re missing something in terms of how to connect the beginning of the universe to the present day,” Riess said.