WASHINGTON, Dec 10: New findings have provided further evidence of the puzzling observation that the universe is expanding more quickly than expected, leaving scientists to consider the role of mysterious cosmic components such as dark energy and dark matter.

Data from NASA's James Webb Space Telescope collected over the past two years has confirmed a previous discovery by the Hubble Space Telescope: the rate of the universe's expansion is about 8% faster than predicted based on our understanding of the cosmos' initial conditions and evolution over billions of years. This discrepancy is known as the Hubble Tension.

The Webb observations, made by the most advanced space telescope ever deployed, seem to rule out the possibility that the Hubble data was flawed due to instrument errors.

"This is the largest sample of Webb Telescope data - its first two years in space - and it confirms the puzzling finding from the Hubble Space Telescope that we have been wrestling with for a decade," said astrophysicist Adam Riess of Johns Hopkins University in Maryland, lead author of the study published Monday in the Astrophysical Journal. "The universe is now expanding faster than our best theories can explain."

Riess, a 2011 Nobel laureate in physics for his role in discovering the universe's accelerating expansion, added, "Yes, it appears there is something missing in our understanding of the universe. Our understanding of the universe contains a lot of ignorance about two elements - dark matter and dark energy - and these make up 96% of the universe, so this is no small matter."

Siyang Li, a Johns Hopkins doctoral student in astronomy and astrophysics and a co-author of the study, explained, "The Webb results can be interpreted to suggest there may be a need to revise our model of the universe, although it is very difficult to pinpoint what this is at the moment."

Dark matter, which makes up about 27% of the universe, is an invisible form of matter inferred from its gravitational effects on ordinary matter, such as stars, planets, and Earth, which account for roughly 5% of the universe. Dark energy, comprising about 69% of the universe, is a hypothesized energy that permeates space and counteracts gravity, causing the universe’s accelerated expansion.

What could explain the anomalous expansion rate?

"There are many hypotheses that involve dark matter, dark energy, dark radiation - for example, neutrinos (a type of ghostly subatomic particle) - or gravity itself having some exotic properties as possible explanations," said Riess.

The researchers used three different methods to measure a crucial metric: distances from Earth to galaxies where a type of pulsating star called Cepheids has been observed. The measurements from Webb and Hubble were in agreement.

The universe's expansion rate, known as the Hubble constant, is measured in kilometers per second per megaparsec, a unit of distance equal to 3.26 million light-years. A light-year is the distance light travels in one year, approximately 5.9 trillion miles (9.5 trillion kilometers). According to the standard model of cosmology, the Hubble constant should be about 67-68. However, the data from both Hubble and Webb point to a value averaging around 73, with a range of 70-76.

The Big Bang, which occurred 13-14 billion years ago, initiated the expansion of the universe, and it has been accelerating ever since. In 1998, scientists discovered that the expansion was speeding up, with dark energy proposed as the cause.

The new study analyzed Webb data covering about one-third of the galaxies studied by Hubble. Earlier in 2023, researchers announced that initial Webb data validated the Hubble findings.

How might the Hubble Tension be resolved?

"We need more data to better characterize this clue," said Riess. "Exactly what size is it (the discrepancy)? Is the mismatch at the lower end - 4-5% - or the higher end - 10-12% - of what the current data allows? Over what range of cosmic time is it present? These will further inform ideas."