Universe expansion study confirms challenge to cosmic theory

The new data confirms Hubble Space Telescope measurements of distances between nearby stars and galaxies, providing a crucial cross-check in resolving a mismatch in measurements of the mysterious expansion of the universe. This difference, known as the Hubble tension, cannot be explained by even the best cosmological models.

“The discrepancy between the observed expansion rate of the universe and the predictions of the Standard Model suggests that our understanding of the universe may be incomplete. With two of NASA’s flagship telescopes now confirming each other’s findings, we must take this [Hubble tension] Nobel laureate and lead author Adam Riess, Bloomberg Distinguished Professor and Thomas J. Barber Professor of Physics and Astronomy at Johns Hopkins University, said:

Posted in The Astrophysical JournalThe research builds on Reese’s Nobel Prize-winning discovery that the expansion of the universe is accelerating as mysterious “dark energy” permeates the vast spaces between stars and galaxies.

Reese’s team used the largest sample of Webb data collected during his first two years in space to verify Hubble’s measurement of the universe’s expansion rate, a number known as the Hubble constant. They used three different methods to measure the distances to galaxies hosting supernovae, focusing on distances previously measured by Hubble and the most precise “local” measurements known to produce that number. The observations from the two telescopes were in close agreement, showing that Hubble’s measurements were accurate and ruling out inaccuracies sufficient to attribute the tension to Hubble errors.

Still, the Hubble constant remains a mystery because measurements based on telescopic observations of the current universe yield higher values ​​than predictions made using the Standard Model of Cosmology, which is A widely accepted framework for how the universe works, calibrated with data on the cosmic microwave background, the faint radiation left behind by the Big Bang.

While the Standard Model yields a Hubble constant of about 67-68 kilometers per second per megaparsec, measurements based on telescopic observations typically give higher values ​​of 70 to 76, with an average of 73 kilometers per second per Mpc . This mismatch has puzzled cosmologists for more than a decade because the 5-6 km/s/Mpc difference is too large to be explained simply by flaws in measurement or observational techniques. (A megaparsec refers to a huge distance. A megaparsec is 3.26 million light-years, and a light-year is the distance that light travels in one year: 9.4 trillion kilometers, or 5.8 trillion miles.)

Reese’s team reports that because Webb’s new data rules out significant biases in Hubble’s measurements, Hubble’s nervousness may stem from unknown factors or gaps in cosmologists’ understanding of as-yet-undiscovered physics.

Li Siyang, a graduate student at Johns Hopkins University who worked on the research, said: “Webb’s data are like observing the universe in high definition for the first time, and it really improves the signal-to-noise ratio of the measurements.”

The new study covers about one-third of Hubble’s entire galaxy sample and uses the known distance to the NGC 4258 galaxy as a reference point. Despite the small data set, the team achieved impressive accuracy, with differences between measurements below 2%, much smaller than the Hubble tension difference of about 8-9%.

In addition to analyzing pulsating stars called Cepheid variables, the gold standard for measuring cosmic distances, the team also cross-checked them against carbon-rich stars and the brightest red giant stars in the same galaxy. All galaxies and their supernovae observed by Webb yielded a Hubble constant of 72.6 km/s/Mpc, almost identical to the 72.8 km/s/Mpc value discovered by Hubble for the same galaxy.

The study included samples of Webb data from two groups working independently to refine the Hubble constant, including one from Riess’s SH0ES group (Supernovae, H₀for the dark energy equation of state) and one from the Carnegie-Chicago Hubble Initiative and other teams. The combined measurements allow the most precise determination of the accuracy of distance measurements from Cepheid using the Hubble telescope, which is the basis for determining the Hubble constant.

Although the Hubble constant has no practical impact on the solar system, Earth, or everyday life, it sheds light on the evolution of the universe on extremely large scales, with vast regions of space stretching themselves out like raisins and pushing distant galaxies away from each other. middle. It is a key value used by scientists to map the structure of the universe, deepen our understanding of the state 13-14 billion years after the Big Bang, and calculate other fundamental aspects of the universe.

Resolving the Hubble tension may reveal new insights into more differences from standard cosmological models discovered in recent years, said Johns Hopkins University cosmologist Marc Kamionkowski, who Helped calculate the Hubble constant and, more recently, suggested a possible new explanation for the Hubble constant.

The Standard Model explains the evolution of galaxies, the cosmic microwave background produced by the Big Bang, the abundance of chemical elements in the universe, and many other key observations based on known physical laws. However, it does not fully explain the nature of dark matter and dark energy, the mysterious ingredients of the universe that are estimated to make up 96% of its composition and accelerating expansion.

“One possible explanation for the Hubble tension is whether something is missing from our understanding of the early universe, such as a new building block of matter—early dark energy—that gave the universe an unexpected boost after the Big Bang. ,” said Kamionkoski, who was not involved in the new study. “There are other ideas, such as interesting dark matter properties, exotic particles, changing electron masses or primordial magnetic fields, that may also play a role. Theorists are creative enough.”

Other authors include Dan Scolnic and Tianrui Wu of Duke University; Gagandeep S. Anand, Stefano Casertano and Rachael Beaton of the Space Telescope Science Institute; Louise Breuval, Wenlong Yuan, Yukei S. Murakami, Graeme E of Johns Hopkins University . Addison and Charles Bennett; Lucas M. Macri, NSF NOIRLab; Caroline D. Huang, Center for Astrophysics | Harvard University and Smithsonian Institution; Saurabh Jha, Rutgers University, The State University of New Jersey; Dillon Jha, Boston University Lauter; Richard I. Anderson of Ecole Polytechnique Fédérale de Lausanne; Alexei V. Filippenko of the University of California, Berkeley; and Anthony Carr of the University of Queensland, Brisbane.

This research was supported by Department of Energy grant DE-SC0010007, the David and Lucile Packard Foundation, the Templeton Foundation, the Sloan Foundation, JWST GO-1685 and GO-2875, HST GO-16744 and GO-17312, and Christopher R. Ray Delic Fund.