24/7 Space News
A new measurement could change our understanding of the Universe
File image showing fluctuations in the cosmic microwave background temperature.
A new measurement could change our understanding of the Universe
by Staff Writers
Lausanne, Switzerland (SPX) Apr 06, 2023

The Universe is expanding - but how fast exactly? The answer appears to depend on whether you estimate the cosmic expansion rate - referred to as the Hubble's constant, or H0 - based on the echo of the Big Bang (the cosmic microwave background, or CMB) or you measure H0 directly based on today's stars and galaxies. This problem, known as the Hubble tension, has puzzled astrophysicists and cosmologists around the world.

A study carried out by the Stellar Standard Candles and Distances research group, lead by Richard Anderson at EPFL's Institute of Physics, adds a new piece to the puzzle. Their research, published in Astronomy and Astrophysics, achieved the most accurate calibration of Cepheid stars - a type of variable star whose luminosity fluctuates over a defined period - for distance measurements to date based on data collected by the European Space Agency's (ESA's) Gaia mission. This new calibration further amplifies the Hubble tension.

The Hubble constant (H0) is named after the astrophysicist who, together with Georges Lemaitre, discovered the phenomenon in the late 1920s. It's measured in kilometers per second per megaparsec (km/s/Mpc), where 1 Mpc is around 3.26 million light years.

The best direct measurement of H0 uses a "cosmic distance ladder," whose first rung is set by the absolute calibration of the brightness of Cepheids, now recalibrated by the EPFL study. In turn, Cepheids calibrate the next rung of the ladder, where supernovae - powerful explosions of stars at the end of their lives - trace the expansion of space itself. This distance ladder, measured by the Supernovae, H0, for the Equation of State of dark energy (SH0ES) team led by Adam Riess, winner of the 2011 Nobel Prize in Physics, puts H0 at 73.0 +/- 1.0 km/s/Mpc.

First radiation after the Big Bang
H0 can also be determined by interpreting the CMB - which is the ubiquitous microwave radiation left over from the Big Bang more than 13 billion years ago. However, this "early Universe" measurement method has to assume the most detailed physical understanding of how the Universe evolves, rendering it model dependent. The ESA's Planck satellite has provided the most complete data on the CMB, and according to this method, H0 is 67.4 +/- 0.5 km/s/Mpc.

The Hubble tension refers to this discrepancy of 5.6 km/s/Mpc, depending on whether the CMB (early Universe) method or the distance ladder (late Universe) method is used. The implication, provided that the measurements performed in both methods are correct, is that there is something wrong in the understanding of the basic physical laws that govern the Universe. Naturally, this major issue underscores how essential it is for astrophysicists' methods to be reliable.

The new EPFL study is so important because it strengthens the first rung of the distance ladder by improving the calibration of Cepheids as distance tracers. Indeed, the new calibration allows us to measure astronomical distances to within +/- 0.9%, and this lends strong support to the late Universe measurement. Additionally, the results obtained at EPFL, in collaboration with the SH0ES team, helped to refine the H0 measurement, resulting in improved precision and an increased significance of the Hubble tension.

"Our study confirms the 73 km/s/Mpc expansion rate, but more importantly, it also provides the most precise, reliable calibrations of Cepheids as tools to measure distances to date," says Anderson. "We developed a method that searched for Cepheids belonging to star clusters made up of several hundreds of stars by testing whether stars are moving together through the Milky Way. Thanks to this trick, we could take advantage of the best knowledge of Gaia's parallax measurements while benefiting from the gain in precision provided by the many cluster member stars. This has allowed us to push the accuracy of Gaia parallaxes to their limit and provides the firmest basis on which the distance ladder can be rested."

Rethinking basic concepts
Why does a difference of just a few km/s/Mpc matter, given the vast scale of the Universe? "This discrepancy has a huge significance," says Anderson. "Suppose you wanted to build a tunnel by digging into two opposite sides of a mountain. If you've understood the type of rock correctly and if your calculations are correct, then the two holes you're digging will meet in the center. But if they don't, that means you've made a mistake - either your calculations are wrong or you're wrong about the type of rock. That's what's going on with the Hubble constant. The more confirmation we get that our calculations are accurate, the more we can conclude that the discrepancy means our understanding of the Universe is mistaken, that the Universe isn't quite as we thought."

The discrepancy has many other implications. It calls into question the very fundamentals, like the exact nature of dark energy, the time-space continuum, and gravity. "It means we have to rethink the basic concepts that form the foundation of our overall understanding of physics," says Anderson.

His research group's study makes an important contribution in other areas, too. "Because our measurements are so precise, they give us insight into the geometry of the Milky Way," says Mauricio Cruz Reyes, a PhD student in Anderson's research group and lead author of the study. "The highly accurate calibration we developed will let us better determine the Milky Way's size and shape as a flat-disk galaxy and its distance from other galaxies, for example. Our work also confirmed the reliability of the Gaia data by comparing them with those taken from other telescopes."

Research Report:A 0.9% calibration of the Galactic Cepheid luminosity scale based on Gaia DR3 data of open clusters and Cepheids

Related Links
Swiss Federal Institute of Technology
Understanding Time and Space

Subscribe Free To Our Daily Newsletters

The following news reports may link to other Space Media Network websites.
Double quasars revealed as space telescopes peer into history of the universe
Washington DC (UPI) Apr 5, 2023
Astronomers have discovered a pair of quasars indicating the merging of a pair of galaxies, according to a report published Wednesday in the journal Nature. These high-energy quasars are providing a glimpse into the universe when it was "just" 3 billion years old. The quasars were revealed through both ground and space-based telescopes that peered into the universe's history. They are allowing scientists to better understand the evolution of galaxies at "cosmic noon." That is when galaxi ... read more

NASA awards innovative concept studies for science, exploration

Russia will use International Space Station 'until 2028'

Axiom Space's upcoming ISS mission part of increasing commercialization of space

NASA Boosts Open Science through Innovative Training

Purdue offering new online Hypersonics Graduate Certificate

SpaceX prepares for rehearsal, test flight of Starship rocket

NASA's TEMPO spacecraft hitched a ride with Intelsat's 40e satellite on a SpaceX rocket

China's 3D printed afterburning liquid rocket engine tested during recent mission

NASA unveils 'Mars' habitat for year-long experiments on Earth

Curiosity software upgrade complete: Sol 3796

Scoping out the next sampling stop for Perseverance

New interactive mosaic uses NASA imagery to show Mars in vivid detail

China's inland space launch site advances commercial services

China's Shenzhou XV astronauts complete 3rd spacewalk

China's Shenzhou-15 astronauts to return in June

China's space technology institute sees launches of 400 spacecraft

Slingshot Aerospace expands network to optically track LEO satellites

Safran to provide GNSS simulation solutions for Xona's LEO constellation

Deloitte announces formal space practice for rapidly growing space industry

Rocket Lab to launch NASA's cyclone-tracking satellite constellation from New Zealand

3D-printed rocket maker to focus on bigger vehicle for commercial launches

Viasat real-time Earth antennas integrated on Microsoft Azure Orbital

Satixfy tests new antenna with OneWeb and Air Force Research Lab

LeoLabs and ClearSpace partner to advance a safer, more sustainable space environment

Do Earth-like exoplanets have magnetic fields

New paper investigates exoplanet climates

JWST confirms giant planet atmospheres vary widely

Planet hunting and the origins of life

NASA's Webb Scores Another Ringed World with New Image of Uranus

A Jovian journey to the icy worlds of a Gas Giant

Juice testing - down to the wire

Guiding JUICE to Jupiter

Subscribe Free To Our Daily Newsletters


The content herein, unless otherwise known to be public domain, are Copyright 1995-2023 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.