Astronomers have made the most precise measurement to date of the universe’s expansion rate

There could be new physics underlying the foundations of the universe.

Using two of the world’s most powerful space telescopes — NASA’s Hubble and ESA’s Gaia — astronomers have made the most precise measurements to date of the universe’s expansion rate. This is calculated by gauging the distances between nearby galaxies using special types of stars called Cepheid variables as cosmic yardsticks. By comparing their intrinsic brightness as measured by Hubble, with their apparent brightness as seen from Earth, scientists can calculate their distances. Gaia further refines this yardstick by geometrically measuring the distances to Cepheid variables within our Milky Way galaxy. This allowed astronomers to more precisely calibrate the distances to Cepheids that are seen in outside galaxies. Credits: NASA, ESA, and A. Feild (STScI)
Using two of the world’s most powerful space telescopes — NASA’s Hubble and ESA’s Gaia — astronomers have made the most precise measurements to date of the universe’s expansion rate. This is calculated by gauging the distances between nearby galaxies using special types of stars called Cepheid variables as cosmic yardsticks. By comparing their intrinsic brightness as measured by Hubble, with their apparent brightness as seen from Earth, scientists can calculate their distances. Gaia further refines this yardstick by geometrically measuring the distances to Cepheid variables within our Milky Way galaxy. This allowed astronomers to more precisely calibrate the distances to Cepheids that are seen in outside galaxies. Credits: NASA, ESA, and A. Feild (STScI)

Utilizing the power and cooperative energy of two space telescopes, astronomers have influenced the most exact estimation to date of the universe’s expansion rate.

The outcomes additionally fuel the mismatch between estimations for the expansion rate of the adjacent universe, and those of the far off, the primitive universe — before stars and galaxies even existed.

This so-called “tension” suggests that there could be new physics hidden in the establishments of the universe. Conceivable outcomes incorporate the association quality of dark matter, dark energy being much more fascinating than already thought, or an obscure new molecule in the tapestry of space.

Combining observations from NASA‘s Hubble Space Telescope and the European Space Agency’s (ESA) Gaia space observatory, astronomers additionally refined the past incentive for the Hubble steady, the rate at which the universe is growing from the big bang 13.8 billion years prior.

However, as the estimations have turned out to be more exact, the group’s assurance of the Hubble constant has turned out to be increasingly inconsistent with the estimations from another space observatory, ESA’s Planck mission, which is thinking of an alternate anticipated an incentive for the Hubble steady.

Planck mapped the primitive universe as it seemed just 360,000 years after the big bang. The whole sky is engraved with the mark of the big bang encoded in microwaves. Planck estimated the sizes of the ripples in this Cosmic Microwave Background (CMB) that were delivered by slight irregularities in the big bang fireball. The fine points of interest of these ripples encode how much dark matter and normal matter there is, the trajectory of the universe around time, and other cosmological parameters.

Planck team member and lead analyst George Efstathiou of the Kavli Institute for Cosmology in Cambridge, England said, “With the addition of this new Gaia and Hubble Space Telescope data, we now have a serious tension with the Cosmic Microwave Background data.”

“The tension seems to have grown into a full-blown incompatibility between our views of the early and late time universe. At this point, clearly, it’s not simply some gross error in any one measurement. It’s as though you predicted how tall a child would become from a growth chart and then found the adult he or she became greatly exceeded the prediction. We are very perplexed.”

Galaxies appear to recede from Earth proportional to their distances, meaning that the farther away they are, the faster they appear to be moving away. This is a consequence of expanding space, and not a value of true space velocity. By measuring the value of the Hubble constant over time, astronomers can construct a picture of our cosmic evolution, infer the make-up of the universe, and uncover clues concerning its ultimate fate.

The two noteworthy strategies for estimating this number give contradictory outcomes. One strategy is immediate, building a cosmic “distance ladder” from estimations of stars in our neighborhood universe. The other strategy utilizes the CMB to gauge the direction of the universe not long after the huge explosion and afterward utilizes physics to depict the universe and extrapolate to the present expansion rate. Together, the estimations ought to give a conclusion to-end trial of our fundamental comprehension of the purported “Standard Model” of the universe. However, the pieces don’t fit.

Using Hubble and newly released data from Gaia, Riess’ team measured the present rate of expansion to be 73.5 kilometers (45.6 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 73.5 kilometers per second faster. However, the Planck results predict the universe should be expanding today at only 67.0 kilometers (41.6 miles) per second per megaparsec. As the teams’ measurements have become more and more precise, the chasm between them has continued to widen, and is now about four times the size of their combined uncertainty.

During the study, scientists used a special type of star as cosmic yardsticks or milepost markers. These pulsating stars, called Cephied variables, brighten and dim at rates that correspond to their intrinsic brightness. By comparing their intrinsic brightness with their apparent brightness as seen from Earth, scientists can calculate their distances.

Gaia additionally refined this yardstick by geometrically estimating the distance to 50 Cepheid factors in the Milky Way. These estimations were joined with exact estimations of their brightnesses from Hubble. This enabled the astronomers to all the more precisely align the Cepheids and after that utilization those seen outside the Milky Way as milepost markers.

Team leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute said, “When you use Cepheids, you need both distance and brightness. Hubble provided the information on brightness, and Gaia provided the parallax information needed to accurately determine the distances. Parallax is the apparent change in an object’s position due to a shift in the observer’s point of view. Ancient Greeks first used this technique to measure the distance from Earth to the Moon.”

The goal of Riess’ team is to work with Gaia to cross the threshold of refining the Hubble constant to a value of only one percent by the early 2020s. Meanwhile, astrophysicists will likely continue to grapple with revisiting their ideas about the physics of the early universe.

The Riess team’s latest results are published in the July 12 issue of the Astrophysical Journal.