Hubble Shows Universe Expanding Faster than Expected

New measurements from NASA’s Hubble Space Telescope show that the universe is expanding about 9% faster than expected. A team led by professor Adam Riess at Johns Hopkins University used a new method, called DASH for Drift and Shift, for capturing quick images of the stars in Earth’s neighboring galaxy. Using the DASH method, the researchers were able to use the Hubble as a “point and shoot” camera to look at groups of these stars known as Cepheids. This allowed the team to observe a dozen Cepheids in the same amount of time it previously took to observe just one.

This is a ground-based telescope’s view of the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The inset image, taken by the Hubble Space Telescope, reveals one of many star clusters scattered throughout the dwarf galaxy. Courtesy of NASA, ESA, Adam Riess, and Palomar Digitized Sky Survey.

With this new data, the team was able to strengthen the foundation of the cosmic distance ladder, which is used to determine distances within the universe, and calculate the Hubble constant, a value of how fast the cosmos expands over time. The team combined its Hubble measurements with additional distance measurements to Earth’s neighboring galaxy made by the Araucaria Project.

This illustration shows the three basic steps astronomers use to calculate how fast the universe expands over time, a value called the Hubble constant. All the steps involve building a strong “cosmic distance ladder,” by starting with measuring accurate distances to nearby galaxies and then moving to galaxies farther and farther away. This “ladder” is a series of measurements of different kinds of astronomical objects with an intrinsic brightness that researchers can use to calculate distances. Courtesy of NASA, ESA, and A. Feild (STScI).

As the researchers’ measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe’s expansion by the European Space Agency’s Planck satellite.

“This is not just two experiments disagreeing,” Riess said. “We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don’t agree, there becomes a very strong likelihood that we’re missing something in the cosmological model that connects the two eras.”

The Johns Hopkins team will continue to fine-tune the Hubble constant, with the goal of reducing the uncertainty to 1%. These most recent measurements brought the uncertainty in the rate of expansion down from 10% in 2001 to 5% in 2009 and now to 1.9% in the present study.

The research was published in The Astrophysical Journal (https://arxiv.org/abs/1903.07603v2).