A team of astronomers from UC Berkeley and other institutions, in their quest to reduce uncertainty about the expansion rate of the universe, has uncovered evidence that the universe is expanding faster than previously predicted.
The team, which was headed by Adam Riess of the Space Telescope Science Institute and included campus astronomy professor Alex Filippenko, took the most precise measurements of the expansion rate of the universe to date and concluded that the universe is now expanding 5 to 9 percent faster than previous predictions indicated.
According to Riess, the team has been working on reducing the uncertainty in the Hubble constant since 2005 and will publish its findings in the Astrophysical Journal.
Original predictions of the Hubble constant — a unit of measurement astronomers use to calculate the expansion rate of the universe — were based on measurements of radiation caused by the Big Bang, according to Lucas Macri, an associate astronomy professor at Texas A&M University and a member of the team. With the aid of the Hubble Space Telescope and refinements in measuring the expansion rate, the team was able to calculate a new Hubble constant that was roughly 10 percent higher than the previous estimate.
“This (evidence) gives us a clue of new things happening in the expansion,” Riess said.
According to Macri, the team’s new, much more precise findings were made possible by measuring the true brightnesses of two types of celestial phenomena — Cepheid variable stars and Type Ia supernovae. Cepheid variable stars pulsate, or “flicker,” which helps astronomers measure relatively short distances in space, while Type Ia supernovae are useful for measuring longer distances.
“Imagine a whole bunch of lights with different brightness (levels) — from Christmas tree lights to stadium lights — lined up,” Macri said. “Christmas lights would flicker once a second, light bulbs would flicker once a day, and stadium lights would flicker once a month.”
With knowledge of how stars of different luminosities pulsate, the team used the apparent brightnesses of Cepheid variable stars from 19 different galaxies to calculate the true brightnesses and hence the distance of 300 Type Ia supernovae.
Although the expansion of the universe was discovered more than 100 years ago, according to Riess, it was not until 20 years ago that an acceleration in the expansion rate was discovered — a finding in which Filippenko had a major role.
Researchers are currently uncertain about what is causing the discrepancy between the observed and predicted expansion rates.
“This discovery gives us a variety of possibilities to explore,” Riess said. “There could be particles that we don’t yet know about, or there could be an influence of dark energy and dark particles.”
According to Macri, the next step for researchers is to garner better quality pictures and measurements of the universe in order to reduce the uncertainty even further.
“We now have evidence that there is something the universe is trying to tell us, but we don’t quite know what it is yet,” Macri said.