NASA’s Hubble telescope finds universe is expanding faster than expected

A team of astronomers using NASA’s Hubble Space Telescope have discovered that the universe is expanding 5 to 9% faster than expected. Led by Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, the team made the observation by refining the universe’s current expansion rate to unprecedented accuracy.

For reference: Hubble is able to accurately measure distance between distant galaxies by constructing something called a “cosmic distance ladder”. The ladder system compares the observable or apparent brightness of Cepheid stars and Type la supernovae in different galaxies to measure their true brightness. Next, the distance measurements are compared to the degree by which the light from the supernovae is stretched to longer wavelengths by the expansion of space. Astronomers then these two values to calculate how fast the universe expands with time, a value called the Hubble constant.

Using Hubble's sharp-eyed Wide Field Camera 3 (WFC3), the observations were made by the Supernova H0 for the Equation of State (SH0ES) team, which worked to refine the accuracy of the Hubble constant and reduce the uncertainty to only 2.4%.

The improved Hubble constant value — measuring 45.5 miles per second per megaparsec (a megaparsec equals 3.26 million light-years) — means the distance between cosmic objects will double in another 9.8 billion years. However, the new expansion rate contradicts the longstanding expansion rate calculated based on the Universe’s trajectory from the Big Bang. According to NASA, “measurements of the afterglow from the Big Bang by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and the European Space Agency’s Planck satellite mission yield predictions which are 5 percent and 9 percent smaller for the Hubble constant, respectively.”

In the past, astronomers have used the measurement of the initial energy and matter in the universe at the time shortly after the Big Bang, and applied that understanding to predict how fast the universe should be expanding today. However, if the discrepancy shown by the Hubble constant proves correct, the universe is expanding faster than ever expected.

“You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” study leader Adam Riess said. “But now the ends are not quite meeting in the middle and we want to know why.” 

There are several possible explanations for the universe’s accelerated speed. One possibility is that dark energy, already known to be accelerating the universe, may be shoving galaxies away from each other with increasing force. 

Another idea is that dark matter, the backbone of the universe upon which galaxies are created, possesses some weird, unexpected characteristics. The cosmos may have contained a new subatomic particle in its early history that traveled close to the speed of light, referred to as “dark radiation.” More energy from previously unaccounted for dark radiation could be throwing off the best efforts to predict today’s expansion rate from its post-Big Bang trajectory.

Finally, the speedier universe may be telling astronomers that Einstein’s theory of gravity is incomplete. The dark universe, comprised of such things as dark energy, dark matter, and dark radiation, makes up 95% of everything and doesn’t emit light. This finding could be a clue in measuring how dark radiation pushes and pulls on space over cosmic history.

From the time Hubble was launched in 1990, the estimates of the Hubble constant have been refined from an error rate of 10% to today’s 2.4%. The SH0ES team is still using the telescope to further reduce the uncertainty in the Hubble constant, with the goal of reaching an accuracy of 1%, thus permitting a better understanding of the universe’s behavior.

Sources: Phys.org, NASA