NASA's Hubble finds mysterious force in young universe

Astronomers using NASA's Hubble Space Telescope have discovered a mysterious force, called dark energy that causes the universe to expand at an increasing rate. This repulsive force has been pulling the universe apart for most of its existence, NASA scientists announced Thursday.

Dark energy, the enigmatic force that acts like gravity in reverse, has been present and constant for at least 9 billion years and jerking galaxies and stars toward the cosmic frontier, scientists said.

The finding that eliminates many of the theories developed to explain its mysterious role in the cosmos is compatible with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space.

Earlier observations with Hubble, which is working with increasingly more powerful ground-based observatories, had uncovered that dark energy's repulsive force started out-muscling gravity's tug five to six billion years ago.

Those observations intimated dark energy was something that emerged at the time when the universe was half the size it is now.

About the latest findings, Adam Riess, the Johns Hopkins University professor who led the NASA's current Hubble study said, "What we have seen most recently is that dark energy is not a new feature. It has been present for most of the history of the universe."

The team of observers announced its findings in a teleconference in Washington. It will be published in the Feb. 10 editions of the Astrophysical Journal.

“Although dark energy accounts for more than 70 percent of the energy of the universe, we know very little about it, so each clue is precious,” said Riess.

Riess, who also led one of the first studies to uncover the presence of dark energy in 1998, further said, “Our latest clue is that the stuff we call dark energy was relatively weak, but starting to make its presence felt 9 billion years ago.”

The latest Hubble data are based on an analysis of the 24 most distant stars that exploded in blasts known as supernovae. All date from about 9 billion years ago and their intrinsic brightness is fully known.

These specific supernovae are useful because they all exploded at the same size, 1.4 times the mass of the own sun, Reese said. By measuring their visible brightness, observers can measure how far away they were and thus how fast the universe is expanding, he added.

"When we subtract the gravity from the known matter in the universe, we can see the dark energy pushing to get out," said team member Louis-Gregory Strolger of Western Kentucky University.

According to theoretical astrophysicist Mario Livio, another team member from the Space Telescope Science Institute in Baltimore, thoroughly comprehending the nature of dark energy is “arguably the biggest problem that physics is facing today.”

"This was a classic case of who ordered that. Suddenly, something was discovered that no one expected," he said.

However, to reach at a concluding decision on which view of dark energy is correct, more information is required. Riess and his fellow astronomers will continue to search for supernovas with Hubble, but more data could come from the proposed Joint Dark Energy Mission, to be sponsored by NASA and the Department of Energy.

This state-of-the-art orbiting observatory would spot as many supernovas in one year as Hubble could in a century.