Quasars arise from supermassive black holes at the centers of galaxies; they are the brightest objects in nature, and can be seen clear across the universe. As standard candles, quasars aren’t ideal because their masses vary widely. Nevertheless, the researchers identified some regularities in the emissions from quasars, allowing the history of the cosmos to be traced back nearly 12 billion years. The team found that the rate of cosmic expansion deviated from expectations over that time span.
One interpretation of the results is that dark energy is not constant after all, but is changing, growing denser and thus stronger over cosmic time. It so happens that this increase in dark energy also would be just enough to resolve the discrepancy in measurements of the Hubble constant.
The bad news is that, if this model is right, dark energy may be in a particularly virulent and — most physicists say — implausible form called phantom energy. Its existence would imply that things can lose energy by speeding up, for instance. Robert Caldwell, a Dartmouth physicist, has referred to it as “bad news stuff.”
As the universe expands, the push from phantom energy would grow without bounds, eventually overcoming gravity and tearing apart first Earth, then atoms.
The Hubble-constant community responded to the new report with caution. “If it holds up, this is a very interesting result,” said Dr. Freedman.
Astronomers have been trying to take the measure of this dark energy for two decades. Two space missions — the European Space Agency’s Euclid and NASA’s Wfirst — have been designed to study dark energy and hopefully deliver definitive answers in the coming decade. The fate of the universe is at stake.
In the meantime, everything, including phantom energy, is up for consideration, according to Dr. Riess.
“In a list of possible solutions to the tension via new physics, mentioning weird dark energy like this would seem appropriate,” he wrote in an email. “Heck, at least their dark energy goes in the right direction to solve the tension. It could have gone the other way and made it worse!”