ASTRONOMERS HAVE finally seen at first hand the powerful effects of the mysterious dark energy that powers our expanding universe.
It has also confirmed their suspicions that the stars that today dot the night sky will eventually wink out, never to shine again.
This first-time direct observation of the power of dark matter comes from the Chandra X-ray observatory. Chandra has a particularly sharp eye, equivalent to being able to see a stop sign 20km away.
Launched by Nasa in July 1999, the satellite’s mirrors captured X-rays coming from some of the largest structures in the universe, galaxy clusters. Some were close by in our own Milky Way galaxy while others were billions of light years away halfway across the universe.
Chandra’s handlers at the Smithsonian Astrophysical Observatory in Cambridge Massachusetts announced yesterday their unexpected finding that rather than pulling the clusters further apart, the dark energy was blocking their expansion.
The nature of dark energy is one of the biggest unsolved problems in physics. It accounts for three-quarters of our entire universe, but we don’t know what it is or how it works.
Astrophysicists hope to learn more about it, however, by looking for signs of its influence, hence the importance of the Chandra findings, which will be published on February 10th in the Astrophysical Journal. We know it is enormously powerful given that its chief effect is to cause all of the visible matter in the universe to accelerate away, acting in effect like a kind of negative gravity.
This visible matter, the stuff we can actually see like stars and planets, only amounts to about 4 per cent of the entire universe. Dark energy represents 75 per cent and the rest is accounted for by the equally mysterious so-called dark matter. We don’t know what that is either.
We have known for decades, however, that matter in the universe is accelerating away, driven by dark energy. Yet the Chandra findings were counter-intuitive given the dark energy is stopping the galaxy clusters from spreading out.
“You have clusters of thousands or even millions of galaxies clustered into alleys or lines in space. The dark energy is pushing on the natural expansion of these clusters,” explained Prof David Fegan, professor of physics at University College Dublin and vice president of the Royal Irish Academy.
The research team believes the effect is caused because the dark energy is stretching out space time, interfering with the clusters’ ability to expand.
Prof Fegan likened the effect to pumping up a balloon. “Imagine you had a huge balloon and you start to pump the balloon up so it begins to spread,” he said. You then place thousands of tiny balloons into the large balloon and continue to pump it up.
“The big balloon will expand but the smaller balloons will feel an increased pressure and they will begin to contract,” Prof Fegan said.
“By the very same effect the dark energy seems to be stopping the expansion of the galaxy clusters,” he added. “The clusters would probably grow quicker if you didn’t have [the dark matter] stultifying their growth.”
Chandra’s handlers also believe the results indicate how the universe will come to a final end, not next year or the year after but 100 billion years from now.
The universe will continue to expand, stopping galaxies from coalescing and isolating them from one another. One by one they will wink out as their internal fires cool. It makes the line from TS Elliot’s poem The Hollow Man seem almost prophetic: “This is the way the world ends, not with a bang, but a whimper.”