Thursday, March 26, 2015
Einstein's Lens Splits Space and Time
This year, we celebrate the 100th anniversary of the first publication of Einstein's greatest masterpiece, the General Theory of Relativity. Now astronomers using the Hubble Space Telescope have found a remarkable quadruple image of a distant exploding star which helps confirm another of that theory's most "far out" predictions.
The General Theory connects space, time, and gravity in mind-boggling ways. Strong gravity can actually warp (or bend) space and distort the flow of time. One example of gravity strong enough to do this is a dense cluster of galaxies, like the one shown on our image. Everything on this Hubble picture that is not a point of light (everything with a shape) is a galaxy of billions of stars. The cluster contains many such galaxies orbiting a common center.
Light from more distant objects behind the cluster has to go through the strong gravity of the cluster on its way to us. Einstein's theory predicts that as gravity warps space, the light from behind the cluster will have to travel through that warped space and will get twisted and bent in eerie ways. From the right angle, a single beam of light can be split into four similar images, something called an "Einstein Cross." That's just what you see in the inset on the picture.
Most amazingly, the four images of the exploding star took slightly different amounts of time to get to us through that warped space, and so we are seeing the same explosion at four different time periods. By studying the details of such complex "gravitational lenses" (as the distortion by the galaxy cluster is called), astronomers hope to learn more about how all the "stuff" in those galaxies is distributed and how much of it is regular matter and how much is dark matter.
The galaxy cluster only has a catalog number, not a name, but we know it is about 5 billion lightyears away (meaning light, traveling at the fastest permitted speed in the universe, took five billion years to reach us.) The exploding star appears to be four billion lightyears further than that -- meaning we are seeing its light from 9 billion years ago. The only reason we can see it at all is that the gravity of the galaxy cluster actually intensifies the light as well as splitting it -- just as Einstein's theory predicts.
What a wonderful image with which to celebrate the 100th anniversary of a theory that Einstein's called "the happiest thought of my life!"
(Click on the image to see it bigger -- believe me, it's worth it!)