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!)

A Beautiful New Image from the Hubble Telescope

Here is a gorgeous picture of a spiral galaxy, which is part of the Coma Cluster of galaxies, roughly 300 million light years away. This galaxy (of billions of stars), like our own, is shaped like a frisbee -- and we are looking at the disk of the frisbee face-on. Its name is just a catalog number: NGC 4921. You can see its huge encircling "arms" of countless stars, blending their light together. And notice a number of clusters of young stars glowing blue, a little distance out from the center.

But what is amazing about this image, if you look at it for a while, is how many OTHER galaxies are visible through and around NGC 4921! All those structures around the galaxy that are not precise pinpoints of light are other great islands of stars -- each containing billions of stars and planets. The cluster of galaxies which NGC 4921 is part of contains more than a thousand galaxies. And there are more galaxies beyond that cluster. Pictures like this help us remember that our problems and disagreements on Earth are such minor issues when seen from the perspective of the universe.

This image, by the way, was assembled from a number of Hubble Space Telescope images and processed by Roberto Colombari, an Italian astronomical photographer working in Brazil.

Galaxy Cluster Abell 1689 Breaks Two World Records

A huge cluster of galaxies so far away that light from it takes 2.2 billion years to reach us has revealed itself to be a record-breaker. It has the largest number of star clusters ever seen in one place and it is farthest place in the universe where we have seen star clusters.

To appreciate this story, you have to distinguish between the two kinds of clusters we're discussing. Stars are often born in groups called "star clusters" and the largest and most impressive of these are called "globular clusters" (because their stars are organized into a big globe-shaped collection of 100,000 stars or more.) Our Milky Way Galaxy has about 150 of these globular clusters and they are among the oldest and most crowded places in our home galaxy.

Galaxies -- the great islands of billions of stars -- also turn out to be organized into clusters. Each cluster might contain hundreds or even thousands of galaxies. (And each galaxy contains billions of stars -- it makes you dizzy if you think too hard about it!)

The late George Abell (an astronomer at UCLA and the author of a famous textbook from which astronomers in my generation first learned astronomy) made a catalog of these galaxy clusters, and the one we are discussing is entry 1689 in his catalog.

A new study of the central region of Abell 1689, made with the Hubble Space Telescope, reveals 10,000 globular clusters of stars in a small region of the galaxy cluster. The astronomers who carried out the work estimate the throughout the entire galaxy cluster, there may be as many 160,000 of these giant old star clusters -- a record unequaled anywhere else we have looked so far.

At a distance of 2.2 billion lightyears, Abell 1689 is also the farthest location in the universe where we have seen a globular cluster.

In the attached picture, you can see part of the cluster of galaxies on the left and then a close-up where the globular clusters look like little yellow dots among the bigger galaxies.

For a scan through the galaxy cluster, you can check out this YouTube video: http://www.youtube.com/watch?v=bumxssc9Cdo
(On this scan, you can also see faint rounded arcs of light -- those are direct proof of one of Einstein's ideas -- that the huge gravity of the galaxy cluster acts like a "gravitational lens" and bends the light of other galaxies behind it into arc like shapes.

We have seen other rich clusters bend light from objects behind them, but the effect is especially clear on this beautifully detailed image.