{mosimage}On January 10, 2008, two researchers from the University of California, Santa Barbara (Rafael Gavazzi and Tommaso Treu) submitted a research paper to the American Astrophysical Journal discussing the discovery of a double Einstein ring. Such double Einstein rings are very rare phenomena. The 211th conference of the American Astronomical Society is about to take place in Austin, Texas, where they will present their discovery. Before discussing this further, it is important to explain what an Einstein ring is.
When an observer, a distant object (star or galaxy), and a lens align along the same line of sight, a phenomenon called gravitational lensing occurs. Here, the term lens does not refer to an object made of glass. In fact, another star or galaxy acts as the lens. As light travels from the distant galaxy to the observer, it is bent by the intervening lens-like galaxy. According to Einstein’s general theory of relativity, a massive object can bend the fabric of space-time, thereby bending the path of light. This results in gravitational lensing. As a result, a ring forms around the intervening galaxy, which is called an Einstein ring. Now, if four objects line up sequentially along the same line—let’s say the observer, star “A,” star “B,” and star “C,” with “C” being the farthest—then two rings form around the lensing star: a larger ring for the more distant star, and a smaller ring for the closer one. This is how a double Einstein ring is created.
{mosimage}
The researchers from the University of California have discovered such a double Einstein ring. Their research project is named “SLACS” (Sloan Lens Advanced Camera for Surveys). In this case, the lensing galaxy is located 3 billion light-years from Earth, while the two source galaxies causing the rings are 6 and 11 billion light-years away, respectively. The image of this phenomenon was captured by the Hubble Space Telescope.
How much a galaxy bends space-time depends on the amount of invisible matter and energy within it. Using the double rings, these two scientists determined how much the light was bent. From this measurement, they calculated the amount of dark matter, and thus also determined the mass of the lensing galaxy. In this way, for the first time, it has become possible to measure the mass of a galaxy at a measurable distance. Everyone believes that further research in this area will yield even more exciting information about dark matter and the nature of the universe.
Leave a comment