While staring into space, two UCSB researchers may have stumbled upon new evidence that could one day answer the cosmic question: How fast is the universe expanding?
Assistant UCSB physics Professor Tommaso Treu and researcher Raphael Gavazzi made the discovery while participating in the Hubble Space Telescope and Sloan Lens Advanced Camera for Surveys Program – an ongoing project designed to find far away galaxies in alignment. By using the Hubble Space Telescope, the two researchers were able to observe a phenomenon that no astronomer had ever seen before: the presence of two glowing rings, with one inside the other.
The phenomenon, dubbed the “double Einstein ring,” results from the bending of light around three galaxies in alignment and is incredibly rare as scientists predict that the chance of seeing it are one in 10,000. The new discovery will now allow scientists to learn more about dark matter and dark energy – materials that are not visually apparent but are known to exist as the result of their gravitational effects – and help to show how fast the universe is expanding, Treu said. The findings were announced last Thursday at the American Astronomical Society meeting in Austin, Texas. Gavazzi and Treu worked with an international team of seven members from the U.S., Italy, United Kingdom and France.
A Ring for Einstein
The Einstein ring is a phenomenon Albert Einstein first predicted in 1912. He theorized that massive objects brighten light emitted from objects behind them by bending space and time. To find one Einstein ring, astronomers must find one massive galaxy – known as a red galaxy because it has older stars, though it looks yellow – directly in front of a smaller galaxy – known as a blue galaxy because it has younger stars and appears blue.
Our own Milky Way galaxy is known as a spiral galaxy, and it is relatively blue because stars are still forming. However, Treu said it also contains some very red, older stars.
In order to find an Einstein ring, astronomers must first look for bright yellow galaxies that can create the gravitational lens – the bending of light around a galaxy.
Since the galaxy has a massive gravitational displacement, it slightly pulls and deflects light that travels through its field. This allows a gravitational lens to work because light bends twice around the larger galaxy and continues through space into the telescope’s view. The two light rays come from different angles and scientists see two blue images: Einstein’s ring.
Treu said the result works like a magnifying glass by focusing on the bent light rays, thus amplifying the size and brightness of the galaxy in the background.
To observe a double Einstein ring, astronomers must find three galaxies in almost perfect alignment, Gavazzi said.
Hitting the Jackpot
Gavazzi and Treu said they were both very excited with their discovery.
“After the first look, I understood the potential and novelty of such a fortunate discovery,” Gavazzi said. “So, I ran to Tommaso’s office and told him he had to take a look at my screen. Then we were both very excited and nicknamed the lensing galaxy after ‘the jackpot.'”
The radius of the Einstein ring is important because it contains information about the mass of the galaxies as well as the distance between us and these galaxies, Gavazzi said. When more double rings are found, scientists can learn more about the dark energy manifestation – the apparent acceleration of the expansion of the universe.
By observing a double ring, scientists can determine the masses and distance between all three galaxies, Treu said.
“In cosmology, the most important thing is determining distances to objects,” he said. “We measure the distance to objects as a function of cosmic time.”
Treu said astronomers can also look more closely at the relation between dark matter – matter with no interaction of light – and normal matter – the substance that composes all physical objects.
According to Treu, dark matter and normal matter are usually distributed differently in terms of density and radius. However, he said the sum of the two matters is always the same, which helps explain how galaxies are formed.
Treu said this is very telling about the nature of galaxies.
“You can’t just form a galaxy any random way you want,” Treu said. “The amount of dark matter increases with galaxy size.”
The Future of Cosmology
Currently, scientists are limited by existing technology and cannot find too many more double rings until a new generation of satellites is developed that will allow astronomers to see a large number of galaxies, Treu said.
“There’s a lot of potential for discovery,” Treu said. “Maybe we’ll turn out to be all wrong but that’s the beauty of science.”