Not a bad photo considering no one planned to shoot this picture of Comet Lovejoy with the world’s most powerful digital camera. That’s right. The comet just happened to “be in the way” during a scan made by the Dark Energy Camera. A member of the observing team said it was a “shock” to see the comet appear on the computer screen.
While the detail in the comet is spectacular, what’s behind it is equally amazing. The image represents a narrow but deep slice into the body of the cosmos, revealing hundreds of distant galaxies beyond the green veil of Lovejoy’s tail. I’ve sectioned off a few portions, but I encourage you to download and explore the original file and see the rest for yourself. We’ve all read there are billions of galaxies out there, but seeing them twinkling beyond the comet gives us a visceral feel of how deep the universe goes.
The camera, a 570 megapixel beast with lenses up to a yard across, is mounted on the 157-inch (4-meter) Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in the Andes Mountains in Chile. With a 2.2° field of view (much larger than most professional telescopes) and the ability to see light from more than 100,000 galaxies up to 8 billion light-years away in each snapshot, it forms the heart of the Dark Energy Survey (DES).
Dark energy is the name given to whatever is causing the universe to accelerate. No one went looking for it, but studies of the brightnesses of extremely distant supernovae in the 1990s turned up a phenomenal increase in the expansion rate of the universe when viewed across billions of light years. Now we’re stuck trying to figure out what it is. If anything, most astronomers expected cosmic expansion to slow down as predicted by Einsteins’ Theory of Relativity. Nope.
Overall, dark energy is thought to comprise 73% of all the mass and energy in the universe. 23% is unseen dark matter known only through its gravitational prowess, leaving just 4% ordinary matter for hamburgers, stars and cars.
The DES designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. The survey will probe dark energy on four fronts:
* Counting galaxy clusters: Dark matter and galaxies’ own gravity hold clusters together, but dark energy tries to pull the clusters apart. The camera will photograph 100,000 clusters across billions of light years of space and time. Counting clusters and mapping their distribution will help us understand how dark energy battles gravity for the fate of the universe.
* Measuring supernovae brightnesses and distances to better determine the expansion rate of the universe. 4,000 new supernovae are expected to be found with the camera.
* Studying how dark energy interacts with dark matter. The light of distant galaxies is bent and distorted when it passes around dark matter, warping their shapes. The survey will measure those shapes to see what role dark energy plays in the interaction.
* When the universe was less than 400,000 years old, matter and light interacted to set off a series of sound waves which left an imprint on how galaxies are distributed throughout the universe. The survey will measure the positions in space of 300 million galaxies to find this imprint and use it to infer the history of cosmic expansion.
Even if we don’t track down the nature of dark energy in our lifetime, we can sure enjoy the side benefits of pictures like this one.