The Ever-changing Lights in the Sky
When you go out and look up at the night sky, you see stars. If it’s out, you can see the Moon, and if you know where to look you can also spot planets. Sometimes asteroids flare across the field of view, and occasionally there’s a comet out there. If you’re a frequent skygazer, you already know that the view changes over time. Really avid stargazers also know that stars can vary in their brightness–and those that do are called variable stars. Other stars explode. They flare up into brilliance very quickly, and then fade away. Some time later, if you look at the area of space where the star was, using a good-sized telescope and special instruments, you can spot the remains of the star blasting out into space. Those are called supernovae.
The brightening and dimming of stars actually holds clues to activities and processes in the cosmos that help us understand such things as star birth, star death, the distances to galaxies, and even the expansion rate of the universe. So, it’s no surprise that astronomers want to pay attention to the flickering universe of stars. In particular, astronomers at the California Institute of Technology have been paying attention to the varying levels of light from stars and other celestial objects; in fact, they’ve released data on 200 million of them! One of the scientists is S. George Djorgovski, a professor of astronomy at Caltech and principal investigator on survey of variable objects called the Catalina Real-time Transient Survey. He’s a fellow whose work I’ve admired since I worked on the Griffith Observatory exhibits and his “Big Picture” was a focus of my writing for several weeks. He explained why astronomers survey objects that flicker in the dark. “Exploring variable objects and transient phenomena like stellar explosions is one of the most vibrant and growing research areas in astrophysics,” he said. “In many cases, this yields unique information needed to understand these objects.”
The data set includes more than a thousand supernovae, as well as hundreds of so-called cataclysmic variables. These are stars that periodically brighten up in what looks like a catastrophic outburst, only to quiet down after a period of time. The survey also shows pairs of stars in which one spills matter onto another. Such a star is called a white dwarf. There are also tens of thousands of other variable stars; and dwarf novae, which are binary stars that dramatically change in brightness.
The survey takes repeated images of large areas of the sky. By comparing them to previous images, the survey can monitor the brightness of about half-billion objects. This process helps astronomers search out objects that dramatically brighten. Our galaxy–and others–are filled with the flickerings of star life, star death, and everything in between, giving astronomers a treasure trove of data that will help them understand what’s out there.
The CRTS is part of a larger umbrella project called the Catalina Sky Survey, which also searches out near-Earth objects (asteroids that could pose a threat to our planet). They, too, have changing brightnesses, which are clues to their surface features and makeup.
If you want to know more about how astronomers are chasing down the dimmings and brightenings of the sky, check out the Catalina Sky Survey and the news released today about the Transient survey. There are discoveries in those distant flickerings!