Worlds In the Darkness

Somewhere out there in space, at this very moment, worlds are forming. This isn’t a science fiction story—it’s fact. We’ve found some of them— the number found by the California and Carnegie Planet Search Project is more than 110, with new ones being spotted by scientists who survey stars looking for the telltale signatures of planets.

The problem with seeking out planets is that they’re incredibly hard to see in the glare of the stars they circle. You can’t just poke Hubble Space Telescope in the direction of some likely looking star and program it to look for little points of light. Long before HST could even see such tiny things, the light from the star would have saturated the detectors!<

So, how do astronomers find other worlds? There are several ways to do it, with the two best-known being the Doppler detection method and transit ph0tometry. In Doppler methods, astronomers use instruments on telescopes to measure the change in the wavelength (its color) of light coming from a star overa period of time. The Doppler shift of the light is measured in the changing wavelength of the light, which itself happens when a star orbits a common center of mass with a planet. For example, Jupiter’s gravitational pull causes the Sun to wobble around in a circle with a velocity of 12 meters per second. A distant observer would see a shift in the wavelengths of light coming from the Sun and would be able to figure out that a planet was causing the wobble and the shift.

Photometry measures the light from a star, including how often it dims and brightens up. Some stars vary in their brightness (which is why they’re called variables). These periodic changes can be charted quite regularly. However, sometimes a star’s light is dimmed regardless of whether it’s a variable or not. This periodic dimming of the star is likely caused when a planet passes in front of it along the line of sight from an observer. During the time a planet transits (passes in front of) a star from our viewpoint, we can measure the amount of light lost by comparing it to the normal brightness of the star. This helps astronomers figure out the size and orbit of a planet in orbit around that star.

As you can imagine, the search for planets around other stars is time-consuming. It’s not easy. There ARE plans to put satellites into orbit to help the search for other worlds, as well as ideas to better use ground-based telescopes in the effort. For more information about these efforts, point your browser here. And, to see what some of these planets might look like (through the eyes of a talented space artist), visit with Lynnette Cook.

What’s Happening Here?

Long filaments of ionized hydrogen gas extending 110,000 light years above the disk of the NGC 4388. Image courtesy Subaru Telescope, Mauna Kea, Hawaii.

Long filaments of ionized hydrogen gas (pink) extending 110,000 light years above the disk of the NGC 4388. Image courtesy Subaru Telescope, Mauna Kea, Hawaii. (NOTE: the long gray straight lines are actually detector artefacts.)

Stare into space long enough, with strong enough eyes at many wavelengths, and eventually you find things that look like the events happening in this image. This is an action shot, capturing a scene from the evolution of a galaxy. A supermassive black hole at the heart of the galaxy is devouring material. This accretion produces vast amounts of energy that outshine the light from all the stars in the galaxy. The surrounding gases are “excited” by the action, resulting in ionization. Light at a specific wavelength is emitted, allowing astronomers to see it.

When we say it’s an exciting universe, we aren’t just talking about cool stuff happening. The processes that heat gases and cause light to shine out across the parsecs so we can see it belie some of the most interesting and energetic events in the cosmos. Astronomy seeks to understand those processes and events. And that’s why snapshots like this one are so important. Build up enough of them and you start to get a feel for what’s happening in the cosmos–and why.