What makes a planet different from a star? A star shines generates its own light by fusing hydrogen atoms in its core. The energy escapes the star from its surface as heat and light. Planets are too small burn elements. They may heat up but they don’t shine. Instead, a planet is visible by the light it reflects from its host sun. Most searches for planets around stars other than the sun don’t photograph planets directly but instead record the dip in a star’s light when an orbiting planet passes in front.
Without some way to block the overwhelming light of a host sun, any planet(s) would be hopelessly swamped by its light. Enter SPHERE, a new instrument on ESO’s Very Large Telescope (VLT) in Chile that allows astronomers to suppress the brilliant light of nearby stars and obtain a better view of the regions surrounding them including giant exoplanets and a wild assortment of dusty disks in which they lurk.
Some of the disks contain bright rings, some dark rings, and some even resemble hamburgers. They also differ dramatically in appearance depending on their orientation in the sky — from circular face-on discs to narrow discs seen almost edge-on.
SPHERE’s primary task is to use direct imaging to discover and study giant extrasolar planets orbiting nearby stars. But it also turns out to be one of the best tools ever made to snap images of the dusty disks around young stars, where planets may be forming. It’s thought that our own solar system and its family of planets, comets and asteroids grew from such a disk (or series of rings in a disk), so studying disks around other stars will help astronomers understand whether planets are present and how they form.
Many of the stars in the photo panel are very young — less than 10 million years old — called T Tauri stars that vary in brightness as they ultimately settle down to lead stable lives like the sun. The disks around these stars contain gas, dust, and planetesimals, the building blocks of planets. And most wonderfully, they hint at what our own solar system may have looked like in the early stages of its formation more than 4.5 billion years ago.
The distances of the targets ranged from 230 to 550 light-years away or relatively close to Earth. Even then, it’s been challenging to obtain good images of the faint reflected light from disks, since they’re outshone by the dazzling light of their parent stars.
Compared to a star, a human lifetime is evanescent — here and gone in an instant. The only way we can come to understand the birth, evolution and death of something as long-live as a star is to look around the universe at lots of stars in all the different stages of their lives, then patch those stories together into a quilt of knowledge. SPHERE is not only helping us make sense of but visualize how it all began.