Cosmic cloudshine

Hubble’s iconic images include many shots of cosmic clouds of gas and dust called nebulae. For example, the famous “Pillars of Creation” mark the birthplace of new stars within the Eagle Nebula. Yet despite their beauty, visible-light images show only the nebulae surfaces. Baby stars may hide beneath, invisible even to Hubble’s powerful gaze.

Harvard astronomers have pioneered a new way to peer below the surface using near-infrared light that is invisible to the human eye. The resulting images are both beautiful and scientifically valuable because they can be used to map the structure of interstellar matter.

“We can now see the structure of gigantic star-forming regions over vast distances with a resolution 50 times better than before,” said Alyssa Goodman of the Harvard-Smithsonian Center for Astrophysics (CfA). “This technique will revolutionize the way we map stellar birthplaces.”

While Hubble’s NICMOS instrument and NASA’s Spitzer Space Telescope also use infrared light to study nebular interiors, ground-based images at near-infrared wavelengths provide an unparalleled combination of wide-field coverage and high resolution.

“Images like these will give astronomers new insight into what those giant complexes of gas and dust really look like,” added Jonathan Foster, a graduate student at Harvard University and the paper’s first author.

The researchers took long-exposure photographs of a star- forming region in the constellation Perseus and were surprised to see something they had never seen before. Just as earthly clouds shine orange at night as they reflect light from streetlights below, they discovered that clouds in outer space show a similar effect. In space, otherwise “dark” clouds of dust and gas are illuminated by faint starlight washing over them.

Goodman and Foster dubbed the new celestial phenomenon “cloudshine.” Their long-exposure, near-infrared images uncovered the faintly shining billows of material. Recent advances in infrared detectors, combined with longer than usual imaging times, led to the discovery.