Anne’s Image of the Day: The Rho Ophiuchi Cloud Complex

March 16, 2014

The Rho Ophiuchi Cloud Complex, a dark nebula in Ophiuchus

Image Credit: NASA/JPL-Caltech/WISE Team

The Rho Ophiuchi Cloud Complex (Rho Oph for short, or the Ophiuchus Molecular Cloud, and pronounced ‘oh-fee-yoo-ki’ and named after a bright star in the region) is a dark nebula, an emission and reflection nebula of about 14 light-years across that is located some 460 light-years away from Earth in the constellation of Ophiuchus (the Serpent-bearer). It is one of the closest star-forming regions to the Solar System.

It consists of two major regions of dense gas and dust. Lynds 1688 (L1688), the bright white main cloud of molecular hydrogen, a key molecule allowing new stars to form from cold cosmic gas, with two long filaments trailing off in different directions. The other, Lynds 1689 (L1688), has a star-forming region with one long filament.

Temperatures of the clouds range from minus 260 degrees Celsius (minus 436 degrees Fahrenheit) to minus 251 degrees Celsius (minus 420 degrees Fahrenheit), and there is a total of about 3,000 times the mass of the Sun in material. Over half of the mass of the complex is concentrated around the bright Lynds 1688 cloud, and this is the most active star-forming region.

A rich collection of colorful astronomical objects is revealed in this image. The bright L1688 cloud is glowing due to heating from nearby stars, resulting in what is called an emission nebula. The same is true for most of the multi-hued gas prevalent throughout the entire image, including the bluish bow-shaped feature near the bottom right.

The bright red area (the Lynds 1689 cloud) in the bottom right is light from the star in the center – Sigma Scorpii – that is reflected off of the dust surrounding it, creating what is called a reflection nebula. And the much darker areas scattered throughout the image are pockets of cool dense gas that block out the background light, resulting in dark (or ‘absorption’) nebulae. WISE’s longer wavelength detectors can typically see through dark nebulae, but these are exceptionally opaque.

The bright pink objects just left of the L1688 cloud are about 425 infrared sources, that are presumed to be young stellar objects (YSOs), including 16 classified as protostars, 123 T Tauri stars with dense circumstellar disks, and 77 with thinner disks. The last two categories of stars – where planets might form – have estimated ages ranging from 100,000 to a million years. In visible light, these YSOs are completely hidden in the dark nebula that surrounds them, which is sometimes referred to as their baby blanket.

The first brown dwarf to be identified in a star-forming region was Rho Oph J162349.8-242601, located in the Rho Ophiuchi Cloud Complex. One of the older objects at the edge of the primary star-forming region was found to be a circumstellar disk seen nearly edge on. It spans a diameter of 300 AU and contains at least twice the mass of Jupiter. The million-year-old star at the center of the disk has a temperature of 3,000 Kelvin and is emitting 0.4 times the luminosity of our Sun.

Rho Oph can be found rising above the plane of the Milky Way in the night sky, bordering the constellations Ophiuchus and Scorpius, 1° south of the star ρ Ophiuchi.

This image is taken with NASA’s Wide-field Infrared Explorer, or WISE. The colors used in this image represent specific wavelengths of infrared light. Blue and cyan (blue-green) represent light emitted at wavelengths of 3.4 and 4.6 microns, which is predominantly from stars. Green and red represent light from 12 and 22 microns, respectively, which is mostly emitted by dust.