WISE: Rho Ophiuchi: Treasure Trove of Beauty (2011 Apr 01)

[bystander]

Rho Ophiuchi: Treasure Trove of Beauty (2011 Apr 01)

WISE Unveils a Treasure Trove of Beauty

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A rich collection of colorful astronomical objects is revealed in this picturesque image of the Rho Ophiuchi cloud complex from NASA’s Wide-field Infrared Explorer, or WISE. The Rho Ophiuchi cloud (pronounced ‘oh-fee-yoo-ki’ and named after a bright star in the region) is found rising above the plane of the Milky Way in the night sky, bordering the constellations Ophiuchus and Scorpius. It’s one of the nearest star-forming regions to Earth, allowing us to resolve much more detail than in more distant similar regions, like the Orion nebula.

The amazing variety of different colors seen in this image represents different wavelengths of infrared light. The bright white nebula in the center of the image 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 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 absorption (or ‘dark’) nebulae. WISE’s longer wavelength detectors can typically see through dark nebulae, but these are exceptionally opaque.

The bright pink objects just left of center are young stellar objects (YSOs). These baby stars are just now forming; many of them are still enveloped in their own tiny compact nebulae. In visible light, these YSOs are completely hidden in the dark nebula that surrounds them, which is sometimes referred to as their baby blanket. We can also see some of the oldest stars in our Milky Way Galaxy in this image, found in two separate (and much more distant) globular clusters. The first cluster, M80, is on the far right edge of the image towards the top. The second, NGC 6144, is found close to the bottom edge near the center. They both appear as small densely compacted groups of blue stars. Globular clusters such as these typically harbor some of the oldest stars known, some as old as 13 billion years, born soon after the Universe formed.

There are two other items of interest in this image as well. At the 3 o’clock position, relative to the bright central region, and about two-thirds of the way from the center to the edge, there is a small faint red dot (more visible in the larger downloadable image files). That dot is an entire galaxy far, far away known as PGC 090239. And, at the bottom left of the image, there are two lines emerging from the edge. These were not created by foreground satellites; they are diffraction spikes (optical artifacts from the space telescope) from the bright star Antares that is just out of the field of view.
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.

Credit: NASA/JPL-Caltech/WISE Team

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[owlice]

Oh, that's lovely!

[neufer]

http://asterisk.apod.com/viewtopic.php?f=9&t=17619
http://asterisk.apod.com/viewtopic.php?f=9&t=17068

Click to play embedded YouTube video.

[bystander]

The Art of Making Stars
NASA JPL-Caltech | 2011 Apr 01

It might look like an abstract painting, but this splash of colors is in fact a busy star-forming complex called Rho Ophiuchi. NASA's Wide-field Infrared Explorer, or WISE, captured the picturesque image of the region, which is one of the closest star-forming complexes to Earth.

The amazing variety of colors seen in this image represents different wavelengths of infrared light. The bright white nebula in the center of the image 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 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 absorption (or 'dark') nebulae. WISE's longer wavelength detectors can typically see through dark nebulae, but these are exceptionally opaque.

APOD: Young Stars in the Rho Ophiuchi Cloud (2011 Apr 14)
http://asterisk.apod.com/viewtopic.php?f=9&t=23385

[bystander]

Astronomy Without A Telescope – Star Seeds
Universe Today | Steve Nerlich | 2011 June 18

[url=http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20080211.html][b]The Rho Ophiuchi cloud complex[/b][/url] - within which the cloud L1688 is the most active star-forming location. Although hidden by dust, it is possible to study star formation by sub-millimetre astronomy. [i](Credit NASA/JPL-Caltech/CfA)[/i]

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Molecular clouds are called so because they have sufficient density to support the formation of molecules, most commonly H2 molecules. Their density also makes them ideal sites for new star formation – and if star formation is prevalent in a molecular cloud, we tend to give it the less formal title of stellar nursery.

Traditionally, star formation has been difficult to study as it takes place within thick clouds of dust. However, observation of far-infrared and sub-millimetre radiation coming out of molecular clouds allows data to be collected about prestellar objects, even if they can’t be directly visualized. Such data are drawn from spectroscopic analysis – where spectral lines of carbon monoxide are particularly useful in determining the temperature, density and dynamics of prestellar objects.

Far-infrared and sub-millimetre radiation can be absorbed by water vapor in Earth’s atmosphere, making astronomy at these wavelengths difficult to achieve from sea level – but relatively easy from low humidity, high altitude locations such as Mauna Kea Observatory in Hawaii.

Simpson et al undertook a sub-millimeter study of the molecular cloud L1688 in Ophiuchus, particularly looking for protostellar cores with blue asymmetric double (BAD) peaks – which signal that a core is undergoing the first stages of gravitational collapse to form a protostar. A BAD peak is identified through Doppler-based estimates of gas velocity gradients across an object. All this clever stuff is done via the James Clerk Maxwell Telescope in Mauna Kea, using ACSIS and HARP – the Auto-Correlation Spectral Imaging System and the Heterodyne Array Receiver Programme.

The physics of star formation are not completely understood. But, presumably due to a combination of electrostatic forces and turbulence within a molecular cloud, molecules begin to aggregate into clumps which perhaps merge with adjacent clumps until there is a collection of material substantial enough to generate self-gravity.

From this point, a hydrostatic equilibrium is established between gravity and the gas pressure of the prestellar object – although as more matter is accreted, self-gravity increases. Objects can be sustained within the Bonnor-Ebert mass range – where more massive objects in this range are smaller and denser (High Pressure in the diagram). But as mass continues to climb, the Jeans Instability Limit is reached where gas pressure can no longer withstand gravitational collapse and matter ‘infalls’ to create a dense, hot protostellar core.

When the core’s temperature reaches 2000 Kelvin, H2 and other molecules dissociate to form a hot plasma. The core is not yet hot enough to drive fusion but it does radiate its heat – establishing a new hydrostatic equilibrium between outward thermal radiation and inward gravitational pull. At this point the object is now officially a protostar.

Being now a substantial center of mass, the protostar is likely to draw a circumstellar accretion disk around it. As it accretes more material and the core’s density increases further, deuterium fusion commences first – followed by hydrogen fusion, at which point a main sequence star is born.

The initial conditions of isolated star formation - X. A suggested evolutionary diagram for prestellar cores - RJ Simpson et al

• arXiv.org > astro-ph > arXiv:1106.1885 > 09 Jun 2011

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