Orion Nebula shines in its grandest portrait

By Ker Than

updated 4:49 p.m. ET Jan. 11, 2006

WASHINGTON - Scientists have created the most detailed portrait ever of the closest known star factory, the Orion Nebula. They have also uncovered new details about the stellar winds responsible for carving out the nebula's ghostly skyscapes.

Meanwhile, another research group identified a glowing gas cloud in another region of the night sky that might replace Orion when it fades from view in about 100,000 years.

The findings were announced here at the 207th meeting of the American Astronomical Society.

Orion is located 1,500 light-years away and is the nearest region of massive star formation. Located at the center of the Orion Nebula are a group of four young, massive stars; they are collectively referred to as the "Trapezium" because of the shape they make. The Trapezium is surrounded by a halo of 1,000 faint, low-mass stars similar to the sun.

Powerful winds
Like all massive stars, those in the Trapezium are radiating a stream of energetic X-rays called a stellar wind. However, the wind from the Trapezium is millions of times denser and more energetic than the flow from our own sun.

When these powerful winds collide with the dense cloud of dust and gas surrounding the stars, they produce shock waves that erode and shape the clouds. Similar to how winds on Earth can sculpt sand dunes in a desert, stellar winds from the Trapezium are carving out a cavity relatively free of dust and gas, filled with strange, ethereal scenes.

"In this bowl of stars we see the entire formation history of Orion printed into the features of the nebula: arcs, blobs, pillars and rings of dust that resemble cigar smoke," said Massimo Roberto, an astronomer at the Space Science Telescope Institute in Baltimore. "Each one tells a story of stellar winds from young stars that impact the environment and the material ejected from other stars."

Roberto is part of a team that stitched together more than 500 highly detailed images taken by the Hubble Space Telescope to create the sharpest portrait of Orion ever produced. The image includes stars that are one-hundredth the brightness of any previously viewed and others that have never before been photographed in visible light.

"Orion may seem very peaceful on a cold winter night, but in reality it holds very massive, luminous stars that are destroying the dusty gas cloud from which they formed," said Tom Megeath, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

Stellar gusts
The Trapezium's stellar winds play a major role in the creation of new stars within the Orion Nebula. If the winds are strong enough, their shock waves act as catalysts for star formation by pushing the clouds together into compact bundles.

C. Robert O’Dell / Vanderbilt University The four super-massive stars in the Orion Nebula form a rough trapezoid called the Trapezium. The curved bright lines in the image are bow shocks.

"When you look closely, you see that the nebula is filled with hundreds of visible shock waves," said Bob O'Dell, an astronomer from Vanderbilt University.

O'Dell used Hubble to map Orion's stellar winds with unprecedented detail; he discovered that the shock waves can have different shapes, depending on whether the dust and gas clouds were moving or stationary when the winds passed through. He also found that different stellar winds can collide with one another, producing yet another type of shock wave shape.

By looking at the orientation of the shock waves, O'Dell was also able to determine the direction the winds blow within the nebula.

O'Dell combined all of this information to create a map of the stellar winds in two of Orion's three star-forming regions and found that some of the winds have been blowing continuously for nearly 1,500 years.

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