Press Release

Silhouette Reveals Hidden Shape of Young Star’s Envelope

By SpaceRef Editor
April 20, 2005
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Silhouette Reveals Hidden Shape of Young Star’s Envelope

Detailed new images of the starbirth nursery in the Omega Nebula (M17)
have revealed a multi component structure in the envelope of dust and
gas surrounding a very young star. The stellar newborn, called M17-SO1,
has a flaring torus of gas and dust, and thin conical shells of
material above and below the torus. Shigeyuki Sako from University of
Tokyo and a team of astronomers from the National Astronomical
Observatory of Japan, the Japan Aeorospace Exploration Agency, Ibaraki
University, the Purple Mountain Observatory of the Chinese Academy of
Sciences, and Chiba University obtained these images and analyzed them
in infrared wavelengths in order to understand the mechanics of
protoplanetary disk formation around young stars. Their work is
described in a detailed article in the April 21, 2005 edition of

The research team wanted to find a young star located in front of a
bright background nebula and use near-infrared observations to image
the surrounding envelope in silhouette, in a way comparable to how
dentists use X-rays to take images of teeth. Using the Infrared Camera
and Spectrograph with Adaptive Optics on the Subaru telescope, the
astronomers looked for candidates in and around the Omega Nebula, which
lies about 5,000 light-years away in the constellation Sagittarius.
They found a large butterfly-shaped near-infrared silhouette of an
envelope about 150 times the size of our solar system surrounding a
very young star. They made follow-up observations of the region using
the Cooled Mid-Infrared Camera and Spectrograph on the Subaru
telescope and the Nobeyama Millimeter Array at the Nobeyama Radio
Observatory. By combining the results from the near-infrared,
mid-infrared, and millimeter wave radio observations, the researchers
determined that the M17-SO1 is a protostar about 2.5 to 8 times the
mass of the Sun, and that the butterfly-like silhouette reveals an
edge-on view of the envelope.

The near-infrared observations reveal the structure of the surrounding
envelope with unprecedented levels of detail. In particular,
observations using the 2.166 emission line of hydrogen (called the
Brackett gamma (Br $B&C (B) line) show that the envelope has multiple
components instead of one simple structure. Around the equator of the
protostar, the torus of dust and gas increases in thickness farther way
from the star. Thin cone-shaped shells of material extend away from
both poles of the star.

The discovery of the multi-component structure puts new constraints on
how an envelope feeds material to a protostellar disk forming within
its boundaries. “It’s quite likely that our own solar system looked
like M17-SO1 when it was beginning to form,” said Sako. “We hope to
confirm the relevance of our discovery for understanding the mechanism
of protoplanetary disk formation by using the Subaru telescope to take
infrared images with high resolution and high sensitivity of many more
young stars.


SpaceRef staff editor.