SETI bioastro: Get to know your neighborhood

From: Larry Klaes (
Date: Sat Apr 15 2000 - 10:15:42 PDT

The Local Interstellar Cloud
Illustration Credit & Copyright: Linda Huff (American Scientist),
Priscilla Frisch (U. Chicago)

Explanation: The stars are not alone. In the disk of our Milky Way
Galaxy about 10 percent of visible matter is in the form of gas,
called the interstellar medium (ISM). The ISM is not uniform, and
shows patchiness even near our Sun.

It can be quite difficult to detect the local ISM because it is so
tenuous and emits so little light. This mostly hydrogen gas, however,
absorbs some very specific colors that can be detected in the light
of the nearest stars.

A working map of the local ISM within 10 light-years based on recent
observations is shown above. These observations show that our Sun is
moving through a Local Interstellar Cloud as this cloud flows outwards
from the Scorpius-Centaurus Association star forming region.

Our Sun may exit the Local Interstellar Cloud during the next 10,000
years. Much remains unknown about the local ISM, including details of
its distribution, its origin, and how it affects the Sun and Earth.

The Local Bubble and the Galactic Neighborhood

Illustration Credit & Copyright: Linda Huff (American Scientist),
Priscilla Frisch (U. Chicago)

Explanation: What surrounds the Sun in this neck of the Milky Way
Galaxy? Our current best guess is depicted in the above map of the
surrounding 1500 light years constructed from various observations and

Currently, the Sun is passing through a Local Interstellar Cloud (LIC),
shown in violet, which is flowing away from the Scorpius-Centaurus
Association of young stars. The LIC resides in a low-density hole in
the interstellar medium (ISM) called the Local Bubble, shown in black.

Nearby, high-density molecular clouds including the Aquila Rift surround
star forming regions, each shown in orange. The Gum Nebula, shown in green,
is a region of hot ionized hydrogen gas. Inside the Gum Nebula is the Vela
Supernova Remnant, shown in pink, which is expanding to create fragmented
shells of material like the LIC.

Future observations should help astronomers discern more about the local
Galactic Neighborhood and how it might have affected Earth's past climate.

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