THE INTERPLAY OF STARLIGHT,
GAS, AND DUST IN THE LARGE MAGELLANIC CLOUD
Complex interactions of starlight with interstellar
gas and dust in a nearby galaxy are revealed in
a new image obtained by NASA's Hubble Space Telescope
and presented by the Hubble Heritage team.
Hubble's Wide Field Planetary Camera 2 (WFPC2)
was positioned on a small region within a gas cloud,
or nebula, called DEM L 106. It belongs to the Large
Magellanic Cloud, a galaxy lying 160,000 light-years
from our own Milky Way galaxy. DEM L 106 appears
in this image as the faint, glowing hydrogen gas
that covers most of the picture. This nebula was
originally cataloged in the 1970's by astronomers
R. Davies, K. Elliot, and J. Meaburn, who created
the "DEM" catalogs of both the Large and
Small Magellanic Clouds.
The smaller and much brighter gas cloud near the
top of the image, called N30B, was discovered in
the 1950's by astronomer K. Henize, who later became
a NASA astronaut. The N30B nebula surrounds a group
of hot, blue stars that have recently formed through
gravitational contraction of the gas. The ultraviolet
radiation streaming out from these blue stars strips
electrons off of the hydrogen atoms in the surrounding
gas, causing the gas to glow through a process of
fluorescence.
The very bright star near the upper left corner
of the picture is cataloged as Henize S22; it is
a very hot and luminous supergiant star, lying only
25 light-years from the N30B nebula. It is a rare
and peculiar type of blue star that is believed
to be surrounded by a dense, dusty disk. This disk
reddens the light from the star, just as the dusty
Earth atmosphere reddens sunlight at sunset. As
viewed from N30B, S22 would appear some 250 times
as bright as the planet Venus does in Earth's sky.
This bright starlight illuminates interstellar dust
particles in N30B, producing a faint glow around
it, called a reflection nebula, that somewhat resembles
the numeral 8 turned on its side. The band of gas
across the bottom of the image is part of the shell
wall of a giant superbubble created by the stellar
wind of S22. The shroud of gas surrounding N30B
also shows a bow shock from the S22 wind.
Lowell Observatory astronomer M.S. Oey and University
of Illinois astronomer Y.-H. Chu are members of
a science team studying DEM L 106. Along with their
collaborators, Oey and Chu have made a clever use
of the reflection nebula around N30B. By obtaining
spectroscopic observations at various points across
the nebula, they can study the spectrum of S22 from
different angles. Remarkably, they have found that
the star's spectrum changes with viewing angle,
confirming that the star is surrounded by a flattened
disk of gas, that is probably expelled from its
equator. (See supplemental
page for more information.)
Archived Hubble images of DEM L 106 taken in 1998
were combined with data taken by the Hubble Heritage
Team in late 2001. The final image shows emission
in hydrogen and ionized sulfur, as well as stellar
colors at blue, visual and infrared wavelengths.
Credits: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: M.S. Oey (Lowell Observatory) and
Y.-H. Chu (U. of Illinois) |
