The Infrared Universe
Many of the most interesting infrared objects are associated with star
Stars form from collapsing clouds of gas and dust. As the cloud collapses,
its density and temperature increase. The temperature and density are
highest at the center of the cloud, where a new star will eventually form.
The object that is formed at the center of the collapsing cloud and which
will become a star is called a protostar. Since a protostar is embedded
in a cloud of gas and dust, it is difficult to detect in visible light.
Any visible light that it does emit is absorbed by the material surrounding
it. Only during the later stages, when a protostar is hot enough for its
radiation to blow away most of the material surrounding it, can it be seen
in visible light. Until then, a protostar can be detected only in the
infrared. The light from the protostar is absorbed by the dust surrounding
it, causing the dust to warm up and radiate in the infrared. Infrared studies
of star forming regions will give us important information about how
stars are born and thus on how our own Sun and Solar System were formed.
Infrared telescopes have cataloged thousands of hot, dense cores within
clouds of gas and dust which could be newly forming stars.
To the right are two infrared images of star forming regions:
an IRAS view of the constellation Orion in which there are several regions
active star formation, and an image from the new Spitzer Space Telescope of
newborn stars in the nebula NGC 7129.
IRAS image of Orion (left) and Spitzer image of NGC 7129 (right)
Laird Close, University of Hawaii
Protostars which are starting to blow away the gas and dust surrounding them
are called T-Tauri stars. The warm dust remaining around T-Tauri stars still
radiates in the infrared.
There is evidence that the remaining dust and gas
surrounding T-Tauri stars form rotating disks which may mark the beginnings
of planetary systems.
Herbig-Haro objects, which are also associated with newly forming stars, can
be studied in the infrared. These are small nebulae which vary in shape and
brightness over a period of only a few years. Both Herbig-Haro objects and
T-Tauri stars are found in regions of active star formation. It is thought
that these nebulae represent high speed gas flowing from young stars
colliding with interstellar clouds. The study of T-Tauri stars and Herbig-Haro
objects will help us understand the details on how stars are formed.
To the left s an infrared adaptive optics
image of a T-Tauri stars (UY Aur).
To the right is an infrared image of the Kleinmann-Low Nebula, a region
of intense star formation in the constellation Orion. In visible light
much of this region is hidden by dust however in the infrared you can
see the effects of the hot winds produced by newly formed massive stars.
These hot winds heat up the surrounding gas and cause them to radiate
strongly in the infrared. The winds will eventually clear much of the
gas and dust surrounding the stars.
CISCO, Subaru 8.3-m Telescope, NAOJ
C. Robert O'Dell, Shui Kwan Wong (Rice University),NASA
and R. Thompson (U. Arizona) et al., NASA
Here is a comparison of a visible light (left) and an infrared (right)
view of OMC-1 (OMC stands for Orion Molecular Cloud) taken by the
Hubble Space Telescope.
In this region of active star formation
you can clearly see the benefits of observing in the infrared.
The visible light image does not show many features because optical
telescopes cannot see past the thick areas of dust and gas in which new
stars are formed. By contrast, in the infrared we can "see" past the
dust. The infrared image shows stars and glowing interstellar dust
heated by the intense starlight of the newborn stars.
Globules are also found in star forming regions. These are small clouds
(~ 1 light year in diameter) which contain 10 to 1000 solar masses of gas
and dust. In visible light, globules are seen in dark silhouette against
bright nebulae. They produce no visible light of their own and are thought
to be collapsing clouds which will produce stars. Infrared observations
from IRAS showed that some globules contain protostars.
To the right is an infrared image of the
globule in the nebula IC 1396 taken
by the new Spitzer Space Telescope.
Spitzer's sensitive infrared detectors unveiled the brilliant hidden interior
of this opaque cloud of gas and dust and revealed, for the first time, a
glowing stellar nursery with never-before-seen young stars and stars still in
the process of formation. The inset shows a visible light view of the same
Infrared Universe Index |
Star Formation |
Extrasolar Planets |
Our Galaxy |
Other Galaxies |
Between the Stars |
Missing Mass - Brown Dwarfs? |
The Early Universe