The Horsehead Nebula is shown in red and green against the surrounding cold molecular cloud (blue). The red areas are carbon monoxide molecules sheltered in the dense nebula and the green areas are carbon atoms and ions that have been affected by the radiation from nearby stars.
Credits: NASA/SOFIA/J. Bally et. al
Two research teams used a map
from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, to
uncover new findings about stars forming in Orion’s iconic Horsehead
Nebula. The map reveals vital details for getting a complete
understanding of the dust and gas involved in star formation.
The Horsehead Nebula is embedded in the much larger Orion B giant molecular cloud
and is extremely dense, with enough mass to make about 30 Sun-like
stars. It marks the boundary between the surrounding cold molecular
cloud -- filled with the raw materials needed to make stars and
planetary systems -- and the area to the west where massive stars have
already formed. But the radiation from the stars erodes those raw
materials. While the cold molecules, like carbon monoxide, deep within
the dense nebula are sheltered from this radiation, molecules on the
surface are exposed to it. This triggers reactions that can affect star
formation, including the transformation of carbon monoxide molecules
into carbon atoms and ions, called ionization.
A team, led by John Bally at the Center for Astrophysics
and Space Astronomy, at the University of Colorado in Boulder, wanted to
learn if the intense radiation from nearby stars is strong enough to
compress the gas within the nebula and trigger new star formation. They
combined data from SOFIA and two other observatories to get a
multifaceted view of the structure and motion of the molecules there.
Bally’s team found that the radiation from the nearby stars
creates hot plasma that compresses the cold gas inside the Horsehead,
but the compression is insufficient to trigger the birth of additional
stars. Nevertheless, they learned key details about the nebula’s
structure.
The radiation caused a destructive ionization wave to crash over the
cloud. That wave was stopped by the dense Horsehead portion of the
cloud, causing the wave to wrap around it. The Horsehead developed its
iconic shape because it was dense enough to block the destructive forces
of the ionization wave.
“The shape of the iconic Horsehead Nebula speaks to the
movement and velocity of this process,” said Bally. “It really
illustrates what happens when a molecular cloud is destroyed by ionized
radiation.”
Researchers are trying to understand how stars formed in
the Horsehead Nebula -- and why additional stars did not -- because its
proximity to Earth allows astronomers to study it in great detail. This
provides clues to how stars may form in distant galaxies that are too
far away for fine details to be observed clearly by even the most
powerful telescopes.
“In studies such as this, we are learning that star
formation is a self-limiting process,” said Bally. “The first stars to
form in a cloud can prevent the birth of additional stars nearby by
destroying adjacent parts of the cloud.”
In another study based on SOFIA’s map, a team of
researchers lead by Cornelia Pabst, of Leiden University, Netherlands,
analyzed the structure and brightness of the gas within cold dark
regions in and around the Horsehead Nebula. This region has very little
star formation compared to the Orion B Cloud or the Great Nebula in Orion,
southwest of the Horsehead Nebula. Pabst and her team wanted to
understand the physical conditions in the dark region that may be
affecting the star formation rate.
They found that the shape, structure and brightness of the gas in the nebula do not fit existing models.
Further observations are
necessary to explore why the models do not match with what was observed.
“We’re just beginning to understand that, even though we
only looked at a very small portion of this molecular cloud, everything
is more complicated than what the models initially indicated,” said
Pabst. “This map is beautiful, valuable data that we can combine with
future observations to help us understand how stars form locally, in our
galaxy, so we can then relate that to extragalactic research.”
The studies were published in The Astronomical Journal and Astronomy and Astrophysics.
The Horsehead Nebula map used by both teams was created
using SOFIA’s upgraded GREAT instrument. It was upgraded to use 14
detectors simultaneously, so the map was created significantly faster
than it could have been on previous observatories, which used only a
single detector.
“We could not have done this research without SOFIA and its
upgraded instrument, upGREAT.” said Bally. “Because it lands after each
flight, its instruments can be adjusted, upgraded and improved in ways
not possible on space-based observatories. SOFIA is fundamental to
developing ever more powerful and reliable instruments for future use in
space.”
SOFIA is a Boeing 747SP jetliner modified to carry a
100-inch diameter telescope. It is a joint project of NASA and the
German Aerospace Center, DLR. NASA’s Ames Research Center in
California’s Silicon Valley manages the SOFIA program, science and
mission operations in cooperation with the Universities Space Research
Association headquartered in Columbia, Maryland, and the German SOFIA
Institute (DSI) at the University of Stuttgart. The aircraft is based at
NASA’s Armstrong Flight Research Center's Hangar 703, in Palmdale,
California. NASA/SOFIA
Media Point of Contact
Nicholas A. Veronico
650.224.8726 cell
Nicholas.A.Veronico@nasa.gov
Written by Kassandra Bell
SOFIA Science Center
Editor: Kassandra Bell
Source: NASA/SOFIA
