SPACEFLIGHT NOW
Array stares into the throat of protostar jet
HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE
Posted: June 16, 2005

Astronomers find jets everywhere when they look into
space. Small jets spout from newborn stars, while huge
jets blast out of the centers of galaxies. Yet despite
their commonness, the processes that drive them
remain shrouded in mystery. Even relatively nearby
stellar jets hide their origins behind almost
impenetrable clouds of dust. All stars, including our
sun, pass through a jet phase during their "childhood,"
so astronomers are eager to understand how jets form
and how they may influence star and planet
formation.
Herbig-Haro 211 consists of two jets of material, visible at
lower right, blasting from a young protostar hidden behind
dust. The Submillimeter Array has looked deep within the inner
regions of the jets, close to their launching point, in order to
test predictions of jet formation models. This infrared image
was taken using the FLAMINGOS camera, which was designed
and constructed at the University of Florida. Credit: A.A.
Muench-Nasrallah, CfA

At this week's meeting on submillimeter astronomy in
Cambridge, Mass., astronomers described the latest
results from an international collaboration using the
Submillimeter Array (SMA) atop Mauna Kea,
Hawaii. The SMA has begun to peer through the dust
and home in on the sources of nearby stellar jets.

"Using the SMA, we can stare into the throat of the
jet," said SMA project scientist Paul Ho of the
Harvard-Smithsonian Center for Astrophysics
(CfA). "We're getting close to seeing its launching
point."

Astronomer Hsien Shang of the Academia Sinica
Institute of Astronomy and Astrophysics (ASIAA)
and her colleagues have created a model of jet
formation that calculates temperatures, densities and
brightnesses within stellar jets. SMA observations of a
young star system prosaically named Herbig-Haro
(HH) 211 have confirmed the validity of the model.

"Our model predicts what we will see about 100
astronomical units from the star," Shang said. (One
astronomical unit is the average Earth-Sun distance
of 93 million miles.) "With the SMA, we can begin to
look at the HH 211 system at the scale of the model
and test those predictions. So far, everything checks
out." HH 211 is located about 1,000 light-years away in the
constellation Perseus. Astronomers estimate that the
small protostar hidden within HH 211 is less than
1,000 years old-a mere baby by astronomical
standards, so young that it is still growing by
accumulating matter from a surrounding disk of gas
and dust. The protostar eventually will become a
low-mass star similar to the sun.

Although most of the matter in the disk will flow onto
the star, some must be ejected outward to carry away
excess angular momentum. Complex physical
processes funnel that
ejected matter into dual jets that shoot outward in opposite directions.

"Jets form very close to a protostar, within about 5
million miles of its surface according to the model we
applied" said researcher Naomi Hirano (ASIAA).
"The SMA can help test the jet model on the youngest
protostars using molecular tracers from within that
innermost region."

SMA's successor, the planned ALMA project, should
finally reveal the nature of the engine powering these
jets by peering into the core where they form.

"The SMA has brought us tantalizingly close to our
goal-the answer to the question of how jets form,"
said Ho. "ALMA will take us those final few steps."

Headquartered in Cambridge, Mass., the
Harvard-Smithsonian Center for Astrophysics (CfA)
is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College
Observatory. CfA scientists, organized into six
research divisions, study the origin, evolution and
ultimate fate of the universe.