Energetic Jets from a Budding Solar System (Forwarded)

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998

April 9, 2008

DG Tau: Energetic Jets from a Budding Solar System
[http://chandra.harvard.edu/photo/2008/dgtau/]

The image on the left from NASA's Chandra X-ray Observatory shows the
first double-sided X-ray jet ever detected from a young star. A similar
jet may have been launched from the young Sun and could have had a
significant impact on the early solar system.

The young star, named DG Tau, is located in the Taurus star-forming
region, about 450 light years from Earth. The bright source of X-rays in
the middle of the image is DG Tau and the jet runs from the top left to
the bottom right, extending to about 70 billion miles away from the star,
or about 700 times the Earth-Sun separation.

A detailed analysis of this image, led by Manuel Guedel of the Institute
of Astronomy, ETH Zuerich in Switzerland, shows that the counter jet
(top-left) has, on average, higher energy X-rays than the forward jet
(bottom-right). The likely explanation is that some of the lower energy
X-rays in the counter jet are absorbed by a disk around DG Tau, as shown
in the accompanying illustration (right graphic), showing the star, disk
and the inner regions of the jets.

Highly energetic X-rays are also detected from the young star, partially
absorbed by streams of material flowing from the disk onto the star. The
disk itself is much too cool to be detected by Chandra. Note that the
faint vertical feature below the star does not show evidence for an
additional jet, but is a chance alignment of four photons.

The effects of the jet on its surroundings may be significant. Other
researchers have previously suggested that X-rays from a typical young
star can significantly affect the properties of its surrounding disk, by
heating it and creating charged particles by stripping electrons off atoms
(a process called ionization). These X-rays will strike the disk at a low
angle, mitigating their effects. In the case of the jets from DG Tau, the
combined X-ray power in the jet is similar to that of a young star with
relatively modest X-ray brightness, but X-rays from the jet have the
advantage of striking the disk much more directly from above and below.

Guedel and colleagues argue that powerful X-ray jets might develop at some
stage during the evolution of most young stars. They could, for example,
have existed during the early stages of the solar system. DG Tau has about
the same mass as the Sun, but is much younger with an age of about one
million years, rather than about 4.5 billion years. Since it is surrounded
by a disk where planets may be forming, this new Chandra image suggests
that the early Earth and its environment may have been bathed in X-rays
from a jet like DG Tau's. Although it is unknown if such X-rays would have
had a significant impact on the forming Earth, it is possible that they
did more good than harm. By ionizing the disk the X-rays may have
generated turbulence, which could have had a substantial effect on the
orbit of the young Earth, possibly helping to prevent it from making a
disastrous plunge into the Sun. Furthermore, X-ray irradiation of disks
may also be important in the production of complex molecules in the disk
that will later end up on the forming planets.

The new X-ray observations of X-ray jets add new features to the already
complex story of star and planet formation. The ionization and heating
power of the X-rays rom jets will have to be included in future model
calculations that will help scientists understand the physical evolution
and chemical processing of environments that eventually lead to planets
like those in our solar system.