Credit: X-ray: NASA/CXC/ETH Zuerich/M.Guedel et al.; Illustration: NASA/CXC/M.Weiss

NASA’s Chandra X-ray Observatory (CXO) recently imaged powerful X-ray emitting jets emanating from an energetic young star. The star, known as DG Tau, is estimated to be only one million years old (the Solar System is believed to have formed about 4,500 million years ago). It is located in the Taurus star-forming region, about 450 light years away.

The star is the bright object in the middle of the X-ray image. The jets run from the top left to the bottom right. They are expansive features stretching to about 70 billion miles, or about 700 times the Earth-Sun distance.

A team of researchers, led by Manuel Guedel of the Institute of Astronomy in Zuerich, carried out a detailed analysis of this image, and showed that the counter jet (top-left) has, on average, higher energy X-rays than the forward jet (bottom-right). A plausible explanation is that some of the lower energy X-rays in the counter jet are absorbed by a disk of material around DG Tau, as illustrated in the 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 fluxes of material streaming from the disk onto the star. The disk’s temperature is too cool for the disk to be detected by Chandra. The faint vertical feature below the star does not show evidence for an additional jet, but is a chance alignment of four photons.

The jet may have a significant influence on its surroundings. Other researchers have previously postulated that X-rays from a typical young star can significantly affect the properties of its surrounding disk, by heating it and by knocking electrons off atoms, a process termed ionization.

These X-rays will impact the disk at a small 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 faint X-ray emission, but X-rays from the jet have the advantage of striking the disk much more directly from above and below.

Guedel and collaborators argue that most young stars might develop powerful X-ray jets at some stage during their evolution. It is believed that jets could have erupted during the early stages of the Solar System. The mass of DG Tau is similar to that of the Sun, but the Sun, believed to be in the middle of its estimated lifetime of about 10,000 million years, is much older.

Since DG Tau is encircled by a disk where planets may be forming, this new Chandra image suggests that the infant Earth and the space around it may have been embedded in X-rays from a jet like that emanating from DG Tau. Although it is unknown if such X-rays would have had a significant impact on the early Earth, they probably were more beneficial than harmful.

By ionizing the disk, the X-rays may have induced turbulence, which could have substantially affected the orbit of the young Earth, possibly preventing it from falling toward the Sun. Moreover, X-ray radiation pouring onto a disk may also be crucial for 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 effects of the X-rays from jets will have to be included in future models that would enable scientists to understand the physical and chemical processes that eventually lead to planets like those in our Solar System.

Further Reading
CXO
http://chandra.harvard.edu/photo/chronological.html

Aymen Mohamed Ibrahem
Senior Astronomy Specialist