Sunday, April 20, 2008

Titanic Blast

Credit: Hubble - News Release Number: STScI-2008-17

Peering across 7.5 billion light-years and halfway back to the Big Bang, NASA's Hubble Space Telescope has photographed the fading optical counterpart of a powerful gamma ray burst that holds the record for being the intrinsically brightest naked-eye object ever seen from Earth. For nearly a minute on March 19, this single "star" was as bright as 10 million galaxies.

Hubble Wide Field and Planetary Camera 2 (WFPC2) images of GRB 080319B, taken on Monday, April 7 show the fading optical counterpart of the titanic blast. Hubble astronomers had hoped to see the host galaxy where the burst presumably originated, but were taken aback that the light from the gamma ray burst is still drowning out the galaxy's light even three weeks after the explosion.

Hubble astronomers had hoped to see the host galaxy where the burst presumably originated, but were taken aback that the light from the GRB is still drowning out the galaxy's light even three weeks after the explosion. This is particularly surprising because it was such a bright GRB initially. Previously, bright bursts have tended to fade more rapidly, which fits in to the theory that brighter GRBs emit their energy in a more tightly confined beam. The slow fading leaves astronomers puzzling about just where the energy came from to power this GRB, and makes Hubble's next observations of this object in May all the more crucial.

Called a long-duration gamma ray burst, such events are theorized to be caused by the death of a very massive star, perhaps weighing as much as 50 times our Sun.

Such explosions, sometimes dubbed "hypernovae," are more powerful than ordinary supernova explosions and are far more luminous, in part because their energy seems to be concentrated into a blowtorch-like beam that, in this case, was aimed directly at Earth.

The Hubble exposure also shows field galaxies around the fading optical component of the gamma ray burst, which are probably unrelated to the burst itself.
Star Formation in the Hinterlands from Centauri Dreams
Stellar Birth in the Galactic Wilderness from Universe Today

Sunday, April 13, 2008

Energetic Jets

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

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.

Tuesday, April 01, 2008

Galaxy Wars

Galaxy Wars: M81 versus M82. - Click on Image to Enlarge.
Astronomy Picture of the Day. - Credit: Rainer Zmaritsch & Alexander Gross

On the left, surrounded by blue spiral arms, is spiral galaxy M81. On the right marked by red gas and dust clouds, is irregular galaxy M82.

This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years.

The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays.

In a few billion years only one galaxy will remain.
Supernova Alert: “Supernova Factories” Discovered from Universe Today