June 26, 2013
Chandra Discovers Supernova Remnant Emission Is Mostly Synchrotron Radiation
Lee Rannals for redOrbit.com – Your Universe Online
In 2008, a team of scientists discovered the remains of a supernova known to have occurred in the Milky Way, about 28,000 light years away from Earth. The explosion would have been visible from Earth a little more than a hundred years ago, assuming it was not obscured by dust and gas. Observations with NASA's Chandra X-ray Observatory has allowed scientists to discover new details about this event.
The source of G1.9+0.3 was most likely a white dwarf star that underwent a thermonuclear detonation and was destroyed after merging with another white dwarf. This class of supernova, Type Ia, are used as distance indicators in cosmology because they are so consistent in brightness.
The explosion ejected stellar debris at high velocities, which created the supernova remnant that is seen today by Chandra and other telescopes. This new image is a composite from Chandra where low-energy X-rays are red, intermediate energies are green and higher-energy ones are blue.
Chandra data has shown that most of the X-ray emission is "synchrotron radiation," produced by extremely energetic electrons accelerated in the rapidly expanding blast wave of the supernova. This emission gives information about the origin of cosmic rays, but not much information about Type Ia supernovae.
Some of the X-ray emission comes from elements produced in the supernova, which helps provide clues to the nature of the explosion. Most Type Ia supernova remnants are symmetrical in shape, with debris evenly distributed in all directions. However, G1.9+0.3 is an asymmetric pattern, which derives from elements like silicon, sulfur and iron in the northern part of the remnant.
G1.9+0.3 also features iron far away from the center and moving at extremely high speeds of over 3.8 million miles per hour.
Due to the uneven distribution of the remnant's debris and their extreme velocities, the researchers believe the original supernova explosion had very unusual properties. They said the explosion itself must have been highly non-uniform and unusually energetic.
The team said G1.9+0.3 experienced a "delayed detonation" where the explosion occurs in two different phases. During the first phase, nuclear reactions occur in a slowly expanding wavefront, producing iron and similar elements. The energy from these reactions causes the star to expand, changing its density and allowing a much faster-moving detonation front of nuclear reactions to occur.
Chandra's data allowed the scientists to have a close-up view of G1.9+0.3's rapidly changing debris. Many of these changes are driven by the radioactive decay of elements ejected during the explosion.
Scientists using NASA's Swift space observatory just recently discovered remains of the youngest-known supernova remnant in the Milky Way. The team believes the shattered star is likely less than 2,500 years old, making it one of the 20 youngest remnants ever found.