August 13, 2013
How Fast Does A Supernova Shockwave Travel? A Japanese Team May Have The Answer
Brett Smith for redOrbit.com - Your Universe Online
Some of the most spectacular explosions this side of the Big Bang, supernovae generate unthinkable amounts of force and energy and new research from Keio University in Japan has measured the expansion velocity of a supernova shockwave for the first time.
The shockwave measured by the research team was from the supernova remnant W44, which is located approximately 10,000 light years from Earth. Quantifying the expansion and kinetic energy of a supernova shockwave has been difficult in the past because a wide area must be observed and the existing equipment demands a long time to make these observations. The results are observations of interstellar gas being affected by a supernova shockwave that are limited to a small area.
In the study, which was published in The Astrophysical Journal, physicists led by Tomoro Sashida and Tomoharu Oka of Keio's Department of Physics began observations of the supernova remnant W44 and the adjacent giant molecular cloud (GMC) using radio telescopes in the late 1990s. The supernova remnant is estimated to be between 6,500 and 25,000 years old and its adjacent GMC has a mass about 300,000 times that of the Sun. Since observation began, the physicists have found molecular spectrum lines throughout W44’s molecular cloud that have been interpreted as gas that has been accelerated by a supernova shockwave.
These spectrum lines created by “galactic winds” were seen throughout the entire area where W44 overlapped the GMC. Based on observations of the spectrum lines, the Japanese team calculated a clear velocity gradient from the center to the edge of W44 – considered the expansion activity of molecular gas affected by a shockwave. They also determined the expansion velocity to be about 8 miles per second.
The physicists also determined the mass of shocked gas was about 1.2 times the mass of the Sun. From these calculations, the team was able to estimate that the entire kinetic energy transmitted from the supernova remnant to interstellar materials was consistent with previous calculations of around 10 percent.
The Japanese physicists said they plan to continue this research with the intent of investigating a larger number of shocked gases surrounding the supernovae to compare them with the results of their most recently published study and refined theoretical models.
NASA recently released images of another supernova remnant thought to be the youngest one in the Milky Way. Slightly farther than W44 at 26,000 light years away, the nebula and black hole that were formed by the exploding star are believed to be about 1,000 years old.
Based on observations from NASA’s Chandra X-ray Observatory, scientists said the star underwent an asymmetric explosion, which is somewhat unusual. Because images showed iron in only half of the remnant while other elements were spread throughout, NASA astronomers said the evidence was consistent for models of asymmetric explosions. The scientists also noted the supernova remnant, dubbed W49B, was more barrel-shaped than other remnants when seen through certain parts of the spectrum.
Most stars that supernovae collapse into have a dense spinning core called a neutron star – a select few, like W49B, leave a black hole behind.