Cosmic ray font: supernova remnants rev up ions.
In 1572, the Danish astronomer Tycho Brahe Tycho Brahe: see Brahe, Tycho. created a sensation when he reported that a star suddenly appeared in the sky, blazing brighter than Venus, and then faded from view. Tycho's "new star" was in fact a supernova, an exploding old star. More than 4 centuries later, observations of the remnant of Tycho's supernova are still revealing information to astronomers. High-resolution X-ray images now offer evidence that shock waves from that and other supernovas generate most of the cosmic rays cosmic rays, charged particles moving at nearly the speed of light reaching the earth from outer space. Primary cosmic rays consist mostly of protons (nuclei of hydrogen atoms), some alpha particles (helium nuclei), and lesser amounts of nuclei of carbon, nitrogen, that bombard bom·bard
tr.v. bom·bard·ed, bom·bard·ing, bom·bards
1. To attack with bombs, shells, or missiles.
2. To assail persistently, as with requests. See Synonyms at attack, barrage2.
X-ray images taken a decade ago showed that shock waves from supernova remnants List of bright supernovas
Name Visible Magnitude distance Type Remnant
Sagittarius A East ? ? 26,000 ly ? Sagittarius A East
W49B ? ? 35,000 ly ? GRB remnant?
W50 ? ? 16,000 ly ? SS 433
Vela Supernova 11th-9th millennium BC ? 800 ly ? Vela Supernova Remnant can accelerate electrons to cosmic ray cosmic ray
High-speed particle (atomic nucleus or electron) that travels through the Milky Way Galaxy. Some cosmic rays originate from the Sun, but most come from outside the solar system. energies, but electrons make up only about 10 percent of cosmic rays. Energetic ions, the main component of cosmic rays, don't generate much light and are much more difficult to trace than electrons. Some cosmic ray researchers have presumed that these heavier cosmic particles also have a supernova origin, but astronomers have had scant evidence.
In a new study with NASA's Chandra X-ray Observatory Chandra X-ray Observatory
U.S. X-ray space telescope. It was named after astrophysicist Subrahmanyan Chandrasekhar and was launched into orbit in 1999. Its mirror, with an aperture of 1.2 m (4 ft) and a focal length of 10 m (33 ft), produces unprecedented resolution. , Jennifer S. Warren of Rutgers University in Piscataway, N.J., and her colleagues found signs of cosmic ray ions in the Tycho supernova. Their work, reported in an upcoming Astrophysical Journal, focuses on the outer part of the remnant. The team measured the width of the gap between the shock wave moving outward from the explosion and the expanding bubble of supernova debris that lies not far behind it.
The gap material consists of gas that has been compressed and energized by the outgoing shock. Standard supernova theory, which doesn't acknowledge that remnants might produce cosmic ray ions, predicts that the gap should be about 2 light-years wide. But Warren's team found that the gap measures only about half a light-year.
The most likely explanation for the narrower gap, the team says, is that the shock wave has accelerated charged particles in the gap to high speeds, thereby producing cosmic rays. High-speed particles are much more easily compressed than slower-moving material. To compress the gas to the extent observed, the high-speed particles must include ions as well as electrons, Warren says.
If other supernova remnants also produce cosmic ray ions, most of the cosmic rays that hit Earth could arise from such remnants.
"This work ... adds to the evidence that supernova remnants produce cosmic ray ions," comments Don Ellison of North Carolina State University History
Area, 52,586 sq mi (136,198 sq km). Pop. State, predicted that remnants would prove to be the main source of cosmic ray ions.
The new finding could force astronomers to rethink basic assumptions about the structure and evolution of supernova remnants, Ellison says.