Two jets of high-speed particles from what appears to be either a black hole or neutron star are shooting off in opposite directions and punching their way into the supernova remnant that surrounds them, stretching what was once a spherical shell of shimmering gas into an egg-shaped remnant.
Dr. Samar Safi-Harb at NASA Goddard Space Flight Center (Greenbelt, Md.) probed the interaction between the jets and the surrounding remnant with the Rossi X-ray Timing Explorer (RXTE) satellite. She presents her findings today at the Rossi 2000 meeting at Goddard.
" For years we have seen with radio and X-ray telescopes what seems to be an elongated supernova remnant called SNR W50," said Safi-Harb, a National Research Council fellow at Goddard. "We could not determine whether particle jets from THE central source, known as SS433, were truly stretching out the remnant, or whether the jets were interacting with the surrounding space in such a way to create the illusion of a remnant. The RXTE data, together with many earlier multi-wavelength imaging studies, show that jets are interacting with a remnant and distorting it."
A supernova remnant forms when a star several times more massive than our sun runs out of its nuclear fuel and explodes. The expanding gases from the explosion form a shell that spreads out into the surrounding universe and eventually dissipates.
Particle jets form as a byproduct of a process called accretion. Black holes and neutron stars, which both exert extreme gravitational force, can pull gas away from a neighboring star. This transfer of gas onto the black hole or neutron star, called accretion, often produces X-ray light as the gas is accelerated by gravity to very high speeds. Through a mechanism still poorly understood, jets of matter can shoot away from the polar regions of neutron stars or perpendicularly from the direction of accretion onto black holes. It is not known whether the central object in SNR W50 is a binary system containing a black hole or one containing a neutron star.
The combination of particle jets trapped within the bubble of the supernova remnant is likely common, for the star that explodes to form a supernova remnant leaves behind a neutron star or black hole as its core. However, this system that Safi-Harb and others have studied for years -- a remarkable object called SS433 inside SNR W50 -- is the only known system of its kind in our galaxy.
Safi-Harb's latest observation of this region with RXTE revealed that particles are slamming into the inner walls of the remnant and are producing X-ray radiation that is non-thermal. Thermal radiation is produced solely by heat, for example, from the hot gas of the star explosion. The supernova remnant itself emits thermal radiation. Non-thermal radiation results from particle interactions, such as electrons or protons running into walls of gas.
These first signs of non-thermal radiation from RXTE provided Safi-Harb with the evidence that the supernova shell is not naturally elongated. Nor is it an illusion created by jets running into interstellar gas -- that is, particles interacting with the surrounding space and blowing a bubble of hot thermal gas. Rather, the remnant is being distorted by the action of the jets on the SNR shell, producing strong shock waves and radiating in higher X-ray energies.
The observation also provides the first hint of cosmic ray acceleration in a supernova remnant powered by a jet. Cosmic rays are atomic particles -- in this case, electrons and positrons -- propelled to near light-speeds and high energies. In a supernova called SN1006, astronomers saw the first evidence of electron cosmic rays produced by the shock waves of the expanding supernova remnant. SNR W50, in contrast, appears to harbor cosmic rays produced in jets. This amazing jet and bubble system is an estimated 10,000 to 16,000 light years from Earth.
The origin of cosmic rays, which constantly bombard the earth, is a long-standing astronomical mystery, and Safi-Harb's work adds one more piece to the puzzle.
Contributors to Safi-Harb's work are Drs. Robert Petre of Goddard and Philippe Durouchoux of Saclay, France.
Rossi 2000 is the first meeting to bring together the diverse pool of observational astronomers and theorists utilizing RXTE, which was built at Goddard and launched by NASA in December, 1995. Over 150 researchers are scheduled to attend the meeting, held March 22-24. Images to support this release are available at: http://universe.gsfc.nasa.gov/press/images/rossi2000/
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