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Cassiopeia A

Through a series of observations in 2004, the Chandra X-ray Observatory accumulated a million seconds of observations on Cassiopeia A, a remnant of a supernova explosion. Cas A was the first object Chandra observed, and it has continued to probe ever deeper into its structure and composition. These new observations were arranged by Una Hwang of Goddard Space Flight Center.

The three color image (below, center) shows an outer ring (enhanced in green via the color coding of the energies) that marks the location of the shock wave generated by the supernova explosion. A large, jet-like structure protruded beyond the shock wave to the upper left. Surprisingly, X-ray spectra show that the jet has relatively large amount of silicon and low amount of iron. The cause for this is part of on-going detailed studies. In addition, enhancing the image to show just the silicon (below, right) reveals a counter-jet to the lower right.

Iron, however, is present in the remnant. The bright blue region just inside the shock wave on the lower left is composed of iron gas. It was somehow ejected in a direction almost perpendicular to the jets.

One curious feature of Cas A is that the central neutron star (visible in the broadband image, below left) is quiet, unlike the pulsars that lie in the center of the Crab nebula and the Vela supernova remnant. A working hypothesis is that the explosion that created Cassiopeia A produced high-speed jets similar to but less energetic than the hypernova jets thought to produce gamma-ray bursts. During the explosion, the neutron star may have developed an extremely strong magnetic field that helped to accelerate the jets. This strong magnetic field later stifled any pulsar wind activity, so the neutron star today resembles other strong-field neutron stars (a.k.a. "magnetars") in lacking a pulsar wind nebula.

broadband image of Cas A
A broadband X-ray image showing the remnant in the Chandra X-ray range of 1.75 - 7.0 keV.
energy-coded image of Cas A
An image of the remnant color coded by energy: Red represents X-rays from 1.78-2.0 keV; Green=4.2-6.4 keV; Blue=6.52-6.95 keV.
silocon image of Cas A
An image enhanced to emphasize the location of silicon in the remnant.

Million-second observation of Cassiopeia A taken by the Chandra X-ray Observatory in 2004. Each image is 8 arcminutes on a side. (Credit: NASA/CXC/GSFC/U. Hwang et al.)

Source: Chandra X-ray Observatory