Given the superb capabilities of the optics and associated instrumentation, the scientific possibilities are almost incredible. The most exciting investigations will no doubt result from the unexpected discoveries that the improved sensitivity, angular resolution, and energy resolution produces. The potential of Chandra is illustrated in Figure 
which shows the official "first-light" image. The target was the supernova remnant Cas A. This image, based on only a few thousand seconds observing time, was taken with the back-illuminated chip at the best focus position on the ACIS-S. We see, for the first time, that there is a compact, x-ray emitting object at the center of the 300-year-old remnant. Studies are underway to establish that the positional coincidence is no accident and to determine the nature of the compact object, possibly the long-sought after neutron star or black hole.
Figure: The official CXO first light image - the supernova remnant CasA.
Perhaps the neutron star - black hole connection and the utility of CXO are best illustrated by an early observation of the Crab Nebula and pulsar taken as part of the HETG calibration. During grating observations, one also obtains an undispersed (zero order) image. The image quality is essentially that of the HRMA/detector combination and not broadened by the insertion of the grating. Figure shows the zeroth-order image of the Crab Nebula. There are numerous new features, especially the inner ellipse with its bright knots. The pulsar itself is so bright that the central region is "piled up" to the point that there are no data - hence the "hole" in the image. Pile-up also is present in the data from the nebula and the study of the spectral dependence of these features ought to be the subject of a future ASI. The ubiquity of the jet phenomenon clearly points to the importance of angular momentum as a physical key and critical parameter towards unlocking secrets to all or part of the emission mechanisms.
Figure: The Chandra zeroth order image of the Crab Nebula.
The capability to perform meaningful, high-spectral-resolution observations with the gratings is illustrated in Figure , which shows a portion of the x-ray spectrum from Capella around the Fe-L complex. The red is a HEG spectrum and the green spectrum was produced by the MEG. Observations such as these - with CXO, XMM, and Astro-E - will be at the center of new developments in astrophysics in the next century.
Figure: HEG and MEG spectra of Capella.