Astronomical Targets

Of the many potential scientific targets for the observatory, black holes were sure to seize the interest of the public, even though so little is known about them. ''We don't really know what happens very close to a black hole and how space and time are warped,'' said Tananbaum. ''Einstein's equations make some predictions and, so far, the data available seem to support that. We are pretty convinced that black holes actually do exist.'' By definition, however, they are 'unobservable', but can be studied indirectly by analysing radiation emitted by material being sucked into them.

As gas and dust is accelerated, for example, it collides with increased energy levels and emits X-rays before vanishing. By examining such emissions in unprecedented detail, Weisskopf explained, astrophysicists hoped ''to really nail down black hole signatures''. Additionally, supernova explosions thought to lead to black holes came under Chandra's X-ray gaze: in fact, one of its first celestial targets was the remnant of a massive star in the Large Magellanic Cloud that was seen to explode in 1989.

''It's thought all sorts of shocks will start to occur in the next few years when the expanding cloud of debris starts hitting all the other stuff that was thrown off from the outer envelope of the star before it exploded,'' said Tananbaum. ''We should be doing assaying of the abundances, the temperature and density and pressure states of that different material. It should look like a Christmas tree.'' Further, as the expanding shockwave from the supernova reaches material thrown off earlier, energetic collisions should create heavier elements and generate radiation to yield clues about the star's original chemical composition.

Tananbaum even hoped, optimistically perhaps, that if Chandra's planned lifespan of ''at least five years'' could be extended to a full decade, as the material expands, it might be possible to slightly separate any central source, ''which could be a pulsar or it could be just a cooling neutron star. We may actually be able to see the surface of the neutron star as it's cooling just a few years after the explosion.''

On a far larger scale, Chandra would also focus on the amount of 'dark matter' present in the Universe by carefully examining galactic clusters. Such galaxies that make up these clusters are deeply embedded in huge clouds of hot, X-ray-emitting gas and are held in place by gravity generated by all the components of the cluster.

''The only thing that can be holding it is gravity,'' said Tananbaum, ''and then you can say to yourself: I see the gas [and] the stars and the galaxies; they generate a certain amount of gravity. Is that enough to hold onto the hot gas? The answer is always 'no' by factors of 10, or in some cases more.'' Chandra's observations were expected to enable astronomers to refine their numbers of how much 'normal' matter is present in a given cluster and thus how much 'dark matter' must be present to generate gravity needed to hold it together.

''It may not be able to tell exclusively what the dark matter is,'' he added, ''but we should be able to see how much is there with greater precision.'' Analyses of supernovae shockwaves and neutron star emissions were also expected to provide insights into the physics behind nuclear fusion. ''We'll be able to dissect the energy spectrum and really get a handle on the nitty-gritty details of the emission mechanisms in a laboratory that you just don't have on Earth,'' said Tananbaum. ''That's going to have some incredibly profound consequences down the road.''

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