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        Fan  of the old TV shows and saws cientists revive nearly dead humanb eings, bringing them back to lifew it high-tech body parts that gavet hem extraordinary capabilities.     Today, replacing parts of the human body using state-of-the-art technology is moving out of the realm of science fiction and into reality.            Replacement of body parts means transplanting organs and tissues from one person to another or using artificial body parts. Organs currently transplanted are the heart, kidneys, liver, lungs, pancreas, and intestines. Tissues and cells include the corneas, cartilage, muscles, tendons, ligaments, skin, and heart valves (mechanical versions of the valves are also used).         Artificial limbs and organs can replace parts throughout the body. Doctors commonly replace knees and hips, along with finger, elbow, and shoulder joints. Cochlear implants are electr...

       Supernovas can occur in one of two ways: through a process of runaway nuclear fusion or through a rapid collapse of the star’s core.         The first process occurs in binary star systems where at least one star is a white dwarf, a dense, aging star that can no longer support nuclear fusion. The secondstar can be another white dwarf, a redgiant, or a main sequence star such as our own Sun, that fuses hydrogen atoms to form helium atoms at its core. In either case, the white dwarf siphons off (or collides with) the mass of its companion star, reigniting nuclear fusion. Once the white dwarf reignites, it gets so hot so fast that it blows apart, outshining an entire galaxy and leaving no remnant behind.           Less luminous, though no less spectacular, are core collapse supernovas.Instead of exploding in a runaway fusion reaction, this type of supernova occurs when the star’s fusion reaction grinds ...