Three powerful recent blasts from three wholly different regions in space have left scientists scrambling. The blasts, which lasted only a few seconds, might be early alert systems for star explosions called supernovae, which could start appearing any day. The first two blasts, called X-ray flashes, occurred on September 12 and 16. These were followed by a more powerful burst on September 24. The burst seems to be on the cusp between an X-ray flash and a full-fledged gamma ray burst, a discovery interesting in its own right. If these signals lead to supernovae, as expected, scientists would have a...