Task: Text Categorization
Input (English): A mass extinction at the end of the Ordovician period is suggested to have been caused by one of these. In 2000, NASA launched the High Energy Transient Explorer 2 to detect them as their signals reach earth so ground observers can better study them. About a million times more numerous than supernovae, they are thought to be the result of a collapse of super-massive stars or collision between compact objects like a black hole and a neutron star. For ten points, name these astronomical phenomena that release a large amount of its namesake radiation.
Output (English): Science