Crab Nebula changes its brightness
It used to be that the Crab nebula’s x-ray and gamma ray brightness was so constant that astronomers used it as a “standard candle” to assess the brightness of other sources in the sky. However, continued observation now shows that its brightness varies over the years. In 2011, astronomers reported finding that the hard x-ray and gamma ray flux from the Crab Nebula was declining by 3.5% per year. More








