Figure 23-13: A Supernova in a Spiral Galaxy These images from the Very Large Telescope show the spiral galaxy M100 (a) before and (b) after a Type Ia supernova exploded within the galaxy in 2006. (The two images were made with different color filters, which gives them different appearances.) Such luminous supernovae, which can be seen at extreme distances, are important standard candles used to determine the distances to faraway galaxies. The distance to M100 is also known from observations of Cepheid variables (see Figure 23-4), so this particular supernova can help calibrate Type Ia supernovae as distance indicators.
(European Southern Observatory)