Astronomy Picture of the Day

Explanation: How much mass do flocculent spirals hide? The above true colour image of flocculent spiral galaxy NGC 4414 was taken with the Hubble Space Telescope to help answer this question. Flocculent spirals -- galaxies without well defined spiral arms -- are a quite common form of galaxy, and NGC 4414 is one of the closest. Stars and gas near the visible edge of spiral galaxies orbit the centre so fast that the gravity from a large amount of unseen dark matter must be present to hold them together. Pictured above is the photogenic centre of NGC 4414. A bright foreground star from our Milky Way Galaxy shines in the foreground of the image. Although NGC 4414's centre likely holds little dark matter, understanding its matter distribution helps calibrate the rest of the galaxy and, by deduction, flocculent spirals in general. By determining a precise distance to NGC 4414, astronomers also hope to help calibrate the scale to the more distant universe.