Astronomy Picture of the Day

Explanation: A bright spiral galaxy of the northern sky, Messier 63 is about 25 million light-years distant in the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way. Known by the popular moniker, The Sunflower Galaxy, M63 sports a bright yellowish core and sweeping blue spiral arms, streaked with cosmic dust lanes and dotted with pink star forming regions. This deep exposure also reveals an enormous but dim arc extending far into the halo above the brighter galactic plane. A collaboration of professional and amateur astronomers has shown the arc to be consistent with the stellar stream from a smaller satellite galaxy, tidally disrupted as it merged with M63 during the last 5 billion years. Their discovery is part of an increasing body of evidence that the growth of large spirals by cannibalizing smaller galaxies is commonplace in the nearby Universe.