December 19, 2015
You were born on a tiny world orbiting an ordinary star in an unremarkable galaxy — and yet, the fact that you exist at all is the most...
Star Streams and the Whale Galaxy
Birthday · December 19, 2015
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APOD published December 19, 2015. Credit: R Jay Gabany. A publication-date match, not a photo taken on your date. Independent of NASA.
NGC 4631 is a spiral galaxy found only 25 million light-years away, toward the well-trained northern constellation Canes Venatici. Seen egde-on, the galaxy is similar in size to the Milky Way. Its distorted wedge shape suggests to some a cosmic herring and to others its popular moniker, The Whale Galaxy. The large galaxy's small, remarkably bright elliptical companion NGC 4627 lies just above its dusty yellowish core, but also identifiable are recently discovered, faint dwarf galaxies within the halo of NGC 4631. In fact, the faint extended features below (and above) NGC 4631 are now recognized as tidal star streams. The star streams are remnants of a dwarf satellite galaxy disrupted by repeated encounters with the Whale that began about 3.5 billion years ago. Even in nearby galaxies, the presence of tidal star streams is predicted by cosmological models of galaxy formation, including the formation of our own Milky Way.
Image credit: R Jay Gabany