Astronomy Picture of the Day

Explanation: How do stars form?Images of the star forming region W5 like those in the infrared by NASA's Wide Field Infrared Survey Explorer (WISE, later NEOWISE) satelliteprovide clear clues with indications that massive stars near the center of empty cavities are older than stars near the edges. A likely reason for this is that the older stars in the center are actuallytriggeringthe formation of the younger edge stars. The triggeredstar formationoccurs when hot outflowing gas compresses cooler gas intoknots denseenough to gravitationally contract into stars. In the featured scientifically colored infrared image, spectacular pillarsleft slowly evaporating from the hot outflowing gasprovide further visual clues.W5 is also known asWesterhout 5 (W5) and IC 1848. Together with IC 1805, the nebulasform a complex region of star formation popularly dubbed theHeartand Soul Nebulas.The featured image highlights a part of W5 spanning about 2,000 light years that is rich instar forming pillars. W5 lies about 6,500 light years away toward theconstellation of Cassiopeia.