NASA captures distant nebula W51, one of the largest 'star factories' in Milky Way

NASA's recently retired Spitzer Space Telescope has captured a spectacular image of one of the largest "star factories" in our Milky Way galaxy. First identified in 1958 by radio telescopes, the nebula known as W51 is one of the most active star-forming regions in our home galaxy.

The most massive stars in the universe are born inside cosmic clouds of gas and dust, where they leave behind clues about their lives for astronomers to decode.

Located about 17,000 light-years from Earth, in the direction of the constellation Aquila in the night sky, W51 is about 350 light-years – or about 2 quadrillion miles – across. It is almost invisible to telescopes that collect visible light (the kind human eyes detect), because that light is blocked by interstellar dust clouds that lie between W51 and Earth. But longer wavelengths of light, including radio and infrared, can pass unencumbered through the dust. When viewed in infrared by Spitzer, W51 is a spectacular sight: Its total infrared emission is the equivalent of 20 million Suns.

If you could see it with your naked eye, this dense cloud of gas and dust would appear about as large as the full Moon.

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Advancing understanding of star formation

This image was taken as part of a major observation campaign by Spitzer in 2004 to map the large-scale structure of the Milky Way galaxy – a considerable challenge because Earth lies inside it. Called the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), the survey also turned up valuable data on many wonders within the Milky Way, including images of multiple stellar factories like W51 that were hidden by dust from visible-light observatories.

"The really spectacular images provided by Spitzer via the GLIMPSE survey... give us insight into how massive stars form in our Milky Way, and then how their powerful winds and radiation interact with the remaining ambient material," said Breanna Binder, an assistant professor of physics and astronomy at California State Polytechnic University, Pomona, who studies the life cycles of massive stars. "We can't observe star-forming regions in other galaxies in anywhere near the level of detail that we can in our own galaxy. So regions like W51 are really important for advancing our understanding of star formation in the Milky Way, which we can then extrapolate to how star formation proceeds in other, nearby galaxies."

NASA's Spitzer Space Telescope launched 17 years ago this week, on August 25, 2003. The spacecraft was retired on January 30, 2020.

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