The Boomerang nebula is the coldest known object in the Universe. Is colder, in fact, than the faint afterglow of the Big Bang, at a cosmologically crisp one degree Kelvin (minus 458 degrees Fahrenheit).   Image © NRAO/AUI/NSF/NASA/STScI/JPL-Caltech

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile have taken a new look at this object to learn more about its frigid properties and to determine its true shape, which has an eerily ghost-like appearance.

“This ultra-cold object is extremely intriguing and we’re learning much more about its true nature with ALMA,” said Raghvendra Sahai, a researcher and principal scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and lead author of a paper published in the Astrophysical Journal. “What seemed like a double lobe, or boomerang shape, from Earth-based optical telescopes, is actually a much broader structure that is expanding rapidly into space.”

The researchers discovered a dense lane of millimeter-sized dust grains surrounding the star, which explains why its outer cloud has an hourglass shape in visible light. These minute dust grains have created a mask that shades a portion of the central star and allows its light to leak out only in narrow but opposite directions into the cloud, giving it an hourglass appearance.

“This is important for the understanding of how stars die and become planetary nebulas,” said Sahai. “Using ALMA, we were quite literally, and figuratively, able to shed new light on the death throes of a sun-like star.”

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