Ghostly Specter Haunts the ‘Coldest Place in the Universe

At a cosmologically crisp one degree Kelvin (minus 458 degrees Fahrenheit), the Boomerang nebula is the coldest known object in the universe -- colder, in fact, than the faint afterglow of the Big Bang, the explosive event that created the cosmos.
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."
As originally observed with ground-based telescopes, this nebula appeared lopsided, which is how it got its name. Later observations with NASA's Hubble Space Telescope revealed a bow-tie-like structure. The new ALMA data, however, reveal that the Hubble image tells only part of the story, and the twin lobes seen in that image may actually be a trick of light as seen at visible wavelengths.
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."
The Boomerang nebula, located about 5,000 light-years away in the constellation Centaurus, is a relatively young example of an object known as a planetary nebula. Planetary nebulas, contrary to their name, are actually the end-of-life phases of stars like our sun that have sloughed off their outer layers. What remains at their centers are white dwarf stars, which emit intense ultraviolet radiation that causes the gas in the nebulae to glow and emit light in brilliant colors.
Read the full ALMA release online at https://public.nrao.edu/news/pressreleases/alma-reveals-coldest-place-in-the-universe .
Additional authors on this paper include Wouter Vlemmings, Chalmers University of Technology, Onsala, Sweden; Patrick Huggins, New York University, New York; Lars-Ake Nyman, Joint ALMA Observatory, Santiago de Chile; and Yiannis Gonidakis, CSIRO, Australia Telescope National Facility.
ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by European Southern Observatory, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The California Institute of Technology in Pasadena manages JPL for NASA.