The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. "It's possible these super cosmic freezers are quite common in the universe, but they can only maintain such extreme temperatures for a relatively short time." "We see this remarkable object at a very special, very short-lived period of its life," noted Lars-Åke Nyman, an astronomer at the Joint ALMA Observatory in Santiago, Chile, and co-author on the paper. Even now, the Boomerang Nebula is slowly warming. These conditions, however, will not last long. Traveling more than 150 kilometers per second, it took material at its outer edges approximately 3,500 years to reach these extreme distances after it was first ejected from the dying star. The ultra-cold outflow is more than 10 times bigger. The hourglass outflow stretches more than three trillion kilometers from end to end (about 21,000 times the distance from the Sun to the Earth), and is the result of a jet that is being fired by the central star, sweeping up the inner regions of the ultra-cold outflow like a snowplow. The new ALMA observations also produced an evocative image of this pre-planetary nebula, showing an hourglass-shaped outflow inside a roughly round ultra-cold outflow. For the Boomerang Nebula to absorb that radiation, it had to be even colder than this lingering, dim energy that has been continually cooling for more than 13 billion years. This radiation provides the natural background temperature of space - only 2.725 degrees above absolute zero. When the Boomerang Nebula was first observed in 1995, astronomers noted that it was absorbing the light of the Cosmic Microwave Background, which is the leftover radiation from the Big Bang. The Boomerang Nebula represents the very early stages of this process, a so-called pre-planetary nebula. Planetary nebulae are dazzling objects created when stars like our sun (or a few times bigger) shed their outer layers as an expanding shell near the end of their nuclear-fusion-powered life. The red giant star at its center is expected to shrink and get hotter, ultimately ionizing the gas around it to produce a planetary nebula. The Boomerang Nebula is located about 5,000 light-years from Earth in the constellation Centaurus. "The extreme properties of the Boomerang challenge the conventional ideas about such interactions and provide us with one of the best opportunities to test the physics of binary systems that contain a giant star," adds Wouter Vlemmings, an astronomer at Chalmers University of Technology in Sweden and co-author on the study.
"The only way to eject so much mass and at such extreme speeds is from the gravitational energy of two interacting stars, which would explain the puzzling properties of the ultra-cold outflow." Such close companions may be responsible for the early and violent demise of most stars in the universe, Sahai noted.
"These new data show us that most of the stellar envelope from the massive red giant star has been blasted out into space at speeds far beyond the capabilities of a single, red giant star, " said Raghvendra Sahai, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author on a paper appearing in the Astrophysical Journal. The ALMA observations enabled the researchers to unravel this mystery by providing the first precise calculations of the nebula's extent, age, mass, and kinetic energy. Zero degrees Kelvin is known as absolute zero, the point at which all thermodynamic motion stops. This outflow is expanding so rapidly - about 10 times faster than a single star could produce on its own - that its temperature has fallen to less than half a degree Kelvin (minus 458.5 degrees Fahrenheit). The answer, according to astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), may be that a small companion star has plunged into the heart of the red giant, ejecting most the matter of the larger star as an ultra-cold outflow of gas and dust.
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