ALMA Telescope Reveals New Shape of Boomerang Nebula, the Coldest Place in the Universe

The latest observations of the coldest place in the universe -- the Boomerang Nebula -- reveal the frigid dying star has a previously unobserved ghost-like shape.

At 5,000 light years away in the constellation Centaurus, the Boomerang Nebula has been a focal point for numerous cosmological studies, revealing that its temperature is only 1 degree Kelvin (minus 458 Fahrenheit); it is even colder than the natural background temperature of space.

But previous observations of the nebula, the first of which were taken from Earth, did not paint a complete picture of its shape. It appeared lopsided, which is how it became known as the Boomerang Nebula. Later, observational from the Hubble Space Telescope revealed an intriguing bow-tie shape in the nebula.

Now, a new round of observations taken by the Atacama Large Millimeter/submillimeter Array (ALMA) telescope suggest that the Hubble images may have been an optical illusion created by light in the visible spectrum.

"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 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 Boomerang Nebula is relatively young for a planetary nebula, not yet hot enough to produce the characteristic glow found in others. Instead, the nebula is illuminated by starlight reflecting off of dust grains swirling within it.

The Hubble images of the nebula suggested it had an hour-glass shape. But other telescopes were unable to detect the narrow "waist" of the hourglass, instead finding a more uniform, spherical shape.

The ALMA observations put the discrepancy to rest.

"By observing the distribution of carbon monoxide molecules, which glow brightly at millimeter wavelengths, the astronomers were able to detect the double-lobe structure that is seen in the Hubble image, but only in the inner regions of the nebula," the researchers said in a statement. "Further out, they actually observed a more elongated cloud of cold gas that is roughly round."

The hour-glass shape documented in the Hubble images was also reconciled. The new research suggests a "mask" of dust particles shade a portion of the dying star at the nebula's core, allowing light to leak out only in narrow, opposite directions and producing the hour-glass shape.

The new observations also suggest that the outer perimeter of the nebula is beginning to warm, even though they are still slightly colder than the cosmic background temperature.

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