The Boomerang Nebula reveals its true shape with ALMA. (Credit: Bill Saxton; NRAO/AUI/NSF; NASA/Hubble; Raghvendra Sahai)
The Atacama Large Millimeter/submillimeter Array (ALMA) is finally complete, after the project's final 12-meter antenna was handed over on Sept. 30, 2013. The 66th dish, shown here, is the last of 25 European-built instruments. The Joint ALMA Observatory (JAO) is a collaboration between the European Southern Observatory (ESO), the National Radio Astronomy Observatory (NRAO) and the National Astronomical Observatory of Japan (NAOJ).
All 66 millimetre/submillimetre-wave radio antennas are expected to be operational by the end of 2013, working together as one large telescope. ALMA will operate as an interferometer, spread over 16 kilometers of the Chajnantor Plateau in the Atacama Desert, Chile.
ALMA is sensitive to millimetre and submillimetre wavelengths, between infrared light and radio waves in the electromagnetic spectrum, a range that will help astronomers peel back the veil on distant objects in the Cosmos.
ALMA (ESO/NAOJ/NRAO)/Jaime Guarda
The giant antenna transporter, called Otto, delivers the final antenna to the array on Sept. 30, 2013.
The final dish was built by the European AEM Consortium, the largest of the project's contracts. North America delivered 25 12-meter antennas and East Asia delivered 16 (four 12-meter and twelve 7-meter).
"This is an important milestone for the ALMA Observatory since it enables astronomers in Europe and elsewhere to use the complete ALMA telescope, with its full sensitivity and collecting area," said Wolfgang Wild, the European ALMA Project Manager.
Clem & Adri Bacri-Normier (wingsforscience.com)/ESO
An artist's impression of the complete ALMA array in the Atacama Desert.
As October progresses and winter slowly but surely approaches in the Northern Hemisphere, trees begin to lose their leaves and temperatures steadily drop. Think it’s been getting cold out at night where you live?
It’s nothing like this.
At a positively frigid one Kelvin (that equates to –458 degrees Fahrenheit or –272 degrees Celsius), the Boomerang Nebula in the constellation Centaurus is officially the coldest known place in the entire Universe. It’s even colder than the background temperature of space!
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers have taken a better look at this freezing cloud of gas and dust to learn more about its frigid properties.
The Boomerang Nebula has been imaged before by both ground-based telescopes and the Hubble Space Telescope, and appears in visible light to be shaped like a bow tie (or two opposing, overlapped boomerangs). But new observations using ALMA’s high-resolution capabilities have revealed its true form.
“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,” 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.
A thick belt of dust particles has also been found – thanks to ALMA – surrounding the star within the nebula, which prevents some wavelengths of light from passing through and creating the bow tie shape seen in previous visible light images.
Hubble image of the Boomerang nebula taken in 1998 with the Wide Field Planetary Camera 2 instrument. Credit: NASA, ESA, R. Sahai and J. Trauger (Jet Propulsion Laboratory) and the WFPC2 Science Team.
So why is this nebula so incredibly cold? It’s actually cooling itself off as it grows, astronomers have found.
As the sun-like star at its center nears the end of its life it expands the nebula with rapidly outpouring gas. That expansion creates a cooling effect — similar to how expanding gas in refrigerators helps keep your ice cream from melting.
The gas in this nebula is traveling much faster than anything in your fridge, though — 500,000 km/hour (310,000 mph).
At one Kelvin the Boomerang nebula is even colder than the coldest known places in our solar system: the permanently-shadowed craters at the moon’s south pole that never receive sunlight. Even those pockets of darkness are a balmy 33 Kelvin. (For comparison, water freezes at 273.15 K.)
For that matter, even in the midst of intergalactic space where there’s “nothing” is still warmer — the cosmic microwave background glows at a steady 2.8 K.
The new research also shows that the outer edges of the nebula are warming as the outward expansion of gas slows — even though they are still slightly colder than the CMB.
“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.”
The Boomerang nebula is located 5,000 light-years from Earth within our Milky Way galaxy.