It’s a little bit spooky, and very very cold.

A recent release from the Atacama Large Millimeter/submillimeter Array (ALMA) has revealed new information about the Boomerang Nebula, resulting in an eerie ghostly shape showing things may not have been quite as they originally seemed.

The Boomerang Nebula, called the “coldest place in the Universe,” reveals its true shape with ALMA. The background blue structure, as seen in visible light with the Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s resolution and ability to see the cold molecular gas reveals the nebula’s more elongated shape, as seen in red. Credit: Bill Saxton; NRAO/AUI/NSF; NASA/Hubble; Raghvendra Sahai.

The Boomerang Nebula, as the name suggests, was originally thought to be a lopsided shape. Observations with the Hubble telescope then suggested it was more of a bow-tie shape. Now, results from the ALMA radio telescope have indicated something slightly different, not previously noticed at visible wavelengths.

At 5000 light years away, the nebula was originally thought to be a lopsided shape (like a boomerang), while later observations with the Hubble Space Telescope seemed to suggest more of a bow-tie appearance. Now, the results from ALMA actually indicate something slightly different.

By pointing ALMA towards the Boomerang Nebula, which is the coldest known object in the Universe (coming in at -272ºC, just one degree above absolute zero), researchers were able to take the temperature of the gas and measure how it absorbed cosmic background radiation. The results showed the “central hourglass is surrounded by a patchy, but roughly round, cold high-velocity outflow” – making the image, as seen above, look something like a perfect last-minute Halloween costume.

From the release:

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. Further out, they actually observed a more elongated cloud of cold gas that is roughly round.

The researchers also discovered a dense lane of millimeter-sized dust grains surrounding the star, which explains why this outer cloud has an hourglass shape in visible light. The 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.

According to one of the paper’s authors, Yiannis Gonidakis, “the ALMA observations enabled us to study the properties and appearance of the Boomerang Nebula in more detail. This is a very important step in understanding the later stages of stellar evolution and how stars similar to our sun evolve to Planetary Nebulae. The discovery of the dense lane of millimetre-sized dust grains – a result for which data from the Australia Telescope Compact Array (ATCA) were also used – explains the hourglass appearance of this intriguing object.”


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