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9 June 2017

Explaining the Boomerang Nebula - The Coldest Object in the Known Universe

Space is pretty darn cold, there’s no denying that. However even the most secluded reaches of space sit at a relatively constant temperature of around 2.725 Kelvin due to the natural background radiation present throughout space, which is considered by the scientific community to be a remnant of the Big Bang. The idea that anything situated within this vast vacuum could be any colder than space itself may seem illogical, but such objects do exist. One such object is the Boomerang Nebula, a largely unremarkable cloud of gas situated approximately 5,000 light-years from Earth. The nebula rests at a temperature of just 1 Kelvin, making it the coldest object in the known universe.

Speculation as to why the nebula is so cold has run rife for years, but now scientists from NASA’s Jet Propulsion Laboratory believe they may have found the answer. However before we can properly understand the mechanisms behind its startlingly low temperature, we must first understand what exactly the Boomerang Nebula really is.

The Boomerang Nebula is believed to be a form of protoplanetary nebula, which is the transitional phase in the death-cycle of a star between red giants and final planetary nebulae. It is essentially a huge shell of ionised gas being ejected from a collapsing red giant star at the centre. Under normal circumstances such nebulae would simply shed their outer layers over a period of thousands of years, losing heat gradually as the star dies and creating nothing particularly noteworthy in the temperature department.

So what makes the Boomerang Nebula any different?

Based on new information from the Atacama Large Millimeter/submillimeter Array (ALMA), a series of radio telescopes situated in the Atacama Desert of northern Chile, researchers now theorise that the somewhat bizarre temperature of the Boomerang Nebula was in fact caused by the presence of a smaller companion star. This companion star is thought to have been drawn in and eventually collided with its larger cousin, forcing the red giant’s matter to be expelled as a super-cooled outflow of gas and dust.

“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,” says lead researcher Raghvendra Sahai, an astronomer at NASA's Jet Propulsion Laboratory.

“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.”

This ultra-cold outflow is travelling at around 150km/s - 10 times faster than it would in a single star - and resulting in the protoplanetary nebula plunging down to a temperature of just 1 Kelvin. The coldest object in the known universe will not stay that way forever though, as it is already beginning to warm up gradually.

“We see this remarkable object at a very special, very short-lived period of its life,” says Lars-Åke Nyman, a researcher from the Joint ALMA Observatory in Chile who contributed his efforts to the study.

“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.”

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.