Newly discovered star is cooler than a lighter flame

According to a new study published in Astrophysical Journal Letters published, researchers have spotted the coolest star emitting radio rays. Complicatedly named WISE J062309.94-045624.6, the brown dwarf has a temperature of just 420 degrees Celsius. That’s about five times hotter than a cup of coffee and also hotter than an oven, but cooler than the flame of a conventional lighter.

For comparison: Our sun has an estimated surface temperature of about 6000 degrees Celsius. “In some cases, [Sterne] cooler than the smoke rising from our campfire – I mean, that’s inspiring,” Kovi Rose, a PhD student in astronomy at the University of Sydney and the study’s lead author, told the New York Times. “It’s inspiring and humbling to understand our place in the universe.”

Brown dwarfs are also called “failed stars”.

According to the scientists, the fact that the brown dwarf emits radio radiation indicates an extraordinary phenomenon, namely that the cool dwarf star has a magnetic field. However, WISE J062309.94−045624.6 is a very different kind of star than our sun.

“A brown dwarf is between a star and a planet in mass and temperature,” Tara Murphy, a professor of astronomy at the University of Sydney and a co-author of the study, told the New York Times.

The brown dwarf is sometimes referred to as a “failed star”. It’s fairly small compared to other stars — smaller than Jupiter — so it doesn’t have nearly enough gravitational pull to perform nuclear fusion.

Like the Sun and Jupiter, however, brown dwarfs are composed mostly of hydrogen gas, possibly with swirling cloud bands. However, unlike the sun, they have no internal source of energy and emit barely any visible light. They are therefore impossible to see with the naked eye.

Instead of relying on conventional telescopes, the researchers carried out measurements with the radio telescopes ASKAP, MeerKAT and the Australia Telescope Compact Array to look for radio waves emitted by the electromagnetic fields of the stars. They found that the star has a maximum mass of 44 times that of Jupiter and emits radio emissions whose intensity fluctuates with a period of about 1.9 hours.

The researchers suspect that the brown dwarf performs a complete rotation around itself during this time. This rapid rotation causes the star to form a magnetic field and emit radio emissions.

In the case of the star WISE J062309, the radiation fluctuated regularly because the axis of the magnetic field is slightly tilted with respect to the axis of rotation of the star. As a result, the alignment of the radiation is repeated every 1.9 hours.

Rose points out that this observation of brown dwarfs like this provides important insights into the evolution of low-mass stars and the formation of magnetic fields and radio waves in such objects.

“Each band of this electromagnetic spectrum opens up a whole new window on the universe,” Murphy told the NYT. “It’s like a detective story.”