Cooler than a campfire and smaller than Jupiter, this brown dwarf star is a rare find — ScienceDaily | Science & Technology

Astronomers at the University of Sydney have shown that a small, faint star is the coldest on record to produce emission at radio wavelength.

The ‘ultracool brown dwarf’ examined in the study is a ball of gas simmering at about 425 degrees centigrade — cooler than a typical campfire — without burning nuclear fuel.

By contrast, the surface temperature of the Sun, a nuclear inferno, is about 5600 degrees.

While not the coldest star ever found, it is the coolest so far analysed using radio astronomy. The findings are published today in The Astrophysical Journal Letters.

Lead author and PhD student in the School of Physics, Kovi Rose, said: “It’s very rare to find ultracool brown dwarf stars like this producing radio emission. That’s because their dynamics do not usually produce the magnetic fields that generate radio emissions detectable from Earth.

“Finding this brown dwarf producing radio waves at such a low temperature is a neat discovery.”

“Deepening our knowledge of ultracool brown dwarfs like this one will help us understand the evolution of stars, including how they generate magnetic fields.”

How the internal dynamics of brown dwarfs sometimes produce radio waves is something of an open question. While astronomers have a good idea how larger ‘main sequence’ stars like the Sun generate magnetic fields and radio emissions, it is still not fully known why fewer than 10 percent of brown dwarf stars produce such emission.

The rapid rotation of ultracool dwarfs is thought to play a part in generating their strong magnetic fields. When the magnetic field rotates at a different speed to the dwarf’s ionised atmosphere, it can create electrical current flows.

In this instance, it is thought the radio waves are being produced by the inflow of electrons to the magnetic polar region of the star, which, coupled with the rotation of the brown dwarf star, is producing regularly repeating radio bursts.

Brown dwarf stars, so called as they give off little energy or light,…

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