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Astronomers Discover Coldest Star Emitting Radio Waves

Ultracool brown dwarf found at 425°C is the coolest star analyzed using radio astronomy

The coldest star yet that emits radio waves has been identified by astronomers.

The “ultracool brown dwarf” is a ball of gas simmering at about 425 degrees Centigrade – cooler than a typical campfire.

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

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

While not the coldest star ever found, it is the coolest so far analyzed using radio astronomy.

Study lead author 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.

An image displaying the relative size of a typical brown dwarf star. PHOTO BY NASA/SWNS

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

He said that 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 such as 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 emissions.

The rapid rotation of ultracool dwarfs is thought to play a role in generating their strong magnetic fields.

When the magnetic field rotates at a different speed from the dwarf’s ionized atmosphere, it can create electrical current flows.

In this particular 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, are not massive enough to ignite the nuclear fusion associated with other stars like our Sun.

Rose, a Ph.D. student in the School of Physics, added: “These stars are a kind of missing link between the smallest stars that burn hydrogen in nuclear reactions and the largest gas giant planets, like Jupiter.”

The star, with the name T8 Dwarf WISE J062309.94−045624.6, is located about 37 light years from Earth. It was discovered in 2011 by astronomers at Caltech in the United States.

The star’s radius is between 0.65 and 0.95 that of Jupiter.

Its mass is not well understood but is at least four times more massive than Jupiter but no more than 44 times more massive. The Sun is 1,000 times more massive than Jupiter.

The analysis of the star, published in The Astrophysical Journal, was made by Rose using new data from the CSIRO ASKAP telescope in Western Australia and followed up with observations from the Australia Telescope Compact Array near Narrabri in New South Wales and the MeerKAT telescope in South Africa.

Study co-author Professor Tara Murphy, head of the School of Physics at the University of Sydney, said: “We’ve just started full operations with ASKAP and we’re already finding a lot of interesting and unusual astronomical objects, like this.”

She added: “As we open this window on the radio sky, we will improve our understanding of the stars around us, and the potential habitability of exoplanet systems they host.”

Produced in association with SWNS Talker

Edited by and

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