Astronomers identify the coldest stars emitting radio waves


July 13, 2023

(Nanowerk News) Astronomers at the University of Sydney have shown that the faintest small star on record is the coldest emitter at radio wavelengths.

The ultracool brown dwarfs studied in this study are balls of gas that boil at about 425 degrees Celsius – colder than an ordinary bonfire – without burning nuclear fuel.

In contrast, the surface temperature of the Sun, a nuclear hell, is about 5600 degrees.

While not the coldest star ever discovered, it is the coldest star so far analyzed using radio astronomy. These findings were published in Astrophysics Journal. relative sizes of brown dwarfs Brown dwarfs are common in the universe but rarely emit radio waves. (Image: NASA)

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

“Finding a brown dwarf that generates radio waves at such low temperatures is a neat find.”

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

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

The fast rotation of ultracool dwarfs is thought to play a role in generating strong magnetic fields. When the magnetic field rotates at a different speed than the dwarves’ ionized atmosphere, it can create a flow of electric current.

In this case, it is thought that radio waves are produced by the flow of electrons into the magnetic pole region of the star, which, coupled with the brown dwarf’s rotation, produces regularly repeating radio bursts.

Brown dwarfs, so called because they emit little energy or light, are not massive enough to power the nuclear fusion associated with other stars like our sun.

Mr Rose said: “These stars are sort of the missing link between the smallest stars that burn hydrogen in nuclear reactions and the biggest gas giant planets, like Jupiter.

This star with the interesting 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 radius is between 0.65 and 0.95 Jupiter radii. Its mass is not well understood but is at least four times as massive as Jupiter but no more than 44 times as massive. The sun is 1000 times larger than Jupiter.

The star analysis was carried out by Rose using new data from the CSIRO ASKAP telescope in Western Australia and followed up with observations from the Australian Compact Array Telescope near Narrabri in NSW and the MeerKAT telescope in South Africa.

Professor Tara Murphy, co-author and Head of the School of Physics at the University of Sydney, said: “We have recently started full operations with ASKAP and we have already discovered many interesting and unusual astronomical objects, such as this one.

“When we open this window in the radio sky, we will increase our understanding of the stars around us, and the potential habitability of the exoplanet systems they occupy.”


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