A group of astronomers has discovered that a small, faint “brown dwarf” star is the coldest star on record yet and still produces emission at radio wavelengths. The findings were published last week in The Astrophysical Journal Letters and describe a star that is only 797 degrees Fahrenheit, compared to campfires on Earth that 1500 to 1650 degrees.
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Called the “ultracool brown dwarf”. T8 Dwarf WISE J062309.94-045624.6 is not the coldest star ever found, but according to the team of this study, it is the coolest that can be analyzed using radio astronomy.
“It is very rare to find ultra-cool brown dwarf stars like this one that emit radio emissions. That’s because their dynamics usually don’t produce the magnetic fields that generate radio emissions that can be detected from Earth,” co-author and University of Sydney doctoral student Kovi Rose said in a statement. “Finding this brown dwarf producing radio waves at such a low temperature is a nice discovery. By deepening our knowledge of ultracool brown dwarfs like this one, we can understand the evolution of stars, including how they generate magnetic fields.”
Astronomers still question the internal dynamics of brown dwarf stars that produce radio waves. They do have a good idea how larger stars such as the sun generate radio emissionsbut it is not fully known why less than 10 percent of brown dwarf stars produce these emissions.
It is possible that the rapid rotation of ultracool dwarfs plays a role in generating their strong magnetic fields. Electric current flows can occur when the magnetic field rotates at a different speed than the star’s ionized atmosphere. For this star the team believes that radio waves could be produced by the influx of electrons into the star’s magnetic polar region, which, when added to the star’s rotation, produces regularly repeating radio bursts.
![Solar system photo](https://www.popsci.com/uploads/2023/07/17/star-comparison-chart.jpeg)
This star is considered a brown dwarf because it doesn’t give off much light or energy and isn’t large enough to unleash nuclear fusion like our sun and other stars do.
“These stars are sort of a missing link between the smallest stars that burn hydrogen in nuclear reactions and the largest gas giant planets, such as Jupiter,” Rose said.
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T8 Dwarf WISE J062309.94-045624.6 was first discovered in 2011 and is about 37 light-years from Earth. Brown dwarfs are considered “failed stars” because, despite typically being larger than gas giants, they are still smaller than other stars. The width of this particular star is believed to be between 65 percent and 95 percent the size of our solar system’s largest planet, Jupiter. However, this brown dwarf is anywhere from four to 44 times denser than Jupiter.
New data from the CSIRO ASKAP telescope in Western Australia followed by observations from the Australia Telescope Compact Array near Narrabri in New South Wales. The MeerKAT telescope in South Africa also helped make this discovery possible.
“We’ve just started full operations with ASKAP and we’re already finding a lot of interesting and unusual astronomical objects, like this one,” co-author and University of Sydney astrophysicist Tara Murphy said in a statement. “Opening this window to the radio sky will improve our understanding of the stars around us, and the potential habitability of exoplanet systems that harbor them.”