September 23, 2023

Failed star is the coldest radio wave source ever discovered

    lines of energy radiate outward from a brownish star

lines of energy radiate outward from a brownish star

Astronomers have discovered the coldest star-like body found to produce emissions at radio wavelengths.

Cooler than a campfire here on Earth and smaller than Jupiter, the faint object called T8 Dwarf WISE J062309.94-045624.6 is an ultracool brown dwarf, often referred to as “failed stars” because, despite usually being larger than gas giants, they are still smaller than stars.

With a temperature of just around 800 degrees Fahrenheit (425 degrees Celsius), the brown dwarf is a cool customer compared to the sun, which has a temperature of around 10,000 degrees Fahrenheit (5,500 degrees Celsius). Still, it’s not the coolest brown dwarf ever discovered; examples of these “failed stars” have been found at temperatures as low as 10 degrees Fahrenheit (minus 23 degrees Celsius), but these ultracold brown dwarfs emitted no radio waves.

“It is very rare to find ultracool brown dwarf stars like this one that produce radioemissions. That’s because their dynamics usually don’t produce the magnetic fields that generate radioemissions that can be detected from Earth,” said PhD student Kovi Rose of the University of Sydney School of Physics in a statement. “Finding this brown dwarf producing radio waves at such a low temperature is a nice discovery.”

Related: Brown dwarfs: failed stars that look like planets

Brown dwarfs lack the mass needed to initiate the nuclear fusion of hydrogen to helium in their cores, the process that defines main-sequence stars. Therefore, the study of these smoldering balls of gas is important, as it could help scientists better determine where the dividing line between gas giant planets and stars really lies.

T8 Dwarf WISE J062309.94-045624.6 was first spotted by scientists at the California Institute of Technology (Caltech) in 2011 using the Wide-field Infrared Survey Explorer (WISE). The brown dwarf is located about 37 light-years from Earth and has a width between 65% and 95% that of Jupiter, the largest planet in the solar system. However, the failed star is much more massive than the gas giant planet, with anywhere from 4 to 44 times the mass of Jupiter.

Related: Brown dwarfs: the coolest stars or the hottest planets?

An old fashioned radio mystery

Scientists have a good understanding of how hydrogen-burning main-sequence stars like the sun generate magnetic fields and radio waves. It is not well understood how the internal dynamics of brown dwarfs such as T8 Dwarf WISE J062309.94-045624.6 generate radio waves. This mystery is compounded by the fact that only 10% of the known population of these failed stars produce radio emissions.

Researchers suspect that it could be the rapid rotation of some ultracool brown dwarfs that helps them generate strong magnetic fields, and when these fields spin at a different speed than the ionized atmosphere of brown dwarfs, it creates an electric current.

A size comparison of stars, brown dwarfs and gas giants.

A size comparison of stars, brown dwarfs and gas giants.

In the case of T8 Dwarf WISE J062309.94-045624.6, the radio waves can be created when electrons flow towards the magnetic poles of the faulty star and give rise to regular bursts of radio waves. Further study of this cool failed star could help to finally solve this puzzle.

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

The analysis of T8 Dwarf WISE J062309.94-045624.6 revealing its radio emissions was performed by the CSIRO ASKAP telescope in Western Australia. This was subsequently confirmed with follow-up surveys by the Australia Telescope Compact Array and the MeerKAT telescope in South Africa.


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

The team’s research was published July 14 in The Astrophysical Journal.

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