A super-cold brown dwarf sent a radio signal to Earth and confused scientists

A giant but "super-cold" brown dwarf has sent out radio signals that have been picked up by scientists on Earth, even though stars of this type simply shouldn't be able to do so. This celestial object, which exists on the edge between a planet and a star, could help scientists learn more about the evolution of small stars.

The scientists reported their discovery in a study published in The Astrophysical Journal Letters. Only 10% of brown dwarfs are capable of generating radio signals, but they must be hot to do so.

The T8 Dwarf object WISE J062309.94-045624.6 (or simply W0623) is a so-called brown dwarf. It is a protostar that is similar in composition to gas giants like our Jupiter but can synthesize hydrogen atoms without being able to sustain full-scale nuclear fusion in the core as most stars do.

W0623 was first discovered in 2011 at a distance of about 37 light-years from Earth. The dwarf has a radius 0.65-0.95 times of Jupiter, but a mass about 44 times greater. This makes W0623 very dense.

W0623 is considered a cold object because its temperature reaches only 425 degrees Celsius. Charcoal, for example, can burn at 750-1200 degrees Celsius. Not to mention our Sun, whose surface heats up to 3700-7700 degrees Celsius.

In their study, scientists note that W0623 is the coldest star emitting weak radio waves. Usually, this type of electromagnetic radiation is produced by much larger and hotter stars.

"It is very rare to find ultra-cold brown dwarf stars like this one that emit radio emission," study's lead author, University of Sydney doctoral student Covey Rose said.

According to him, the inability of brown dwarfs to generate radio emission happen because such protostars do not create the necessary magnetic field, as they do not occur in nuclear fusion.

At the same time, about 10% of brown dwarfs are still able to emit radio waves, but most of them have a surface temperature of about 2200 degrees Celsius. Scientists admit that they "don't fully know" why super-cold W0623 emits signals that can be detected from Earth.

However, the researchers believe that the magnetic fields of radio-emitting brown dwarfs rotate much faster than their ionized upper atmospheres. This creates an electrical flow in which electrons fall into the magnetic polar regions of the star. This electrical rain combines with the star's rotation to create regularly recurring radio bursts.

Astronomers are particularly interested in brown dwarfs because of how close they stand to the boundary between star and planet.

"These stars are a kind of missing link between the smallest stars burning hydrogen in nuclear reactions and the largest gas giant planets like Jupiter," Rose explained.

According to him, if scientists knew more about them, they would be able to understand how both types of celestial bodies evolve.

Earlier OBOZREVATEL shared the fact that astronomers managed to catch a strange radio signal from a rocky exoplanet YZ Ceti b, orbiting its star 12 light years from Earth. Scientists suggest that the received signal may indicate the existence of a magnetic field necessary for life.

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