Science and Tech

A small star is the coldest that emits radio waves

The relative size of a typical brown dwarf star.  The star in this study is between 0.65 and 0.95 the radius of Jupiter.

The relative size of a typical brown dwarf star. The star in this study is between 0.65 and 0.95 the radius of Jupiter. -NASA/JPL

July 14 () –

Astronomers from the University of Sydney have shown that a small and faint star is the coldest known to produce emission at radio wavelengths.

The “ultracold brown dwarf” examined in the study published in ‘The Astrophysical Journal’ is a ball of gas that simmers at about 425 degrees Celsius –cooler than a typical bonfire– without burning nuclear fuel. Instead, the surface temperature of the Sun, a nuclear hell, is about 5,600 degrees. Although it is not the coldest star ever found, yes, it is the coldest analyzed so far by radio astronomy.

Lead author and PhD student in the Faculty of Physics, Kovi Rose, notes that “Ultracold brown dwarf stars that emit radio are very rare. This is because their dynamics do not typically produce the magnetic fields that generate radio emissions.” detectable from Earth,” explains it’s a statement.

“Finding this brown dwarf producing radio waves at such a low temperature is a great discovery,” he continues. “Deepening our knowledge of ultracold brown dwarfs like this one will help us understand the evolution of stars, including how they generate magnetic fields.”

How the internal dynamics of brown dwarfs sometimes produce radio waves is something of an open question. Although astronomers have a good idea of ​​how larger “main sequence” stars, such as the Sun, generate magnetic fields and radio emissions, It is not yet fully understood why less than 10 percent of brown dwarf stars produce these types of emissions.

The rapid rotation of ultracool dwarfs is thought to contribute to their strong magnetic fields. When the magnetic field spins at a different speed than the dwarf’s ionized atmosphere, can create electrical current flows.

In this case, it is believed that the radio waves are produced by the entry of electrons into the magnetic polar region of the star, which, together with the rotation of the brown dwarf, produces regularly repeated radio bursts.

Brown dwarf stars, so named because they emit little energy or light, are not massive enough to initiate the nuclear fusion associated with other stars like our Sun.

According to Rose, “these stars are a kind of missing link between the smaller stars that burn hydrogen in nuclear reactions and the largest gas giant planets, such as Jupiter.

The star, under 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 radius of the star is between 0.65 and 0.95 that of Jupiter. Its mass is not well known, but it is at least four times as massive as Jupiter, but not more than 44 times as massive. The Sun is 1,000 times more massive than Jupiter.

The analysis of the star was carried out by Rose using new data from CSIRO’s ASKAP telescope in Western Australia, and supplemented with observations from the Australia Telescope Compact Array near Narrabri in New South Wales and the MeerKAT telescope in South Africa.

“We have only just gone live with ASKAP and are already finding many interesting and unusual astronomical objects, such as this one,” said Professor Tara Murphy, co-author of the study and Director of the School of Physics at the University of Sydney. As we open this window to the radio sky, we will improve our understanding of the stars around us and of the possible habitability of the exoplanet systems they host”.

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