The T8-dwarf WISE J062309.94-045624.6 is the coolest and latest-type star observed to produce radio emission, according to an analysis of data from CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP), a radio telescope situated about 800 km north of Perth, in the Murchison region of Western Australia.
Brown dwarfs are common in the Universe but are rarely found to emit radio waves. Image credit: NASA.
WISE J062309.94-045624.6 (WISE J0623 for short) is located about 37 light-years away from Earth in the constellation of Monoceros.
First discovered in 2011 by Caltech astronomers, the star has a radius between 0.65 and 0.95 Jupiter radii and a mass between 4 and 44 Jupiter masses.
While not the coldest star ever found, WISE J0623 is the coolest so far analyzed using radio astronomy.
“It’s very rare to find ultracool brown dwarf stars like this producing radio emission,” said Kovi Rose, a Ph.D. student
“That’s because their dynamics do not usually produce the magnetic fields that generate radio emissions detectable from Earth.”
“Finding this brown dwarf producing radio waves at such a low temperature is a neat discovery.”
“Deepening our knowledge of ultracool 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.
While astronomers have a good idea how larger main-sequence stars like our Sun generate magnetic fields and radio emissions, it is still not fully known why fewer than 10% of brown dwarf stars produce such emission.
The rapid rotation of ultracool dwarfs is thought to play a part in generating their strong magnetic fields.
When the magnetic field rotates at a different speed to the dwarf’s ionized atmosphere, it can create electrical current flows.
In this instance, it is thought the radio waves are being produced by the inflow of electrons to the magnetic polar region of the star, which, coupled with the rotation of the brown dwarf star, is producing regularly repeating radio bursts.
“These stars are a kind of missing link between the smallest stars that burn hydrogen in nuclear reactions and the largest gas giant planets, like Jupiter,” Rose said.
The study will be published in the Astrophysical Journal Letters.
Kovi Rose et al. 2023. Periodic Radio Emission from the T8 Dwarf WISE J062309.94-045624.6. ApJL, in press; arXiv: 2306.15219
Source : Breaking Science News