Uncovering the Coldest Star Ever Found to Produce Radio Waves

Key Highlights :

1. A new Australian radio telescope called SKA Pathfinder has found evidence of radio emissions from a cool brown dwarf star called WISE J0623.

2. The star has a temperature of around 420 degrees Celsius (700 degrees Kelvin), which is equivalent to the temperature of a pizza oven.

3. This star is joining the ranks of just a small handful of known ultra-cool dwarfs that generate repeating radio bursts.

4. Previous research has shown that radio emissions detected from other cool brown dwarfs are generally repeated at the same rate as the star rotates.

5. Using this same search method, we expect future surveys to detect even cooler brown dwarfs.

     Astronomers have detected radio waves from fewer than 1,000 stars in our Milky Way galaxy. This is because radio waves and optical light are generated by different physical processes. However, a new discovery published in the Astrophysical Journal Letters has uncovered the coldest star ever found to produce radio waves—a brown dwarf too small to be a regular star and too massive to be a planet.

     The star, called WISE J0623, is roughly the same size as Jupiter but has a magnetic field much more powerful than our Sun’s. Despite having a temperature of around 700 Kelvin (equivalent to 420℃), this ultra-cool dwarf star generates repeating radio bursts.

     The detection of pulsed radio emission from this star was made possible by the improved sensitivity and coverage of new radio telescopes, such as the Australian SKA Pathfinder radio telescope located at the CSIRO Murchison Radio-astronomy Observatory in Western Australia. This telescope has an array of 36 antennas, each 12 meters in diameter, and has already surveyed nearly 90% of the sky, identifying close to three million radio sources.

     To differentiate between stars and other sources, astronomers looked for something called “circularly polarized radio emission”. This occurs when the electric field of the wave rotates in a spiraling or corkscrew motion as it propagates. By selecting only highly circularly polarized radio sources from an earlier survey of the sky, they were able to find WISE J0623.

     Follow-up observations with CSIRO’s Australian Telescope Compact Array and the MeerKAT telescope operated by the South African Radio Astronomy Observatory showed that every 1.9 hours there were two bright, circularly polarized bursts from WISE J0623 followed by a half an hour delay before the next pair of bursts.

     The discovery of WISE J0623 is significant as it is the first case of persistent radio pulsations from a cool brown dwarf. With the search method used, astronomers expect future surveys to detect even cooler brown dwarfs. Studying these missing link dwarf stars will help improve our understanding of stellar evolution and how giant exoplanets (planets in other solar systems) develop magnetic fields.

     Ultimately, understanding the atmospheres and magnetic fields of stars could tell us more about the potential for life to survive on any planets that orbit them. Therefore, uncovering the coldest star ever found to produce radio waves is an exciting step forward in the search for life beyond our Solar System.

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