We’ve identified the coolest star ever found to produce radio waves – a brown dwarf too small to be a normal star and too massive to be a planet.
Our findings, published today Astrophysical Journal LettersDescribe in detail the detection of pulsed radio emission from this star, called WISE J0623.
Although about the same size as Jupiter, this dwarf star has a much stronger magnetic field than our Sun. It joins a handful of known ultra-cool dwarfs that produce repeated radio bursts.
Radio waves are generated by stars
With more than 100 billion stars in our Milky Way galaxy, you might be surprised to find that astronomers have detected radio waves in fewer than 1,000 of them. One reason is that radio waves and optical light are created by different physical processes.
Unlike thermal (heat) radiation from a star’s hot outer layer, radio emission is the result of particles called electrons accelerating and interacting with the magnetized gas surrounding the star.
Because of this, radio emission can be used to study the atmospheres and magnetic fields of stars, which can ultimately tell us more about the potential for life on any planets orbiting them.
Another factor is the sensitivity of radio telescopes, which historically have only been able to detect very bright sources.
Most of the star detections with radio telescopes over the past few decades have been flares from very active stars or energetic bursts from interacting binary (two) star systems. But with the improved sensitivity and coverage of new radio telescopes, we can find fainter stars like Kool. Brown dwarfs.
WISE J0623 has a temperature of about 700 Kelvin. That equates to 420 degrees, or the same temperature as a commercial pizza oven — pretty hot by human standards, but too cold for a star.
These cool brown dwarfs cannot sustain the level of atmospheric activity that generates radio emission in hot stars, making stars like WISE J0623 difficult for radio astronomers to detect.
How did we find the best radio star?
Here’s what’s new Australian SKA Pathfinder The radio telescope is coming. It is located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-Astronomy Observatory in Western Australia, and has an array of 36 antennas 12 meters in diameter.
The telescope can see large areas of the sky in a single observation, and 90 percent of it has already been surveyed. We have identified about three million radio sources from this survey, most of them Active galactic nuclei – Black holes at the centers of distant galaxies.
How can we tell which of these millions of sources are radio stars? One way is to look for something called “circularly polarized radio emission.”
Radio waves, like other electromagnetic radiation, oscillate as they travel through space. Circular polarization occurs when the electric field of the wave rotates in a spiral or corkscrew motion as it propagates.
We used for the search the fact that stars are the only astronomical objects that emit a significant fraction of circularly polarized light. Pulsars (rotating neutron stars).
By selecting only highly circularly polarized radio sources An early survey of the sky, we found WISE J0623. As you can see with the slider in the image above, once you switch to polarized light, only one object is visible.
What does this finding mean?
Was the radio emission from this star some rare event that occurred during our 15 minute observation? Or can we rediscover it?
Previous research Radio emissions detected from other cool brown dwarfs have been shown to be coupled to their magnetic fields and generally repeat at the same rate as the star rotates.
We conducted follow-up observations by CSIRO to investigate this Australian Telescope Compact Arrayand with Meerkat The telescope is operated by the South African Radio Astronomy Observatory.
These new observations show that two bright, circularly polarized bursts from WISE J0623 occur every 1.9 hours, followed by a half-hour delay before the next pair of bursts.
WISE J0623 is the coolest brown dwarf detected by radio waves and is the first case of continuous radio pulses. Using the same search method, we expect future surveys to find even cooler brown dwarfs.
Studying this missing link dwarf stars can help us understand stellar evolution and how giant exoplanets (planets in other solar systems) develop magnetic fields.
We recognize the Wajari Yamatji as the traditional owners of the Murchison Radio-Astronomy Observatory site where the Australian SKA Pathfinder is located, and the Gomaroi people as the traditional owners of the Australian Telescope Compact Array site.
Covey RoseAstrophysics PhD Candidate, University of Sydney And Tara Murphyprofessor, University of Sydney
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