A bizarre rogue planet without a star is roaming the Milky Way just 20 light-years from the Sun. And according to a recently published study in The Astrophysical Journal, this strange, nomadic world has an incredibly powerful magnetic field that is some 4 million times stronger than Earth’s. Furthermore, it generates spectacular auroras that would put our own northern lights to shame.

The new observations, made with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), not only are the first radio observations of a planetary-mass object beyond our solar system, but also mark the first time researchers have measured the magnetic field of such a body.

Sizing up SIMP

The peculiar and untethered object, succinctly named SIMP J01365663+0933473 (we’ll call it SIMP for simplicity’s sake), was first discovered back in 2016. At the time, researchers thought SIMP was a brown dwarf: an object that’s too big to be a planet, but too small to be a star. However, last year, another study showed that SIMP is just small enough, at 12.7 times the mass and 1.2 times the radius of Jupiter, to be considered a planet — albeit a mammoth one.

“This object is right at the boundary between a planet and a brown dwarf, or ‘failed star,’ and is giving us some surprises that can potentially help us understand magnetic processes on both stars and planets,” said Arizona State University’s Melodie Kao, who led the new study on SIMP, in a press release.

For a planet, SIMP is also pretty hot: The world has a surface temperature of over 1,500 degrees Fahrenheit (825 Celsius). For comparison, the hottest planet in our solar system is Venus, which sports an average temperature of around 875 F (470 C), while the Sun, a relatively small and cool star, has a surface temperature of about 10,000 F (5,500 C). However, it’s important to note that Venus gets most of its heat from the Sun. And since solitary SIMP is not orbiting a star, its heat must be leftover from its initial formation some 200 million years ago. So, over time, the planetary goliath will continue to radiate away its warmth.

Unparalleled magnetism

According to the most recent study, SIMP is not only gigantic by planetary standards, but it also possesses a magnetic field that is millions of times stronger than that of our home planet. And although this magnetic field helps SIMP produce stunning light shows, the auroras are not generated in the same way as they are here on Earth.

Full story here

The paper: The Strongest Magnetic Fields on the Coolest Brown Dwarfs

Abstract

We have used NSF’s Karl G. Jansky Very Large Array to observe a sample of five known radio-emitting late-L and T dwarfs ranging in age from ~0.2 to 3.4 Gyr. We observed each target for seven hours, extending to higher frequencies than previously attempted and establishing proportionally higher limits on maximum surface magnetic field strengths. Detections of circularly polarized pulses at 8–12 GHz yield measurements of 3.2–4.1 kG localized magnetic fields on four of our targets, including the archetypal cloud variable and likely planetary-mass object T2.5 dwarf SIMP J01365663+0933473. We additionally detect a pulse at 15–16.5 GHz for the T6.5 dwarf 2MASS 10475385+2124234, corresponding to a localized 5.6 kG field strength. For the same object, we tentatively detect a 16.5–18 GHz pulse, corresponding to a localized 6.2 kG field strength. We measure rotation periods between ~1.47–2.28 hr for 2MASS J10430758+2225236, 2MASS J12373919+6526148, and SDSS J04234858–0414035, supporting (i) an emerging consensus that rapid rotation may be important for producing strong dipole fields in convective dynamos, and/or (ii) rapid rotation is a key ingredient for driving the current systems powering auroral radio emission. We observe evidence of variable structure in the frequency-dependent time series of our targets on timescales shorter than a rotation period, suggesting a higher degree of variability in the current systems near the surfaces of brown dwarfs. Finally, we find that age, mass, and temperature together cannot account for the strong magnetic fields produced by our targets.

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