Astronomers using NSF’s Karl G. Jansky Very Large Array have detected a ‘rogue’ planetary-mass object with a surprisingly powerful magnetic field.
Artist’s conception of SIMP01365, an object with 12.7 times the mass of Jupiter, but a magnetic field 200 times more powerful than Jupiter’s. Image credit: Chuck Carter, Caltech / NRAO / AUI / NSF.
The object, called SIMP J01365663+0933473 (SIMP0136 for short), has roughly 12.7 times the mass of Jupiter and its radius is about 1.22 times that of Jupiter.
“This object is right at the boundary between a planet and a brown dwarf and is giving us some surprises that can potentially help us understand magnetic processes on both stars and planets,” said Dr. Melodie Kao, a postdoctoral researcher at Arizona State University.
SIMP0136 was originally discovered in 2006 by another team of researchers, led by University of Montréal astronomer Dr. Étienne Artigau. The discovery was made as part of a near-infrared proper-motion survey, SIMP (Sondage Infrarouge de Mouvement Propre).
In 2016, Dr. Kao and co-authors observed SIMP0136 with the Very Large Array (VLA) in order to gain new knowledge about magnetic fields and the mechanisms by which some of the coolest brown dwarfs can produce strong radio emission.
Brown dwarf masses are notoriously difficult to measure, and at the time, SIMP0136 was thought to be an old and much more massive brown dwarf.
Last year, Dr. Artigau’s team discovered that the object was part of a very young group of stars. Its young age meant that it was in fact so much less massive that it could be a free-floating planet.
At 200 million years old and approximately 20 light-years from Earth, SIMP0136 has a surface temperature of about 1,500 degrees Fahrenheit (825 degrees Celsius).
The difference between a gas giant planet and a brown dwarf remains hotly debated among astronomers, but one rule of thumb that they use is the mass below which deuterium fusion ceases, known as the ‘deuterium-burning limit,’ around 13 Jupiter masses.
Simultaneously, Dr. Kao’s team observed SIMP0136 in a new study at even higher radio frequencies and confirmed that its magnetic field was even stronger than first measured — more than 200 times stronger than Jupiter’s.
“When it was announced that SIMP0136 had a mass near the deuterium-burning limit, I had just finished analyzing its newest VLA data,” Dr. Kao said.
The VLA observations provided both the first radio detection and the first measurement of the magnetic field of a possible planetary mass object beyond our Solar System.
“Such a strong magnetic field presents huge challenges to our understanding of the dynamo mechanism that produces the magnetic fields in brown dwarfs and exoplanets and helps drive the auroras we see,” said Caltech astronomer Gregg Hallinan.
“This particular object is exciting because studying its magnetic dynamo mechanisms can give us new insights on how the same type of mechanisms can operate in extrasolar planets,” Dr. Kao said.
“We think these mechanisms can work not only in brown dwarfs, but also in both gas giant and terrestrial planets.”
“Detecting SIMP0136 with the VLA through its auroral radio emission also means that we may have a new way of detecting exoplanets, including the elusive rogue ones not orbiting a parent star,” Dr. Hallinan said.
The findings appear in the Astrophysical Journal Supplement Series.
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Melodie M. Kao et al. 2018. The Strongest Magnetic Fields on the Coolest Brown Dwarfs. ApJS 237, 25; doi: 10.3847/1538-4365/aac2d5
