Editing Brown dwarf (section)

=== Brown dwarfs as radio sources ===
[[File:Fig. 2 Epoch 2 composite image of LSR J1835 + 3259 aurora and quiescent emission.png|thumb|Resolved quiescent emission (contours) of [[LSR J1835+3259]], which has a similar shape to [[Magnetosphere of Jupiter|Jupiters radiation belts]]. The dark spot in the middle is radio emission from the right-[[Circular polarization|circularly polarized]] aurora.]]
The first brown dwarf that was discovered to emit radio signals was [[LP 944-20]], which was observed since it is also a source of X-ray emission, and both types of emission are signatures of coronae. Approximately 5–10% of brown dwarfs appear to have strong magnetic fields and emit radio waves, and there may be as many as 40 magnetic brown dwarfs within 25 pc of the Sun based on [[Monte Carlo method|Monte Carlo]] modeling and their average spatial density.<ref>{{cite journal |last1=Route |first1=Matthew |title=Radio-flaring Ultracool Dwarf Population Synthesis |journal=The Astrophysical Journal |date=10 August 2017 |volume=845 |issue=1 |page=66 |doi=10.3847/1538-4357/aa7ede |arxiv=1707.02212 |bibcode=2017ApJ...845...66R |s2cid=118895524 |doi-access=free }}</ref> The power of the radio emissions of brown dwarfs is roughly constant despite variations in their temperatures.<ref name="ReferenceA"/> Brown dwarfs may maintain magnetic fields of up to 6 [[Gauss (unit)|kG]] in strength.<ref>{{cite journal |last1=Kao |first1=Melodie M. |first2=Gregg |last2=Hallinan |first3=J. Sebastian |last3=Pineda |first4=David |last4=Stevenson |first5=Adam J. |last5=Burgasser |title=The Strongest Magnetic Fields on the Coolest Brown Dwarfs |journal=The Astrophysical Journal Supplement Series |date=31 July 2018 |volume=237 |issue=2 |page=25 |doi=10.3847/1538-4365/aac2d5 |arxiv=1808.02485 |bibcode=2018ApJS..237...25K |s2cid=118898602 |doi-access=free }}</ref> Astronomers have estimated brown dwarf [[magnetosphere]]s to span an altitude of approximately 10<sup>7</sup> m given properties of their radio emissions.<ref>{{cite journal |last1=Route |first1=Matthew |title=Is WISEP J060738.65+242953.4 Really A Magnetically Active, Pole-on L Dwarf? |journal=The Astrophysical Journal |date=10 July 2017 |volume=843 |issue=2 |page=115 |doi=10.3847/1538-4357/aa78ab |arxiv=1706.03010 |bibcode=2017ApJ...843..115R |s2cid=119056418 |doi-access=free }}</ref> It is unknown whether the radio emissions from brown dwarfs more closely resemble those from planets or stars. Some brown dwarfs emit regular radio pulses, which are sometimes interpreted as radio emission beamed from the poles but may also be beamed from active regions. The regular, periodic reversal of radio wave orientation may indicate that brown dwarf magnetic fields periodically reverse polarity. These reversals may be the result of a brown dwarf magnetic activity cycle, similar to the [[solar cycle]].<ref>{{cite journal |last1=Route |first1=Matthew |title=The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence? |journal=The Astrophysical Journal Letters |date=20 October 2016 |volume=830 |issue=2 |page=L27 |doi=10.3847/2041-8205/830/2/L27 |arxiv=1609.07761 |bibcode=2016ApJ...830L..27R |s2cid=119111063 |doi-access=free }}</ref>

The first brown dwarf of spectral class M found to emit radio waves was [[LP 944-20]], detected in 2001. The first brown dwarf of spectral class L found to emit radio waves was [[2MASS J00361617+1821104|2MASS J0036159+182110]], detected in 2008. The first brown dwarf of spectral class T found to emit radio waves was [[2MASS J10475385+2124234]].<ref>{{cite press release |title=Record-breaking radio waves discovered from ultra-cool star |author=Phys.org |url=https://phys.org/news/2012-04-record-breaking-radio-ultra-cool-star.html}}</ref><ref>{{cite journal|last1=Route|first1=M.|last2=Wolszczan|first2=A.|title=The Arecibo Detection of the Coolest Radio-flaring Brown Dwarf|journal=The Astrophysical Journal Letters|date=10 March 2012|volume=747|issue=2|page=L22|doi=10.1088/2041-8205/747/2/L22|arxiv=1202.1287|bibcode=2012ApJ...747L..22R|s2cid=119290950}}</ref> This last discovery was significant since it revealed that brown dwarfs with temperatures similar to exoplanets could host strong >1.7 kG magnetic fields. Although a sensitive search for radio emission from Y dwarfs was conducted at the [[Arecibo telescope|Arecibo Observatory]] in 2010, no emission was detected.<ref>{{cite journal|last1=Route|first1=Matthew|title=ROME. IV. An Arecibo Search for Substellar Magnetospheric Radio Emissions in Purported Exoplanet-hosting Systems at 5 GHz|journal=The Astrophysical Journal|date=1 May 2024|volume=966|issue=1|page=55|doi=10.3847/1538-4357/ad30ff|arxiv=2403.02226|bibcode=2024ApJ...966...55R|doi-access=free }}</ref>