mollwollfumble said:
Tau.Neutrino said:
Radio telescope detects a super-planet for the first time
Scientists in Europe and Hawaii have scored a world’s first by detecting a “super-planet,” also known as a cold brown dwarf or a failed star, using a radio telescope. Located 212 light-years away in the constellation of Hercules, the detection of BDR J1750+3809 may help in the search for habitable exoplanets.
more…
Radio telescope. How do you detect a brown dwarf with a radio telescope? (Reads on)
> the usual way of studying these objects was to detect them on infrared sky surveys, then training radio telescopes on them for further analysis.
Yes.
> “We asked ourselves, ‘Why point our radio telescope at catalogued brown dwarfs?’” says Harish Vedantham, team leader at ASTRON in the Netherlands. “Let’s just make a large image of the sky and discover these objects directly in the radio.”
As simple as that?
> Here we report the discovery of BDR J1750+3809, a circularly polarized radio source detected around 144 MHz with the LOFAR telescope.
“Polarized”, why didn’t I think of that? Reflected light (such as from a planet or brown dwarf) is polarised, remember Brewster angle. Light directly from the star is not polarised.
> Follow-up near-infrared photometry and spectroscopy show that BDR J1750+3809 is a cold methane dwarf of spectral type T6.5 at a distance of 65 parsecs.
Good. That’s relatively close. Reminding myself: MLTY. This is the second coolest type, Y’s tend to be planets, and 6.5 is a high number, so I’ll accept “super-planet” this time, though I normally wouldn’t.
> The quasi-quiescent radio spectral luminosity is over two orders of magnitude larger than that of the known population of comparable spectral type.
Do they mean spectral type of star? Or spectral type of brown dwarf?
> the emission is expected to occur close to the electron gyrofrequency, the magnetic field strength is comparable to planetary-scale magnetic fields.
Oooh, that’s different. They’re actually detecting the magnetic field rather than the reflected light. That’s a whole new set of information.
Can you see behind the paywall?
Found it.
https://arxiv.org/pdf/2010.01915.pdf
> Brown dwarfs (BD), with masses between that of stars and planets, display auroral radio emission powered by the electron cyclotron maser instability. In addition, because there appears to be no clear demarcation between the atmospheres and magnetospheres of the smallest coldest brown dwarfs and the largest planets.
The aurora of Jupiter is well known.
> the magnetic fields of planets, brown dwarfs, and low-mass stars of sufficiently rapid rotation are dipolar and that the field strength scales with the heat-flux from the bodies’ interior. The simplicity and universality of this law is a giant leap in modeling exoplanet atmospheres and habitability.
That’s new to me.
> sensitive metre-wave telescopes such as LOFAR
Metre-wave, that’s 300 MHz and below. Not too far off the FM radio band.
> There are three known types of radio emitter with high circularly polarized (CP) fraction: (a) stars, (b) brown dwarfs and planets, and © pulsars. Lack of an optical counterpart to a CP source generally rules out a stellar association.
These are free brown dwarfs, not those orbiting stars. So I was totally wrong about polarisation from reflection that I mentioned above. This looks good.
> BDR J1750+3809 stood out due to its high CP fraction.
> the intensity of magn-tospheric radio emission, that is non-thermal in nature, need not have a one-to-one scaling with the object’s infrared luminosity, which is thermal in nature, BDR J1750+3809’s discovery also shows that ongoing low-frequency radio surveys could discover objects that are too cold and/or distant to be discovered and studied via their infrared emission.
Yes :-)
> We searched publicly available optical and NIR archives for an association with the radio source.The source has no counterpart in the Pan-STARRS, 2MASS or AllWISE survey catalogs. We found a faint detection in the UKIRT Hemisphere Survey.
> unWISE catalog
LOL
> T-dwarfs are characterized by the presence of methane in their atmosphere due to their low surface temperatures that range from a few hundred to 1000 degrees K.
> the radio luminosity is 500 times that of a typical brown dwarf of this spectral type.