Quote:
Originally Posted by CometGuy
That seemed a simple enough question that David posed...at 0.01 Solar masses it should be quite bright even at 190 AU. Even Jupiter at 0.001 solar masses, would be magnitude 12-13 at that distance. How it could be at the limit of a 16" telescope + CCD camera beats me. This would indicate something closer to earth size.
I also I see one of the most experienced amateur astronomers on this list (David Higgins) being told off for challenging this claim and giving good reasons.....come on guys !
Terry
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(I've posted additional information about this to Dr. Van Flandern's messageboard over the last few weeks.)
Uranus is +5.7 at opposition and almost 20 AU out. Barbarossa is almost 200 AU out. The brightness goes as the fourth power of distance because the inverse square law holds both ways (it's farther away, and also the sun is dimmer there). Four powers of 10, is 10 magnitudes. So, if Barbarossa were just like Uranus, it would be about +15.7 (more precisely, +15.9).
Uranus has a rather high albedo, 66% according to a 1983 college textbook. Albedos of 4 to 8% often have been used in recent years as "canonical" albedos in academic journal articles about comet nuclei and Kuiper Belt Objects. Also, a recent article theoretically estimated the albedo of one type of borderline brown dwarf, as 1%! So, it would be fair to use 6.6%, i.e., about 1/10 the albedo of Uranus: +15.9+2.5=+18.4. Using 1% albedo would give +20.45.
The objects I've found and suspected of being Barbarossa, have comparison albedos (these are necessarily somewhat inaccurate) ranging from +17.3 to +20, but mainly +18 to +19. Theoretically, Barbarossa (assuming 1 to 10 Jupiter masses) should be the size of Jupiter only if Barbarossa has a H/He composition like the sun or Jupiter. The same article predicts that if a medium-weight brown dwarf isn't made of hydrogen (even if it's helium or oxygen), it has 1/2 to 1/3 the diameter of the hydrogen version. Of course, this is only theory. That's why observation is so important.