A Genuinely Dark Star?
The Widefield Infrared Survey Explorer has been doing some interesting stuff. And, it’s found a brown dwarf:
The brown dwarf is the green dot in the above image. (The picture links to a larger version – you can see it clearly on there.) It’s green because of the choices of colours they’ve used to represent different infrared wavelengths, I should add – the object itself almost certainly wouldn’t look green.
In fact, it probably wouldn’t look much like anything. The estimated temperature for this object is about 600 K, or not much more than 300 degrees Celsius. It presumably emits next to no light in the optical range. I’ve heard it claimed that something has to reach a temperature of about 400-500 degrees before any glow at all is visible to the human eye (I don’t have the citation to hand, unfortunately). If this is the case, then even from nearby, this object wouldn’t appear to glow. Probably, I suppose, there would be some hotter regions on its surface, so you would have a mix of a dark disk with deep reddish-magenta bands or splodges here and there, where hot gas is upwelling from the interior … but even from close up, it would be quite dark.
Also, this is interesting because it’s nearby – the estimated distance is inside of 10 parsecs. The presence of one such object could suggest many more in the local neighbourhood. It’s possible that there may even be a brown dwarf or two closer than Proxima Centauri, in which case our nearest neighbour would actually be one of these.
(The discovery paper for the brown dwarf, WISEPC J0458+6434, is here.)