Oops, I see what you mean. I thought a star was a self-luminous gaseous spheroidal celestial body of great mass which produces energy by means of nuclear fusion reactions. In fact, as you point out, the brown dwarf star produces heat and light; but not by nuclear fusion, (because it doesn't have enough mass for the crush of gravity to ignite nuclear fusion at its core). So I’m revising my definition of a star to ‘a natural luminous body visible in the sky especially at night’. I’m not quite sure of the exact chemical reactions causing the heat and light but at least understand it’s not due to nuclear fusion. Thanks for pointing out the error.
Ref: https://news.nationa...-space-science/
From what I read, the object in this case has a temperature so low that it is only emitting a bit of IR and microwave radiation, as expected for a body at that temperature. There are no stellar processes going on at all. It has ceased to be a star in any useful sense of the term. It is not producing any light, so far as I can see.
It may technically be a "brown dwarf" in terms of stellar evolution, but this example is black as the ace of spades.