I think this "Brown Dwarf" can only been seen in the infrared spectrum. p
Brown dwarfs typically emit heat in the form of infra red as their main form of emission. As with all matter they are also able to reflect light. Jupiter has a similar composition to a brown dwarf and is easy to spot in the night sky because it reflects the sun so well.
Think of it this way, a cup full of hot drinks emits heat. It does not emit in the optical part of the spectrum. Yet it is easy to see since it reflects light.
