Oh really? Threads like these:
Thread: THIS SCIENTIFICALLY EXPLAINS HOW A BROWN DWARF STAR CALLED NIBIRU EXISTS In OUR SOLAR SYSTEM
Are not validated by stories like these:
Thread: A Potential "Planet X" Discovered by ALMA
A brown dwarf at Oort cloud distances does not equal "Nibiru." Nibiru is supposed to be in a 3600 year elliptical orbit which brings it within the inner solar system at perihelion. At such close distances it would be plainly obvious even to amateur telescopes.

Also, claiming that brown dwarfs are categorically "only visible in infrared" is wrong, and so is claiming that you cannot purchase a telescope capable of recording celestial objects in infrared.

Oh look, the infrared bright star CW Leonis recorded in infrared just fine by my telescope.

Now, the potential discovery in this case involving what might be a brown dwarf at Oort cloud distances was not even detected in infrared. Let me repeat that; the potential discovery in this case involving what might be a brown dwarf at Oort cloud distances was not even detected in infrared. But the thread you linked to claimed that brown dwarfs could ONLY be seen in infrared.

Wrong. In this case the object in question was discovered with an array of radio telescopes searching in the millimeter/submillimeter portion of the EM spectrum. A brown dwarf so close as to be in a 3600 year orbit would also reflect a large amount of sunlight, large enough to be plainly visible to amateur telescopes.

How do we know this? Because the orbital period of an object is directly proportional to its semi-major axis. An orbital period of 3600 years corresponds to a semi-major axis of about 235 AU. For an elliptical orbit that brings Nibiru as close to the sun as earth, that equates to an eccentricity of about 0.9957 and an aphelion distance of about 469 AU. That's orders of magnitude closer than the Oort cloud distances this potential brown dwarf discovery would be at (20,000 AU). Furthermore, a brown dwarf's reflectivity is very similar to either Jupiter or Uranus depending on the presence or absence of clouds ( [link to arxiv.org] ). Given that fact, here's the formula for computing the apparent magnitude of a Jupiter-like body at a given distance from the sun, from "Photometry and colorimetry of planets and satellites" by Daniel Harris, using Harris' number for V(1,0):
Apparent magnitude = -9.39+5*log(distance from sun*distance from earth)
Plugging in the distance for "Nibiru" at aphelion (469 AU) we get about magnitude 17.3 - and that's if it's as far from the sun as it can get, to say nothing of how bright it would be if it were near the inner solar system and approaching perihelion. Asteroids are routinely discovered at magnitudes much dimmer than that, and even most comets (which are harder to see for a given magnitude since the light is spread out over a larger area) are discovered even by amateurs are magnitudes dimmer than that. C/2015 X4 Elenin is a perfect example of exactly that ( [link to www.minorplanetcenter.net] ). Nibiru, if it existed, would be entirely visible to amateur telescopes. The newly discovered object near Alpha Centauri, if it's really a brown dwarf, is nowhere close to matching the description of "Nibiru."