Are brown dwarfs failed stars or are they Jupiter and Saturn like planets?
Brown dwarf planets, not ultra cool dwarf (star) Jupiters (planet)?
Sometimes a brown dwarf is actually a planet—or planet-like anyway. A team ... discovered that what astronomers had previously thought was one of the closest brown dwarfs to our own Sun is in fact a planetary mass object.
... "This means that the temperatures of brown dwarfs can range from as hot as stars to as cool as planets, depending on how old they are," said the AMNH's Jackie Faherty, a co-author on this discovery.
... The implication that the well-known SIMP0136 is actually more planet-like than we previously thought will help us to better understand the atmospheres of giant planets and how they evolve," Gagné said ... "This newest addition to the very select club of free-floating planetary like objects is particularly remarkable, because we had already detected fast-evolving weather patterns on the surface of SIMP0136, back when we thought it was a brown dwarf."
Surprise! When a brown dwarf is actually a planetary mass object
That is a lot of Jupiter and Saturn gas giant like planet systems out there.
Brown dwarf binary systems are giant gas planet binary systems?
Brown dwarf planet similar temperature to Jupiter
A new citizen-science tool released earlier this year to help astronomers pinpoint new worlds lurking in the outer reaches of our solar system has already led to a discovery: a brown dwarf a little more than 100 light years away from the Sun
... confirmed that it was a previously unknown brown dwarf just a few hundred degrees warmer than Jupiter ... Brown dwarfs are strikingly similar to Jupiter so we study their atmospheres in order to look at what weather on other worlds might look like
Citizen scientists uncover a cold new world near sun | Phys Org
Planet hotter than Red Dwarf star
If our sun and all stars energy is created internally by some form of thermonuclear processes why are stars surfaces relatively so cold?
"We know pretty well how big the planet is and how massive it is: it's about three times the mass of Jupiter and twice as big as Jupiter. "We know the parent star's properties reasonably well: it's about two and a half times more massive than the Sun; it's almost twice as hot as the Sun; and it's rotating very rapidly and so it would appear very flattened to our eyes."
... This raises the temperature on the "day side" of KELT-9b to over 4,300C - hotter than the surface of the average Red Dwarf star, by far the most common type of star in the Milky Way
Planet is 'hotter than most stars' | BBC