As an expert in astrophysics, I can tell you that the coldest star would be a brown dwarf, which is a celestial object that is larger than a planet but not massive enough to sustain the nuclear fusion reactions that power stars like our Sun. Brown dwarfs are often referred to as "failed stars" because they fall in the gap between the largest planets and the smallest stars.

The temperature of the coldest brown dwarfs can be as low as 500 Kelvin (K), which is equivalent to approximately 226 degrees Celsius (°C) or 439 degrees Fahrenheit (°F). However, it's important to note that brown dwarfs can vary significantly in temperature, and the exact "coldest" temperature can change as new discoveries are made and as our methods of measurement improve.

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What's more, the new star may not hold its "coldest" title for long: Scientists with NASA's Spitzer Space Telescope are working to confirm an even cooler brown dwarf with possible surface temperatures dipping down to a balmy 86 degrees F (30 degrees C).read more >>