Recent news articles about a black hole discovery use size and mass as if they were the same thing, but they are not. They are two completely different properties.
I recently read some news articles about the discovery of the smallest black hole. It is an interesting discovery, but the headlines should read the lowest mass black hole rather than the smallest black hole.
Reading the articles, I notice that no distinction is made between size and mass. The two words are used as if they are interchangeable terms. They are not. Size and mass are two distinct properties. We can measure an objects mass, which is in grams or kilograms, with a scale. We measure its size, which is in meters or similar units, with a ruler or similar device. An object with a larger mass is not always bigger in size. For example a 10 kilogram lead weight will be smaller in size than a feather pillow having a mass of 1 kilogram.
The astronomers who discover a black hole measure its mass from its gravitational effects. They then use the mass to infer its size, which we can not measure directly. It turns out that the size of a black hole is directly proportional to its mass. Hence, a more massive black hole will be larger in size, as long as we are referring to the size of the event horizon or Schwarzschild radius rather than the central singularity point.
Not all stars however have this property. For white dwarf stars or neutron stars the size decreases as the mass increases. Using the words size and mass as synonyms for these stars will result in many incorrect statements.
Language in physics is must be very precise. Words have very specific meanings that should not be interchanged. Science writers and journalists need to use the terms correctly to avoid confusing their readers.
