An ordinary lump of coal left under the blazing sun just heats up. But if you take it into space and bring it twenty times closer to the Sun than Earth is, it won't survive for more than a few minutes. That's roughly how dark, carbon-rich asteroids behave. They are rarely found on orbits that dive deep inside Mercury's orbit.
In the lab, researchers recreated the vacuum of space and shone light of the same intensity as the Sun delivers at 0.2 astronomical units (about 30 million kilometers, twice as close as Mercury) onto samples mimicking the material of such asteroids. Within minutes, the samples began to crack and crumble into fine dust. The light wasn't just heating them: it was destroying the very structure of the material.
This solves the mystery: why, among asteroids that approach the Sun closer than 0.2 astronomical units, there are almost no dark, carbon-rich ones. They simply don't survive: they turn into a cloud of dust that sunlight then carries away. The data also matched observations of the peculiar object 322P/SOHO 1, which loses mass as expected for such fragile material.
At 0.2 astronomical units from the Sun, the surface temperature of a dark asteroid can exceed 500 degrees Celsius, like an oven cranked to maximum.
In Arthur C. Clarke's novel "A Solar Storm," astronauts watch a comet evaporate as it approaches the Sun — very much like the fate of carbonaceous asteroids.