If the black hole inside S5 0014+81 replaced the Sun, its event horizon would swallow Pluto and stretch nearly 20 times farther into deep space.
In 2009, a team led by astronomer Gabriele Ghisellini used NASA's Swift spacecraft to analyze the light from S5 0014+81, a blazar located in the constellation Cepheus. Based on the thermal glow of the matter spiraling into it, they estimated the central black hole's mass at 40 billion solar masses. That makes it roughly 10,000 times heavier than Sagittarius A*, the black hole at the center of the Milky Way.
At 40 billion times the mass of the Sun, the black hole's Schwarzschild radius—the boundary beyond which light cannot escape—measures about 118 billion kilometers, or 790 astronomical units. Its full diameter spans 236 billion kilometers, or about 1,580 astronomical units.
To feed a gravitational well of that scale, the quasar devours up to 4,000 solar masses of gas and dust every year. As that material compresses and heats up in the surrounding accretion disk, it shines with a luminosity of roughly watts—about 300 trillion times brighter than the Sun, or more than 10,000 times the combined starlight of the entire Milky Way.
That 40-billion-solar-mass figure carries an important observational caveat. Because S5 0014+81 lies 12.1 billion light-years away, telescopes cannot track individual stars orbiting the black hole to weigh it directly. Instead, astronomers inferred its size by modeling the ultraviolet and optical spectrum of its accretion disk under the assumption that the disk radiates evenly in all directions. If the disk is geometrically thick and funnels its radiation along the poles—or if an intervening galaxy gravitationally lenses the light—the true mass could be several times smaller.
Even at the lower end of those estimates, S5 0014+81 poses a puzzle for cosmologists. Because its light has traveled for 12.1 billion years, telescopes show this black hole as it existed just 1.6 billion years after the Big Bang—requiring it to have grown to tens of billions of solar masses before the universe had reached 12 percent of its current age.