What Are the Brightest and Darkest Things in Space?

Brightest Stars: Luminosity & Magnitude (SPACE.com)

"When taking Earth as a reference point [...] the scale of magnitude fails to account for the true differences in brightness between stars. The apparent brightness, or apparent magnitude, depends on the location of the observer. Different observers will come up with a different measurement, depending on their locations and distance from the star. Stars that are closer to Earth, but fainter, could appear brighter than far more luminous ones that are far away. "

Darkest (NASA)
"Black holes are infinitely dense and infinitely small so they end up bending the space around them so much that they end up turning it into a sort of funnel that would cause anything that came too close to fall in."
"Here the gravity is too strong and everything, including photons of light, gets pulled down to the point of infinite density and smallness called the singularity."

What Is a Black Hole? (NASA)
"Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object. Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way. The largest black holes are called "supermassive."

Brightest (NASA)
"Our Milky Way galaxy has one of these supermassive black holes at its center, but our galaxy is not an active one. Active galaxies require that gas and dust are in the act of falling into the black hole and glowing brightly on the way in. The Milky Way isn't currently doing this and when material isn't falling into the black hole, it simply sits."