Where Is Space Darkest? Comets, Black Holes, and Cosmic Shadows Explained

Where Is Space Darkest?

Look up and the night sky appears overwhelmingly black, but true pitch-black regions are rare. How dark a place seems depends on how you define "darkness" and which wavelengths of light you consider, experts told Live Science. Dust and diffuse radiation produce a faint background glow across much of the cosmos, and many regions that look black in visible light emit at other wavelengths.

Why true darkness is uncommon

Interstellar dust scatters starlight, creating a pervasive faint glow. Marc Postman, an astronomer at the Space Telescope Science Institute (STScI), notes this diffuse light even determines the universe's overall hue — the so-called "cosmic latte," a beige-white color. Andreas Burkert, a theoretical astrophysicist at the University of Munich, points out that if you include other bands of the electromagnetic spectrum (ultraviolet, infrared, gamma rays), almost everything is touched by radiation, so apparent darkness often depends on the wavelength observed.

Very dark places in visible light

If we restrict the question to visible light, several types of objects and regions are exceptionally dark for different reasons:

• Low-albedo bodies: Albedo is the fraction of incident light a surface reflects. Comet 19P/Borrelly has one of the lowest measured visible-light albedos in the solar system; its nucleus (about 5 miles / 8 km long) reflected under ~3% of sunlight in 2001 imaging. Outside our system, the exoplanet TrES-2b reflects less than 1% of incident starlight, likely because of highly absorbing atmospheric constituents such as sodium vapor and gaseous titanium oxide. By comparison, Earth reflects roughly 30% of incoming sunlight.
• Black holes: These are dark for a different reason — light that crosses the event horizon cannot escape. As Burkert explains, that doesn't mean there is no light at all; rather, light and radiation become trapped. The physics inside an event horizon is extreme and not directly observable, so descriptions of brightness there are theoretical.
• Permanent shadows: Some lunar polar craters never receive direct sunlight and remain in permanent shadow. Similar permanently shadowed depressions on distant bodies such as Pluto receive extremely little solar illumination due to their distance from the Sun.
• Bok globules and molecular cores: Dense interstellar clouds composed of molecular hydrogen, carbon oxides, helium and silicate dust — often called Bok globules — can block nearly all visible light from background stars and appear as “holes in the sky.” They are much more transparent at infrared wavelengths; Barnard 68, a well-studied globule about 500 light-years away, is a prime example.
• Remote sky regions: The far outskirts of galaxies and the deep sky can be exceptionally dark simply because they are far from bright sources. Observations from NASA's New Horizons mission and a 2021 paper in The Astrophysical Journal (co-authored by Postman) found that some remote regions are on average about 10 times darker than skies near Earth, though even these regions retain a faint cosmic background glow.

Why our perspective matters

Earth sits inside a relatively low-density cavity of the Milky Way known as the Local Bubble. That emptier environment reduces obscuring dust along many sightlines, giving us unusually clear views of distant stars and galaxies — a local advantage for astronomers.

Bottom line

There is no single "darkest place" in space; it depends on definition and wavelength. Some objects and regions are among the darkest in visible light — low-albedo surfaces like comet 19P/Borrelly and TrES-2b, permanently shadowed craters, dense Bok globules, and the remote outskirts of galaxies — but even these can emit or transmit radiation at other wavelengths.