A guide to dark nebulae
What is a dark nebula, and why do they exist? Find out in our guide.
A dark nebula is an interstellar cloud of cosmic dust that's so dense it absorbs, scatters and blocks visible light, making it appear inky black when viewed against the starry cosmos.
Many dark nebulae are known as Barnard objects and are catalogued using the 'Barnard' designation followed by a number, like Barnard 363 (below).
These are named after Edward Emerson Barnard, an American astronomer who published a record of dark nebulae known as the Barnard Catalogue in 1919, and an extended list posthumously in 1927.
Dark nebulae are irregular in shape, unlike certain kinds of nebulae like planetary nebulae, which generally have a spherical appearance.
While dark nebulae may seem like foreboding, lifeless cosmic objects, in actual fact many of them are active regions where hydrogen molecules form and stars are born.
These stars are often hidden from optical light due to the density of the dark nebula in which they're born, but radio and infrared telescopes allow astronomers to peer through the cosmic dust and get a closer look at the star formation occurring within.
A dark nebula may be the dense core of a Giant Molecular Cloud a million times more massive than the Sun, or they could take the form of compact molecular clouds known as Bok Globules, just 2,000 times the mass of the Sun.
Bok globules are a type of dark nebula named after the Dutch-American astronomer Bart Bok, and are thought to be the precursor to protostars, just waiting to gain enough mass that they collapse, igniting the process of star formation.
It is also worth pointing out that a dark nebula is not the same as dark matter. Dark matter is an invisible substance thought to make up about 27% of all matter in the Universe, and which is hypothesised because of its gravitational effect on directly observable objects like galaxies.
Below is a selection of images of dark nebulae captured by BBC Sky at Night Magazine readers and astrophotographers.
Iain Todd is BBC Sky at Night Magazine's Content Editor. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.