NASA's Spitzer Space Telescope has captured cosmic clumps so dense, dark and dusty that they cast the deepest shadows ever recorded in space.

Located about 16,000 light-years away from Earth lay a cosmic cloud so massive it weighs the equivalent of 70,000 Suns, packed into an area spanning about 50 light-years in diameter.

These large concentrations of dust and gas could light the way to understanding how the brightest stars form. Astronomers expect these shadows will evolve into one of the most massive young clusters of stars in our galaxy - called O-stars.

O-stars have major impacts on their local cosmic environments and also help to create the heavy elements needed for life - their formation process has long puzzled scientists.

"The map of the structure of the cloud and its dense cores we have made in this study reveals a lot of fine details about the massive star and star cluster formation process," lead author Michael Butler, postdoctoral researcher at the University of Zurich in Switzerland, said in a statement.

Spitzer observations at infrared wavelengths - a wavelength that is less easily scattered by dust - have allowed researchers to create a map of the cloud, but it was not easy.

In this case, the densest clouds of dust managed to block not only visible light, but also all background infrared light. Astronomers instead gauged the amount of background infrared light obscured by the cloud, using these shadows to infer where material had lumped together within the cloud, they reported in The Astrophysical Journal Letters.

Most of the universe's stars, perhaps even our Sun, are believed to form in these sorts of environments as groups of low-mass stars that are common and therefore well studied. But clusters like this current find that give birth to stars of higher mass are distant and scarce, making them more difficult to investigate, according to researchers.

"In this rare kind of cloud, Spitzer has provided us with an important picture of massive star cluster formation caught in its earliest, embryonic stages," said study co-author Jonathan Tan of the University of Florida.

Short-lived O-type stars shine with an intense blue-white light, and are at least 16 times as massive as our Sun, exploding as supernovas to forge the heavier elements that can create planets and life.