New images show dust in nearby galaxies, and you’ve never seen them like this

When we see images of galaxies outside the Milky Way, what we usually see is mostly the light from their stars. But stars are far from the only ingredient that makes up a galaxy. Think of the stars as bits of vegetables in galactic soup.

The broth, then, in which they float, is the intergalactic medium – not empty space, but filled with often tenuous, sometimes dense clouds of dust and gas that float between the stars. As the stars are much brighter, dust often takes a back seat; but this dust, from which stars are born, to which stars return, can tell us a lot about the structure and activity within a galaxy.

Now, four new images have been released, showing the distribution of dust in four of the closest galaxies to the Milky Way: the Large and Small Magellanic Clouds, dwarf galaxies orbiting our own; the Andromeda Galaxy, a large spiral galaxy at a distance of 2.5 million light years; and the Triangulum galaxy, a spiral galaxy 2.73 million light-years away.

The Large Magellanic Cloud. (ESA, NASA, NASA-JPL, Caltech, Christopher Clark/STScI, S. Kim/Sejong University, T. Wong/UIUC)

Without dust and gas, galaxies as we know them would not exist. Stars form when a dense knot of material in a cold cloud of molecular gas collapses under gravity, incorporating material from the surrounding cloud. When that star dies, it ejects its outer material back into the space around it, with the heavier new elements it has fused during its lifetime.

New stars being born incorporate the dust of dead stars, making each subsequent generation of stars slightly different. We are, in fact, all made of stellar material – even the stars.

But the dust is not evenly distributed. Stellar winds, galactic winds, and the effects of gravity can push and sculpt interstellar dust into complex, cavity-filled shapes. Mapping the structures and the composition of the elements within them is a crucial tool for understanding the formation of… well… pretty much everything.

The new images, revealed at the 240th meeting of the American Astronomical Society, were taken by the Herschel Space Observatory operated by the European Space Agency between 2009 and 2013. Until the launch of Webb – which has yet to deliver its first scientific images – Herschel was the world’s largest infrared telescope. already released.

Herschel Small Magellanic CloudThe Small Magellanic Cloud. (ESA, NASA, NASA-JPL, Caltech, Christopher Clark/STScI, S. Stanimirovic/UW-Madison, N. Mizuno/University of Nagoya)

Like the Webb, its ultra-cold operating temperature meant that Herschel could peer into the far infrared, viewing some of the coldest and dustiest objects in space, down to temperatures around -270 degrees Celsius (-454 degrees Fahrenheit). This includes the cold clouds in which stars are born and the dust in interstellar space.

However, it was less adept at detecting more diffuse dust and gas. To fill in the gaps, a team of astronomers led by Christopher Clark of the Space Telescope Science Institute used data from three other retired telescopes: ESA’s Planck and NASA’s Infrared Astronomical Satellite (IRAS) and Cosmic Background Explorer (COBE).

The results reveal complex interactions within the dust. Hydrogen gas appears in red; this is the most abundant element in the Universe, so there’s plenty. Cavities in the dust where newborn stars took it with their intense winds appear as empty regions, surrounded by a green glow that indicates cold dust. The blue regions represent hotter dust, heated by stars or other processes.

herschel galaxy triangleThe Triangle Galaxy. (ESA, NASA, NASA-JPL, Caltech, Christopher Clark/STScI, E. Koch/University of Alberta, C. Druard/University of Bordeaux)

The images also reveal new information about the complex interactions that occur in interstellar dust, the researchers said. Heavy elements such as oxygen, carbon and iron can often stick to dust grains; in denser clouds, most elements are bound to dust, increasing the dust-gas ratio. This can affect how light is absorbed and re-emitted by dust.

However, violent processes such as star birth or supernovae can release radiation that breaks up the dust, releasing the heavy elements back into the gaseous clouds. This tilts the dust-gas ratio back towards gas.

Herschel’s images reveal that the proportions can vary by up to a factor of 20 in a galaxy. This is much higher than astronomers thought, important information that could help scientists better understand this cycle.

And, they are just spectacularly beautiful. Who knew that Andromeda soup could be such a dazzling rainbow of colors.

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