September 20, 2019

Cosmic dust: Though it be but tiny, it is fierce!

We have always been intrigued by the origin of things; that of oceans, stars, planets, and even our own. Yet perhaps one of the biggest puzzles is the origin of the universe. This would probably explain why almost every civilisation that ever lived attempted to explain the existence of the universe and its nature. Galileo Galilei, the Italian astronomer, physicist and mathematician, wasn’t very optimistic when he said “The universe is irrelevant to study, because we will never be able to say anything about it”. Einstein, 350 years later, showed more confidence in the ability of the human mind, saying “The most incomprehensible about the universe is that it is comprehensible”.

All astronomy starts from the night sky

Gazing up at a moonless night sky, it appears very patchy. With nothing but the scrutiny afforded by our eyes, we can distinguish between the brightness of the stars, and the blackness between them. Ancients believed that stars were pinpricks in the fabric of the heavens, and dark patches in between were devoid of stars. When astronomer William Herschel observed such a dark patch in the constellation of Scorpio more than two centuries ago, he exclaimed “Truly there is a hole in the sky here!”, as reported by his sister Caroline.

Science has since revealed that stars are not light holes in the sky but huge luminous balls of burning gas, mostly helium and hydrogen. We now also know that dark regions are not devoid of stars, but are rather dense clouds of gas and dusthiding the stars and blocking their light. We cannot see these clouds with our eyes or in visible wavelength bands. However, they are very bright in the infrared and radio wavelength windows which pierce through their dusty veils and provide us with a peek into their hideaways.

Cosmic dust: The making and the baking

Cosmic dust is small, solid, smoke-like particles that originate around stars. This is why it is often called ‘stardust’. As a star like our Sun ages, it sheds its outer layers in copious amounts. The resulting environment is thus dense and cool, providing a sweet spot for dust particles to form.

Dust also forms in exploding stars that blast huge amounts of material into space when they go boom. These particles then travel through a harsh environment where they may get destroyed by the ravages of radiation, or may survive and end up drifting in space. If they spend time in dense regions they may stick together and grow into larger grains.

Unlike household dust which is made of dead cells, carpet fibres, or bacteria for example, cosmic dust is either made of carbon like barbecue soot, or of silicates like beach sand. It comes in a range of sizes from extremely tiny, almost the width of a DNA strand, to nearly the width of a pin.

Although it makes less than 1% of the space between stars, dust has a crucial role. It is the building block of stars and the material that makes up rocky planets, meteorites, asteroids, and solar systems.

The universe is a dusty place.

To some astronomers, dust is a curse. It is the annoying “fog” that dims stars and distorts the light we see from distant galaxies. It conceals parts of the universe thus limiting our understanding. To others, dust is the heart of their science.

While much has been understood about cosmic dust, it remains frustrating and mysterious at the same time, both for what it veils and for what it doesn’t reveal about itself. Understanding its nature is a necessary step towards unraveling the mysteries that govern our universe.

As a researcher, I probe the secrets of dust. Within the NANOCOSMOS project, I use a radio telescope to observe the skies and try to understand the birth of a dust grain, which in turn will be a part of something even bigger!

Why should we care?

Indeed, why should we? Being mere specks drifting freely in the vast spaces between the stars, dust grains are far too distant and far too tiny to affect our lives in any significant way. They introduce no material profit or threat to anyone. Most of them cannot even be seen without a powerful telescope. If dust did nothing except quietly fill the gaps between the stars, then it would deserve nothing but a footnote in the annals of the universe. Yet everything we see was once a simple molecule or a microscopic dust grain. These grains hold a wealth of information about places far, far away, and even places nearby. This is the adventurous journey of dust, from a dying star to the very essence of matter, from the minuscule to the massive, because everything happens in cycles.

Original artwork “Cosmic Dusk” is by Latesha Houston Art.


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