July 5, 2018

A journey from your backyard to the stars

Last time you lay down in your backyard gazing at a night sky studded with twinkling lights, could you imagine them being born, living eventful lives then fading away and donating matter back to the Universe, matter which may form new stars and planets one day?

 

As you lay there, did you wonder why some people spend their lives studying stars?

 

I’ve been studying them for the past ten years. True story! Tax money pays my salary, so I can’t help but wonder, how does society feel about the stars? Does society even care at all?

 

If you’re undecided, here are a couple of interesting facts that perhaps you never thought of before..

 

In the spiral arms of a galaxy far, far away, lives a giant cold cloud of gas and molecules called a nebula, hundreds of thousands the mass of our Sun. The nebula gets blasted by a shock wave from a nearby star or event which sends things tumbling. Over millions of years this giant cloud fragments itself into smaller clouds of dust and gas which collapse and get pulled closer and closer by gravity. The core of a cloud gets denser and hotter and eventually becomes the kernel of a new-born star. This settling core radiates in the infrared, before it gets smothered by new layers of infalling matter which increases its mass.

 

Meanwhile, the cloud continues to churn around the young forming star. As it collapses it swirls faster and faster much like an ice-skater as she pulls in her arms closer to her. It eventually flattens out into a thin disk of gas and dust called a “circumstellar” or “protoplanetary” disk, because it’s a source of planetary systems. It hosts swarms of clumps of matter that sweep up surrounding material which grow into embryonic planets or “planetesimals” and later become mature planets that go on hugging close to their parent star. A planetary system is thus born.

 

So you see, stars are the birthplace of planets, of fascinating new worlds. By studying the star one can learn about the history of its planets, their nature, chemistry and the atmospheres they are likely to have. Are they habitable? Can they sustain liquid water on their surfaces? Are they tucked under a stable atmosphere? Do they harbour a biosphere or are they barren lands, torched by their host star’s activity?

 

All these answers require a careful understanding of the host star. Even more, the evolution of life on planets, or abiogenesis, needs the light of the star!

 

The planets scientists have found so far seem to be vastly diverse. We have no reason to think otherwise, but we’ll leave that for another story.

 

As stars mature over billions of years, they become beacons in the darkness of the Universe. They illuminate their surroundings and are easy to detect in the Galaxy, even in outer galaxies millions of light years away.

 

While they illuminate our Universe, they unleash their energy and radiation into their surroundings. Fast winds and streams of charged particles traveling at several million miles an hour energise their host environments. If embedded within a larger cloud, the scorching ultraviolet stellar radiation blasts loitering gas and dust and sculpts them into huge fertile pillars which mediate the creation of new stars. Their winds spew enormous amounts of material synthesised in their hot interiors and infused with chemical elements. This enriches their medium with elements heavier than the hydrogen and helium of which they are mostly made.

 

In order to survive, stars need to counterbalance gravity by burning nuclear fuel in their cores. Their generated energy seeps to the surface in two ways: radiation and the physical motion of charged stellar material, called convection. This motion of plasma weaves strong magnetic fields.

 

This is why stars are threaded with magnetic field lines.

A magnetic field pushes stellar material to the photosphere, creating coronal loops and star spots like those observed on our Sun. This magnetic activity affects space weather which influences our planet, electronic equipment and astronauts in space, and even staffed missions to the moon or to Mars.

 

Ending our journey in the stellar core, we reach the origin of our stellar ancestry. This is where stars forge all the chemical elements found in the Universe except for hydrogen. The Big Bang created the hydrogen, most of the helium and traces of lithium. Everything else is the making of stars, including the carbon and oxygen which make all living organisms.

 

Thus stars are our intimate connection with the cosmos and exploring them is an exploration of our own cosmological heritage.

 

Stars never cease to fascinate. When you study them, you can make predictions about their lives, and the life of the Sun and the galaxies.

 

Can you now see how stars are the atoms of our Universe and the core of most of its events? Do you now care slightly more about them? Can you feel our curious and fascinating connection? I bet you will never see them the same way again.

 

They are certainly not boring balls of fire. They have their own lifestyles, relationships, and body language. If you only knew the secrets of their lives, you’d be orbiting them endlessly like a planet. But that’s a different story, for the next time our star goes down…

 

Image: The star cluster Westerlund 2 (NASA/ESA/Hubble)

 

 

 

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