The life and fate of our mortal Sun

Today I woke up on the wrong side of the clouds. Having been graced with unusually genial sunshine for more than a month, today looks particularly grim.

“Return, alas! return, O radiance dear!

And drive from me that foul, consuming Fear”

pleads Bradamante in 16th century “Orlando Furioso”.

This got me thinking about our 4.6 billion year-old beast and her glittering head. She bewitchingly promises warmth and cheer and when she’s beclouded our moods flop like a wet towel. But what’s going on in that head of hers? At times she scoffs and flares up, spewing fiery flames. She is spotty and certainly has her moods. Last month a scientist even suggested she may be having a midlife crisis. But we’re certainly lucky to be around when she’s at her best, because in a few billion years, she will unintentionally melt our planet into a sticky blob before meeting her final demise. It’s all quite dazzling, to say the least.

Hot and fiery

A powerful furnace, her core is 15 million degrees. Things cool off away from the core to 5500 degrees Celsius at her visible surface which we call the photosphere. This is the layer where parcels of light, or photons, escape freely to outer space. One would expect things to keep cooling down the farther one is from the Sun but in the atmosphere, something very odd happens. The temperature starts to increase and peaks to more than 8000 degrees Celsius. Even higher up above the solar atmosphere, called the corona, temperature soars to a million degrees! This is because the solar magnetic field affects the way energy is carried around and dissipated through her very sparse and diffuse atmosphere. Despite the searing temperature, it’s not really “hot” because the density is very low. It’s like getting in a car on a hot sunny day. While the dashboard may burn if touched, sitting in the car wouldn’t really burn you. But hey, I’m not suggesting you can go sit in the corona.

The Sun is not idle, she spins. Because she’s gaseous, she spins faster at the equator than at the poles. Rotating once every 25 days at the equator, she takes more than 30 days to rotate once at the poles. So her magnetic field, bundling in tubes just below the surface, gets twisted and tangled and bursts out through the surface at certain spots. This slows down the emergence of sizzling material from the inner parts, making these spots cooler, thus look darker compared to their surroundings. We call those the sun spots. Sometimes the magnetic field gets drastically distorted so its lines get sheared off causing the most violent eruptions in our solar system, called solar flares. These flares are often accompanied by streams of supersonic winds and produce as much energy as a billion hydrogen bombs. When the solar wind reaches Earth a few days later, it can sneak into the Earth’s natural shield through its magnetic funnel near the poles. The energetic particles of the wind blast the atoms and molecules in the air, exciting them into that magnificent spectacle, the northern lights.

A midlife crisis?

It has long been known that the Sun’s spinning and her magnetic field have a very intimate relationship. Remember the streams pouring out of the surface that I just talked about? The particles swimming in those streams follow the magnetic field lines like ants on a pheromone trail. Upon reaching a large enough distance, they break free and carry away the rotational momentum or oomph they’ve stolen from the Sun. This gradually slows the Sun down, and is aptly called magnetic braking.

However, this picture seems to have changed only last month. Turns out that the Kepler Space Telescope has been spying on thousands of stars, and a few clusters too. It revealed that in certain clusters young members are very well-behaved. However, the middle aged members, particularly those of the exact type as our Sun, were not acting their age! They were in fact spinning too fast for their old age. They don’t seem to be slowing down either.

Their brakes seem to have gone faulty, and scientists suspect this has to do with the motion lurking just underneath the stellar surface, or convection. Things may very well be more complicated than we had thought!

The Inescapable demise

She will shine normally for the next several billion years but for us earthlings, life will be far from normal. Earth’s temperature will steadily rise making life more challenging before the final cataclysm arrives. In about 1 or 2 billion years it will be hot enough to boil most of our water and seriously destabilise our biosphere, turning our planet into an arid desert. A few billion years later, whatever has remained of our oceans will evaporate and Earth will be a barren lifeless planet, like Venus.

Well perhaps that’s for the best, because what’s coming afterwards is a hellish ordeal no human would wish to witness. In about 6 billion years, the sun’s core runs out of hydrogen and she will swell up into an angry fiery giant, swallowing Mercury and Venus. She will melt our planet into a blob of magma, even Mars will not be habitable, and distant icy worlds like Uranus and Neptune will start to defrost.

Things will only continue hell-ward from there. Eventually the helium in her core, the product of burnt hydrogen, will run out too. Like a desperado with nothing left to lose, she’ll rage into a giant once again and that’s the point of no return. Ripping herself apart in despair, she will tear away her layers into glowing rings of gas and dust, or planetary nebula, that drift away in the wind. This tragedy will only spare her Earth-size beating heart, an abandoned naked inanimate object called a white dwarf. Left to its fate, it will cool and fade away into the dark as the solar system turns into a chilly, forsaken place.

Thus the tragedy unfurls and the rest is silence..

The dawn has now cracked and its light is streaming in through my window. I shall soon stroll to the beach and bask in the golden shimmer of our Sun, before it’s too late.

Image credit: The Economist

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: NASA-Langley.