Category: Physics

First generation Star formation

Our Sun is a typical, smallish star, it has been around for some five billion years so far and probably has about another five billion years to go. No need to panic, the Sun is middle aged! Steady as you go.

Artist’s impression of early stars (Wikimedia)

Part 4 of a series – Emergence

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RequiresExtensive cold gas clouds
Results inStars producing elements up to iron, gas giant planets
EnablesNovae, Supernovae

Two features of the birth of a star system are important here, matter and energy. The first stars formed from the gradual collapse of clouds of cold gas consisting mainly of hydrogen with some helium and a trace of lithium. Gravity slowly pulls a gas cloud into an ever-shrinking volume, and slow, drifting motions lead to increasing rates of rotation as this shrinkage proceeds. Compression of gases always results in heating, so over a long period of time, a diffuse cloud of cold gas becomes a rotating mass of increasingly hot gas.

Sufficient collapse eventually causes the internal pressure and temperature to reach a critical point at which nuclear fusion becomes not just possible, but inevitable, and conditions then settle to a point where the fusion energy dramatically increases the core temperature and pressure, pushing outwards more and more strongly until the the gravitational collapse is stopped. The rotating, hot mass is a young star, converting hydrogen to helium.

Over time it settles down more and more to a stable state, though this lasts for a limited time, basically until no further hydrogen fusion is possible because there is insufficient hydrogen remaining. The length of time of that stable state is related to the mass of the star. Small, light stars process their hydrogen slowly. Large, very massive stars burn through their supply much faster. Although they have a great deal more to begin with, the temperatures and pressures at the centre are much higher so there is a faster reaction in a larger volume of core. That’s why large stars run out of fuel faster than small ones. These earliest stars are called Population III stars by astronomers, it seems they were usually very large and therefore short-lived.

Our Sun is much more recent, a typical, smallish star, it has been around for some five billion years so far and probably has about another five billion years to go. No need to panic, the Sun is middle aged! Steady as you go.

Eventually, as the hydrogen is used up, energy production falls and gravity can no longer be resisted, so the star shrinks and heats up further. As the internal temperatures and pressures increase, the star shrinks until the temperature at the core is sufficient to fuse helium. Once again, further gravitational collapse is halted by increasing core temperatures and this lasts until the helium supply is exhausted. Through a whole series of similar steps the star creates heavier and heavier elements all the way up to iron, but fusing atoms of iron absorbs energy so gravity wins out in the end. Small stars slowly cool and eventually become inactive and unchanging. Particularly large stars have a different fate.

We’ll consider those details in a future article.

See also:

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Image of the day – 27

In the natural way of things, each Aloe will produce an average of one new plant, and the population will remain in balance.

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What’s in an image? Sometimes quite a lot, more than meets the eye.

I’m posting an image every day (or as often as I can). A photo, an image from the internet, a diagram or a map. Whatever takes my fancy.

Aloe aristata

Today’s picture is a close up of an Aloe aristata plant with a developing flower bud. All plants, animals, fungi, bacteria and even viruses have ways of reproducing themselves. That’s one of the defining characters of life of any kind. We can be absolutely confident that the same will be true of any life forms anywhere in the universe.

The Aloe flower bud will develop on a tall stalk and if the flowers that form are pollinated they will produce and release seeds that stand a chance of germinating and growing into new, similar, Aloe plants. In the natural way of things, each Aloe will produce an average of one new plant, and the population will remain in balance.

The only choices available to life are to survive for ever with no reproduction, or to live for a limited time and leave behind new versions to carry on the process. What life cannot do is live forever and reproduce: that would lead to overpopulation and catastrophic failure of resources. Even with reduced family sizes, the planet is no longer capable of supporting the billions of people on our planet. We face catastrophic population collapse due to lack of resources at some point unless we can reduce our population size in some other way first. That’s a matter of simple arithmetic, not a political statement or some kind of guesswork. If we don’t face and fix the issue, something else will sooner or later.

Themed image collections

The links below will take you to the first post in each collection

Cirencester, Favourites, Irish holiday 2024, Roman villa

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Image of the day – 21

The plant, on the other hand, is a living organism. Nobody designed or manufactured it – life is much more wonderful than that!

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What’s in an image? Sometimes quite a lot, more than meets the eye.

I’m posting an image every day (or as often as I can). A photo, an image from the internet, a diagram or a map. Whatever takes my fancy.

It’s quite amazing how life clings on, even in the most adverse circumstances. This plant was growing in my front drive, somehow finding a way to get its roots into a narrow gap in the block paving. The blocks were designed by a garden landscaping company and manufactured to particular standards of hardness and resistance to my car rolling over them. They were designed to last.

The plant, on the other hand, is a living organism. Nobody designed or manufactured it – life is much more wonderful than that! The universe we live in is tailored to build ever more complex things from very simple beginnings. A handful of quantum fields is all it takes, and these are exquisitely able to give rise to fundamental subatomic particles. These group together, eventually settling into simple atomic nuclei. As the universe expanded and cooled, atoms of simple elements appeared, almost entirely hydrogen and helium. Stars condensed and formed heavier elements up to iron. I could go on, but it’s a long story! Maybe some other time?

For now, just consider the battle between order (my paving blocks and the urge I have to remove weeds that neither I nor my wife want to see growing there) and disorder (weeds thriving wherever they can, despite my best efforts). Life always wins in the end, it seems!

Themed image collections

The links below will take you to the first post in each collection

Cirencester, Favourites, Irish holiday 2024, Roman villa

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Useful? Interesting?

If you enjoyed this or found it useful, please like, comment, and share below. My material is free to reuse (see conditions), but a coffee is always welcome!

Combining atoms

Atoms began emerging very early in the formation of the universe, perhaps 18 000 years after the origin.

Part 3 of a series – Emergence

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A hydrogen atom

Here’s a simple diagram of a hydrogen atom. The little black ball is the nucleus, a proton, 10 000 times smaller than the atom as a whole, the white part represents an electron, spread out like a cloud around the nucleus. The proton and the electron were once thought of as fundamental particles that had no underlying structure. For the electron that remains true. The proton on the other hand consists of three quarks, but for the purposes of chemistry we can still think of it as ‘fundamental’.

A hydrogen atom can react with other atoms in quite specific ways. New and more complex behaviour emerges as atoms combine. Here are some of those emergent properties:

A molecule of methane, four hydrogens attached to a carbon atom
  • Two atoms of hydrogen can combine as a molecule of hydrogen, a gas that can become explosive when mixed with air.
  • Two hydrogen atoms and an oxygen atom can combine as a water molecule. Everyone knows that pure water is safe to drink.
  • Four hydrogens and a carbon atom can combine as a molecule of methane gas. This is the domestic gas that we use for cooking and for heating our homes. Methane is also a powerful greenhouse gas, contributing to global heating.
  • Three hydrogens and a nitrogen atom can combine as a molecule of ammonia, a poisonous gas that dissolves readily in water.
  • Two hydrogens and a suphur atom can combine as a molecule of hydrogen suphide, a gas that smells like rotten eggs.

There are many other molecules that include hydrogen.

Protons, and similar particles called neutrons can combine in larger numbers to make heavier and larger nuclei surrounded by much larger clouds of electrons (we’re leaving out a great deal of detail here). Together, these are the various chemical elements; there are more than 100 different kinds. Sodium, oxygen, phosphorus, chlorine, nitrogen, lead, iron, gold, sulphur, copper, tin and so on.

Chemistry

So – Take 100 different atoms and combine them together in various ways and you can clearly see that many, many different molecules are possible. Imagine 100 different kinds of Lego bricks and you begin to see the range of possibilities. There are rules of chemistry that restrict the combinations that can form, but even allowing for those rules, the number of possible molecules is huge . Here are some examples.

  • Sulphuric acid – two hydrogens, a sulphur, and four oxygen atoms
  • Table salt – one sodium and one chlorine atom
  • Bleach – two chlorine atoms
  • Laughing gas – two nitrogens and two oxygen atoms

We see chemistry appearing as soon as we have atoms. Chemistry just isn’t there in the world of subatomic particles like protons, neutrons and electrons. Like every object you can think of, we are made of atoms in complex chemical combinations so it’s quite hard for us to imagine a universe without chemistry. And atoms began emerging very early in the formation of the universe, perhaps 18 000 years after the origin. Chemistry started around 370 000 years as the universe continued to cool and atoms were able to begin combining ever more freely. At first hydrogen, helium and a small amount of lithium were the only elements available, all the others up to iron formed inside stars, while exploding stars (supernovae) generated the heavier elements and scattered these and the lighter elements far and wide. Once that had happened, perhaps 500 million years ago, the full range of atoms were available and chemistry took off in earnest.

Atoms are emergent, beginning to form once the universe became cool enough. And chemistry emerges given the presence of atoms and even lower temperatures. Could atoms and chemistry have been predicted given the presence and behaviour of subatomic particles? Perhaps. But it would have taken a real genius, a physicist with great foresight and imagination. But physicists are made of atoms and complex chemistry – so the real answer must be ‘no’!

That’s the thing about emergence – new kinds of objects and new processes ’emerge’ when the materials and conditions to do so exist. Sometimes emergence is rapid, even sudden. But as we shall see in a future post, sometimes it’s very slow indeed, or long delayed even after the possibility of emergence has existed for a very long time. Chemistry emerged quickly once atoms and low enough temperatures became available. So the opportunity was ‘slow’ to occur, but the emergence was immediate thereafter. We can think of these things separately – emergence opportunity, emergence delay, and emergence rate.

See also:

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In the beginning – a field

The properties of the universe itself (whatever they may have been) seem to have resulted in the emergence of four fields, each with its own properties.

Part 2 of a series – Emergence

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Fields underlie everything we’re familiar with in the universe in which we live. We know nothing about the universe at the time it began, though we know a surprising amount about the universe just a tiny fraction of a second after that beginning.

No, I’m not writing about a field with hedges around it, but a field as defined and understood by physicists. The first thing to exist in our universe was a field, quite possibly just a single field (or so I like to imagine). This is the second article on the topic of emergence, and you’ll see why later.

Various kinds of field (from Wikimedia Commons)

So let’s begin by thinking about the nature of a field. Physicists talk about several different fields – a gravitational field for example. In 1865 James Clerk Maxwell published ‘A Dynamical Theory of the Electromagnetic Field’ in which he explained that magnetism, electricity and light are all functions of a field. Fields are not particles, or forces (though they can and do give rise to these). Instead, a field permeates all of space. Right now you are exposed to the gravitational field and you are being acted on by the sun, the moon and the earth (and everything else in the universe). The pull these objects exert on you are in proportion to your mass and the mass of the distant object (let’s say the Sun) and by the distance between you. The strongest pull and the only one you will be aware of is the pull of the Earth, you’ll certainly notice it if you trip and fall over, or if you drop something. The Moon is not as massive as the Earth and is far away, so has much less pull. The Sun is much more massive than the Earth, but it’s also far, far more distant, and therefore pulls on you much less than the Earth does. These rules apply to every object in the universe, there is gravitational attraction between you and your cat (if you have one) also there’s gravitational attraction between you and the Andromeda galaxy. These attractions are very tiny as neither you nor the cat have much mass, and the Andromeda galaxy is exceedingly far away.

All of this can be quantified and a mathematical formula exists so that, given the masses of two objects and the distance between them, it’s easy to calculate the strength of the attraction.

So, where does emergence come in?

We don’t know how the universe began, or why, but we do know more or less when – almost 13.8 billion years ago. When the universe was still very new (if it makes sense to talk about time at all in the first picosecond (a billionth of a second), the still very tiny universe was filled by the gravitational field (as it still is today). This field became distinct from other fields repeatedly as the universe grew, giving rise to the electromagnetic field, then the weak field, and finally the strong field.

This represents the earliest event we might describe as emergence. The properties of the universe itself (whatever they may have been) seem to have resulted in the emergence of four fields, each with its own properties, four things that were not originally present. There’s probably little more to say about any of this, and the way I’ve portrayed it is speculative. But given these four fields, further steps of emergence can be discerned rather more clearly. And that’s something we’ll look at in another part of this series.

See also:
Part 2 of a series – Emergence

< Emergence – an introduction | Index | Combining atoms >

The snowflake designer

I’ve always been interested in their symmetry, their beautiful shapes, and their infinite variety

Since I first saw a photograph of a snowflake under the microscope, I’ve always been interested in their symmetry, their beautiful shapes, and their infinite variety. But never had I imagined that it would be possible to create such snowflakes in the lab or control their growth to order.

Meet Ken Libbrecht, the snowflake guy. He began by investigating how they form, and can now build snowflakes more or less to order. Amazing! Watch this video in which Ken demonstrates his work to Derek Muller on Veritasium.

Ken has discovered so much about the conditions that cause snowflakes to form. He also understands the subtleties of humidity, temperature and so on that produce different kinds of snowflake growth, why they show the six-fold radial symmetry that they do, why they branch at particular places, and why individual ‘arms’ of a snowflake are almost identical to one another while different snowflakes are unique.

See also