Gravity has pulled massive amounts of hydrogen and helium together. The first nuclear fires, the stars, are born.
Action at last. Frankly the last 560,000,000 years since the excitement of the Big Bang have been a bit boring. Sure the protons and neutrons were rounding up the electrons and forming into nice stable atoms and the atoms were getting together making interesting things like ice, but really, something more exciting is overdue.
Before we get to that, we should get some perspective on numbers. Our world is so small and our time so short, we barely get a glimpse of big numbers unless we try counting grains of sand or something similar.
Imagine an egg carton containing 12 eggs. You know the sort, a cardboard container stacked up in your local supermarket. For this exercise, we are going to need a lot of cartons.
Begin by stacking cartons until you have a wall, 6 metres (20 foot) across and as tall as a man. Now backup and make another row the same and then just keep going, stacking up the egg cartons as high as a man and 6 metres across. If you keep going at it for long enough, you will end up a mile away (1.6 kilometres) from the first row.
But we are just beginning. We must keep stacking those cartons until we are nearly 100 miles from the beginning. Now hire a small aeroplane and climb to 10,000 feet and look down on the rows of egg cartons stretching away to the horizon in both directions. What you can see is one, yes my son just one, billion eggs.
If each of these eggs was a star, much like our Sun (which is a million times bigger than the earth) altogether they would make a smallish galaxy, a bit like the very first galaxy. It was not large as it only takes about 300 years for the light from the outside stars to reach the middle of the pack.
That galaxy could be MACS0647-JD. It’s not a very glamorous name for what may be the first galaxy, but that’s what we have called the light picked up by one of the Hubble Telescope’s programs called the Cluster Lensing and Supernova survey. The scientists had chosen a “quiet spot” to look, somewhere southwest of Orion. It is hardly sufficient to say it is long way from here because the light from this galaxy has been scooting along at 186,000 miles per second for 13,300,000,000 years and only just arrived this morning.
OK, so we accept the first one is a long way from here, but there are at least 10,000 others out there too in the same outer region and each one had their own billion stars (had, as they have almost certainly expired already).
The probing of this particular part of the universe is an extremely small window, an area equal to about one tenth of the night sky obscured by the moon. In between us and the long distant galaxy, new galaxies are still being formed so the universe is a pretty dynamic place these days.
To collect all that light from even a small part of the night sky takes time. You can’t just take a shot with your digital camera and head off to the pub. The instruments are set for lengthy periods of exposure with multiple readings collated via complex computer computations for the right result. To get the same level of detail for the whole night sky, the photography session would need to last a million years, give or take so we may have to settle for just this one spot for now.
The first fireworks display came about when massive volumes of hydrogen and helium atoms were attracted to each other by gravity, by far the weakest of the four forces of nature. But because the strength of gravity is governed by the mass of the objects, qualified by how close they are to each other, gravity can become somewhat pressing.
(Actually, gravity always wins because despite being the weakest force, well behind the nuclear forces and electromagnetism, it acts long-range. Eventually objects become bigger, making gravity stronger as the mass increases.)
In this case, as the atoms bumped into each other they gradually became bound together in an ever increasing mass. The strength increased with each additional atom until the new additions were pressing down on the earlier atoms with so much force, the temperature soared something approaching 15 million degrees.
When the temperature reached the critical point, the whole lot erupted in a nuclear fire that we call a star. Fortunately, the star does not explode in the normal sense or even “burn” in the normal sense as there is no appreciable oxygen to facilitate combustion.
As it happens, the temperature is so high, the pressure so great that hydrogen atoms begin to fuse creating helium and energy. Strangely, the level of energy produced by a star is fairly low when measured as a percentage of its mass, but it has a lot of mass. As a result we get a very bright spot in the sky which releases a lot of energy and in the case of the earth, that is a good thing.
Fortunately the action in the core is counter-balanced by the gravity pull on the outer two thirds, so we end up with a stable firework that will persist for about 8,000,000,000 years. Our star is about half way through and while the temperature its core is 15 million degrees, where the fusion is taking place, out on the “surface” it’s a very much milder 5800 degrees, very much less than 1% of the core temperature.
Curiously, the outer corona is hotter than the surface, 300 times hotter in fact which does not make sense, intuitively at least. Hopefully the Parker Solar probe which is scheduled to fly close to the sun in 2024 and hang around for about 8 years after that, will shed some light on the subject.
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