Recent observations of difficult visible distant galaxies over ten billion years old show that they are remarkably mature for their age. How could more developed galaxies have emerged so soon after the Big Bang? Are our theories correct?
From dwarf galaxy to mega-system
Galaxies come in all shapes and sizes. For example, there are galaxies (think of the Magellan Clouds) that are much smaller than ours. These consist of several hundred million stars. According to the currently popular cosmological theories these were (from a billion years after the Big Bang) the first galaxies ever formed. Due to many collisions of the dwarf galaxies, they formed larger galaxies. It was only after several billion years that these galaxies formed the size of our own Milky Way.
However, new observations from the Gemini Observatory of galaxies in the so-called “Redshift desert”, a period three to six billion years after the Big Bang, have turned this well-organized picture completely upside down. The researchers observed galaxies that were much older than this popular model allows. The age of a galaxy can be seen, among other things, by its brightness. A lot of star formation takes place in a young galaxy.
How do you determine the age of a galaxy?
The main method is to measure the redshift. Because the Universe is expanding at approximately the same rate everywhere, galaxies appear to be moving rapidly away from us many billions of light-years away. As a result, their light is stretched. The degree of stretching can be measured. This is because spectral lines occur in light: a kind of fingerprint of the atoms through which the light is emitted or absorbed. Every single atom or molecule has a unique fingerprint: the absorption (or emission) spectrum. For example, sodium ions have two characteristic bright yellow spectral lines. The reason you see a yellow light when you drop table salt (sodium chloride) in a gas flame. If this fingerprint suddenly appears in much redder light than usual, the astronomer knows that this object is moving away from him.
However, this does not say much about the condition of the galaxy. For that you can pay better attention to the light distribution. When a lot of star formation takes place, a lot of giant stars are also formed. Giant stars have a very short life span, a few tens of millions of years, and emit a lot of blue light. As a result, a young galaxy lights up like a Christmas tree. When star formation stops, these giant stars will soon be over and the galaxy will enter a more stable, "more mature" phase. For example, the star formation rate in our own Milky Way is only a quarter of what it was billions of years ago. In more mature galaxies, the light from long-lived sun-like stars and red dwarf stars becomes predominant. Before that, it was outshone by the bright giant stars.
A second technique is to pay attention to the occurrence of metals. According to astronomers, metals are all elements except hydrogen and helium. In practice: all atoms that were not formed during the big bang. During their existence, stars form heavier elements through nuclear fusion. Thus hydrogen is fused to helium, helium to carbon and so on. If the light from a galaxy contains many traces of, for example, carbon, oxygen or iron, that is proof that it is already of an advanced age.
You can also pay attention to the size and shape. Large galaxies (such as our own) are the result of many mergers of dwarf galaxies and are therefore probably much older than dwarf galaxies. If a dwarf galaxy never merges, this too can of course reach a very old age. Several examples of this are known.
Gemini Deep Deep Survey
Observations so far have focused only on the brightest, ie “youngest” galaxies. These are the easiest to observe (the faint galaxies are three hundred times fainter than the light of the atmosphere). Naturally, this produces a very distorted picture. The Gemini telescopes are two completely identical eight-meter mirror telescopes, one on the volcanic cone Mauna Kea in Hawaii and the other in Chile. GDDS is an international collaboration that investigated the spectrum of three hundred galaxies from the “redshift desert”, including a proportionate number of faint specimens, which astronomers have only “briefly” left behind. This created a more realistic image. As it turns out, the faint galaxies are much more mature than the theories suggest. The gas between the stars in the galaxies contains far more metals than expected.
First alien life much earlier than expected?
Planets could not form near the very first stars, because only hydrogen and helium existed. Metal-rich galaxies contain many raw materials for planets: iron, silicon, oxygen. Now that we have discovered that very young galaxies could also form planets, life should have quickly gained a foothold in the universe long before the Earth was even formed. Could our distant descendants find ruins of alien civilizations near burnt-out stars?