Stardust (astronomy)

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A source of stardust - The nova in 2002 of the giant star V838 Monoceros in the constellation Unicorn, 20,000 light years away . The brown stardust vortices came from an eruption 10,000 years ago. Their diameter is about 7 to 8 light years.

As a scientific term, stardust describes small, sometimes microscopic particles of matter in interstellar space . They are products of novae and supernovae and contribute a small part to the interstellar dust .

In common parlance, the term stardust is also used to describe any interstellar matter that emerged from stars and is not bound in solid structures such as stars, planets or asteroids. This matter forms the various types of astronomical nebulae , globules , dark clouds and the admixtures to the hydrogen of molecular clouds . Stardust in this word meaning consists of all chemical elements except hydrogen (which theories suggest was formed during the supposed Big Bang), even in a gaseous state.

Importance for research


The surrounding

In certain development stages of stars (expansion and cooling), low temperatures and high gas densities enable the formation of stardust. This temperature / density range is called the dust formation window . Depending on the composition of the star, it starts at different temperatures.

In addition, the following must be given for the formation of stardust:

Contrary to the state of knowledge of the 1990s, the formation of crystalline minerals is not limited to planetary surfaces: infrared observations have shown that mineral formation takes place even with extremely low gas densities in the extensive shells of pulsating red giant stars .

Long-period variables or novae form dust shells. There are sound waves that become shock waves when the density drops outwards . At low temperatures (around 1,500 Kelvin ) and increasing density, there is a high degree of condensation . Further to the outside, backwarming (see below) ends as the distance from the star increases and the shell becomes thinner. The compression of the gas behind the shock waves promotes dust growth in the multiplex coupling of the reaction processes.

When a star enters the phase of great luminosity , a planetary nebula is formed from the stardust by the superwind ( stellar wind of a variable star) .

Steps of dust formation

  • First, a primary condensate forms . It consists of molecules of more common elements and low binding energy .
  • The next step is nucleation ; Germs are the first agglomerations (accumulations) of molecules.
  • The germ growth follows. This creates particles that are stable in the star's radiation field.

Dust growth

There are several options for dust growth. A simple possibility is growth through a linear reaction chain of molecules. In long-period variables, the dust forms with the mutual coupling of many reaction processes, with the following dominating:


Stardust consists of crystals , amorphous solids and chains of molecules. The particle sizes range from 5 nanometers to 10 micrometers and are barely visible to the naked eye. They are sometimes referred to as grains . Common elements in the compounds are hydrogen , helium , oxygen , nitrogen , neon , silicon , iron and magnesium . Because of the condition of heat resistance , gemstone molecules are relatively common in stardust. Typical examples are diamonds , corundum (or colored by titanium as sapphires ), spinels and olivines .


Stardust makes up about one percent of mass of the interstellar medium , which in turn comprises about 10% of the visible mass of the universe. The distribution of stardust corresponds to that of the gases; it is very uneven within the galaxies : in the spiral arms the concentration of stardust, just like the number of stars, is much higher than outside.

Despite its small share in the interstellar medium, stardust has a clear influence on starlight: it is the reason why the center and the opposite side of the Milky Way are not visible in visible light.


X-ray analysis of a stardust particle

The first exam is the spectral analysis by X-ray telescopes . The spectral lines are compared with terrestrial laboratory data. This method provides information about the composition of the dust in stellar atmospheres, about the extinction and about the scattering .

Another possibility is the extraction of dust particles from meteorites , which are ultimately derived from asteroids , or from comets, as in the Stardust mission . Around 150 scientists worldwide were involved in investigating the particles from comet Wild 2. The examined dust samples appear tiny to outsiders, but are sufficient for mineralogists . In meteorites, stardust occurs in the form of presolar minerals . B. can be examined by means of secondary ion mass spectrometry. These particles are examined in the laboratory. Investigations with the mass spectrometer , chemical analysis and laser ablation provide information about the composition. The isotope ratios are also examined here. Investigations with the electron microscope (especially a transmission electron microscope ) show the surface structures of the particles.

Open questions

The measurement data from a supernova explosion in the Small Magellanic Cloud called into question the current theories on planet formation . The resulting amounts of dust correspond to only one hundredth of what is necessary for planets to form.

The formation of stars cannot be explained without dust; conversely, the formation of star dust without stars is also inexplicable. The investigated comet Wild 2 comes from the Oort cloud . This remote edge region of our solar system contains comets that are as old as the solar system, about 4.6 billion years. However, the comet contains material that can only have formed at very high temperatures in the central region of the solar system. Scientists are discussing whether and how the material could have got out there.

Another question in connection with stardust is that not all isotope ratios detected can be fully explained with the known fusion processes .

Furthermore, the dust shells of stars show strong instabilities, the shape of which has not yet been explained.

See also


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