The Presolar grains originated even before the sun was formed. They are interstellar solid matter. Interstellar means between the stars. They are in the form of grains.
Composition of Presolar grains
The Presolar grains are made of diamond, graphite, silicon carbide, titanium carbide, silicon nitride, titanium oxide, hibonite, silicate minerals, spinel, corundum. The Presolar grains are investigated using electron microscopes and spectroscopic methods. The diamonds in the Presolar grains are nanometric in size.
Significance
It is important to study about the Presolar grains as it provides information about the stellar evolution (that is star formation and its changes with time) and nucleosynthesis. Nucleosynthesis is the process by which chemical elements are created by nuclear fusion reactions. As the Presolar grains carry isotopic signatures, they are highly helpful to test supernova explosions.
Discoveries
The Murchison meteorite hit Australia in 1969. In 2020, scientists discovered that the meteorite consists of star dust (or Presolar grains) that formed five to seven billion years ago. It is to be noted that the sun is 4.6 billion years old.
Stardust and interstellar grains
Presolar grains are interstellar grains. They are formed from interstellar cloud matter that were accreted by Presolar grains. On the other hand, the star dust originates from a single star. All stardust is Presolar grains. But not all Presolar grains are stardust.
Presolar grains in meteorites
The Presolar grains in the meteorites were identified in the laboratories due to their abnormal isotopic abundances and refractory materials. Refractory materials are those that contain high equilibrium condensation temperature. They are opposite of volatile.
Information provided by the Presolar grains
The Presolar grains have provided information about asymptomatic giant branch stars. These stars appear like a bright red giant. Their luminosity ranges are thousand times higher than the sun. The set of collected particles from the Presolar grains helped to learn about the galactic evolution. They also provide information about the physio-chemical conditions under which they condensed.
How are Presolar grains released?
The Presolar grains are released in to the interstellar medium by radiation pressure. It is the mechanical pressure exerted upon the surface of the matter. It is exerted due to the exchange of momentum between the object and the electromagnetic field. In simple words, momentum is the strength of the object that allows it to move faster.