Origin of meteoritic stardust has been finally located

30 January, 2017

The Solar System was born out of an interstellar cloud of gas and dust grains. Some of these grains were made around previous generations of stars and are effectively tiny condensed pieces of stars. While most of the original dust was destroyed to make up new dust, rocks, and planets, including Earth, a small fraction of stardust survived the destruction process trapped in meteorites. This special dust can be used to trace the evolution of the nebula from which the planets were born and to understand the physical processes inside the stars where the grains formed.

However, studies of one class of stardust – oxygen-rich grains like silicates and aluminum oxide – revealed a long-standing puzzle. Intermediate-mass stars For the original scientific article, please click here(roughly six times heavier than the Sun) are seen by infrared telescopes to produce huge amounts of dust, but we had not been able to find any dust from these stars in the Solar System meteoritic record so far.

The Helix Nebula: a star at the end of its life. The star has blown off its outer layers, which show up in a nebula. These outer layers are rich in stardust grains of the sort that we find in meteorites in our Solar System Picture credit: NASA, ESA, and C.R. O'Dell, Vanderbilt University

A new study, led by Maria Lugaro from Konkoly Observatory (MTA-CSFK) and published in Nature Astronomy, solves this problem by identifying in the make-up of some meteoritic stardust grains the effect of the nuclear reactions that occur in these particular stars. The breakthrough was possible thanks to experiments carried out under the Gran Sasso mountain (Italy) at the Laboratory for Underground Nuclear Astrophysics (LUNA, https://luna.lngs.infn.it/).

The result of the LUNA experiment led by C. G. Bruno (and published on Physical Review Letters in 2016), showed that the probability of for the fusion of protons and of 17O (a heavier type of oxygen almost three thousand times less abundant than 16O) to occur is twice as large as previously thought. This process, with a faster rate, leads to a faster destruction of the rare 17O isotope. Lugaro and her colleagues included this new rate in their stellar models, to see how the chemical compositions of stars might change. They discovered that the effects of the new reaction rate clearly agreed with the measured properties of some stardust grains, resolving the mystery of the missing grains from intermediate-mass stars.

LUNA is currently the only underground accelerator worldwide specifically devoted to the study of nuclear reactions of astrophysical interest. The facility is hosted by the Italian Institute for Nuclear Physics (INFN) Gran Sasso Laboratory and is located under more than one kilometer of rocks.

Electron microscopic image of a corundum (crystallized aluminium-oxide) stardust grain discovered within a meteorite. Picture credit: A. Takigawa, University of Tokyo

Zsolt Fülöp from MTA-Atomki explains: “The rock provides ­effective shield against the interferences that spoil measurements of very rare events above ground. It allows us to reproduce more effectively the nuclear reactions that happen inside stars, including those where stardust is formed.”

Maria Lugaro says: “The long-standing question of the missing dust was making us very uncomfortable: it undermined what we know about the origin and evolution of dust in the Galaxy. It is a relief to have finally identified this dust thanks to the renewed LUNA investigation of a crucial nuclear reaction.”

LUNA is an international collaboration of about 40 scientists from Germany, Italy, United Kingdom and Hungarian partners at the MTA-Atomki and MTA-CSFK.

For more information please contact:

Maria Lugaro maria [dot] lugaro [at] csfk [dot] mta [dot] hu

Zsolt Fülöp fulop [at] atomki [dot] mta [dot] hu

website: http://w3.atomki.hu/atomki/IonBeam/nag/index_en.html