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Supernovae – factories of dust?


A study published in Science, analyzing a remnant of supernova that was found in our galaxy, suggests that the dust provided by explosion can survive the successive shock wave. This submits the fact that the dust of first galaxies may have been mainly produced by supernovae.
In older galaxies, or those already in the primordial age of the universe and that we now observe as the most distant, astrophysicists have found a lot of dust. Far from being a nuisance, in the galactic kitchen, dust is a crucial ingredient for the success of a new batch of stars.

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Credit: Ryan Lau et al./SOFIA/FORCAST/Chandra/ACIS

A good explanation would be the explosion of a supernova, but so far it has not been clarified whether the dust produced by a supernova explosion can withstand the stages following the explosion itself. Scientists have calculated that little of dust explosion can survive the next shock wave, triggered the pressure difference between the thermal material ejected at high speed from the supernova and the dense circumstellar half, relatively cold.
Now a group of Sino-US astronomers, led by Ryan M. Lau at Cornell University, has acquired new evidence in favor of the fact that dust can survive the aftermath of supernova, and then supernovae may indeed have been the dominant mechanism of dust production in the first galaxies.
To carry out their study, published in the journal Science, Lau and colleagues took the plane: a Boeing 747SP, equipped with an infrared observatory called SOFIA, Stratospheric Observatory for Infrared Astronomy, a collaboration between NASA and the German space agency DLR.
With the instrument FORCAST SOFIA, the group analyzed the dust in the middle of a supernova remnant, known as Sagittarius A East, located very close to the center of our galaxy and that is the result of a particularly powerful explosion that occurred around 10,000 years ago.
Thanks to new observations, the researchers believe that approximately between 7 and 20% of the initial mass of dust produced by the supernova has survived to its own creative shock. According to the authors, these results imply that a higher percentage of dust than expected could be preserved in the conditions of the early Universe, billions of years ago, and that the dust in oldest galaxies might actually come from supernovae.
This is a thesis that seems to convince Andrea Pastorello, from Astronomical Observatory of Padova. “The discovery is part of a quite controversial context,” said Pastorello, “since not all scientists who deal with this topic – myself included – believe that supernovae are among the leading manufacturers of dust in the Universe “.

Stratospheric Observatory for Infrared Astronomy (SOFIA).

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Credit: NASA/Jim Ross

The difficulty, says the researcher, reside mainly in two factors: on the one hand, in the observations, it is difficult to discriminate the new dust generated in the explosion of a supernova from environmental contamination; on the other hand, the amount of dust estimated varies from the initial assumptions, concerning, for example, the chemical composition and size of the grains of powder.
But, as it has been mentioned, one of the fundamental issues to consider supernovae real “factories of dust” was linked to the fact that the passage of the reverse shock in the material ejected by the supernova would have to be an effective weapon to destroy the dust that had possibly formed. In this sense, explains Pastorello, “the new and interesting aspect provided by this study is the surprising evidence that the particular environmental conditions (for example, the high density of the medium) are able to ensure the survival of a part of the powder, in the form of smaller and hotter grains, even after the passage of the shock front “.
The total mass of the particles resisted the shock, says in closing Pastorello, “is a significant amount, so we conclude that supernovae could contribute significantly to the dust fraction observed in the cosmos, especially in regions of high density of the primordial Universe.”

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