A grain of lab-grown stellar dust as imaged by NASA Ames' Scanning Electron Microscope.
Sometimes, to better understand astrophysical phenomena, you can’t beat recreating the extreme space environment in the laboratory. And in the case of the mysterious mechanisms behind stellar dust formation, you sometimes just have to build a special oven to ‘cook up’ the extreme conditions near a dying star.
Scientists of NASA’s Ames Research Center in Moffett Field, Calif., have, for the first time, reproduced tiny particles of dust that are known to accumulate around red giant stars. Dust is usually a mild annoyance here on Earth, but stellar dust is very special stuff — it forms the building blocks for planets.
Using the Cosmic Simulation Chamber (COSmIC), Ames scientists have been able to create the same dust that is ejected into the interstellar medium (the tenuous dust and gas occupying the space between the stars) as a star approaches the end of its life. Our sun, for example, will puff up into a red giant star after it has run out of hydrogen fuel in its core (in a few billion years time) and starts the violent process of losing its outer layers, pumping dusty material into space.
However, until now, the production mechanisms behind these small dust grains have been a mystery and impossible to recreate in a laboratory setting.
“The harsh conditions of space are extremely difficult to reproduce in the laboratory, and have long hindered efforts to interpret and analyze observations from space,” said Ames space science researcher Farid Salama. “Using the COSmIC simulator we can now discover clues to questions about the composition and the evolution of the universe, both major objectives of NASA’s space research program.”
The key to COSmIC is its extreme-low pressure chamber at its heart. Able to simulate the stellar environment down to densities billions of times less than that of Earth’s atmosphere, jets of cold argon gas seeded with hydrocarbons are sprayed into the vacuum. The extreme cold, high radiation environment can then be simulated, blasting the whole system with an electrical discharge.
After the gas mixture was exposed to the mini space environment analogue, the researchers detected the production of tiny grains of dust that carry similar characteristics as the dust generated by dying stars. Using an electron scanning microscope, these primordial dust grains were studied (pictured top).
“During COSmIC experiments, we are able to form and detect nanoparticles on the order of 10 nanometers size, grains ranging from 100 to 500 nanometers and aggregates of grains up to 1.5 micrometers in diameter, about a tenth the width of a human hair, and observe their structure with SEM (Ames’ Scanning Electron Microscope), thus sampling a large size distribution of the grains produced,” said Ella Sciamma-O’Brien, of the BAER Institute and Ames research fellow.
In space, this dust becomes a critical part of the structure of the interstellar medium and, over millions to billions of years, accumulates around stars to form the building blocks of planets. Understanding planetary formation processes is becoming critical, especially during this ‘golden age’ of exoplanetary science.
“Today we are celebrating a major milestone in our understanding of the formation and the nature of cosmic dust grains that bears important implications in this new era of exoplanets discoveries,” said Salama.