Tiny dust particles found in meteorites show evidence of having been formed long before the Solar System. Testing suggests they may have formed in exploding stars that long predate the Sun, and their composition could tell us the temperatures of those explosions.
The early universe was made entirely of hydrogen, helium, and lithium. The rest of the periodic table was formed in stars, with the heavier elements coming from stellar explosions. Most of these elements however are spread across the galaxy as gases, or tiny dust particles, to form new stars like the Sun.
Michael Bennett, a PhD student at Michigan State University, has been attempting to isolate this pre-solar dust and determine the conditions under which it formed. His theory is that the dust was formed in a nova – an explosion that takes place on the surface of a white dwarf that is part of a close binary pair. Material drawn from a main sequence star onto the denser white dwarf causes an explosion on one side of the recipient star.
On Earth, dust particles have been dissolved and mixed, destroying any ancient identity. We have found evidence of pre-Solar System dust raining down on our upper atmosphere. However, meteorites represent our main source of such material.
Grains of dust in some meteorites contain ratios of isotopes (atoms of an element with varying numbers of neutrons) that are different from those in the rest of the Solar System, suggesting they formed elsewhere. Bennett compared the ratios seen in these grains with what would be expected to be produced in a nova.
Silicon-30 is particularly abundant in this meteoric dust, relative to the Si-28 that dominates on Earth.
In their study published in Physical Review Letters, Bennett and his colleagues looked at which elements produced Silicon-30, first producing Phosphorous-30, which undergoes Beta decay to Si-30, with a half-life of 2.5 minutes. They then created an alternative reaction, where P-30 becomes Sulfur-31, rather than decaying to silicon. The frequency with which this occurs affects how much Silicon-30 we would expect to see in particles formed in novae.
"These particular grains are potential messengers from classical novae that allow us to study these events in an unconventional way," said coauthor Dr. Christopher Wrede in a statement. "Normally what you would do is point your telescope at a nova and look at the light. But if you can actually hold a piece of the star in your hand and study it in detail, that opens a whole new window on these types of stellar explosions."