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June 13, 2019
from
UniversityOfGuelph Website
Artist's impression of a collapsar
(NASA
Goddard Space Flight Centre)
That gold on your ring finger is stellar - and not just in a
complimentary way...
In a finding that may overthrow our understanding of where Earth's
heavy metals (elements) such as gold and platinum come from,
new research by a University of Guelph (U of G) physicist
suggests that most of them were spewed from a largely overlooked
kind of star explosion far away in space and time from our planet.
Some 80 per cent of the
heavy elements in the universe
likely formed in
collapsars, a rare but heavy
element-rich form of
supernova explosion from the
gravitational collapse of old, massive stars typically 30 times as
weighty as our sun, said physics professor
Daniel Siegel.
That finding overturns the widely held belief that these elements
mostly come from collisions between neutron stars or between a
neutron star and a
black hole, said Siegel.
His paper (Collapsars
as a Major Source of R-Process Elements) co-authored with
Columbia University colleagues appears today in the journal Nature.
The research received coverage on
CNET , the
Times of India, and
The Tribune.
Using supercomputers, the trio (Daniel M. Siegel, Jennifer Barnes,
Brian D. Metzger) simulated the dynamics of collapsars, or old stars
whose gravity causes them to implode and form black holes.
Under their model, massive, rapidly spinning collapsars eject heavy
elements whose amounts and distribution are,
"astonishingly
similar to what we observe in our solar system," said Siegel.
He joined U of G
this month and is also appointed to the Perimeter Institute for
Theoretical Physics, in Waterloo, Ont.
Most of the elements found in nature were created in nuclear
reactions in stars and ultimately expelled in huge stellar
explosions.
Heavy elements found on Earth and elsewhere in the universe from
long-ago explosions range from gold and platinum, to
uranium and plutonium used in nuclear reactors, to
more exotic chemical elements such as neodymium found in
consumer items such as electronics.
Until now, scientists thought that these elements were cooked up
mostly in stellar smashups involving neutron stars or black holes,
as in a collision of two neutron stars observed by Earth-bound
detectors that made headlines in 2017.
Ironically, said Siegel, his team began working to understand the
physics of that merger before their simulations pointed toward
collapsars as a heavy element birth chamber.
"Our research on
neutron star mergers has led us to believe that the birth of
black holes in a very different type of stellar explosion might
produce even more gold than neutron star mergers."
What collapsars
lack in frequency, they make up for in generation of heavy elements,
said Siegel.
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Collapsars also
produce intense flashes of gamma rays.
"Eighty per cent of
these heavy elements we see should come from collapsars.
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Collapsars are
fairly rare in occurrences of supernovae, even more rare than
neutron star mergers - but the amount of material that they
eject into space is much higher than that from neutron star
mergers."
The team now hopes to see
its theoretical model validated by observations.
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Siegel said infrared
instruments such as those on the
James Webb Space Telescope, set
for launch in 2021, should be able to detect telltale radiation
pointing to heavy elements from a collapsar in a far-distant
galaxy.
"That would be a
clear signature," he said,
...adding that
astronomers might also detect evidence of collapsars by
looking at amounts and distribution of heavy elements in other stars
across our
Milky Way galaxy.
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Siegel said this research
may yield clues about how our galaxy began.
"Trying to nail down
where heavy elements come from may help us understand how the
galaxy was chemically assembled and how the galaxy formed.
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This may actually
help solve some big questions in cosmology as heavy elements are
a nice tracer."
This year marks the 150th
anniversary of Dmitri Mendeleev's creation of the periodic
table of the chemical elements.
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Since then, scientists
have added many more elements to the periodic table, a staple of
science textbooks and classrooms worldwide.
Referring to the Russian chemist, Siegel said,
"We know many more
elements that he didn't.
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What's fascinating
and surprising is that, after 150 years of studying the
fundamental building blocks of nature, we still don't quite
understand how the universe creates a big fraction of the
elements in the periodic table."
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