- 3908 - HEAVY ELEMENTS - how did the stars create them? Atomic elements are all the atoms that make up the chemistry in the periodic table of elements. The chemical elements are distinguished from each other by the number of protons in their nuclei.
---------- 3908 - HEAVY ELEMENTS - how did the stars create them
- The simplest element is hydrogen that
has only one proton in the nucleus.
There are 92 protons in the natural element uranium. Where did all this come from?
-
- Some of these
elements arrived on Earth by surfing supernova shock waves. When stars die, they spread the elements
they’ve created in their cores out to space. But, other objects and processes
in space also create elements.
-
- Eventually,
that “star stuff” scatters across the galaxy in giant debris clouds. Millions
of years later, it settles onto planets.
How do heavy elements like manganese, iron, and plutonium show up on
Earth.
-
- It turns out
they’re made in different processes, often in different parts of the Milky Way.
Yet, they’ve been found layered together on Earth’s seabed. That implies they
arrived about the same time, despite their different origins.
-
- The
elements from faraway events are carried by supernova shock fronts just like
surfers catching a wave. First, there
are the Type II supernovae. They occur when a supermassive star dies. That’s
one at least eight times the mass of the Sun. These stars fuse heavier and heavier
elements, carbon, in their cores.
-
- When they
get to creating iron, they don’t have enough energy to keep up the production
line. The cores collapse and then everything expands outward very rapidly in a
supernova explosion. That’s enough to send its heavy elements racing through
space.
-
- Next, there
are Type Ia supernovae. These happen in a binary pair of stars. Material from a
main-sequence star accrets onto its partner, a white dwarf. When too much
material accumulates, there’s an explosion. That results in the “nucleosynthesis”
of heavier elements, including manganese.
-
- Another
catastrophic event that likely creates heavy elements is the collision, or
merger, of two neutron stars. As they spiral in toward each other and
eventually smash up, they release a shower of neutrons. Those, in turn, bombard
nearby atoms. This “r-process” event very quickly produces heavy elements such
as plutonium.
-
- Somehow, all
this material from different sources ended up on Earth at about the same time.
Scientists found puzzling evidence of that in radioactive isotope deposits on
the seabed in 2021. They weren’t formed normally on Earth or during the birth
of the solar system some 4.5 billion years ago. They had to come from somewhere
else.
-
- For the
resulting “star stuff” to end up on any world in any star system, there needs
to be a consistent galaxy-wide delivery service. Scientists have been working
on the origins of stable elements in the periodic table for many years. Their abundance can be measured by gamma-ray
telescopes in space as well as by digging the rocks underwater of the Earth.
-
- The rocks
came from the underwater exploration of Earth’s oceans. They created computer models showing that
nearly continuous supernova shock waves could be a viable transporter mechanism
to deliver these elements to Earth, or other planets.
-
- Atomic
isotopes can propagate through large areas of a galaxy via supernova shock
waves. These fronts sweep up collections of elements from various sites. Understanding this delivery process is
particularly crucial as astronomers begin large-scale studies of exoplanets
where life might be possible. Knowing how they got their elemental composition
is a big step toward understanding the possibilities for life.
-
- Isotopic
abundances are a strong factor in determining whether an exoplanet is able to
hold liquid water, which is key to life.
-
- Scientists
have new evidence about how cosmic cataclysms forge gold, platinum and other
heavy members of the periodic table. Two
neutron stars spiral toward an explosive collision. Recent evidence supports
the theory that many of the periodic table's heavier elements form through such
crashes.
-
- Bits of the
stars are all around us, and in us, too. About half of the abundance of elements
heavier than iron originates in some of the most violent explosions in the
universe.
-
- As the
universe churns and new stars and planets form out of old gas and dust, these
elements eventually make their way to Earth and other worlds. After 3,700,000,000 years of evolution on our planet, humans and
many other species have come to rely on them in our bodies and our lives.
-
- Iodine is a
component of hormones we need to control our brain development and regulate our
metabolism. Ocean micro plankton called Acantharea use the element strontium to
create intricate mineral skeletons. Gallium is critical for the chips in our
smartphones and our laptop screens. And the mirrors of the JWST are gilded with
gold, an element useful for its un-reactive nature and ability to reflect
infrared light.
-
- Eons ago a
star more than 10 times as massive as our sun died in a spectacular explosion,
giving birth to one of the strangest objects in the universe: a neutron star.
-
- This
newborn star was a remnant of the stellar core compressed to extreme densities
where matter can take forms we do not understand. The neutron star might have
cooled forever in the depths of space, and that would have been the end of its
story.
-
- But, most massive stars live in binary systems
with a twin, and the same fate that befell our first star eventually came for
its partner, leaving two neutron stars circling each other. In a dance that
went on for millennia, the stars spiraled in, slowly at first and then rapidly.
-
- As they
drew closer together, tidal forces began to rip them apart, flinging
neutron-rich matter into space at velocities approaching one-third the speed of
light. At last the stars merged, sending ripples through spacetime and setting
off cosmic fireworks across the entire electromagnetic spectrum.
-
- At the time
of the crash, our own pale blue planet, in a quiet part of the Milky Way about
130 million light-years away, was home to the dinosaurs. The ripples in
spacetime, called gravitational waves, began making their way across the
cosmos, and in the time it took them to cover the vast distance to Earth, life
on the planet changed beyond recognition.
-
- New species
evolved and went extinct, civilizations rose and fell, and curious humans began
looking up at the sky, developing instruments that could do incredible things
such as measure minute distortions in spacetime
-
- Our
newfound ability to detect gravitational waves, as well as light from the same
cosmic source, promises to help us understand astrophysical explosions and the
synthesis of elements in a way that was previously impossible.
-
- The quest
to understand heavy-element formation is part of a larger scientific effort to
answer a fundamental question: Where did everything come from? The cosmic
history of the elements of the periodic table extends from a few minutes after
the big bang to the present. The synthesis of the first elements, hydrogen,
helium and lithium, occurred roughly three minutes after the birth of the
universe.
-
- From these
ingredients, the first stars formed, shining bright and fusing new elements in
their cores during both their lives and their explosive deaths. The next
generation of stars was born from the debris of these blasts, enriched with the
elements formed by the first stars.
-
- This
process continues today and accounts for all the elements from helium on the
light end, with two protons per atom, all the way up to iron, which has 56
protons in its atomic nucleus.
-
- A nucleus
can rapidly balloon into a highly unstable isotope, going all the way up to
what’s called the “neutron drip line”,
the absolute limit of the neutron-to-proton ratio allowed by nature
inside a nucleus.
-
- The
extremely heavy nucleus will then convert many of its neutrons to protons via
beta decays or even break into smaller nuclei, ultimately producing a range of
stable heavy elements.
-
- After a
nucleus absorbs extra neutrons but before it becomes stable, exotic nuclei
arise that scientists don’t understand. These in-between nuclei have properties
that push the bounds of physics, and measuring them in a laboratory is
difficult and sometimes even impossible.
-
- A neutron
star is born when a massive star runs out of nuclear fuel and its gravity causes
the core to collapse inward. The overwhelming force of the star’s mass on the
core compresses it to extremely high densities, causing electrons and protons
to fuse together to become neutrons.
-
- While the
rest of the star gets expelled in the supernova, the neutron star remains
intact, a compact remnant containing the densest matter known in the universe.
Neutron stars more massive than a certain limit further collapse into black
holes.
-
- The inner
structure of neutron stars is an open question. They might contain mostly
neutrons and a small fraction of protons inside a crust of heavier nuclei at
their surfaces. But their interiors could be even weirder than that.
-
- Deep inside
the neutron star, matter may take on truly bizarre forms, ranging from a soup
of quarks and gluons, the particles that make up normal matter, to a sea of
“hyperons,” which are made of so-called “strange quarks”.
-
- By 1982
scientists favored a scenario involving two neutron stars smashing together.
While some researchers were working to understand how these crashes could
synthesize new elements, others were trying to predict what kind of light we
would expect to see from a neutron star merger.
-
- Some
suggested a connection between neutron star collisions and gamma-ray bursts,
highly energetic explosions in space that emit a flash of gamma rays. And
because r-process nuclei would be unstable and undergo radioactive decay, they
should be able to heat up the material surrounding them and power an electromagnetic
flare that would carry signatures of the elements produced.
-
- In 2010
Brian Metzger and his collaborators introduced the term “kilonova” to refer to
such flares, first proposed in 1998, after determining that they would be
approximately 1,000 times brighter than a regular flash of light called a nova.
-
- In 2015 the
“Laser Interferometer Gravitational-wave Observatory” (LIGO) did something
extraordinary: it made the first observation of gravitational waves, which were
generated by two black holes spiraling toward each other and merging.
-
- The
detection was designated “GW150914”.
LIGO and its sibling observatory “Virgo” detected more binary black hole
collisions. Yet neutron star mergers remained elusive.
-
- Then, in
the fall of 2017 LIGO-Virgo had seen a neutron star collision for the first
time. In addition to the
gravitational-wave signal, astronomers had observed a short gamma-ray burst and
something that looked a lot like a kilonova.
-
- The event
forecasted the promise of multi messenger astronomy, the ability to see cosmic
phenomena through different “messengers” and combine the information to achieve
a fuller understanding of the event. This was the first time astronomers saw
gravitational waves and light, including radio, optical, x-ray and gamma-ray
light, coming from the same celestial source.
-
- The
gravitational waves seen by LIGO-Virgo originated in the crash of a pair of
neutron stars about 130 million light-years from Earth. The details of the signal, such as how the
waves’ frequency and strength changed with time, allowed researchers to
estimate that each neutron star had weighed about 1.17 to 1.6 times the mass of
our sun and had a radius of roughly 11 to 12 kilometers.
-
- Roughly
1.7 seconds after the gravitational waves came in, gamma-ray telescopes
Fermi-GBM and INTEGRAL detected a faint burst of gamma rays lasting only a
couple of seconds that came from the same direction as GW170817.
-
- Images taken
with the Henrietta Swopes one-meter telescope at the Las Campanas Observatory
in Chile showed a new source of light located in the old but bright galaxy NGC
4993. By breaking up the light into its constituent colors and examining its
spectrum, astronomers concluded that the signal was consistent with the idea
that heavy elements were being forged there. A true kilonova.
-
- The way the
kilonova’s spectrum changed over time the shorter wavelengths of light, which
are bluer, peaked early, and longer, red wavelengths became predominant later.
These peaks can be explained by the composition and velocity of the material
ejected from the merger.
-
- A blue
kilonova can be produced by fast-moving ejecta made mainly of lighter heavy
elements without any “lanthanides”—the metallic periodic elements from
lanthanum to lutetium, which are highly opaque to blue light.
-
- A red
kilonova, in contrast, requires slow-moving ejecta containing lots of heavy
elements, including lanthanides.
-
- Kilonova
spectra are very difficult to disentangle because the material is moving so
fast, the fingerprints of various elements get smeared and blended together. We
also lack reliable atomic data for many of the heavier elements, so it’s hard
to predict what their spectral signatures look like.
-
- The only
plausible detection of an individual element in the GW170817 kilonova spectrum
so far is of strontium. This is enough to show that the r-process took place.
-
- The
discovery of this singular event has confirmed decades of theoretical predictions.
Astrophysicists have finally established a connection between neutron star
mergers and short gamma-ray bursts. The kilonova spectrum carries signatures of
heavy elements, confirming that neutron star mergers are at least one site
where r-process elements are produced.
-
- We can’t
expect all kilonovae to look the same as the one associated with GW170817. We
suspect they come in many forms, each with distinctive features, and we’re in
for a lot of surprises.
-
- Decades of
progress in many fields have brought us to a point where we can investigate the
origin of heavy elements in ways that were inaccessible just a few years ago.
We are finally poised to put all the pieces together. Every isotope of every
element in the periodic table has the potential to tell us something about the
nuclear history of the universe.
-
March 10, 2023 HEAVY
ELEMENTS - how did the stars create them? 3908
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--- Saturday, March 11, 2023 ---------------------------
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