Saturday, March 11, 2023

3908 - HEAVY ELEMENTS - how did the stars create them

 

-   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                                                                                                                          

----------------------------------------------------------------------------------------

-----  Comments appreciated and Pass it on to whomever is interested. ---

---   Some reviews are at:  --------------     http://jdetrick.blogspot.com ----- 

--  email feedback, corrections, request for copies or Index of all reviews

---  to:  ------    jamesdetrick@comcast.net  ------  “Jim Detrick”  -----------

--------------------- ---  Saturday, March 11, 2023  ---------------------------

 

 

 

 

         

 

-

 

 

 

 

           

 

 

No comments:

Post a Comment