Stars and the Elements

[Admin]

Our sun is average — about half of the known stars are larger, half are smaller. Naturally we have chosen it to be exactly 1 solar mass.

The solar mass (M☉) is equal to approximately 2×1030 kg, about 333000 times the mass of Earth (M⊕), or 1047 times the mass of Jupiter (MJ).

Fusion reactions within a new star require at least 7% of a solar mass to begin.

1. Hydrogen requires the Smallest Stars

2. Helium To begin burning helium a star must have at least 8% solar mass.


Fusion of helium in the core of low mass stars.

3. Carbon

4. Oxygen

5. Neon

6. Magnesium

7. Silicon

8. Iron

Largest Stars
the most massive star. That honor goes to R136a1, which weighs in at about 300 times the mass of the sun but only about 30 solar radii.





blog.sdss.org/2017/01/09/origin-of-the-elements-in-the-solar-system/





Origin of the Elements in the Solar System
January 9, 2017 / Jennifer Johnson

“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” — Carl Sagan

This is an evocative statement. It gets at the heart of the matter. However, it leaves out all the different ways that stars make the elements. It is not just collapsing stars, it is merging stars, burping stars, exploding stars, and the start of the Universe itself.

Below is the latest version of an evolving periodic table color-coded by the origin of the elements in the Solar System. An original version of this was made by Inese Ivans and me in 2008 and refined and improved by Anna Frebel. Versions highlighting different aspects of the physical processes are available on Inese Ivans’ website.
My current version of the periodic table, color-coded by the source of the element in the solar system.

My current version of the periodic table, color-coded by the source of the element in the solar system. Elements with more than one source have the approximate amount due to each process indicated by the amount of area. Tc, Pm, and the elements beyond U do not have long-lived or stable isotopes. I have ignored the elements beyond U in this plot, but not including Tc and Pm looked weird, so I have included them in grey.

For this version, I tried to avoid the technical terms and jargon used in the original plot. I also updated the sources of the heavy elements to reflect the current semi-consensus. This graphic draws on an enormous amount of labor from astronomers and physicists. In an upcoming blog post, I will give details on my sources and assumptions for interested parties. Note that this is for the solar system. There will be additional versions showing what this plot would look like if you were in the early Universe, or if you consider the origin of the elements on the Earth, etc.

However, the main point of this blog post is to present the chart and address the following question:

Why does your version have different information than the well-known Wikipedia entry?

The former figure on Wikipedia was based on this plot from Northern Arizona Meteorite Laboratory

Here is a discussion of the some of the differences between the Wikipedia version and mine. In many cases, the Wikipedia graphic is presenting information that is flat-out wrong. I am trying to avoid going into all details in this single blog post. The underlined phrases below represent possible topics for future blog posts where I (or colleagues I coerce bribe ask) can go into more in more detail later, including why we think we are on the right track.

I will assume that “Large Stars” and “Small Stars” are “High-Mass Stars” and “Low-Mass Stars”, respectively. It does not make sense to think of nucleosynthesis origin having to do with the radius of the stars. As this wonderful graphic from NASA’s Chandra website shows, all stars at the end of their lives swell up to red giant and supergiant stars. In its death throes, a low-mass star can have a much larger radius than a normal high-mass star. Note that the original source cited by the Wikipedia article just has the chart, with no additional information or links that I can find.
High-mass stars end their lives (at least some of the time) as core-collapse supernovae. Low-mass stars usually end their lives as white dwarfs. But sometimes white dwarfs that are in binary systems with another star get enough mass from the companion to become unstable and explode as so-called Type-Ia supernovae. Which “supernova” is being referred to in the Wikipedia graphic is not clear. The interpretation that makes the graphic the least wrong is the “supernova” here means “Type Ia Supernovae” or “exploding white dwarfs” as I call them. I will assume that “Large Stars” refers to the production in high-mass stars both during their lives and during the explosion that spews products of their nuclear fusion into the interstellar gas. It would also be possible to think that “Supernovae” refers to both massive star core-collapse supernovae and exploding white dwarfs. In this case, “Large Stars” could mean that massive stars make it before they explode and the supernovae is just the mechanism for kicking out. These categories are therefore 1) confusing and 2) incorrect no matter how you slice it.
Dying low-mass stars (aka “Small Stars”) make substantial amounts of the heavy elements, including most of the Pb in the solar system. There should be a lot of orange in the bottom half of the diagram. I don’t agree that Cr and Mn are made only in “Large Stars”, but Fe is made in both “Large Stars” and “Supernovae”. Basically all the iron in the Universe is made in explosive nucleosynthesis. The iron that massive stars make right before they explode as supernova is all destroyed/collapsed in the remnant. And so on.
The information for Li is incorrect. 6Li is indeed made by cosmic rays (fast-moving nuclei) hitting other nuclei and breaking them apart. But most of the far more common 7Li isotope is without question made in low-mass stars and spewed out out into the Universe as the star dies. Some 7Li is also made in the Big Bang and a small fraction by cosmic ray fission.
This post does not need to be any longer, but I would like to end by pointing out a difference between the Wikipedia graphic and my graphic caused by the fact that we still don’t know everything. A fraction of the heavy elements, including most of the Au, are formed in the “rapid neutron-capture process“. Where that happens is currently in dispute. It could be in massive star supernovae close to the forming neutron-star. More recently, there is compelling evidence that most of the r-process happens when two neutron stars spiral together and merge. That is why “merging neutron stars” is a category in my chart, but “Supernovae” takes the role in the Wikipedia chart.

Note

Backing this statement up with actual evidence may be the basis for a future blog post. Please let me know in comments if you are interested in a blog post on a particular subject.

www.astronomy.ohio-state.edu/~jaj/

[Admin]

Souped-up supernovas

www.sciencenews.org/article/star-explosion-hypernova-supernova-universe-heavy-elements-origin


Souped-up supernovas may produce much of the universe’s heavy elements
Analysis of a rare, ancient star suggests a new birthplace for elements like uranium and silver
illustration of a hypernova

Explosions of massive, magnetized stars (similar to the one illustrated) may be the source of much of the universe’s heavy elements.

By Mara Johnson-Groh

July 7, 2021 at 12:10 pm

Violent explosions of massive, magnetized stars may forge most of the universe’s heavy elements, such as silver and uranium.

These r-process elements, which include half of all elements heavier than iron, are also produced when neutron stars merge (SN: 10/16/17). But collisions of those dead stars alone can’t form all of the r-process elements seen in the universe. Now, scientists have pinpointed a type of energetic supernova called a magnetorotational hypernova as another potential birthplace of these elements.

The results, described July 7 in Nature, stem from the discovery of an elderly red giant star — possibly 13 billion years old — in the Milky Way’s halo (SN: 1/9/20). By analyzing the star’s elemental makeup, which is like a star’s genetic instruction book, astronomers peered back into the star’s family history. Forty-four different elements seen in the star suggest that it was formed from material left over “by a special explosion of one massive star soon after the Big Bang,” says astronomer David Yong of the Australian National University in Canberra.

The ancient star’s elements aren’t from the remnants of a neutron star merger, Yong and his colleagues say. Its abundances of certain heavy elements such as thorium and uranium were higher than would be expected from a neutron star merger. Additionally, the star also contains lighter elements such as zinc and nitrogen, which can’t be produced by those mergers. And since the star is extremely deficient in iron — an element that builds up over many stellar births and deaths — the scientists think that the red giant is a second-generation star whose heavy elements all came from one predecessor supernova-type event.
Sign Up For the Latest from Science News

Headlines and summaries of the latest Science News articles, delivered to your inbox
E-mail Address*

Simulations suggest that the event was a magnetorotational hypernova, created in the death of a rapidly spinning, highly magnetized star at least 25 times the mass of the sun. When these stars explode at the end of their lives as a souped-up type of supernova, they may have the energetic, neutron-rich environments needed to forge heavy elements.

Magnetorotational hypernovas might be similar to collapsars — massive, spinning stars that collapse into black holes instead of exploding. Collapsars have previously been proposed as birthplaces of r-process elements, too (SN: 5/8/19).

The researchers think that magnetorotational hypernovas are rare, composing only 1 in 1,000 supernovas. Even so, such explosions would be 10 times as common as neutron star mergers today, and would produce similar amounts of heavy elements per event. Along with their less energetic counterparts, called magnetorotational supernovas, these hypernovas could be responsible for creating 90 percent of all r-process elements, coauthor Chiaki Kobayashi, an astrophysicist at the University of Hertfordshire in Hatfield, England, had previously calculated. In the early universe, when massive, rapidly rotating stars were more common, such explosions could have been even more influential.

The observations are impressive, says Stan Woosley, an astrophysicist at the University of California, Santa Cruz, who was not involved in the new study. But “there is no proof that the [elemental] abundances in this metal-deficient star were made in a single event. It could have been one. It could have been 10.” One of those events might even have been a neutron star merger, he says.

The scientists hope to find more stars like the elderly red giant, which could reveal how frequent magnetorotational hypernovas are. For now, the newly analyzed star remains “incredibly rare and demonstrates the need for … large surveys to find such objects,” Yong says.

Questions or comments on this article? E-mail us at [e-mail]
Editor's Note:

This story was updated July 8, 2021, to clarify that the estimate of the proportion of r-process elements made in hypernovas and their less energetic counterparts came from previous research and to note that the red giant star is located in the Milky Way's halo.

A version of this article appears in the August 14, 2021 issue of Science News.
Citations

D. Yong et al. r-Process elements from magnetorotational hypernovae. Nature. Posted online July 7, 2021. doi: 10.1038/s41586-021-03611-2.

C. Kobayashi, A.I. Karakas and M. Lugaro. The origin of elements from carbon to uranium. The Astrophysical Journal. Published online September 15, 2020. doi: 10.3847/1538-4357/abae65

[Admin]

www.sciencenews.org/article/supernova-heavy-elements-source-earth-crust-deep-sea


A study of Earth’s crust hints that supernovas aren’t gold mines
The stellar explosions can’t be the main source for heavy elements, new data suggest


image of the Crab Nebula

Supernovas like the one that formed the Crab Nebula (pictured) have long been thought to forge heavy elements. But a new study suggests that the bulk of those elements must come from other sources.

J. Hester and A. Loll/ASU, NASA, ESA

By Emily Conover

May 13, 2021 at 2:00 pm

A smattering of plutonium atoms embedded in Earth’s crust are helping to resolve the origins of nature’s heaviest elements.

Scientists had long suspected that elements such as gold, silver and plutonium are born during supernovas, when stars explode. But typical supernovas can’t explain the quantity of heavy elements in our cosmic neighborhood, a new study suggests. That means other cataclysmic events must have been major contributors, physicist Anton Wallner and colleagues report in the May 14 Science.

The result bolsters a recent change of heart among astrophysicists. Standard supernovas have fallen out of favor. Instead, researchers think that heavy elements are more likely forged in collisions of two dense, dead stars called neutron stars, or in certain rare types of supernovas, such as those that form from fast-spinning stars (SN: 5/8/19).

Heavy elements can be produced via a series of reactions in which atomic nuclei swell larger and larger as they rapidly gobble up neutrons. This series of reactions is known as the r-process, where “r” stands for rapid. But, says Wallner, of Australian National University in Canberra, “we do not know for sure where the site for the r-process is.” It’s like having the invite list for a gathering, but not its location, so you know who’s there without knowing where the party’s at.

Scientists thought they had their answer after a neutron star collision was caught producing heavy elements in 2017 (SN: 10/16/17). But heavy elements show up in very old stars, which formed too early for neutron stars to have had time to collide. “We know that there has to be something else,” says theoretical astrophysicist Almudena Arcones of the Technical University of Darmstadt, Germany, who was not involved with the new study.

If an r-process event had recently happened nearby, ­some of the elements created could have landed on Earth, leaving fingerprints in Earth’s crust. Starting with a 410-gram sample of Pacific Ocean crust, Wallner and colleagues used a particle accelerator to separate and count atoms. Within one piece of the sample, the scientists searched for a variety of plutonium called plutonium-244, which is produced by the r-process. Since heavy elements are always produced together in particular proportions in the r-process, plutonium-244 can serve as a proxy for other heavy elements. The team found about 180 plutonium-244 atoms, deposited into the crust within the last 9 million years.

chunk of deep-sea crust
Scientists analyzed a sample of Earth’s deep-sea crust (shown) to search for atoms of plutonium and iron with cosmic origins.Norikazu Kinoshita

Researchers compared the plutonium count to atoms that had a known source. Iron-60 is released by supernovas, but it is formed by fusion reactions in the star, not as part of the r-process. In another, smaller piece of the sample, the team detected about 415 atoms of iron-60.

Plutonium-244 is radioactive, decaying with a half-life of 80.6 million years. And iron-60 has an even shorter half-life of 2.6 million years. So the elements could not have been present when the Earth formed, 4.5 billion years ago. That suggests their source is a relatively recent event. When the iron-60 atoms were counted up according to their depth in the crust, and therefore how long ago they’d been deposited, the scientists saw two peaks at about 2.5 million years ago and at about 6.5 million years ago, suggesting two or more supernovas had occurred in the recent past.

The scientists can’t say if the plutonium they detected also came from those supernovas. But if it did, the amount of plutonium produced in those supernovas would be too small to explain the abundance of heavy elements in our cosmic vicinity, the researchers calculated. That suggests regular supernovas can’t be the main source of heavy elements, at least nearby.

That means other sources for the r-process are still needed, says astrophysicist Anna Frebel of MIT, who was not involved with the research. “The supernovae are just not cutting it.”

The measurement gives a snapshot of the r-process in our corner of the universe, says astrophysicist Alexander Ji of Carnegie Observatories in Pasadena, Calif. “It’s actually the first detection of something like this, so that’s really, really neat.”