Starship Asterisk*

HEAPOW: Old Star Blowing Bubbles (2020 Nov 16)

Stars like the Sun create energy in their cores by fusing hydrogen into helium. This process of thermonuclear fusion is a steady process which allows these stars to shine stably for billions of years, time enough to give advanced life forms the possibility of evolving. But at some point such stars run out of fuel. This will happen to our Sun in about 5 billion years from now. Near the end of its nuclear burning life, the star expands to a few hundred times its former size, and begins to lose its outer atmosphere, which drifts away from the star and forms a visually stunning structure called a planetary nebula (another in a long list of astronomical misnomers, since the ejected gas and dust has no direct connection to planets or planet formation). The central remnant of the core of the star eventually becomes visible as a glowing, hot, earth-sized, dense white dwarf. Because this central "star" is initially so hot when it first appears (having surface temperatures about 5 to 10 times hotter than the temperature of the living star), it produces an enormous amount of energetic ultraviolet radiation. This radiation packs quite a punch and powers a strong stellar wind which blows outward from the star at speeds of millions of miles per hour. This powerful wind eventually catches up to and supersonically collides with the slow moving material in the planetary nebula, converting kinetic energy to heat, raising temperatures of the shock-heated gas to millions of degrees, forming a wind-blow bubble glowing in X-rays. The image above is an optical image from the Hubble Space Telescope of a planetary nebula called IC 4593. The X-ray emission from IC 4593 as seen by the Chandra X-ray Observatory is shown in purple. The X-ray emission seen by Chandra shows the bubble of hot, million-degree gas produced by the strong collision between the wind from the central star and the matter in the planetary nebula. This hot bubble is more than 10 times the size of Pluto's orbit.

X-ray: NASA/CXC/UNAM/J. Toalá et al.; Optical: NASA/STScI

---

On Earth, amethysts can form when gas bubbles in lava cool under the right conditions. In space, a dying star with a mass similar to the Sun is capable of producing a structure on par with the appeal of these beautiful gems.

As stars like the Sun run through their fuel, they cast off their outer layers and the core of the star shrinks. Using NASA's Chandra X-ray Observatory, astronomers have found a bubble of ultra-hot gas at the center of one of these expiring stars, a planetary nebula in our galaxy called IC 4593. At a distance of about 7,800 light years from Earth, IC 4593 is the most distant planetary nebula yet detected with Chandra.

This new image of IC 4593 has X-rays from Chandra in purple, invoking similarities to amethysts found in geodes around the globe. The bubble detected by Chandra is from gas that has been heated to over a million degrees. These high temperatures were likely generated by material that blew away from the shrunken core of the star and crashed into gas that had previously been ejected by the star.

This composite image also contains visible light data from the Hubble Space Telescope (pink and green). The pink regions in the Hubble image are the overlap of emission from cooler gas composed of a combination of nitrogen, oxygen, and hydrogen, while the green emission is mainly from nitrogen. ...

• Monthly Notices of the RAS 494(3):3784 (May 2020) DOI: 10.1093/mnras/staa1024
• arXiv.org > astro-ph > arXiv:2004.04542 > 09 Apr 2020

https://en.wikipedia.org/wiki/Amethyst wrote:

Amethyst geodes form when large crystals grew in open spaces inside the rock.

---

<<Amethyst is a purple variety of quartz (SiO2) and owes its violet color to irradiation, impurities of iron and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω (Ancient Greek), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. The ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication. Amethyst is produced in abundance from the state of Rio Grande do Sul in Brazil where it occurs in large geodes within volcanic rocks. Many of the hollow agates of southwestern Brazil and Uruguay contain a crop of amethyst crystals in the interior.>>

neufer wrote: ↑Mon Nov 16, 2020 6:19 pm

https://en.wikipedia.org/wiki/Amethyst wrote:

Amethyst geodes form when large crystals grew in open spaces inside the rock.

---

<<Amethyst is a purple variety of quartz (SiO2) and owes its violet color to irradiation, impurities of iron and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω (Ancient Greek), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. The ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication. Amethyst is produced in abundance from the state of Rio Grande do Sul in Brazil where it occurs in large geodes within volcanic rocks. Many of the hollow agates of southwestern Brazil and Uruguay contain a crop of amethyst crystals in the interior.>>

... on August 30–31, 1870, Lt. Gustavus C. Doane described the canyon with a bit more scientific detail:

As we approached the Grand Cañon a dull roaring sound warned us that the falls were near at hand. ... I had descended the cañon at a point where the creek joined the river, precipitated into a gorge just above its juncture in a lovely cascade of three falls, in the aggregate 100 feet in height. This was named Crystal Cascade, and the stream Cascade Creek. In the bed of the gorge were to be found an infinite variety of volcanic specimens, quartz, feldspar, mica, granites, lavas, basalts, composite crystals; in fact, everything, from asbestos to obsidian, was represented by fragments in the bed of this stream. There were also beautiful clay stone specimens, of which we afterward learned the origin. At the foot of the gorge and on the margin of the Yellowstone stood a high promontory of concretionary lava, literally filled with volcanic butternuts. Many of these were loose, and could be taken out of the rock with the hand; broken open they were invariably hollow, and lined with minute quartz crystals of various tints. This formation is rare, but occurs frequently in the great basin. From the outer point of this promontory can be seen the foot of the upper fall of the Yellowstone, and I climbed to the summit to obtain a view. In scenic beauty, the upper cataract far excels the lower. It has life, animation, while the lower one simply follows its channel; both, however, are eclipsed, as it were, by the singular wonders of the mighty cañon below. This deepens rapidly; the stream flowing over rapids continually. ... Several of the party descended into the chasm a short distance below the fall, but could not reach its foot. ... The walls of the cañon are of gypsum, in some places having an incrustation of lime white as snow, from which the reflected rays of the sun produce a dazzling effect, rendering it painful to look into the gulf. In others the rock is crystalline and almost wholly sulphur, of a dark yellow color, with streaks of red, green and black, caused by the percolations of hot mineral waters, of which thousands of springs are seen, in many instances, flowing from spouts high up on the walls on either side. The combinations of metallic lusters in the coloring of the walls is truly wonderful, surpassing, doubtless, anything of the kind on the face of the globe. The ground slopes to the cañon on the opposite or east side, and from it to the low valley on the west. Three miles below the fall the chasm is 1,050 feet deep. In some places masses of the rock have crumbled and slid down in a talus of loose material at the foot; in others, promontories stand out in all manner of fantastic forms, affording vistas of wonder utterly beyond the power of description. On the caps of these dizzy heights, mountain sheep and elk rest during the night. ... We had come down the ravine at least four miles, and looking upward the fearful wall appeared to reach the sky. It was about 3 o'clock p.m., and stars could be distinctly seen, so much of the sunlight was cut off from entering the chasm. Tall pines on the extreme verge appeared the height of two or three feet. The cañon, as before said, was in two benches, with a plateau on either side, about half way down. This plateau, about a hundred yards in width, looked from below like a mere shelf against the wall; the total depth was not less than 2,500 feet, and more probably 3,000. There are perhaps other canons longer and deeper than this one, but surely none combining grandeur and immensity with peculiarity of formation and profusion of volcanic or chemical phenomena.[3]