Hexbyte Glen Cove First clear view of a boiling cauldron where stars are born thumbnail

Hexbyte Glen Cove First clear view of a boiling cauldron where stars are born

Hexbyte Glen Cove

The RCW 49 galactic nebula pictured above is one of the brightest star-forming regions in the Milky Way. By analyzing the movement of carbon atoms in an expanding bubble of gas surrounding the Westerlund 2 star cluster within RCW 49, a UMD-led team of researchers have created the clearest image to date of a stellar-wind driven bubble where stars are born. Credit: NASA/JPL-Caltec/E.Churchwell (University of Wisconsin).

University of Maryland researchers created the first high-resolution image of an expanding bubble of hot plasma and ionized gas where stars are born. Previous low-resolution images did not clearly show the bubble or reveal how it expanded into the surrounding gas.

The researchers used data collected by the Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope to analyze one of the brightest, most massive star-forming regions in the Milky Way galaxy. Their analysis showed that a single, expanding bubble of warm gas surrounds the Westerlund 2 and disproved earlier studies suggesting there may be two bubbles surrounding Westerlund 2. The researchers also identified the source of the bubble and the energy driving its expansion. Their results were published in The Astrophysical Journal on June 23, 2021.

“When form, they blow off much stronger ejections of protons, electrons and atoms of heavy metal, compared to our sun,” said Maitraiyee Tiwari, a postdoctoral associate in the UMD Department of Astronomy and lead author of the study. “These ejections are called , and extreme stellar winds are capable of blowing and shaping bubbles in the surrounding clouds of cold, dense gas. We observed just such a bubble centered around the brightest cluster of stars in this region of the galaxy, and we were able to measure its radius, mass and the speed at which it is expanding.”

The surfaces of these expanding bubbles are made of a dense gas of ionized carbon, and they form a kind of outer around the bubbles. New stars are believed to form within these shells. But like soup in a boiling cauldron, the bubbles enclosing these star clusters overlap and intermingle with clouds of surrounding gas, making it hard to distinguish the surfaces of individual bubbles.

Tiwari and her colleagues created a clearer picture of the bubble surrounding Westerlund 2 by measuring the radiation emitted from the cluster across the entire electromagnetic spectrum, from high-energy X-rays to low-energy radio waves. Previous studies, which only radio and submillimeter wavelength data, had produced low-resolution images and did not show the bubble. Among the most important measurements was a far-infrared wavelength emitted by a specific ion of carbon in the shell.

A team led by UMD astronomers created the first clear image of an expanding bubble of stellar gas where stars are born using data from NASA’s SOFIA telescope on board a heavily modified 747 jet as seen here in this artist’s rendering. Credit: Artist Rendering by Marc Pound/UMD

“We can use spectroscopy to actually tell how fast this carbon is moving either towards or away from us,” said Ramsey Karim (M.S. ’19, astronomy), a Ph.D. student in astronomy at UMD and a co-author of the study. “This technique uses the Doppler effect, the same effect that causes a train’s horn to change pitch as it passes you. In our case, the color changes slightly depending on the velocity of the carbon ions.”

By determining whether the carbon ions were moving toward or away from Earth and combining that information with measurements from the rest of the electromagnetic spectrum, Tiwari and Karim were able to create a 3-D view of the expanding stellar-wind bubble surrounding Westerlund 2.

In addition to finding a single, stellar wind-driven bubble around Westerlund 2, they found evidence of new stars forming in the shell region of this bubble. Their analysis also suggests that as the bubble expanded, it broke open on one side, releasing hot plasma and slowing expansion of the shell roughly a million years ago. But then, about 200,000 or 300,000 years ago, another bright star in Westerlund 2 evolved, and its energy re-invigorated the expansion of the Westerlund 2 shell.

“We saw that the expansion of the bubble surrounding Westerlund 2 was reaccelerated by winds from another very massive star, and that started the process of expansion and star formation all over again,” Tiwari said. “This suggests stars will continue to be born in this shell for a long time, but as this process goes on, the new will become less and less massive.”

Tiwari and her colleagues will now apply their method to other bright star clusters and warm gas bubbles to better understand these star-forming regions of the galaxy. The work is part of a multi-year NASA-supported program called FEEDBACK.

More information:
“SOFIA FEEDBACK Survey: Exploring the Dynamics of the Stellar-wind-driven Shell of RCW 49” Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abf6ce

First clear view of a boiling cauldron where stars are born (2021, June 23)
retrieved 23 June 2021
from https://phys.org/news/2021-06-view-cauldron-stars-born.html

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Hexbyte Glen Cove A theory as clear as glass thumbnail

Hexbyte Glen Cove A theory as clear as glass

Hexbyte Glen Cove

Scientists at The University of Tokyo use computer simulations to model the effects of elemental composition on the glass-forming ability of metallic mixtures, which may lead to tough, electroconductive glasses Credit: Institute of Industrial Science, the University of Tokyo

Researchers from the Institute of Industrial Science at the University of Tokyo used molecular dynamics calculations to simulate the glass-forming ability of metallic mixtures. They show that even small changes in composition can strongly influence the likelihood that a material will assume a crystalline versus a glassy state upon cooling. This work may lead to a universal theory of glass formation and cheaper, more resilient, electroconductive glass.

If you have important guests coming over for dinner, you might set your table with expensive crystal glasses. To scientists, however, crystal and are actually two very different states that a liquid might assume when cooled. A crystal has a defined three-dimensional lattice structure that repeats indefinitely, while glass is an amorphous solid that lacks long-range ordering. Current theories of glass formation cannot accurately predict which metallic mixtures will “vitrify” to form a glass and which will crystallize. A better, more comprehensive understanding of glass formation would be a great help when designing new recipes for mechanically tough, electrically conductive materials.

Now, researchers at the University of Tokyo have used of three prototypical metallic systems to study the process of glass formation. “We found that the ability for a multi-component system to form a crystal, as opposed to a glass, can be disrupted by slight modifications to the composition,” first author Yuan-Chao Hu says.

Stated simply, glass formation is the consequence of a material avoiding crystallization when cooled. This locks the atoms into a “frozen” state before they can organize themselves into their energy-minimizing pattern. The simulations showed that a critical factor determining the rate of crystallization was the liquid-crystal interface energy.

The researchers also found that changes in elemental composition can lead to local atomic orderings that frustrate the process of crystallization with arrangements incompatible with the crystal’s usual form. Specifically, these structures can prevent tiny crystals from acting as “seeds” that nucleate the growth of ordered regions in the sample. In contrast with previous explanations, the scientists determined that the chemical potential difference between the liquid and crystal phases has only a small effect on glass formation.

“This work represents a significant advancement in our understanding of the fundamental physical mechanism of vitrification,” senior author Hajime Tanaka says. “The results of this project may also help glass manufacturers design new multi-component systems that have certain desired properties, such as resilience, toughness and electroconductivity.”

The work is published in Science Advances as “Physical origin of glass formation from multi-component systems.”

More information:
Physical origin of glass formation from multicomponent systems Science Advances (2020). advances.sciencemag.org/lookup … .1126/sciadv.abd2928

A theory as clear as glass (2020, December 11)
retrieved 14 December 2020
from https://phys.org/news/2020-12-theory-glass.html

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part may be reproduced without the written permi

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