How do Astronomers Study the Formation of Stars?

By using supercomputers to simulate the birth and evolution of individual stars and star clusters in the Milky Way  

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Simulation of star formation region using specially created computer code and a state-of-the-art supercomputer. Credits: NASA Ames/David Ellsworth/Tim Sandstrom

Space news (astrophysics: studying star formation; 3-D computer simulations) – NASA Advanced Supercomputing laboratory located at NASA’s Ames Research Center – 

How do astronomers study the formation of stars? Astronomers use complex computer code, run on one of the fastest, most powerful supercomputers on Earth to simulate the processes involved in the formation of individual stars and star clusters in the Milky Way. Using simulations capturing a mix of gas, dust, magnetic fields, gravity and other physical phenomena, astrophysicists study the birth and evolution of young, nearby stars and star clusters.  

The image above was created using state-of-the-art Orion2 computer code written by geniuses at the University of California, Berkeley, and Lawrence Livermore National Laboratory and simulated on the powerful, ultra-fast Pleiades supercomputer located at NASA Advanced Supercomputing complex. Considered the seventh most powerful supercomputer in the US, it was necessary to achieve results closely matching data obtained through observations made with the Hubble Space Telescope. 

“Our simulations, run on Pleiades and brought to life by the visualization team at the NAS facility at Ames, were critical to obtaining important new results that match with Hubble’s high-resolution images and other observations made by a variety of space and Earth-based telescopes,” said Richard Klein, adjunct professor at UC Berkeley and astrophysicist at LLNL. “A key result, supported by observation, is that some star clusters form like pearls in a chain along elongated, dense filaments inside molecular clouds—so-called “stellar nurseries.” 

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Richard Klein. Credits: The University of California, Berkeley Department of Astronomy.

The video simulation here shows the evolution of a massive cloud of gas and dust over a period of 700,000 years. Astrophysicists used the computing power of the Pleiades supercomputer, operating using the Orion2 code to create this amazing cosmic tapestry. The gravitational collapse of the cloud results in the birth of a stellar object called an infrared dark cloud (IRDC) filament. Protostars begin to form within the cloud, highlighted by bright orange regions strewn across the body of the central and bordering filaments. 

“Without NASA’s vast computational resources, it would not have been possible for us to produce these immense and complex simulations that include all the output variables we need to get these new results and compare them with observations,” Klein explained. “The ORION2 simulations incorporate a complex mix of gravity, supersonic turbulence, hydrodynamics (motion of molecular gas), radiation, magnetic fields, and highly energetic gas outflows. The science team conducted many independent tests of each piece of physics in ORION against known data to demonstrate the code’s accuracy.” 

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The Pleiades supercomputer. Credits: Ames Research Facility/NASA Advanced Supercomputing facility.

The team’s back at work trying to devise even better simulations of star formation by improving the resolution and zooming into the action. “Higher resolution in the simulations will enable us to study the details of the formation of stellar disks formed around protostars. These disks allow mass to transfer onto the protostars as they evolve, and are thought to be the structures within which planets eventually form,” said Klein.  

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Dr. Richard Klein talking about a simulation of star formation. Credits: NASA/Ames Research Facility/NASA Advanced Supercomputing

More work to do

They’ll need additional time on Pleiades and lots of extra storage during the next few years to tweak their simulations. The team seems to be on the trail of a real breakthrough in understanding and knowledge concerning the processes leading to star formation in the Milky Way. They appear to have their collective eye on the bigger picture. “Understanding star formation is a grand challenge problem. Ultimately, our results support NASA’s science goal of determining the origin of stars and planets, as part of its larger challenge of figuring out the origin of the entire universe.” 

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Wolf-Rayet Star “Nasty 1” Transitional Stage in Evolution of Massive Stars

A very rapidly evolving, supermassive star with a newly formed nebula only a few thousand years old

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Space news (supermassive stars: Wolf-Rayet stars; star NaSt1) – 3,000 light-years away on the edge of a pancake-shaped disk of gas moving at 22,000 mph – 

Astronomers using the Hubble Space Telescope have discovered new clues concerning a nearby supermassive, rapidly aging star they have nicknamed “Nasty 1”. Designated NaSt1 in astronomy catalogs, “Nasty 1” when first discovered decades ago was identified as a non-typical Wolf-Rayet star with an orbiting disk-like structure. A vast disk estimated to be almost 2 trillion miles wide astronomers now think formed due to a companion star snacking on its outer envelope. Putting NaSt1 in a class of Wolf-Rayet stars astronomers haven’t observed often during the human journey to the beginning of space and time. A star type possibly representing a transition stage in the evolution of supermassive stars. 

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“We were excited to see this disk-like structure because it may be evidence for a Wolf-Rayet star-forming from a binary interaction,” said study leader Jon Mauerhan of the University of California, Berkeley. “There are very few examples in the galaxy of this process in action because this phase is short-lived, perhaps lasting only a hundred thousand years, while the timescale over which a resulting disk is visible could be only ten thousand years or less.” 

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Study leader Jon Mauerhan of the University of California, Berkley. Credit: University of California, Berkley.

In the case of NaSt1, computer simulations show a supermassive star evolving really fast and swelling as it begins to run out of hydrogen. Its outer hydrogen envelope is loosely bound and is gravitationally stripped from the star- astronomers call this process stellar cannibalism – by a more compact, nearby companion star. In the process the more compact star gains mass, while the more massive star loses its hydrogen envelope, exposing its helium core and eventually becoming a Wolf-Rayet star. 

The mass-transfer model is the favored process for how Wolf-Rayet stars evolve at the moment and considering at least 70 percent of supermassive stars detected, so far, are members of binary star system, this seems logical. Astronomers used to think this type of star could also form when a massive sun ejects its hydrogen envelope. But the direct mass loss model by itself can’t account for the number of Wolf-Rayet stars observed relative to less-evolved supermassive suns in the Milky Way.  

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“We’re finding that it is hard to form all the Wolf-Rayet stars we observe by the traditional wind mechanism because the mass loss isn’t as strong as we used to think,” said Nathan Smith of the University of Arizona in Tucson, who is a co-author on the new NaSt1 paper. “Mass exchange in binary systems seems to be vital to account for Wolf-Rayet stars and the supernovae they make, and catching binary stars in this short-lived phase will help us understand this process.” 

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Co-author of study Nathan Smith of the University of Arizona in Tucson. Credit: The University of Arizona.

Astronomers computer models show that the mass-transfer process isn’t always perfectly efficient. Matter can only transfer from NaSt1 at a certain rate, left over material begins orbiting, creating a disk-like structure. 

“That’s what we think is happening in Nasty 1,” Mauerhan said. “We think there is a Wolf-Rayet star buried inside the nebula, and we think the nebula is being created by this mass-transfer process. So this type of sloppy stellar cannibalism actually makes Nasty 1 a rather fitting nickname.” 

Observing Nasty 1 (star NaSt1) through the clock of gas and dust surrounding this star system hasn’t been easy. The intervening disk-like structure even blocks the view of the Hubble Space Telescope. Scientists haven’t been able to measure the distance between the stars, their mass, or the volume of material transferring to the smaller companion star.  

Astronomers have been able to discover a few items concerning the disk-like structure surrounding Nasty 1. Measurements indicate it’s traveling at around 22,000 mph in the outer nebula, a slower speed than recorded in other stars of this type. Scientists think this indicates a much less energetic supernova than was recorded for other events, like Era Carinae. In this case and other similar stars, the gas in the outer nebula has been recorded in the hundreds of thousands of miles per hour. Nasty 1 could be different supernova animal altogether.  

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High atop the Cerro Manqui peak at the Las Campanas Observatory in Chile the twin the Walter Baade Telescope is the first of the twin 6.5-meter Magellan telescopes to be completed. Credit: Ico.cl

Nasty 1 could also lose its outer envelope of hydrogen intermittently. Previous studies in the infrared light provided clues indicating the existence of a dense pocket of hot gas and dust close to the central stars in the region. More recent observations using the Magellan Telescope located at the Las Campanas Observatory in Chile has also detected a bigger pocket of cooler gas and dust possibly indirectly blocking light from these stars. Astronomers think the existence of warm dust in the region implies it formed just recently, perhaps intermittently, as elementally enriched matter from the stellar winds of massive stars collides, mixes, flows away, and cools. Irregular stellar wind strength, the rate at which star NaSt1 loses its outer envelope, could also help explain the observed clumpy structure and gaps noted in the outer regions of the disk.  

Astrophysicists used NASA’s Chandra X-ray Observatory to measure the hypersonic winds screaming from each star. Readings showed a scorching hot plasma, indicating colliding stellar winds producing high-energy shockwaves that glow in X-rays. This is consistent with previous data collected on other evolving Wolf-Rayet star systems. We’ll get a better view once the outer hydrogen of Nasty 1’s (star NaSt1) depleted, and the mass-transfer process completes. Eventually, the gas and dust in the lumpy, disk-like structure will dissipate, giving us a clearer view of this mysterious binary star system.   

 

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NASA’s Chandra X-ray Observatory has shown the cosmos is full of objects and events far beyond anything we imagined when we first started the human journey to the beginning of space and time. Credit: NASA/Chandra

Nasty 1’s still evolving!

“What evolutionary path the star will take is uncertain, but it will definitely not be boring,” said Mauerhan. “Nasty 1 could evolve into another Eta Carinae-type system. To make that transformation, the mass-gaining companion star could experience a giant eruption because of some instability related to the acquiring of matter from the newly formed Wolf-Rayet. Or, the Wolf-Rayet could explode as a supernova. A stellar merger is another potential outcome, depending on the orbital evolution of the system. The future could be full of all kinds of exotic possibilities depending on whether it blows up or how long the mass transfer occurs, and how long it lives after the mass transfer ceases.” 

Astronomers continue to study Nasty 1 and its peculiar, unusual disk-like structure looking for clues to explain the mysteries surrounding its origin. 

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