CASTRO Simulations reveal an unusual death for ancient stars

This image is a slice through the interior of a supermassive star of 55,500 solar masses along the axis of symmetry. 

It shows the inner helium core in which nuclear burning is converting helium to oxygen, powering various fluid instabilities (swirling lines). 

This "snapshot" from a CASTRO simulation shows one moment a day after the onset of the explosion, when the radius of the outer circle would be slightly larger than that of the orbit of the Earth around the sun. 

Visualizations were done in VisIT. 

Credit: Ken Chen, University of California at Santa Cruz

Certain primordial stars, those 55,000 and 56,000 times the mass of our Sun, or solar masses, may have died unusually.

In death, these objects, among the Universe's first-generation of stars, would have exploded as supernovae and burned completely, leaving no remnant black hole behind.

Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota came to this conclusion after running a number of supercomputer simulations at the US Department of Energy's (DOE's) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota.

They relied extensively on CASTRO, a compressible astrophysics code developed at DOE's Lawrence Berkeley National Laboratory's (Berkeley Lab's) Computational Research Division (CRD).

Their findings were recently published in Astrophysical Journal (ApJ).

First-generation stars are especially interesting because they produced the first heavy elements, or chemical elements other than hydrogen and helium.

In death, they sent their chemical creations into outer space, paving the way for subsequent generations of stars, solar systems and galaxies.

With a greater understanding of how these first stars died, scientists hope to glean some insights about how the Universe, as we know it today, came to be.

"We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole, no one has ever found this mechanism before," says Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the ApJ paper.

"Without NERSC resources, it would have taken us a lot longer to reach this result."

"From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science."

More information: Astrophysical Journal, iopscience.iop.org/0004-637X/790/2/162

Pluto: Three possible models of Dwarf Planet ahead of New Horizons visit

Interior structure models assumed for Pluto.

Two space researchers, Amy Barr, with Brown University and Geoffrey Collins with Wheaton College, have published a paper in the journal Icarus in which they describe three possible interior models of the former planet Pluto.

They suggest the possibilities include: 

1. an undifferentiated rock/ice mixture, 
2. a differentiated rock/ice mixture, and an ocean covered with ice. 
3. The third possibility suggests the likelihood, they claim, of tectonic action on the dwarf planet.

Pluto

A close up view of the planet by space probe New Horizons due to arrive next year, should help clarify which scenario is most likely.

Amy Barr

Scientists believe that Pluto came to exist as it does today, in part due to a collision billions of years ago that led also to the formation of its moon Charon.

Charon

When celestial bodies collide, not only do they knock each other around, they produce heat—heat, the researchers suggest that could still be evident today.

Barr and Collins are leading towards a theory that suggests that shortly after impact, Pluto and Charon were much closer together, the gravity attraction between them would have caused both to be egg shaped.

As time passed, melted ice from the impact would have created an icy crust on top of an ocean on Pluto, and then, as Charon moved farther away, the attractive pull would have diminished, causing ice plates to form and crack against one another, a form of tectonics.

Geoffrey Collins

If that were the case, the two add, then in all likelihood, when New Horizons begins sending back images, they should see evidence of such tectonic action—plate edges thrust into the air, for example.

There's just one catch, Pluto circles the sun in an elliptical orbit, thus sometimes it's much closer to the sun than other times.

When near, it has a defined atmosphere, when far away however, its atmosphere actually freezes to its surface, something that could hide ridges in the ice and thus evidence of both tectonic activity and an ocean beneath the crust of ice.

New Horizons

Artist concept of New Horizons spacecraft.

Johns Hopkins University Applied Physics Laboratory (JHUAPL) /Southwest Research Institute (SwRI)

Since New Horizons will arrive during a time when its atmosphere is frozen to the surface, it might be difficult to determine which of the three proposed models actually describes the relationship between its exterior and interior.

Barr and Collins are optimistic that even in such a scenario, ridges should be apparent, proving that beneath Pluto's icy surface, lies an ocean, one that future researchers might one day sample.

More information: Tectonic Activity on Pluto After the Charon-Forming Impact, Icarus, Available online 4 April 2014. dx.doi.org/10.1016/j.icarus.2014.03.042 . Available on Arxiv: xxx.lanl.gov/abs/1403.6377

NASA's OSIRIS-REx Spacecraft will visit the newly named asteroid Bennu

An asteroid that will be explored by a NASA spacecraft has a new name, (Bennu) thanks to a third-grade student in North Carolina. 

NASA's Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx) spacecraft will visit the asteroid now called Bennu, named after an important ancient Egyptian avian deity.

OSIRIS-Rex is scheduled to launch in 2016, rendezvous with Bennu in 2018 and return a sample of the asteroid to Earth in 2023.

Check here for the OSIRIS-REx Fact Sheet

The name for the carbon-rich asteroid, designated in the scientific community as (101955) 1999 RQ36, is the winning entry in an international student contest.

Michael Puzio

Nine-year-old Michael Puzio suggested the name because he imagined the Touch-and-Go Sample Mechanism (TAGSAM) arm and solar panels on OSIRIS-REx look like the neck and wings in drawings of Bennu, which Egyptians usually depicted as a gray heron.

Puzio wrote the name suits the asteroid because it means "the ascending one," or "to shine."

TAGSAM will collect a sample from Bennu and store it for return to Earth. The sample could hold clues to the origin of the solar system and the source of water and organic molecules that may have contributed to the development of life on Earth.



The mission will be a vital part of NASA's plans to find, study, capture and relocate an asteroid for exploration by astronauts.

NASA recently announced an asteroid initiative proposing a strategy to leverage human and robotic activities for the first human mission to an asteroid while also accelerating efforts to improve detection and characterization of asteroids.