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THEORETICAL PHYSICIST LISA RANDALL

FROM:  NATIONAL SCIENCE FOUNDATION
After the lecture: Extra dimensions, interacting dark matter, and the power of uncertainty
A conversation with theoretical physicist Lisa Randall

In her most recent book, physicist Lisa Randall--Harvard professor, libretto composer, Lego figurine, star in the world of theoretical physics--writes that the universe repeatedly reveals itself to be cleverer than we are. This is not a submission to the mysteries of the universe; rather, it's a recognition that the more we discover about the fundamental nuts and bolts of this world, the more questions we have.

Randall works to uncover those fundamental nuts and bolts. She studies theoretical particle physics and cosmology, and her research has advanced our understanding of supersymmetry, models of extra dimensions, dark matter and more. She's made a career out of sharing these discoveries--what they are, how we know them and why they matter--with the public.

Randall is the author of three books and has appeared in dozens of media outlets--from Charlie Rose and The New York Times to The Colbert Report and Vogue. We sat down with Randall after her lecture "New ideas about dark matter" as part of the National Science Foundation's Distinguished Lecture Series in Math and Physical Sciences.

I liked doing math. And I liked understanding how things work. I took a physics class in high school, and I didn't really know for sure that I would be doing it [long term], but I kept going. I enjoyed it. I like that you got answers. I kind of liked that it was challenging.

I think it's important to explain these theories are evolving and what it means for the world. Uncertainty in science isn't actually a bad thing. It actually drives you forward. You can have a lot of certainty even with uncertainty at the edges.

Sometimes it's a question not just of saying 'I'm going to figure this out,' but just with being smart enough to recognize something interesting when it happens. When we found this warped geometry we hadn't been looking for it, it just was a solution. Then we realized what kind of implications it could have. Both in terms of solving the hierarchy problem and explaining particle masses, but also in terms of having an infinite extra dimension.

There's usually a moment when you realize it. Then there are a lot of moments when you think you're wrong and you go back.

I think there's just a lot of ideas about creativity that people don't fully appreciate for scientists. I think there's a lot of ideas about right and wrong that people don't fully appreciate, and how science advances.

I'd just written a book where you try so hard to do everything in a liner order. I'd just written Warped Passages and it was kind of nice the idea of just introducing ideas without having to explain them. And just have different voices. You sort of realize the richness of operas and just expressing ideas and just getting people familiar with something. You have music, you have art, you have words. It's very exciting.

I don't think anyone should just set themselves up to be a role model. I think every person is different, and certainly there's a few enough women that we're all different. But it is true that one of the small advantages you have as a woman is that you are doing something important beyond your work, which is just establishing that women can be out there doing these things. And it is definitely true that when I wrote my book I thought it's good to have someone out there in the public eye, so that people know there are women physicists. And in terms of the response, I can say that--both negative and positive--people do not realize there are women out there sometimes. So it was really important. But it also means you have to put up with a lot of distracting comments and questions sometimes that you wouldn't otherwise.

-- Jessica Arriens,
Investigators
Lisa Randall
Related Institutions/Organizations
Harvard University
Massachusetts Institute of Technology

NSF ON EARLY COSMOS AND HEAVY METAL

FROM:  NATIONAL SCIENCE FOUNDATION 
Heavy metal in the early cosmos
Simulations shed light on the formation and explosion of stars in the earliest galaxies

Ab initio: "From the beginning."

It is a term that's used in science to describe calculations that rely on established mathematical laws of nature, or "first principles," without additional assumptions or special models.

But when it comes to the phenomena that Milos Milosavljevic is interested in calculating, we're talking really ab initio, as in: from the beginning of time onward.

Things were different in the early eons of the universe. The cosmos experienced rapid inflation; electrons and protons floated free from each other; the universe transitioned from complete darkness to light; and enormous stars formed and exploded to start a cascade of events leading to our present-day universe.

Working with Chalence Safranek-Shrader and Volker Bromm at the University of Texas at Austin, Milosavljevic recently reported the results of several massive numerical simulations charting the forces of the universe in its first hundreds of millions of years using some of the world's most powerful supercomputers, including the National Science Foundation-supported Stampede, Lonestar and Ranger systems at the Texas Advanced Computing Center.

The results, described in the Monthly Notices of the Royal Astronomical Society in January 2014, refine how the first galaxies formed, and in particular, how metals in the stellar nurseries influenced the characteristics of the stars in the first galaxies.

"The universe formed at first with just hydrogen and helium," said Milosavljevic. "But then the very first stars cooked metals and after those stars exploded, the metals were dispersed into ambient space."

Eventually the ejected metals fell back into the gravitational fields of the dark matter haloes, where they formed the second generation of stars. However, the first generation of metals ejected from supernovae did not mix in space uniformly.

"It's as if you have coffee and cream but you don't stir it, and you don't wait for a long enough time," he explained. "You would drink some cream and coffee but not coffee with cream. There will be thin sheets of coffee and cream."

According to Milosavljevic, subtle effects like these governed the evolution of early galaxies. Some stars formed that were rich in metals, while others were metal-poor. Generally there was a spread in stellar chemical abundances because of the incomplete mixing.

Another factor that influenced the evolution of galaxies was how the heavier elements emerged from the originating blast. Instead of the neat spherical blast wave that researchers presumed before, the ejection of metals from a supernova was most likely a messy process, with blobs of shrapnel shooting in every direction.

"Modeling these blobs properly is very important for understanding where metals ultimately go," Milosavljevic said.

Predicting future observations

In astronomical terms, early in the universe translates to very far away. Those fugitive first galaxies are unbelievably distant from us now, if they haven't been incorporated into more recently-formed galaxies already. But many believe the early galaxies lie at a distance that we will be able to observe with the James Webb Space Telescope (JWST), set to launch in 2018. This makes Milosavljevic and his team's cosmological simulations timely.

"Should the James Webb Space Telescope integrate the image in one spot for a long time or should it mosaic its survey to look at a larger area?" Milosavljevic said. "We want to recommend strategies for the JWST."

Telescopes on the ground will perform follow-up studies of the phenomena that JWST detects. But to do so, scientists need to know how to interpret JWST's observations and develop a protocol for following up with ground-based telescopes.

Milosavljevic and others' cosmological simulations will help determine where the Space Telescope will look, what it will look for, and what to do once a given signal is observed.

Distant objects, born at a given moment in cosmic history, have tell-tale signature--spectra or light curves. Like isotopes in carbon dating, these signatures help astronomers recognize and date phenomenon in deep space. In the absence of any observations, simulations are the best way of predicting these light signatures.

"We are anticipating observations until they become available in the future," he said.

If done correctly, such simulations can mimic the dynamics of the universe over billions of years, and emerge with results that look something like what we see... or hope to see with new farther-reaching telescopes.

"This is a really exciting time for the field of cosmology," astronomer and Nobel Laureate Saul Perlmutter said in his keynote address at the Supercomputing '13 conference in November. "We are now ready to collect, simulate and analyze the next level of precision data... There's more to high performance computing science than we have yet accomplished."

Understanding our place in the universe

In addition to the practical goals of guiding the James Webb Space Telescope, the effort to understand these very early stars in the first galaxies has another function: to help tell the story of how our solar system came to be.

The current state of the universe is determined by the violent evolutions of the generations of stars that came before. Each generation of stars (or "population," in astronomy terms) has its own characteristics, based on the environment it was created in.

The Population III stars, the earliest that formed, are thought to have been massive and gaseous, consisting initially of hydrogen and helium. These stars ultimately collapsed and seeded new, smaller, stars that clustered into the first galaxies. These in turn exploded again, creating the conditions of Population I stars like our own, chock full of materials that enable life. How stars and galaxies evolved from one stage to another is still a much-debated question.

"All of this was happening when the universe was very young, only a few hundred million years old," Milosavljevic said. "And to make things more difficult, stars--like people--change. Every hundred million years, every 10 million years--it's like a kid growing up, all the time something new is happening."

Simulating the universe from birth to its current age, Milosavljevic and his team's investigations help disentangle how galaxies changed over time, and provide a better sense of what came before us and how we came to be.

Said Nigel Sharp, program director in the Division of Astronomical Sciences at the National Science Foundation: "These are novel studies using methods often ignored by other efforts, but of great importance as they impact so much of what happens in later cosmology and galaxy studies."
Investigators
Volker Bromm
Milos Milosavljevic
Chalence Safranek-Shrader
Related Institutions/Organizations
University of Texas at Austin
Locations
Austin , Texas

UNDERSTANDING A STAR'S SURFACE AND THE EXTREME FORCES OF NATURE

ILLUSTRATION FROM:  NASA:  A neutron star is the densest object astronomers can observe directly, crushing half a million times Earth's mass into a sphere about 12 miles across, or similar in size to Manhattan Island, as shown in this illustration.
Credit: NASA's Goddard Space Flight Center
Neutron Stars’ X-ray 


STORY FROM:  LOS ALAMOS NATIONAL LABORATORY 

Superbursts Mystify, Inspire Los Alamos Scientists

New neutrino cooling theory changes understanding of stars’ surface

LOS ALAMOS, N.M., Dec. 6, 2013—Massive X-ray superbursts near the surface of neutron stars are providing a unique window into the operation of fundamental forces of nature under extreme conditions.

“Scientists are intrigued by what exactly powers these massive explosions, and understanding this would yield important insights about the fundamental forces in nature, especially on the astronomical/cosmological scale,” said Peter Moller of Los Alamos National Laboratory’s Theoretical Division.



A neutron star is created during the death of a giant star more massive than the sun, compressed to a tiny size but with gravitational fields exceeded only by those of black holes. And in the intense, neutron-rich environment, nuclear reactions cause strong explosions that manifest themselves as X-ray bursts and the X-ray superbursts that are more rare and 1000 times more powerful.

Los Alamos researchers and former postdocs contributed to the paper “Strong neutrino cooling by cycles of electron capture and beta decay in neutron star crusts” that was published in Nature’s online edition of Dec. 1, 2013.
The importance of discovering an unknown energy source of titanic magnitude in the outermost layers of accreting neutron star surfaces is heightened by the unresolved issue of neutrino masses, the recent discovery of the Higgs boson and the fact that highly-neutron-rich nuclei with low-lying states enable “Weak Interactions,” prominent in stellar explosions. (The weak nuclear force is one of four fundamental sources, such as gravity, which interacts with the neutrinos; it is responsible for some types of radioactive decay.)

These hitherto celestially operative nuclei are expected to be within the experimental reach of the Facility for Rare Isotope Beams (FRIB), a proposed user facility at Michigan State University funded by the U.S. Department of Energy Office of Science.

“The terrestrial experimental study of Weak Interactions in highly deformed, neutron-rich nuclei that FRIB can potentially provide is lent support by this ground-breaking Nature letter, since Los Alamos has been one of the few homes to theoretical studies of deformed nuclei and their role in astrophysics, and remains so to this day,” said Moller, who coauthored the paper with a multidisciplinary team including former Los Alamos postdoctoral researchers Sanjib Gupta, now a faculty member at the Indian Institute of Technology (IIT), Ropar and Andrew Steiner, now a research assistant professor at INT, Seattle.

Previously a common assumption was that that the energy released in these radioactive decays would power the X-ray superburst explosions. This was based on simple models of nuclear beta-decay, sometimes postulating the same decay properties for all nuclei. It turns out, however, that it is of crucial importance to develop computer models that realistically describe the shape of each individual nuclide since they are not all spherical.

At Los Alamos scientists have carried out detailed calculations of the specific, individual beta-decay properties of thousands of nuclides, all with different decay properties, and created databases with these calculated properties.

The databases are then used at MSU as input into models that trace the decay pathways with the passage of time in accreting neutron stars and compute the total energy that is released in these reactions.

The new, unexpected result is that so much energy escapes by neutrino emission that the remaining energy released in the beta decays is not sufficient to ignite the X-ray superbursts that are observed. Thus the superbursts’ origin has now become a puzzle.

Solving the puzzle will require that we calculate in detail the consequences of shapes of neutron-rich nuclei, the authors said, and it requires that they simultaneously analyze the role played by neutrinos in neutron star X-ray bursts whose energetic magnitudes are exceeded only by explosions in the nova/supernova class.

The strong nuclear deformations that formed the basis for the neutrino cooling in neutron star crusts also play a role in a number of astrophysical settings, and have been taken into account in studies of supernovae explosions and subsequent collapses, funded by Los Alamos’ Laboratory Directed Research and Development (LDRD) programs.

Nuclear-structure databases valued worldwide

The large databases compiled by use of these and other nuclear-structure models are also used in several other Los Alamos programs. For example in modeling nuclear-reactor behavior, researchers have had to take into account beta-decay both because delayed neutrons are emitted, which governs the criticality of the reactor, and because it generates heat, just as in the neutron star.

Another current application is in nuclear non-proliferation programs. One method for detecting clandestine nuclear material in cargo shipments is to bombard cargoes with a small number of neutrons. If emission of delayed neutrons is detected after neutron bombardment, scientists have a sure signature of fissile nuclear material. The theoretical databases compiled at Los Alamos are not just used internally but are also part of nuclear-structure databases maintained by the International Atomic Energy Agency.

The authors, an international team

The authors on the paper are Hendrik Schatz from MSU; Sanjib Gupta from IIT Ropar; Peter Mller from LANL; Mary Beard and Michael Wiescher from the University of Notre Dame; Edward F. Brown, Alex T. Deibel, Laurens Keek, and Rita Lau from MSU; Leandro R. Gasques from the Universidade de Sao Paulo; William Raphael Hix from Oak Ridge National Laboratory and the University of Tennessee; and Andrew W. Steiner from the University of Washington.