Monthly Archives: April 2022

How fast is the universe expanding? How much does matter clump up in our cosmic neighborhood? Different methods of answering these two questionseither by observing the early cosmos and extrapolating to present times, or by making direct observations of the nearby universeare yielding consistently different answers. The simplest explanation for these discrepancies is merely that our measurements are somehow erroneous, but researchers are increasingly entertaining another, more breathtaking possibility: These twin tensionsbetween expectation and observation, between the early and late universemay reflect some deep flaw in the standard model of cosmology, which encapsulates our knowledge and assumptions about the universe. Finding and fixing that flaw, then, could profoundly transform our understanding of the cosmos.

One way or another, an answer seems certain to emerge from the fog over the coming decade, as eager astronomers gear up for a host of new space and terrestrial telescopes to gain clearer cosmic views. Pursuing these tensions is a great way to learn about the universe, says astrophysicist and Nobel laureateAdam Riess of Johns Hopkins University. They give us the ability to focus our experiments on very specific tests, rather than just making it a general fishing expedition.

These new telescopes, Riess anticipates, are about to usher in the third generation of precision cosmology. The first generation came of age in the late 1990s and early 2000s with the Hubble Space Telescope (HST) and with NASAs WMAP satellite that sharpened our measurements of the universes oldest light, the cosmic microwave background (CMB). It was also shaped by a number of eight-meter-class telescopes in Chile and the twin 10-meter Keck behemoths in Hawaii. Collectively, these observatories helped cosmologists formulate the standard model of cosmology, which is a cocktail of 5 percent ordinary matter, 27 percent dark matter and 68 percent dark energy that can with uncanny accuracy account for most of what we observe about galaxies, galaxy clusters and other large-scale structures and their evolution over cosmic time. Ironically, by its very success, the model highlights what we do not know: the exact nature of 95 percent of the universe.

Driven by even more precise measurements of the CMB from ESAs Planck satellite and various ground-based telescopes, the second generation of precision cosmology supported the standard model, but also brought to light the tensions. The focus shifted to reducing so-called systematics: repeatable errors that creep in because of faults in the design of experiments or equipment.

The third generation has been waiting in the wings for years and is only now starting to take center stage with the successful launch and deep-space deployment of Hubbles successor, the James Webb Space Telescope (JWST). On Earth, CMB measurements are poised to reach new Planck-surpassing levels of precision via radio telescope arrays such as the Simons Observatory in the Atacama Desert and the nascent CMB-S4, a future assemblage of 21 dishes and a half million cryogenically cooled detectors that will be divided between sites in the Atacama and at the South Pole.

But the jewels in the third generations crown will be telescopes that stare at wide swathes of the sky. The first of these is likely to be ESAs 1.2-meter Euclid space telescope, due for launch in 2023 to study the shapes and distributions of billions of galaxies with a gaze that spans about a third of the sky. Euclids studies will dovetail with those of NASAsNancy Grace Roman Space Telescope, a 2.4-meter telescope with a field of view about 100 times bigger than Hubbles that is slated for launch in 2025. Finally, when it begins operations in the mid-2020s, the ground-basedVera C. Rubin Observatory will map the entire overhead sky every few nights with its 8.4-meter mirror and a three-billion-pixel camera, the largest ever built for astronomy.

Were not going to be limited by noise and by systematics, because these are independent observatories, says astrophysicist Priyamvada Natarajan of Yale University. Even if we have a systematic in our framework, we should [be able to] figure it out.

Riess, for one, would like to see a resolution of the Hubble tension, which arises from differing estimates of the value of the Hubble constant, H0, the rate at which the universe is expanding. Riess leads the Supernovae, H0, for the Equation of State of Dark Energy (SH0ES)project to measure H0. The SH0ES process starts with astronomers climbing onto the first rung of the so-called cosmic distance ladder, a hierarchy of methods to gauge ever-greater celestial expanses. The first rungthat is, the one concerning the nearest cosmic objectsrelies on geometric parallax to determine the distance to special stars called Cepheid variables, which pulsate in proportion to their intrinsic luminosity. Pegging the distance to a Cepheid via parallax allows astronomers to calibrate the relationship between its brightness and variability, making it a workhorse standard candle for estimating greater cosmic distances. This forms the basis of the second rung, which uses telescopes like the HST to find Cepheids in more remote galaxies, measure their variability to determine their distance and then use that distance to calibrate another, more powerful set of standard candles called type Ia (pronounced one-A) supernovae, or SNe Ia, in those very same galaxies. Ascending further, astronomers locate SNe Ia in even more far-flung galaxies, using them to establish a relationship between distance and a galaxys redshift, a measure of how fast it is moving away from us. The end result is an estimate of H0.

Others, besides SH0ES, have also been on the case, including the Pantheon+ team, which has compiled a large dataset of type Ia supernovae.

In December, Riess says, after a couple of years of taking a deep dive on the subject, the SH0ES team and the Pantheon+ team announced the results of nearly 70 different analyses of their combined data. The data included observations of Cepheid variables in 37 host galaxies that contained 42 type Ia supernovae, more than double the number of supernovae studied by SH0ES in 2016. Riess and his co-authors suspect this latest study represents the HSTs last stand, the outer limits of that hallowed telescopes ability to help them climb higher up the cosmic scale. The set of supernovae now includes all suitable SNe Ia (of which we are aware) observed between 1980 and 2021 in the nearby universe. In their analysis, H0 comes out to be 73.04 1.04 kilometers per second per megaparsec.

That is way off the value obtained by an entirely different method that looks at the other end of cosmic historythe so-called epoch of recombination when the universe became transparent to light, about 380,000 years after the big bang. The light from this epoch, now stretched to microwave wavelengths because of the universes subsequent expansion, is detectable as the all-pervading cosmic microwave background. Tiny fluctuations in temperature and polarization of the CMB capture an all-important signal: the distance a sound wave travels from almost the beginning of the universe to the epoch of recombination. This length is a useful metric for precision cosmology and can be used to estimate the value of H0 by extrapolating to the present-day universe using the standard LCDM model (where L stands for lambda or dark energy, and CDM for cold dark matter; cold refers to the assumption that dark matter particles are relatively slow-moving). Published a year ago, the latest analysis combined data from the Planck satellite and two ground-based instruments, the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT), to arrive at an H0 of 67.49 0.53.

The discrepancy between the two estimates has a statistical significance of five sigma, meaning there is only about a one-in-a-million chance of it being a statistical fluke. Its certainly at the level that people should take seriouslyand they have, Riess says.

The other tension that researchers are starting to take seriously concerns a cosmic parameter called S8, which depends on the density of matter in the universe and the extent to which it is clumped up rather than evenly distributed. Estimates of S8 also involve, on one end, measurements of the CMB, with measurements of the local universe on the other. The CMB-derived value of S8 in the early universe, extrapolated using LCDM, generates a present-day value of about 0.834.

The local universe measurements of S8 involve a host of different methods. Among the most stringent of these are so-called weak gravitational lensing observations, which measure how the average shape of millions of galaxies across large patches of the sky is distorted by the gravitational influence of intervening concentrations of dark and normal matter. Astronomers used the latest data from the Kilo-Degree Survey (KiDS), which more than doubled its sky coverage from 350 to 777 square degrees of the sky (the full moon, by comparison, spans a mere half a degree), and estimated S8 to be about 0.759. The tension between the early- and late-universe estimates of S8 has grown from being at 2.5 sigma in 2019 to three sigma now (or, a one-in-740 chance of being a fluke). This tension isnt going away, says astronomerHendrik Hildebrandtof the Ruhr University Bochum in Germany. It has hardened.

There is yet another way to arrive at the value of S8: by counting the number of the most massive galaxy clusters in some volume of space. Astronomers can either do that directly (for example, by using gravitational lensing), or by studying the imprint of these clusters in the cosmic microwave background, thanks to something called the Sunyaev-Zeldovich effect (which causes CMB photons to scatter off the hot electrons in clusters of galaxies, creating shadows in the CMB that are proportional to the mass of the cluster). A detailed 2019 study using data from the South Pole Telescope estimated S8 to be 0.749again, way off from the CMB+LCDMbased estimates. These numbers could be reconciled if the estimates of the masses of these clusters were wrong by about 4050 percent, Natarajan says. However, she thinks such substantial revisions are unlikely. We are not that badly off in the measurement game, she says. So thats another kind of internal inconsistency, another anomaly pointing to something else.

Given these tensions, it is no surprise cosmologists are anxiously awaiting fresh data from the new generation of observatories. For instance, David Spergel of Princeton University is eager for astronomers to use the JWST to study the brightest of the so-called red-giant-branch stars. These stars have a well-known luminosity and can be used as standard candles to measure galactic distancesan independent rung on the cosmic ladder, if you will. In 2019, Wendy Freedman of the University of Chicago and colleagues used this technique to estimate H0, finding that their value sits smack in the middle of the early- and late-universe estimates. The error bars on the current tip of the red-giant-branch data are such that theyre consistent with both possibilities, Spergel says. Astronomers are also planning to use JWST to recalibrate the Cepheids surveyed by Hubble, and separately the telescope will help create another new rung for the distance ladder by targeting Mira stars (which, like Cepheids, have a luminosity-periodicity relation useful for cosmic cartography).

Whereas JWST might resolve or strengthen the H0 tension, the wide-field survey data from the Euclid, Roman and Rubin observatories could do the same for the S8 tension by studying the clustering and clumping of matter. The sheer amount of data expected from this trio of telescopes will reduce S8 error bars enormously. The statistics are going to go through the roof, Natarajan says.

Meanwhile, theoreticians are already having a field day with the twin tensions. This is a playground for theorists, Riess says. You throw in some actual observed tensions, and they are having more fun than we are.

The most recent theoretical idea to garner a great deal of interest is something called early dark energy (EDE). In the canonical LCDM model, dark energy only started dominating the universe relatively late in cosmic history, about five billion years ago. But, Spergel says, we dont know why dark energy is the dominant component of the universe today; since we dont know why its important today, it could have also been important early on. That is partly the rationale for invoking dark energys effects much earlier, before the epoch of recombination. Even if dark energy was just 10 percent of the universes energy budget during those times, that would be enough to accelerate the early phases of cosmic expansion, causing recombination to occur sooner and shrinking the distance traversed by primordial sound waves. The net effect would be to ease the H0 tension.

What I find most interesting about these models is that they can be wrong, Spergel says. Cosmologists EDE models make predictions about the resulting EDE-modulated patterns in the photons of the CMB. In February 2022, Silvia Galli, a member of the Planck collaboration at Sorbonne University in Paris, and colleagues published an analysis of observations from Planck and ground-based CMB telescopes, suggesting that they collectively favor EDE over LCDM, by a statistical smidgen. Confirming or refuting this rather tentative result, however, will require more and better datawhich could come soon from upcoming observations by same ground-based CMB telescopes. But even if EDE models prove to be better fits and fix the H0 tension, they do little to alleviate the tension from S8.

Potential fixes for S8 exhibit a similarly vexing lack of overlap with H0. In March, Guillermo Franco Abelln of the University of Montepellier in France and colleagues published a study in Physical Review D showing that the S8 tension could be eased by the hypothetical decay of cold dark matter particles (into one massive particle and one warm massless particle). This mechanism would lower the value of S8 arising from CMB-based extrapolations, bringing it more in line with the late universe measurements. Unfortunately, it does little to solve the H0 tension.

It seems like a robust pattern: whatever model you come up with that solves the H0 tension makes the S8 tension worse, and the other way around, Hildebrandt says. There are a few models that at least dont make the other tension worse, but also dont improve it a lot.

Once fresh data arrive, Spergel foresees a few possible scenarios unfolding. First, the new CMB data could turn out to be consistent with early dark energy, resolving the H0 tension, and the upcoming survey telescope observations could separately ease the S8 tension. That would be a win for early dark energy modelsand would constitute a major shift in our understanding of the opening chapters of cosmic history.

Or, it is possible that both H0 and S8 tensions resolve in favor of LCDM. This would be a win for the standard model, and a possibly bittersweet victory for cosmologists hoping for paradigm-shifting breakthroughs rather than business as usual.

Outcome three would be both tensions become increasingly significant as the data improvesand early dark energy isnt the answer, Spergel says. Then, LCDM would presumably have to be reworked differently, but absent further specifics the impact of such an outcome is difficult to foresee.

Natarajan thinks that the tensions and discrepancies are probably telling us that LCDM is merely an effective theory, a technical term meaning that it accurately explains a certain subset of the current compendium of cosmic observations. Perhaps whats really happening is that there is an underlying, more complex theory, she says. And that LCDM is this [effective] theory, which seems to have most of the key ingredients. For the level of observational probes that we had previously, that effective theory was sufficient. But times change, and the data deluge from precision cosmologys third generation of powerful observatories may demand more creative and elaborate theories.

Theorists, of course, are more than happy to oblige. For instance, Spergel speculates that if early dark energy could interact with dark matter (in LCDM, dark energy and dark matter do not interact), this could suppress the fluctuations of matter in the early universe in ways that would resolve the S8 tension, while simultaneously taking care of the H0 tension. It makes the models more baroque, but maybe thats what nature will demand, Spergel says.

As an observational astronomer, Hildebrandt is circumspect. If there was a convincing model that beautifully solves these two tensions, wed already have the next standard model. That were instead still talking about these tensions and scratching our heads is just reflecting the fact that we dont have such a model yet.

Riess agrees. After all, this is a problem of using a model based on an understanding of physics and the universe that is about 95 percent incomplete, in terms of the nature of dark matter and dark energy, he says. It wouldnt be crazy to think that we are missing something.

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Astronomers Gear Up to Grapple with the High-Tension Cosmos - Scientific American

Photos Special to The Record by Holly McGuire

Kentuckians invaded the Vaticans astronomical observatory this winter.

Chris Graney

The Vatican Observatory has two sites: near Rome, and in Arizona (where the skies are darker and clearer than Rome). In January, the VO held its Astronomy for Catholics in Ministry and Education workshop in Arizona. Among those there, talking religion and science and stomping around mountaintop telescopes, were two Kentuckians: me and Holly McGuire of Trinity High School.

Coincidentally, we both grew up in Owensboro, Ky., and graduated from Owensboro Catholic High School five years apart. I am a lifelong science nerd at the ACME workshop because I am on the staff of the VO.

The journey of Ms. McGuire (as her students call her) to ACME, where she ended up querying astronomers at the University of Arizona about their adaptive-optics machines, was very different.

She kindly agreed to write an essay about that journey for the VO (www.vaticanobservatory.org). Following is an abridged version of her essay:

Holly McGuire

The Catholic Church proclaims the Christian journey begins at the waters of Baptism, is strengthened by the grace of Confirmation and is renewed by the Eucharist. But the means of each Christians journey differ.

My maternal grandfather, Howard Baum, was a machinist for GE. I was often found with my grandpa in his garage machine shop. GE subcontracted him to make satellite parts, and I helped him do this. He also supported my artistic talents by sending me to art lessons with a local artist.

In college, I majored in fine arts with a minor in business administration. I married Sean McGuire. I had three sons, Lance, Alec and Luke. I worked for an east coast signage corporation, occasionally showing my artwork in galleries.

Returning to Kentucky, I helped with the art and environment committee at Immaculate Conception Church in La Grange, Ky., including a Morning Star glass mosaic project that provides the background for the Easter Candle. The opportunity to create liturgical art allowed me to pray and work.

I followed the Christian example of my grandparents, so I was drawn into the beauty of liturgical life. I started teaching at Trinity and studying theology, receiving my masters in theological studies from St. Meinrad School of Theology in 2016.

In teaching, I would stumble over my students supposed conflict between science and religion. Even a colleague would say that faith and reason opposed one another. Eventually, I found the Science and Theology Seminar at Notre Dame, and I started to talk about the Big Bang, Galileo and evolution. Through all of this, I continued to have more questions than answers. I looked up the VO, and found the ACME workshop.

The workshop gave me the experience of doing science instead of simply talking about it. Over the course of four days, participants enjoyed presentations on the Big Bang, dark matter, dark energy, asteroids, meteorites, Johannes Kepler and astrophotography.

We traveled to Steward Observatory, where researchers showed us how they removed noise with code they wrote. The Caris Mirror Lab displayed the manufacturing of seven 8.4-meter mirrors for the Giant Magellan Telescope, which will be the largest in the world. We drove through the desert, pine forest and snow to tour different observatories.

Each evening we celebrated Mass. After dusk we looked through telescopes and learned astrophotography, taking amazing pictures of the night sky. The clear night sky displayed a glimpse of the Creator.

It was truly a beautiful moment in my Christian journey. The dialogue between science and theology is essential, but it is the ability to do science, not just talk about it, that will keep me intrigued in the journey. Holly McGuire

Chris Graney, a parishioner at St. Louis Bertrand Church, is on the staff of the Vatican Observatory, http://www.vaticanobservatory.org.

Read the rest here:

Science in the Bluegrass Astronomy for ministry and education - The Record

Since time immemorial, Indigenous peoples worldwide have observed, tracked and memorised all the visible objects in the night sky.

This ancient star knowledge was meticulously ingrained with practical knowledge of the land, sky, waters, community and the Dreaming and passed down through generations.

One of the most well-known and celebrated Aboriginal constellations is the Emu in the Sky, which appears in the southern sky early in the year. It is an example of a dark constellation, which means its characterised by particularly dark patches in the sky, rather than stars.

Conversely, space technology companies such as Starlink are increasingly competing to dominate the skies, and potentially change them forever.

The modern-day space race has led to thousands of satellites being scattered through Earths outer orbits. If left unchallenged, these companies risk overpopulating an already crowded space environment potentially pushing dark skies to extinction.

Mega-constellations are groupings of satellites that communicate and work together as they orbit Earth.

Since 2018, the Starlink project, run by Elon Musks SpaceX, has launched about 1,700 satellites into low Earth orbit. The company plans to launch another 30,000 over the next decade.

British company OneWeb has launched nearly 150 satellites, with plans for another 6,000. And Amazon intends to launch an additional 3,000 satellites into multiple orbits.

Each of these companies is taking to the skies to increase internet access across the globe. But even if they deliver on this, sky gazers and especially Indigenous peoples are left to wonder: at what cost?

People across the globe began noticing streaks across our skies not long after the first Starlink launch in May 2019. They were unlike anything anyone had seen before.

Astronomers are very used to viewing the sky and dealing with interference, often originating from aircraft or the occasional satellite. However, the goal of mega-constellations is to engulf the entire planet, leaving no place untouched. Mega-constellations alter our collective view of the stars. And there is currently no known way to remove them.

One mega-constellation has been observed to produce up to 19 parallel streaks across the sky. These streaks disturb astronomical observations, and a significant amount of scientific data can be lost as a result.

As they travel across the entire sky, scattering the Suns light, dark constellations become even fainter further desecrating Indigenous knowledge and kinship with the environment.

Further research on the impacts of mega-constellations have found that as they orbit Earth, the Suns rays are reflected off them and scattered into the atmosphere.

The authors of that study conclude we are collectively experiencing a new type of skyglow as a result: a phenomenon in which the brightness of the sky increases due to human-made light pollution.

Initial calculations indicate this new source of light pollution has increased the brightness of night skies globally by about 10%, compared with the natural skyglow measured in the 1960s.

Currently, the upper limit of light pollution tolerable at observatories is 10% above the natural skyglow, which suggests we have already reached the limit.

In other words, scientific observations of the sky are already at risk of being rendered redundant. If this excess skyglow increases even more, observatories are at serious risk.

Indigenous knowledge systems and oral traditions teach us about the intricate and complex relationships Indigenous peoples have with the environment, including the sky.

For example, many Aboriginal and Torres Strait Islander cultures have no concept of outer space. They only have a continuous and connected reality where coexistence with all things is paramount.

As captured by the Bawaka Country group, based in northeast Arnhem Land:

to hurt Sky Country, to try and possess it, is an ongoing colonisation of the plural lifeworlds of all those who have ongoing connections with and beyond the sky.

Desecrating the sky impacts Indigenous sovereignty as it limits access to their knowledge system, in the same ways desecrating the land has removed First Peoples from their countries, cultures and ways of life.

For example, the Gamilaraay and Wiradjuri peoples of New South Wales observe the Emu in the Sky to gauge when it is time to hunt for emu eggs and most importantly, when it is time to stop. How would the Gamilaraay know when to stop collecting eggs, or when to conduct annual ceremonies signalled by the Celestial Emu, if it was no longer visible?

Similarly, important parts of the Jukurrpa, or Dreaming of the Martu people of Western Australia is embedded in the Seven Sisters constellation. How would they keep this knowledge safe if they cant locate any of the Sisters?

Indigenous histories teach us about the devastating consequences of colonialism, and how the impacts of the colonial agenda can be mitigated through prioritising the health of country and community.

In the words of astronomer Aparna Venkatesan and colleagues:

the manner and pace of occupying near-Earth space raise the risk of repeating the mistakes of colonisation on a cosmic scale.

Active Indigenous sky sovereignty acknowledges the interconnected nature between land and sky, and that caring for country includes sky country. By doing so, it challenges the otherwise unimpeded authority of technology corporations.

By understanding that the world (and indeed the Universe) is interconnected, we see that no living creature is immune to the consequences of polluting the skies.

Currently, native fauna such as the tammar wallaby, magpie, bogong moth and marine turtles are experiencing a reduction in populations and quality of life due to the impacts of light-pollution.

Migratory species are particularly affected by light pollution, which can result in them losing access to their migratory route. This is a crisis Australias fauna has faced since before the introduction of mega-constellations.

With more skyglow and light pollution, positive outcomes for native fauna and migratory species diminish.

Read more: Skyglow forces dung beetles in the city to abandon the Milky Way as their compass

Several companies have made attempts to reduce the impact of mega-constellations on skyglow.

For example, OneWeb has opted to rollout fewer satellites than initially proposed, and has designed them to be positioned at a higher altitude. This means they will produce less skyglow, while also covering a larger area.

Starlink, on the other hand, has not shown any public interest in operating at higher and less impactful altitudes, for fears it will impact the Starlink networks speed and latency.

That said, they have attempted to reduce their satellites luminosity by painting them with a novel anti-reflective coating. Coating techniques have demonstrated a reduction in reflected sunlight by up to 50%. Unfortunately, not all wavelengths of light being scattered are reduced using this method. So multi-wave astronomy, and different species of animals, are still at risk.

Well need more solutions to navigate our increasingly polluted atmosphere, particularly if communication monopolies continue to rein over near-Earth space.

Just as some companies have started considering tactics to avoid increasing skyglow, all space tech companies must be held responsible for adding to an already polluted space.

Guidelines such as those set by the Inter-Agency Space Debris Coordination Committee offer solutions to this problem. They suggest lowering the height of a satellites orbit when its no longer needed, allowing it to disintegrate as it falls down to Earth.

However, these are international guidelines, so theres no legal framework to enforce such practices.

And given that near-miss collisions have already taken place between some mega-constellations, and an estimated 20,000 pieces of space debris already floating above, reducing orbital pollution must also now be a priority.

Reducing air pollutants has also been shown to drastically decrease natural sky brightness, offering a potential solution for improving night sky visibility not to mention cleaner breathing air for all.

In valuing Indigenous knowledge systems, that value must be extended to the natural environment in which that knowledge is embedded and founded upon. In Australia, preserving dark skies is not just vital for the continuation of Indigenous knowledge and astronomers it benefits us all.

A major tenet of life for Indigenous peoples is valuing the sustainability of ones actions. By adopting this at a larger scale, we could create a reality in which were not a threat to our own survival.

Read more: Darkness is disappearing and that's bad news for astronomy

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Thousands of satellites are polluting Australian skies, and threatening ancient Indigenous astronomy practices - The Conversation Indonesia

Congratulations to six graduate students in the Department of Physics and Astronomy who successfully defended their doctoral theses in April!

The students (with their degree, thesis title, and thesis committee) were:

Evan Abbuhl Ph.D. in Physics.

Thesis Title: "Very Long Baseline Interferometry of Chromospherically Active Binary Stars.

Thesis Committee: Professors Kenneth Gayley (Advisor), Cornelia Lang, Robert Mutel, and Dr. Robert Zavala from the U.S. Naval Observatory"

Arran Gross Ph.D. in Physics (Astronomy subtrack).

Thesis Title: Testing the Radio-Selection Method with Optical Spectroscopy in the Stripe 82 Field

Thesis Committee: Professors Hai Fu (Advisor), Casey DeRoo, Keri Hoadley, Adam Myers (University of Wyoming), and Dr. Andrea Prestwich (Astrophysicist at Center for Astrophysics, Harvard & Smithsonian)

Kwangyul Hu Ph.D. in Physics

Thesis Title: Spin-wave Dynamics in Non-trivial Magnetic Geometries

Thesis Committee: Profs. Michael Flatt (thesis director), Craig Pryor, Yannick Meurice, Markus Wohlgenannt, and Ezekiel Johnston-Halperin

Dylan Par Ph.D. in Physics

Thesis Title: Investigating Properties of Multi-stranded Non-thermal Filaments in the Galactic Center

Thesis Committee: Prof. Cornelia Lang and (Advisor), Professors Phil Kaaret, Ken Gayley, Cornelia Lang, Hai Fu, and Dr. James Green

Joshua Steffen Ph.D. in Physics (Astronomy subtrack)

Thesis Title: The Volume Density of AGN in Interacting Galaxies

Thesis Committee: Professors Hai Fu (advisor), Casey DeRoo, Phil Kaaret, Keri Hoadley, and Julia Comerfield from the University of Colorado, Boulder

Ashok Tiwari Ph.D. in Physics

Thesis Title: Monte Carlo Simulations and Phantom Measurements towards more Quantitative Dosimetry and Imaging in Nuclear Medicine

Thesis Committee: Dr. John Sunderland (advisor), Professors Craig Pryor, Wayne Polyzou, Vincent Rodgers, Dr. Tiwari, and Dr. Ryan Flynn from the Dept. of Radiation Oncology.

Banner photo:Joshua Steffen's thesis defense committee - Professors Hai Fu (advisor), Julia Comerfield (via computer) from the University of Colorado, Boulder, Casey DeRoo, Phil Kaaret, and Keri Hoadley.

Read more:

Six Graduate Students Successfully Defend Theses | Physics and Astronomy - The University of Iowa - The University of Iowa

ProfessorIoannis Daglis; University of Athens

Abstract:Electrons in the outer Van Allen belt occasionally reach relativistic energies and therefore become a hazard for spacecraft operating in geospace, leading to significant potential risks. The energy and flux of these electrons can vary over time scales of years (related to the solar cycle), seasons (semi-annual variation), hours (magnetic storms), minutes (sudden storm commencements). Electric fields and plasma waves are the main factors regulating the electron transport, acceleration and loss. Both the fields and the plasma waves are driven directly or indirectly by disturbances originating at the Sun, propagating through interplanetary space and impacting the Earth. We review our current understanding of the response of outer Van Allen belt electrons to solar eruptions and their interplanetary extensions, i.e. interplanetary coronal mass ejections and high-speed solar wind streams and the associated stream interaction regions. We also discuss the magnetospheric processes that link interplanetary drivers with geospace electrons.

Short Bio:Ioannis (Yannis) Daglis is Professor and Head of the Space Physics Group at the National & Kapodistrian University of Athens and President of the Hellenic Space Center. His scientific expertise pertains to space physics and space applications. He is a Full Member of the International Academy of Astronautics and Editor-in-Chief of Annales Geophysicae. He has been a co-investigator of several ESA and NASA space missions and the Principal Investigator of a number of EU-funded and ESA-funded projects. He currently leads the Horizon2020 project SafeSpace (https://www.safespace-h2020.eu), which aims at advancing space weather nowcasting and forecasting capabilities through the development of a sophisticated model of the Van Allen electron belt and of a prototype space weather forecast service with a target lead time of 2 to 4 days.He has published 110+ papers and has edited and co-authored 6 textbooks on space physics and space weather.Prof. Daglis served as a Member of ESA's advisory Solar System Working Group (2005-2010) and as scientific advisor and technical expert for (among others) NASA, the Academy of Finland, Research Council of Norway, BELSPO (Belgian Federal Science Policy Office), Helmholtz Association of German Research Centres, and the European Commission.

Continued here:

Physics & Astronomy Colloquium - Professor Ioannis Daglis | Physics and Astronomy | The University of Iowa - The University of Iowa