Year: 2020

Please join me in congratulating Dr. Amy Pope for being awarded the Jerry G. Gaff Faculty Award for Outstanding Teacher. This recognition is awarded annually by the Association for General and Liberal Studies to recognize a significant record of outstanding teaching and/or course development in general education programs, core curricula, or liberal studies. Founded in 1960, the Association for General and Liberal Studies is a community of practitioner-scholars that provides strategic, effective and innovative support for peers engaged in the day-to-day work of general and liberal learning in 21st century higher education. Dr. Pope is a beloved instructor who continues to find innovative ways to engage her students – especially those who enter their first physics course with more than a little trepidation. She tirelessly works to find new ways to communicate the relevance of physics to students from all backgrounds. Indeed, her most recent work at finding a way to reach students with Physics has been the development of a new course, “The Physics of Sports”. This award is well deserved recognition for her contributions to the mission of the Department of Physics & Astronomy.

Supermassive black holes are the universe’s most immense single objects. These monsters can weigh more than a billion suns, and are the subjects of intense interest in the astronomical community. They are the engines powering the spectacular jets of material (so-called AGN jets) that emanate from the cores of some galaxies, and they offer precious clues about the growth of cosmic structure. One very famous supermassive black hole — lurking at the center of the galaxy M87, more than 50 million light years from Earth — made headlines last year when the Event Horizon Telescope (the name given to a global network of radio telescopes) made it the first black hole to be imaged directly.

These black holes were probably born in the early universe, left behind following the explosive deaths of first-generation stars. But how did they grow from seedlings (only 10 – 100 times the mass of the sun) into the giants they are today? This question is something astronomers have been trying to answer for decades. Most will agree that some of their growth is due to consuming the gas and debris from their host galaxies, but will concede this cannot be the entire story — there is a well-known maximum rate (called the Eddington limit) at which a black hole can accrete gas, and many black holes are simply too massive to have grown by accretion alone since the beginning of the universe. These black holes have likely grown faster by merging with partners: falling into orbit around one another, and eventually coalescing after after a long, inward spiraling dance. The details of this process are still murky — why, and how often do supermassive black hole mergers take place? And crucially, where are the supermassive black hole binaries, dancing toward coalescence?

Currently the best supermassive black hole binary candidate is a system known as OJ-287. This system exhibits regular outbursts (twice every 12 years), which can be explained if the smaller of the two black holes has a highly inclined and eccentric orbit, punching through and lighting up the larger one’s accretion disk (its meal of swirling debris) twice each orbit. These two objects are fatefully bound. On each orbit they get closer together, converting their orbital kinetic energy into gravitational wave radiation. In roughly 10,000 years from now, they will collide and merge together, producing a powerful burst of gravitational wave (GW) emission. Merger events like this would be detected by a space-based interferometric GW detector, such as the proposed LISA mission.

If OJ-287 is indeed a binary black hole, it would be proof that supermassive black holes do merge. But it raises a new question: how did these objects become bound to one another in first place? Such pairs might have been introduced when their respective host galaxies merged together. They could then have “sunk” to the center and become gravitationally bound when separated by 100’s to 1000’s of light-years. This is where things get tricky: when they are so widely separated, the orbit is barely affected by GW radiation. But the binary in OJ-287 has somehow shrunk to less than 0.1 light-year separation, close enough for GW’s to drive it to coalesce. The question of how a binary black hole’s separation can shrink to sub-light-year scales is so critical that it’s acquired a special name: “the final parsec problem.”

The solution to the final parsec problem is likely connected to a critical fact — black holes do not exist in a vacuum. The density of interstellar gas is small, on average one proton per cubic centimeter, but its effect on binary black holes over the course of billions of years can be critical. The black holes’ gravity pulls gas into a disk that swirls around the binary — a so-called circumbinary disk, or CBD. The dynamics of the binary and its CBD are complex, and beautiful: the circling black holes induce tidal interactions that push and pull gas in the CBD, causing some of it to fall inwards along narrow streams, and gather into smaller so-called minidisks which then accrete onto their respective black holes. The gas, in turn, exerts a gravitational pull on the binary, which might ultimately drive the black holes to spiral inwards… but it also might drive them apart!

To determine the effect of gas on the evolution of binary black holes, we need to unravel the complex dynamics of gas orbiting two black holes. This type of nonlinear physics problem can only be tackled with the aid of large-scale computer simulations, which solve the equations of gas dynamics and gravitation together, and at a very high level of detail.

Space Physicist Jens Oberheide is co-author on a study selected as a research highlight by the American Geophysical Union.  The Global-Scale Observations of the Limb and Disk (GOLD) instrument is the first NASA/ComSat owner-operator partnership for delivering a science payload into a geostationary orbit. GOLD’s unique observing geometry mitigates the decade-old problem of low Earth orbiting satellites to separate temporal from spatial changes in Earth’s ionosphere and thermosphere. First results from GOLD have yielded surprising discoveries that may help to develop better models of space weather, an important task for a technological society

Dr. Jian He of the Department of Physics & Astronomy Clemson is a corresponding author of a Science article describing a new van der Waals inorganic semiconductor. The van der Waals inorganic semiconductors are generally brittle and prone to cleavage in its bulk form at room temperature. However, an international team of scientists found that this is not always the case. In a recent article entitled “Exceptional plasticity in the bulk single-crystalline van der Waals semiconductor InSe” published in Science , the authors show that bulk single crystalline InSe can be morphed into simple origami, Mobius ring, engineeringly strained to 80% in compression, > 10% in tensile and bending strain along specific direction, without losing the structural integrity. The peculiar long-range Coulomb interaction across the van der Waals gap plays a key role in the observed bulk superplastic deformability. The scientific and technical implications of this discovery include flexible and plastic electronics, sensors, and energy harvesting devices.  A perspective article, “Ductile van der Waals materials”, was published in the same journal issue to highlight this discovery.

As the pandemic continues to spread and keep our economy at a standstill, one Clemson researcher is hard at work to create a faster COVID-19 test. With funding from an NSF Rapid grant, Dr. Ding is working on a way to provide test results in 15 minutes. Such a test will enable near real-time testing and open the door to allowing the people to engage in more public activities without fear of spreading or catching the virus. Please join me in congratulating Dr. Ding on his very important work!

Please join me in congratulating the Medical Physics group for placing 2^nd place in the Summer COVID Challenge.

The COVID Challenge was a competition for undergraduate students and their mentors across all disciplines to create a video pitch for any research, product, or service that addresses one of the many issues we’re dealing with due to the COVID pandemic including the virus itself, mental health in isolation, and alternative learning opportunities. The combined Physics/BioEngineering Creative Inquiry group proposed expanding our previous radiosensitizer work — typically used for cancer treatment — to target and destroy COVID-infected cells with low-dose x-ray radiation and, hopefully, reduce or eliminate the viral load on the patient’s immune system. If successful, the treatment would be as simple as getting a basic imaging x-ray and could improve outcomes for infected patients.

The undergrads’ video pitch (https://youtu.be/KYRCHRW10rQ) won second place and $2500 to do our proof of concept experiments! They also have a lead on private funding. Jaclyn D’Azvanzo is now doing preliminary calculations to make this a reality in the lab. We are excited to see where this leads!

It has been quite a spring semester. I’d like to thank all of our faculty and GTAs for their excellent efforts at moving our courses online! This has been a Herculean effort, and I’m sure that our students appreciate all you have done for them. In the midst of all of the bad news we hear about COVID-19 and the ongoing challenges that come with social distancing, I thought I would update you on a couple of recent items of good news.

First, join me in congratulating Roshani Silwal. After completing her post-doc at Triumf in Canada, she will be moving back closer to Clemson to start a tenure-track position at Appalachian State. She will continue to collaborate with her advisor at Clemson, Prof. Takacs, and mentor her own group of aspiring young physicists.

Speaking of Dr. Takacs’s group, they have been extremely active lately – publishing six papers in the last few months! One of these was published in Phys Rev A and recognized by Kaleidoscope. This paper characterizes the x-ray spectra of highly charged tungsten – an important tool for studying plasmas in fusion reactors.

The high energy astrophysicists at Clemson have been busy as well. A paper led by a Clemson postdoc, Dr. Paliya and including Profs. Ajello and Hartmann. In this paper, they provide the first unambiguous evidence of merging galaxies resulting in AGN accretion and the launching of a relativistic jet. This paper was featured in the AASNova and an image from this paper was chosen as the NASA picture of the week.

One of our newest postdocs, Nuria Torres-Alba, just published a fascinating News and Views article for Nature Astronomy. This article explores the effect of stars on the declaration of relativistic AGN jets.

In addition to this exciting scholarship, our students and faculty continued to be recognized for their excellent work. Dr. Sanabria was selected as a CUSHR fellow. Fanchen Meng was recognized as an Outstanding Graduate Student in Discovery. Hugh Bates was recognized as a Outstanding Graduate Student in Learning. Lea Marcotulli was recognized as an Outstanding Graduate Student in Engagement. Paul “Marston” Copeland was recognized as a Goldwater Fellow.

Finally, join me in welcoming our most recent members of the faculty. Yao Wang and Kasra Sardashti. Dr. Wang is a theorist who is primarily interested in the study of quantum many-body problems. Dr. Sardashti is an experimentalist primarily interested in hybrid superconducting-semiconducting materials as they apply to quantum computing.

These are just a few of the exciting developments that have occurred in our department since we moved all of our classes online and limited access to campus to essential operations. I hope to have much more to report about our graduates as we near the end of the semester.