Amyloids are abnormal proteins that aggregate into fibrils, causing dreadful human diseases. They are strongly implicated in Alzheimer’s disease, a leading cause of dementia in elderly people. Mad cow disease, a neurodegenerative disease, results from infection by prions, which are amyloids that can spread between cells and organisms.  

Despite voluminous research on amyloids and prions, researchers still cannot explain how harmless, normal protein sequences go awry and assume the deadly amyloid shape.

“The initial amyloid ‘nucleation’ is extremely difficult to investigate in animal models,” says Yury Chernoff, a professor in the School of Biological Sciences. “To begin with, initial nucleation is extremely rare. We have no idea where the initial amyloid ‘nucleus’ comes from and what promotes its formation. And then accumulation of an amyloid to detectable levels takes a very long time.”

For these reasons, Chernoff’s Georgia Tech team and collaborators in Germany and Russia (St. Petersburg State University, where Chernoff also directs a research group) turned to yeast as a model to study the human amyloids. They published their findings in the Journal of Biological Chemistry in early January 2018.

According to Chernoff, yeast also form prions, and the initial nucleation of a yeast prion is also rare. “However,” he says, “it is easier to detect prion nucleation in yeast that in humans, because it is possible to analyze large numbers of yeast cells, and because yeast prions cause easily detectable traits.”

The researchers fused mammalian amyloid-forming proteins to the yeast prion-forming protein. They found that the resulting chimeric proteins nucleate an amyloid state in yeast much more frequently than yeast prion-forming protein does on its own. “Because the resulting amyloid nucleus further converts a normal yeast protein,” Chernoff says, “amyloid formation could be detected by the appearance of an easily observable trait, such as growth on specific medium.”

The researchers successfully applied the method to several proteins, including amyloid beta (associated with human Alzheimer’s disease), PrP (associated with mad cow disease), alpha synuclein (associated with Parkinson’s disease), and amylin (associated with type II diabetes).

“This assay opens a wide window to the early stages of dreadful human diseases caused by abnormal protein aggregation,” Chernoff says. “The more we understand how these diseases originate, the better we can develop treatments.”

Beyond revealing how human proteins undergo amyloid nucleation, Chernoff says, the assay will help researchers discover factors affecting amyloid nucleation in cells, find agents that favor the development of diseases, and identify treatments and conditions that can prevent the triggering cause of a disease.

Chernoff’s Georgia Tech team working on this project included current  Ph.D. student Pavithra Chandramowlishwaran and former Ph.D. student Meng Sun, who are co-first authors on the paper, as well as undergraduate researcher Kristin Casey and research scientist Andrey Romanyuk.

Figure Caption
Growth of the specially designed yeast strain on a specific medium enables researchers to detect nucleation of disease-related fibrils by human amyloid beta protein, associated with Alzheimer’s disease.

This work was supported by grants from the National Institute of Aging, NIH (through Emory University’s Alzheimer’s Disease Research Center) and the Creutzfeldt-Jakob Disease Foundation, as well as the Russian Science Foundation and the Russian Foundation for Basic Research (to the St. Petersburg group).  

There are vast, invisible, churning communities of organisms living all around and inside every living thing on Earth, overwhelmingly outnumbering us. We can’t see them, but their influence is profound – their processes can connect us, sustain us, protect us, or destroy us.

They are the bacteria, fungi, viruses and other microbes that comprise the world’s many microbiomes, which were the focus of this year’s Suddath Symposium (Jan. 30-31) at the Petit Institute for Bioengineering and Bioscience at the Georgia Institute of Technology.

“A microbiome is, generally, the collection of interacting microbes in a particular location, and the locations vary in scale,” said Brian Hammer, associate professor in Georgia Tech’s School of Biological Sciences and a Petit Institute researcher.

Hammer and Frank Stewart, also a Petit Institute researcher, were co-chairs of what may have been the best-attended Suddath Symposium in the event’s 26-year history. Every session, for all 12 speakers, featured standing-room crowds in the Suddath Room, in addition to people watching the simulcast in the Petit Institute atrium, and across campus – symposium seating was sold out before the early registration deadline, in early January.

It was an opportunity to showcase work being done at Georgia Tech and across the country and the attendance reflected growing and diverse interest in microbial science.

“Over the last five years or so, the importance of and interest in microbial science at Georgia Tech has really increased,” said Stewart, associate professor in the School of Biological Sciences. “We’ve added faculty, resources, the field is growing. All of those things are coming together right now.”

Microbes Are Popular

The topic of microbiomes has infiltrated public consciousness – this is a popular subject, Hammer said. “You’ll see microbiome research in high profile journals every week now, it’s one of those things that’s made it into the mainstream. You go home and your parents are starting to ask about these things. Everybody seems to care about their microbiomes, and we’re all trying to figure out how these things work, and we’re right at the forefront here at Tech.”

The interest, like the science, is deep and wide. For instance, there’s a lot of research into the microbiomes of the human gut and lungs, much of it fueled by initiatives like the ongoing NIH Human Microbiome Project. Meanwhile, there’s the Earth Microbiome Project, across ecologies and habitats and environments.

“There are so many scales, some more narrowly focused, some broader, and we tried to reflect that range of interest in this symposium,” Hammer said.

The symposium, which was entitled, “The Chemical Ecology of Microbiome Interactions,” presented research unified by the goal of understanding microbe-microbe and microbe-host interactions, spanning diverse specialties, including biomedicine and genomics, chemical ecology, biogeochemical cycling, environmental science, biophysics, and the evolution of microbial interactions, including those involving pathogens.

Two Days of Brain Candy

Accordingly, the symposium drew speakers who are among the nation’s thought leaders in both environmental and human microbiome research (including several from Georgia Tech), presenting their research over, “two days of brain candy,” which is how Bonnie Bassler of Princeton University described the gathering.

“It was a thrill,” said Bassler. “There was such a diverse range of science discussed, and every speaker still made sure that everyone understood their talks, which is remarkable when you consider the range of topics.”

As tradition demands, the two-day symposium began with a research presentation from the grad student who was named the Suddath Award winner during the Petit Institute holiday party back in December. These presentations often have little connection with the symposium theme. This year, David Hanna, a doctoral candidate in the lab of Petit Institute researcher Amit Reddi, presented his research, entitled, “Shedding Light on Heme Signaling Networks with Heme Sensors and Quantitative Mass Spectrometry.”

Then it was all about the many interactions of very tiny things, the contact and communication between microbes. Bassler, who was Hammer’s postdoctoral advisor, led off the microbiome presentations on Tuesday with a talk entitled, "Bacterial Quorum Sensing and its Control."

Bassler is a wet lab microbiologist, said Hammer, and she was followed by a who’s who list of microbial researchers from beyond the Georgia Tech campus. On Tuesday, Jon Clardy, a chemical biologist from Harvard University, spoke on, “Microbiomes, Chemical Ecology, and Animal Development.” Seth Bordenstein, a classically trained evolutionary biologist from Vanderbilt University, delivered a presentation that asked, “How do Microbes Form Relationships With Animals?”

Tuesday’s sessions ended with a presentation from Mary Voytek, a microbiologist who heads up NASA’s Astrobiology Program, that really took the subject to far out places – like, deep onto our solar system, to the moons of Jupiter and Saturn and the search for life beyond Earth, with a talk entitled, “How can Microbiomes Serve as a Model for the Emergence and Early Evolution of Life.”

“Mary is very interested in how microbial systems that we can study on Earth might inform our understanding of how life might look on other planets,” said Stewart.

Mary Ann Moran from the University of Georgia led off Wednesday with her talk, “Chemical Currencies of the Ocean Microbiome,” followed by Tim Read from the Emory School of Medicine, and his presentation, “Pathogen Genomic Variation in the Context of a Human Microbiome.”

Rebecca Vega Thurber from Oregon State University who has focused much of her research on coral systems in the oceans, delivered a presentation entitled, “The Roles of Environmental Nitrogen in Coral Microbiome Dysbiosis and Disease.”

Karine Gibbs, the second speaker from Harvard and the final presenter from outside Georgia Tech, stressed the importance of contact-dependent interactions in her talk, “Know Thy Neighbors: The Influences of Self/Non-Self Recognition on the Collective Migration of a Bacterial Population.”

Gibbs, said Hammer, “was one of the pioneers that figured out bacteria have ways to discriminate self from non-self, and use that information to organize microbial communities.”

Civics at the microscale? No, not quite. But Gibbs, who has observed wholesale warfare between microbial armies, is working with her lab to develop models that clarify the differences between lethal and non-lethal contact dependent interactions. “The predominant theory in microbiology is that all of these interactions would be about death,” Gibbs said. “Our evidence shows that’s not the case.”

Tech Researchers Take Stage

A quartet of Georgia Tech researchers also took research center stage – or, center projection screen – during the two-day symposium.

Neha Garg, assistant professor in the School of Chemistry and Biochemistry, gave a talk on Tuesday entitled, “Chemical Chatter between the Cystic Fibrosis-associated Microbiome.” She’s one of the new microbiology-focused faculty members at Georgia Tech, arriving last year following her postdoctoral work at the University of California-San Diego.

“She’s studying the lungs of people with cystic fibrosis, trying to understand the nature of the chemical compounds that organisms use to interact with other micro-organisms, or a host,” Hammer said.

While most researchers engaged in this area would typically remove the organisms that cause a bacterial infection in a cystic fibrosis patient, and study them in a petri dish, Garg has developed a method to study all of the bacterial chemicals in an infected lung, based on their DNA.

“She’s doing it spatially, building a three-dimensional map of the infected lung,” Hammer said. “She’s taking the research to the next level.”

The other three Georgia Tech researchers were part of the Wednesday lineup.

Joel Kostka, professor and associate chair of research in the School of Biological Sciences, delivered a talk called, “The Sphagnum Phytobiome: Ecosystem Engineers of the Global Carbon Cycle.”

“Joel is one of the leaders in thinking about microbes in real world environmental settings, which are often quite diverse,” Stewart said. “He studies systems ranging from the Gulf of Mexico to the Arctic. He combines a wide range of approaches in thinking about the system holistically.”

Petit Institute researcher James Gumbart, from the School of Physics, talked about, “Molecular Mechanisms of Nutrient Acquisition and Virulence Revealed by Molecular Dynamics Simulations.”

Gumbart is one of that breed of physicist who calls himself a ‘squishy,’ according to Hammer. “They work in ‘squishy physics.’ His expertise is in using mathematical simulations to look at these molecular machines that bacteria use to interact with one another,” Hammer said.

The last speaker of the symposium was Marvin Whiteley, a professor in the School of Biology and the Emory School of Medicine, whose talk was entitled, “Biogeography of in vivo Biofilms.”

Like Hammer, Whiteley was trained as a classical bacterial geneticist, “which is, you take an organism and dissect it at the level of DNA to figure out how it’s capable of accomplishing certain tasks,” Hammer said. “Marvin has transitioned in the last 10 to 15 years to focusing on the organism that causes disease in cystic fibrosis patients.”

At some point, Whiteley’s work in cystic fibrosis as a geneticist would ideally dovetail with Garg’s work in the same disease as a chemist. That isn’t by accident.

“That’s an example of complementary expertise that Georgia Tech is bringing together,” Hammer said. And it gets to the heart of the reason for this topic at this symposium at this time. “We’ve reached a stage now where these interactions are allowing us to move the science forward in ways we weren’t able to at Georgia Tech until fairly recently. We think we’re at a turning point.”

Microbiology, the study of the smallest living organisms, is playing an increasingly expanded role in the further understanding of life, and how it evolves, thrives, or doesn’t. As she left to catch a plane back to Boston, Gibbs thought about the two days of multifaceted brain candy, and its impact on her.

“This was an amazing community of science,” she said. “The breadth of it! This was a nice reflection of the dynamics that are in place right now in microbiology, and I think it helped illustrate how microbes, whether we like it or not, are integral to so many aspects of our lives and our living planet.”

Basic research by Georgia Tech and KAUST researchers to understand the electronic behavior of perovskites is the cover feature of the Dec. 11, 2018, issue of Chemistry of Materials. The work is by School of Chemistry and Biochemistry Professor Jean-Luc Brédas and collaborators led by Omar Mohammed at King Abdullah University of Science and Technology (KAUST), in Saudi Arabia.

“Layer-Dependent Rashba Band Splitting in 2D Hybrid Perovskites” was published online in October. It details fundamental studies to understand the spin-orbit coupling in perovskites due to the presence of heavy atoms.

Hybrid organic-inorganic perovskites have attracted attention because of their promising properties for optoelectronic devices such as solar cells, light-emitting diodes, photodetectors, and scintillators. The work advances the development of perovskites for spintronic applications.

From July 2014 to 2016, while on leave from Georgia Tech, Brédas served as Distinguished Professor of Materials Science and Engineering at KAUST, as well as director of the KAUST Solar Center. 

Editor's Note. This story was published originally by the Scheller School of Business on Dec. 12, 2018. It has been adapted for the College of Sciences.

Georgia Tech’s Carbon Reduction Challenge (CRC), a program that helps students design and implement large-scale projects to save energy, received two first-place awards at the 2019 Reimagine Education Conference & Awards in San Francisco. The international competition spotlights innovative initiatives aimed at enhancing student learning outcomes and employability across five disciplines and 17 categories.

The CRC is co-directed by College of Sciences Professor and Georgia Tech Global Change Program Director Kim Cobb and Scheller College of Business Professor and Ray C. Anderson Center for Sustainable Business (“Center”) Faculty Director Beril Toktay. The CRC pairs teams of undergraduate students with a diverse set of local organizations to identify opportunities for large-scale energy efficiency gains that will save greenhouse gas emissions and deliver significant energy cost savings.

This year’s competition received 1,184 project submissions from 39 countries. Submissions were evaluated by 160 international judges. The CRC won first place in the “Sustainability” category as well as first place in the “Natural Sciences” discipline. It was also selected as one of ten finalists to advance to the Grand Finale.

The CRC began as a class project that Cobb initiated in 2007. In 2017, it was expanded to include co-op and internship students across Georgia Tech in collaboration with Toktay and with funding from the Ray C. Anderson Foundation’s NextGen Committee and the Scheller College of Business Dean’s Innovation Fund. It also became an affiliated project of the Georgia Tech Serve-Learn-Sustain initiative.

In 2018, the CRC expanded its reach by inviting Emory University students to participate as well. The CRC became an official activity of the Georgia Climate Project, a statewide, multi-year effort to improve understanding of climate impacts and solutions across the state and to encourage Georgia residents to take effective, science-based climate action. CRC projects launched since 2017 have already resulted in over two million pounds of avoided CO2 emissions and are projected to deliver hundreds of thousands of dollars in avoided energy costs to partner organizations. Finalists present their projects at a public poster expo, and judges score projects to decide the winners who receive cash prizes thanks to a gift from the Sheth Family Foundation.

Reimagine Education is sponsored in part by the Alfred West Jr. Learning Lab of the Wharton School of Business at the University of Pennsylvania.

They chose to study at Georgia Tech. Once here, they discovered that the academic rigor and leading-edge science research they’ve heard so much about is true – and demands their best. Some found Tech overwhelming at times, but all succeeded.

Whether their journey started in Georgia, in another state, or in another country, our graduates discovered something else in the heart of Atlanta: the Tech experience, which involves forming new and lasting friendships, stretching out of their comfort zones, becoming part of the Georgia Tech family, and more.

Meet five graduating students from the College of Sciences. Headed in various directions—in the U.S. or overseas—each feels well-prepared for the next step in their professional life because of their Georgia Tech education. Georgia Tech helped them achieve their goals and join a larger community, one that values friendship and collaboration, as well as scholarship.

Meet five of the College of Sciences' Fall 2018 graduates:

• Bharath Hebbe Madhusudhana, M.S. in Mathematics, Ph.D. in Physics
• Lucas Liuzzo, Ph.D. in Earth and Atmospheric Sciences
• Katherine Reuben, B.S. in Psychology
• Sarthak Sharma, M.S. in Bioinformatics
• Avery Zickar, B.S. in Biochemistry with a minor in Biology

Congratulations, Fall 2018 graduates! We can't wait to see what comes next for you! The world awaits you. 

Georgia Tech researchers have expanded the synthetic value of the common building block dihydroxyfumaric acid (DHF). The diester derivative of DHF has been used exclusively as an electron-seeking (electrophilic) reagent in organic synthesis.

Research by George Ward, in the School of Chemistry and Biochemistry, has expanded the scope of DHF chemistry by using it as a nucleus-seeking (nucleophilic) player in organic reactions in the presence of bases. Ward is a Ph.D. student of Stefan France, an associate professor of chemistry and member of the Parker H. Petit Institute of Bioengineering and Bioscience. They collaborated with Charles Liotta, professor of chemistry, and Ramanarayanan Krishnamurthy, of The Scripps Research Institute, in La Jolla, California. 

The newly unleashed reactivity of the well-known reagent opens alternative routes to complex building blocks needed to prepare pharmaceutically relevant compounds. The researchers demonstrated the versatility of nucleophilic DHF in the synthesis of C-veratroylglycol – an expensive, bioactive naturally occurring compound – in one step from vanillin.

 The work was published online in September in The Journal of Organic Chemistry and is featured in the journal’s December 2018 issue.

The work was supported by the National Science Foundation and the NASA Astrobiology Program under the NSF Center for Chemical Evolution (CHE-1504217).

Nemo, the adorable clownfish in the movie Finding Nemo, rubs himself all over the anemone he lives in to keep it from stinging and eating him like it does most fish. That rubbing leads the makeup of microbes covering the clownfish to change, according to a new study.

Having bacterial cooties in common with anemones may help the clownfish cozily nest in anemones’ venomous tentacles, a weird symbiosis that life scientists - including now a team from the Georgia Institute of Technology - have tried for decades to figure out. The marine researchers studied how populations of microbes shifted on clownfish who mixed and mingled with fish-killing anemones.

“It’s the iconic mutualism between a host and a partner, and we knew that microbes are on every surface of each animal,” said Frank Stewart, an associate professor in Georgia Tech’s School of Biological Sciences. “In this particular mutualism, these surfaces are covered with stuff that microbes love to eat: mucus.”

Swabbing mucus 

Clownfish and anemones swap lots of mucus when they rub. So, the researchers brought clownfish and anemones together and analyzed the microbes in the mucus covering the fish when they were hosted by anemones and when they weren’t.

“Their microbiome changed,” said Zoe Pratte, a postdoctoral researcher in Stewart’s lab and first author of the new study. “Two bacteria that we tracked in particular multiplied with contact with anemones.”

“On top of that, there were sweeping changes,” said Stewart, the study’s principal investigator. “If you looked at the total assemblages of microbes, they looked quite different on a clownfish that was hosted by an anemone and on one that was not.” 

The researchers chased 12 clownfish in six fish tanks for eight weeks to swab their mucus and identify microbes through gene sequencing. They published their results in the journal Coral Reefs. The research was funded by the Simons Foundation. 

Questions and Answers

Here are some questions and answers about the experiment, which produced some amusing anecdotes, along with fascinating facts about anemones and clownfish. For example, fish peeing on anemones makes the latter stronger. Clownfish change genders. And it was especially hard to catch one fish the researchers named “Houdini.”

Does this solve the mystery about this strange symbiosis?

No, but it’s a new approach to the clownfish-anemone conundrum.

“It’s a first step that’s asking the question, ‘Is there part of the microbial relationship that changes?’” Stewart said. The study delivered the answer on the clownfish side, which was “yes.”

An earlier hypothesis on the conundrum held that clownfish mucus was too thick to sting through. Current ideas consider that mucus swapping also covers the clownfish with anemone antigens, i.e. its own immune proteins, or that fish and fish killer may be exchanging chemical messages.

“The anemone may recognize some chemical on the clownfish that keeps it from stinging,” Stewart said. “And that could involve microbes. Microbes are great chemists.”

Going forward, the researchers want to analyze mucus chemistry. They also don’t yet know to what extent the microbes on the fish change because of bacteria the fish gleans from the anemone. It’s possible the fish mucus microbiome just develops differently on the fish due to the contact.

What do anemones normally do to fish?

Kill them and eat them. 

“The anemone evolved to kill fish. It shoots little poison darts into the skin of a fish to kill it then pull it into its mouth,” Stewart said. “The clownfish gets away with living right in that.”

By the way, the tentacles are not harmful to people.

“If you touch an anemone, it feels like they’re sucking on your finger,” Pratte said. “Their little harpoons feel like they’re sticking to you. It doesn’t hurt.”

What do the anemones and clownfish get out of the relationship?

For starters, they protect each other from potential prey. But there’s lots more. Some clownfish even change genders by living in an anemone.

“When they start being hosted, the fish make a big developmental switch,” Stewart said. “The first fish in a group that establishes itself in an anemone in the wild transitions from male to female, grows much bigger and becomes the dominant member of the group.”

She is then the sole female in a school of smaller male mates.

Anemones appear to grow larger and healthier, partly because the clownfish urinate on them.

“When the fish pee, algae in the anemone take up the nitrogen then secrete sugars that feed the anemone and make it grow,” Pratte said. “Sometimes the fish drop their food, and it falls into the anemone which eats it.”

Any fun anecdotes from this experiment? 

Plenty: It was scientifically straightforward but laborious to carry out, partly because the researchers were taking meticulous care of the fish at the same time.

“You have to get fish and anemones to pair up, and the fish can host in other places, like nooks in the rock,” Pratte said.

“Clownfish are smarter than other fish, so they’re harder to catch, especially when we want to minimize stress on the animals,” said Alicia Caughman, an undergraduate research assistant in the School of Biological Science’s Fast Track to Research program. “We named one fish ‘Houdini.’ He could wiggle between nets and tight spaces and usually outsmart whoever was trying to catch him."

“We also had 'Bubbles,' who blew a lot of bubbles, 'Biggie' and 'Smalls,' 'Broad,' 'Sheila,' 'Earl,' and 'Flounder,' who liked to flounder (flop around),” Pratte said. Clownfish have differing sizes and details in their stripes, which allow people to tell them apart.

The anemone side of the microbial question may prove harder to answer because for all Houdini's wiles, anemones, which are squishy non-vertebrates, are even more trying. They can squeeze into uncomfortable niches or plug up the aquarium drainage, and they also have temperamental microbiomes.

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Also READ: When boy fish build castles to impress girl fish, boy genes get a rise

Also READ: Teeny bacteria do a dirty job to clean a huge fish tank

The following researchers coauthored the paper: Nastassia V. Patin, Mary E. McWhirt and Darren J. Parris, all of Georgia Tech. DOI: 10.1007/s00338-018-01750-z. The research was funded by the Simons Foundation (award 346253). Any findings, opinions or recommendations are those of the authors and not necessarily of the Simons Foundation.

Media relations assistance: Ben Brumfield (404) 660-1408, ben.brumfield@comm.gatech.edu

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Writer: Ben Brumfield

Major Scientific Society's Decision to Honor Anti-Environment Senator Sparks Outcry
Earther
November 6, 2018

Members of the American Geophysical Union (AGU) are up in arms over the organization’s decision to give a prestigious award to Senator Cory Gardner, who in 2015 voted against ameasure declaring human activity “significantly contributes to climate change.”

The School of Earth and Atmospheric Sciences' Kim Cobb is leading the charge to challenge the AGU's decision. "It really becomes an issue of integrity," she told Earther.

"We Had to Go": The Threat of Worse Hurricanes Forced These Panama City Residents Out
VICE News
December 5, 2018

After Hurricane Michael, residents of the Panhandle say the prospect of even more intense storms, and the subsequently difficult recoveries, made them want to leave. Hurricane Michael slammed the Gulf Coast with $30 billion in combined economic losses, including storm damage. And it resulted in the loss of 9,300 jobs. 

“This is going to take time, and it’s not going to be easy to come to solutions here,” said Kim Cobb of the School of Earth and Atmospheric Sciences, "Slowly but surely Mother Nature is going to remind us that our entire economy is on the line.”

In February 2016, astronomers shook the scientific world with the announcement that they had observed gravitational waves from a cataclysmic event in the distant universe — the collision of two massive black holes, celestial objects so dense that not even light can escape from them. 

Gravitational waves, hard-to-see ripples in the fabric of space-time, had been predicted by Albert Einstein’s General Theory of Relativity in 1915. These gravitational waves carry information about their origins, potentially offering a new way to observe the cosmos. Three years ago, however, researchers didn’t know if this first observation was merely an anomaly or part of a widespread phenomenon that could teach us about the population of black holes in the universe.

A dozen Georgia Tech faculty members, postdoctoral researchers, and students participated with hundreds of other researchers in the National Science Foundation-sponsored LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration that reported the first gravitational waves. After the announcement, the work continued, and scientists from around the world have now observed 10 black hole collisions and a merger of two binary neutron stars using LIGO and the European-based Virgo gravitational wave detector. 

Catalog of Coalescing Cosmic Objects

The records of these cataclysmic cosmic events, including four black hole observations disclosed for the first time, have been collected into a catalog released December 1 at the Gravitational Wave Physics and Astronomy Workshop held in College Park, Maryland. Production of the catalog suggests that gravitational wave astronomy will indeed offer astronomers a new way to view the secrets of the universe.

“The individual black hole detections previously announced allow us to confirm, after many years of searching, that gravitational wave astronomy is a feasible endeavor,” said James Alexander Clark, a research scientist in Georgia Tech’s Center for Relativistic Astrophysics (CRA) in the School of Physics and a member of the LIGO collaboration. “We now know that pairs of massive black holes exist and collide frequently enough for us to detect gravitational waves within a human lifetime. We also know that the instruments and analysis procedures we use are capable of detecting and characterizing gravitational wave sources and we have been able to start probing some basic features of the theory of general relativity.”

Astronomers do not have the luxury of repeating laboratory experiments to build confidence in their findings, Clark pointed out. “Instead, we rely on observing large samples of objects and phenomena spread throughout the universe. By building a ‘census’ of this population, we are rapidly learning more about how common these objects are, what their general properties are like, and about the diversity of black holes in the universe.”

Expanding the Observations

That census should expand more rapidly starting in April 2019 when LIGO begins its next observing run. The two instruments, one in Livingston, Louisiana, and the other in Hanford, Washington, are shut down periodically for upgrades to improve sensitivity. “By observing a larger sample of binary black hole sources, we are more likely to find systems with more extreme configurations that allow more stringent tests of our models — and of general relativity,” Clark added.

The new Gravitational Wave Catalog shows that gravitational waves from powerful cosmic phenomena arrive at the Earth almost once every 15 days of observation, noted Karan Jani, a postdoctoral fellow in the CRA and also a member of the LIGO collaboration. “Future releases will provide much stronger tests of Einstein’s theory of gravity, and help provide a better understanding of how black holes are formed in the universe.”

Data collected on the 10 black hole mergers describe objects that are as much as 100 times more massive than our own sun. Among the reports is a July 29, 2017, signal that represents the most distant, most energetic, and most massive black hole collision detected so far. That collision happened about five billion years ago — even before the birth of our sun — and released an amount of energy equivalent to converting almost five solar masses to gravitational radiation.

What We Learn from Black Hole Observations

Black holes are among the few objects in the universe massive and dense enough to produce gravitational waves that can be measured, said Sudarshan Ghonge, a CRA graduate student and also a member of the collaboration. But those measurements can be quite worthwhile.

“These waves have signatures that depend on the properties of the black holes from which they originated,” he said. “By measuring these waves, we can infer the masses, spin, sky location, and distance from us. It’s similar to how you can listen to a sound and roughly figure out where it’s coming from, how far away it is, and what’s causing it.”

LIGO works by observing infinitesimally small changes caused by gravitational waves passing through the Earth. The changes affect laser beams traveling through twin four-kilometer arms of the L-shaped observatories. The Hanford and Livingston facilities, separated by 1,865 miles, confirm the observations, as both facilities should detect the waves. Additional information comes from the Virgo facility in Italy.

Observing Runs Produce New Records 

From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational wave events reported December 1. The new events are known as GW170729, GW170809, GW170818 and GW170823, in reference to the dates they were detected.

GW170814 was the first binary black hole merger measured by the three-detector network made possible by collaboration between LIGO and Virgo, and allowed for the first tests of gravitational wave polarization, which is analogous to light polarization. 

One of the new events, GW170818, detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next-best localized gravitational wave source after the GW170817 neutron star merger.

The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were observed from the merger of a binary neutron star system. What's more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

Advancing Gravitational Wave Observation

“The release of four additional binary black hole mergers further informs us of the nature of the population of these binary systems in the universe and better constrains the event rate for these types of events,” said Caltech’s Albert Lazzarini, deputy director of the LIGO Laboratory.

"In just one year, LIGO and Virgo working together have dramatically advanced gravitational wave science, and the rate of discovery suggests the most spectacular findings are yet to come,” said Denise Caldwell, director of NSF's Division of Physics. "The accomplishments of NSF's LIGO and its international partners are a source of pride for the agency, and we expect even greater advances as LIGO's sensitivity becomes better and better in the coming year."

"The next observing run, starting in Spring 2019, should yield many more gravitational wave candidates, and the science the community can accomplish will grow accordingly,” said David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “It’s an incredibly exciting time.” 

“It is gratifying to see the new capabilities that become available through the addition of Advanced Virgo to the global network,” said Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is the spokesperson for the Virgo Collaboration. “Our greatly improved pointing precision will allow astronomers to rapidly find any other cosmic messengers emitted by the gravitational wave sources.” The enhanced pointing capability of the LIGO-Virgo network is made possible by exploiting the time delays of the signal arrival at the different sites and the so-called antenna patterns of the interferometers.

The scientific papers describing these new findings, which are being initially published on the arXiv repository of electronic preprints, present detailed information in the form of a catalog of all the gravitational wave detections and candidate events of the two observing runs as well as describing the characteristics of the merging black hole population. Most notably, we find that almost all black holes formed from stars are lighter than 45 times the mass of the sun. Thanks to more advanced data processing and better calibration of the instruments, the accuracy of the astrophysical parameters of the previously announced events increased considerably.  

Added Georgia Tech professor Laura Cadonati, deputy spokesperson for the LIGO Scientific Collaboration, “These new discoveries were only made possible through the tireless and carefully coordinated work of the detector commissioners at all three observatories, and the scientists around the world responsible for data quality and cleaning, searching for buried signals, and parameter estimation for each candidate — each a scientific specialty requiring enormous expertise and experience.”

About LIGO and Virgo

LIGO is funded by NSF and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the United Kingdom (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration. A list of additional partners is available at http://ligo.org/partners.php.

The Virgo Collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique in France; 11 from the Istituto Nazionale di Fisica Nucleare in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN and Nikhef. A list of the Virgo Collaboration can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at www.virgo-gw.eu.

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Writer: LIGO Scientific Collaboration / John Toon