New director appointed to the Center for Theoretical And Observational Cosmology
We are delighted to announce Donghui Jeong as the next Director of the Center for Theoretical And Observational Cosmology. Donghui is a highly regarded member of the international cosmology community, with a very successful and broad research program that extends to all three Centers of the IGC. We look forward to Donghui’s leadership, and the new ideas he will bring to this next phase of the CTOC!
The largest catalog of gravitational wave events ever assembled has been released by an international collaboration that includes members of the Institute for Gravitation and the Cosmos. Gravitational waves are ripples in space time produced as aftershocks of huge astronomical events, such as the collision of two black holes. Using a global network of detectors, the research team identified 35 gravitational wave events, bringing the total number of observed events to 90 since detection efforts began in 2015.
Supermassive black holes, even if they are not so active, can be major factories of high-energy cosmic particles in the universe, according to a new model proposed by an international research team including Penn State scientists. A paper describing the model that may explain the mysterious connection between observed gamma rays, with relatively low energies measured in the megaelectron volt range, and neutrinos appears September 23, 2021 in the journal Nature Communications.
Two previously invisible galaxies completely hidden by clouds of cosmic gas and dust have been discovered by an international team of researchers. While investigating new data of young, extremely distant galaxies observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers noticed unexpected emissions coming from seemingly empty regions of space. The team, which includes a Penn State scientist, discovered that the radiation was emitted billions of years ago and came from two dust-enshrouded galaxies. This discovery suggests that numerous such galaxies might still be hidden in the early universe, many more than researchers were expecting.
On September 14, 2021, IGC held an event to commemorate Professor Abhay Ashtekar's tenure as the founding Director of the institute which he has led with great vision for almost three decades. During this period, the institute has grown enormously and has had great impact on generations of graduate students, postdoctoral fellows and faculty. Several speakers at the event gave tribute to Abhay's leadership in making IGC an international leader in several areas in Fundamental Physics, Theoretical and Observational Cosmology, and Multi-messenger Astrophysics. The meeting culminated with a short talk by Abhay on his recollections of how the institute was founded, transformations it has undergone and its impact on science and the role played by staff in maintaining a great atmosphere.
Chad Hanna was awarded a $3.4 million grant from the National Science Foundation to help develop software and services for discovering gravitational waves from black holes and neutron stars in real-time in order to facilitate the detection of prompt electromagnetic counterparts.
Specifically, the funds will be used to develop robust signal processing software and the creation of a suite of cyberinfrastructure services that will allow scientists to analyze LIGO data in real time. The goal is to allow scientists to make more discoveries, as well as be able to easily share those discoveries with the scientific community, which ultimately, will improve our understanding of the universe.
“We hope that this grant will benefit the entire scientific community and that, with it, we’ll make robust detections of increasingly more gravitational waves from neutron star mergers, and other signals that might have electromagnetic or neutrino counterparts,” said Hanna.
Hanna’s group leads efforts to detect gravitational waves in real-time to support multi-messenger astrophysics. The group is also involved with developing detection algorithms and software to identify the neutron star mergers in the gravitational wave data and using machine learning to cut through noisy data gathered during the gravitational wave observations. Both are integral to the real-time infrastructure and improvements will help facilitate future LIGO research.
Since the first detection of Gravitational Waves six years ago, the field has literally exploded in multiple directions that include multi-wavelength astronomy and astrophysics, approximation methods in general relativity, numerical relativity, application of Machine Learning to waveform model building, forefront cosmological issues such as the Hubble tension, and nuclear physics issues related to the equation of state of neutron stars and nuclear processes at extreme temperature. Therefore Gravitational Wave Science has emerged as one of the most exciting research areas that now attracts young researchers in large numbers. At the same time this very explosion of the field makes it difficult for young researchers to grasp, even in broad terms, the conceptual and mathematical foundation of the theory of Gravitational Waves since the investigations that built these foundations are rarely discussed in the specific areas these researchers work in everyday. The purpose of these six lectures by Abhay Ashtekar is to fill this gap. The notion of `radiation’ requires global and rather subtle constructions. Because of these subtleties, there was considerable confusion even about the physical reality of gravitational waves in full general relativity for several decades! This confusion was dispelled, thanks to a beautiful interplay between physics and geometry. Every theoretical researcher in the field should be aware of how difficulties associated with coordinate invariance are overcome and fully gauge invariant quantities representing physical observables are extracted. This awareness would provide a broad perspective that can guide their own research. Furthermore, as discussed in the last two lectures, foundational issues can also have concrete applications in addressing `practical issues’.
Light cannot escape from a black hole, but for the first time ever, researchers have observed light from behind a black hole — a scenario that was predicted by Einstein’s theory of General Relativity but never confirmed, until now. In a paper published July 28 in Nature, a team including Niel Brandt reports recordings of X-ray emissions from the far side of a black hole.
The LIGO-Virgo-KAGRA Scientific Collaboration, has announced the discovery of two neutron star-black hole mergers in the data from the third observing run, separated by 10 days on 5 and 15 January 2021. The IGC LIGO group played a crucial role in this new discovery: Both of these mergers were detected as part of real-time gravitational wave processing conducted by members of the IGC LIGO group. LIGO and Virgo detectors have previously observed the merger of dozens of binary black holes and two binary neutron stars. Neutron star-black hole binaries were believed to exist but this is the first time ever astronomers have witnessed such a phenomena. In each case, the neutron star was likely swallowed whole by its black-hole partner without emitting any electromagnetic radiation. The system observed on January 5 had companion masses of 1.5 solar mass for the neutron star and 5.6 solar mass for the black hole, while the one observed on January 15 had masses 1.9 solar mass for the neutron star and 8.7 solar mass for the black hole. Both the systems came from roughly a distance of 300 Mpc. The details of the announcement can be found in the Penn State News Article.
Using cutting-edge machine-learning techniques, a team of Korean-American astrophysicists was able to produce the most detailed map yet of the local Universe that shows what the cosmic web looks like. The team responsible for this breakthrough was led by senior researcher Sungwook E. Hong from the University of Seoul and the Korea Astronomy and Space Science Institute (KASI). He was joined by associate professor Donghui Jeong of the Institute for Gravitation and the Cosmos (IGS) at Penn State, and researchers Ho Seong Hwang and Juhan Kim of Seoul National University and the Korea Institute for Advanced Study (KIAS), respectively.
New director appointed to the Center for Multimessenger Astrophysics
The IGC Internal Advisory Board has unanimously approved the appointment of Professor Miguel Mostafá to the Directorship of the Center for Multimessenger Astrophysics. As per IGC Charter, this will be a renewable 3-year appointment. We all look forward to his leadership to tackle forthcoming opportunities in multi-messenger astrophysics, and his vision to propel the Center to new heights. Welcome to the IGC Board of Directors!
We are also happy to announce that Professor Péter Mészáros has agreed to continue to serve on the IGC Executive committee for a period of 3 years to assure continuity, and to share his wisdom with the current Directors. We are all very grateful to Peter for his leadership over the years which made the Center a pioneer in the international community in many different ways and look forward to his guidance in the coming years.
B. Sathyaprakash is a lead author on the cover story of the May 2021 issue of Nature Physics Reviews on the future of gravitational-wave astronomy. As Abhay Ashtekar explained, “Gravitational-wave observations of binary black-hole and neutron-star mergers by LIGO and Virgo have opened a completely new window on the Universe. The gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy.” Pulsar timing arrays probe the nanohertz to microhertz frequency band to detect gravitational-wave remnants from past mergers of supermassive black holes. The space-based Laser Interferometer Space Antenna will target gravitational-wave sources from microhertz up to hundreds of millihertz and trace the evolution of black holes from the early Universe through the peak of the star formation era. Einstein Telescope and Cosmic Explorer, two future ground-based observatories now under development for the 2030s, are pursuing new technologies to achieve a tenfold increase in sensitivity to study compact object evolution to the beginning of the star formation era. As Sathyaprakash put it, “Gravitational-wave observations provide a new tool for observing the Universe, and future observatories are guaranteed to make discoveries that could transform our understanding of many of the current problems in physics and Astronomy.”
Established in 1980, the award recognizes scholarly or creative excellence represented by a single contribution or a series of contributions around a coherent theme. At LIGO, Hanna developed data analysis pipelines responsible for discovery of gravitational waves generated by the merger of binary black holes and binary neutron stars. The nomination said “Dr. Hanna has proven himself to be a leading scientist who has made forefront contributions to one of the major physics discoveries of modern times”.
Twenty years ago, in an experiment at Brookhaven National Laboratory, physicists detected what seemed to be a discrepancy between measurements of the muon’s magnetic moment — the strength of its magnetic field — and theoretical calculations of what that measurement should be, raising the tantalizing possibility of physical particles or forces as yet undiscovered. The Fermi lab team has just announced that their precise measurement re-enforces this possibility. However, an extensive new calculation of the strength of the muon magnetic moment by an international team led by Zoltan Fodor closes the gap between theory and experimental measurements, bringing it in line with the standard model that has guided particle physics for decades. These seminal results, discussed in numerous conferences over the last 6 months and published in Nature on April 8th, 2021, have reduced the tension between theory and observations significantly, so that the muon’s magnetism is likely not mysterious at all. To achieve this result, instead of relying on experimental data, researchers simulated every aspect of their calculations from the ground up — a task that required massive supercomputing power.
Big Bang, Black Holes, Big Bang and Gravitational Waves now appear as compelling –even obvious– consequences of general relativity. Therefore it may seem surprising that none of these ideas were readily accepted. Not only was there considerable debate, but in fact leading figures were often arguing on what turned out to be the `wrong side’ of history. These developments provide excellent lessons for younger researchers on how science unfolds. Paradigm shifts in science occur when younger researchers have the courage not to accept ideas merely because they are mainstream; patience to systematically develop novel avenues they deeply believe in; and maturity to accept that a variety of factors –not all logical or even science related– can drive or slow down scientific progress.
Besides tests of GR, Gravitational Wave (GW) observations of compact binary mergers also play a unique role for cosmology: They facilitate the measurement of the Hubble constant through a luminosity distance estimate in combination with an independent, electromagnetic redshift measurement from the GW source’s host galaxy. In the light of the tension between the electromagnetic measurements of the Hubble constant from the early and late universe, the GW-assisted method has gained even more importance. While other studies have investigated methods to resolve the Hubble-Lemaître tension with binary neutron stars, IGC researchers Ssohrab Borhanian, Arnab Dhani, Anuradha Gupta, K.G. Arun and B.S. Sathyaprakash demonstrated that there is an observable population of golden dark sirens that could facilitate this resolution in the next five years without direct electromagnetic counterparts or statistical methods. Instead, improved waveform models using higher spherical harmonic modes and planned upgrades to GW detectors will compound together to localize these golden events with high-precision—in distance and on the sky—to uniquely determine their host galaxies in the local universe and consequently measure the Hubble constant to the required precision.”
Professor Wissel and her team in the IGC will search for the highest energy neutrinos using the long duration balloon experiment, PUEO, flown in Antarctica. PUEO is the first and only balloon payload to date selected for the new NASA Pioneers program. As Dr. Thomas H. Zurbuchen, associate administrator of NASA’s Science Mission Directorate of the new program, put it, “These concept studies bring innovative, out-of-the-box thinking to the problem of how to do high-impact astrophysics experiments on a small budget.”
Abhay Ashtekar was interviewed by the American Institute of Physics under their Oral History Program which aims to “offer unique insights into the lives, works, and personalities of modern scientists.” The transcript of this 2 hour long interview is now available at the Niels Bohr Library & Archives. Interview of Abhay Ashtekar by David Zierler.