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Tag: Gravitational waves
From AAS NOVA: “Could We Detect the Merger of Stellar-Mass and Supermassive Black Holes?”
An illustration of the warping of spacetime around a stellar-mass black hole that is orbiting a supermassive black hole. [NASA]
We’ve detected gravitational waves from mergers of compact objects like stellar-mass black holes, and we’ve found promising evidence for the spacetime disturbances from binary supermassive black holes. But what about when these two mass scales meet — could we detect the merger of a stellar-mass black hole with a supermassive black hole?
Stellar-Mass and Supermassive
Many galaxies host a central supermassive black hole, which may have the opportunity to consume stellar-mass black holes from its surroundings. Based on theoretical calculations, it’s likely fairly rare for a stellar-mass black hole to merge with a supermassive black hole, with each galaxy experiencing just a few dozen of these events every billion years.
Infographic showing the typical frequency ranges of the gravitational waves produced by different sources. Credit: ESA.
Surprisingly, adding another supermassive black hole into the mix may greatly increase the odds of such an interaction. When stellar-mass black holes encounter a supermassive black hole binary, the likelihood of a merger is boosted up to hundreds of thousands of events per galaxy per billion years. The gravitational waves from this type of merger are too low frequency to be detected with our current observatories, but a recent research article has explored the possibility of detecting gravitational waves from these encounters in the not-too-distant future.
Simulating Gravitational Waves
Smadar Naoz (University of California-Los Angeles) and Zoltán Haiman (Columbia University) simulated the gravitational waves that would result from a stellar-mass black hole spiraling in to merge with one member of a supermassive black hole binary. This type of merger is called an extreme-mass-ratio inspiral. First, Naoz and Haiman estimated the number of extreme-mass-ratio inspirals as a function of the mass of the black holes in the binary system. Perhaps counterintuitively, stellar-mass black holes are much more likely to merge with the less massive black hole in a binary system, thanks to gravitational perturbations.
Predicted gravitational wave amplitude as a function of frequency for resolved (purple lines) and unresolved (grey lines) systems, compared to LISA’s estimated sensitivity. [Naoz & Haiman 2023]
The team then calculated the amplitude of the gravitational waves produced in each merger and found that future observatories should be able to detect these events. They focused on the Laser Interferometer Space Antenna (LISA) — a proposed space-based gravitational wave observatory that would consist of three spacecraft trailing Earth in its orbit — which should detect individual extreme-mass-ratio inspirals as well as a background signal composed of thousands of events too faint to be detected individually.
During the proposed 4-year LISA mission, the observatory could detect hundreds of individual sources.
Observing gravitational waves from a stellar-mass black hole as it spirals toward a supermassive black hole can help us understand many aspects of how supermassive black holes grow and merge. In particular, these observations may help us put a number on how many companions a supermassive black hole is likely to have; do these behemoths mostly fly solo, or are pairs, triples, or quartets more likely? Hopefully, it’s just a matter of time before LISA is in place in its berth in space — the planned launch date is 2037 — and ready to open a new window onto gravitational waves.
The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.
The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.
Adopted June 7, 2009
The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.
The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.
In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.
The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.
A European team involving the Max Planck Institutes for Gravitational Physics and Radio Astronomy, together with Indian and Japanese astronomers, has discovered the first evidence of a gravitational wave background originating from the formation and evolution of the universe and its galaxies. The team used the European Pulsar Timing Array and the Indian Pulsar Timing Array, which comprise six of the most sensitive radio telescopes in the world. With these instruments, the researchers observed a previously unexplored window in the gravitational wave spectrum at wavelengths comparable to the distances between stars in the Milky Way over a period of 25 years. The target of the observations was not the gravitational waves directly, but 25 pulsar stars distributed in the Milky Way, which form the largest gravitational-wave detector to date. The data give hope for new insights into the formation and development of our universe and its galaxies.
A trembling of space-time
Gravitational waves propagate at the speed of light and cause a periodic stretching and squeezing of the narrow web of space and time.
The most likely origin of the background of gravitational waves at wavelengths of a few light years is the cosmic distribution of binary black-hole systems with millions to billions of solar masses. These were formed when galaxies frequently collided and merged in the early universe. In that process, supermassive black holes from the centres of these galaxies approached each other to form close binaries.
Gravitational wave detectors on Earth have been developed to measure the effects of shorter waves that occur when two stellar-mass black holes orbit close together and eventually merge.
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Long gravitational waves from the active early universe cannot be measured directly from Earth, but they do change the clock frequency of pulsar stars.
Pulsars are stellar remnants that, like cosmic lighthouses, emit radio light in two opposite directions while rotating around an axis. If the cone of radio beams passes over the Earth, the pulsar can be measured by its periodic radio pulses. “Pulsars are excellent natural clocks. We use the incredible regularity of their signals to search for minute changes in their ticking to detect the subtle stretching and squeezing of space-time by gravitational waves originating from the distant Universe”, says David Champion of the Max Planck Institute for Radio Astronomy. Here, results are based on the subset of 25 pulsars chosen to give the greatest sensitivity to a gravitational-wave background.
The results are based on decades of coordinated observing campaigns with the six of the largest radio telescopes in Europe and India. These are the 100-m radio telescope in Effelsberg (Germany), the Westerbork Synthesis Radio Telescope (Netherlands), the Lovell Telescope at Jodrell Bank Observatory (United Kingdom), the Sardinia Radio Telescope (Italy), the Nançay Radio Telescope (France) and the Giant Metrewave Radio Telescope in India.
“Analyzing the data from pulsar timing arrays is complicated by the fact that Pulsar Timing Arrays use astrophysical objects as detectors“, says Jonathan Gair from the Max Planck Institute for Gravitational Physics. While you can manipulate and optimize a detector on Earth, this is not possible with the rapidly rotating stars. To detect gravitational waves as a weak signature in pulsar timing signals, researchers need to understand precisely the periodic radio light they receive from pulsars and also the inaccuracies in their clock frequency. They also make use of their long-standing knowledge of the properties of gravitational waves, which propagate in space and influence pulsars that are located inside that space. Thus, it is to be expected that changes in the timing of the observed pulsars are interlinked in a certain way. Whether this correlation becomes visible in the data is a question of statistics.
Certain or uncertain?
According to the gold-standard of physics, the measured signal, i.e. the pattern according to which the clocks of all observed pulsar clocks deviate from the norm, is only reliably proven if it is not a random signal with a probability of 99.99997 percent. A signal such as is to be expected should therefore occur purely by chance only once in a million measurements. Since this can hardly be tested in practice, the scientists simulate the standard recurrent signals of all pulsars on the computer for the specific case that no gravitational waves are present to change these signals. The measurements of the European Pulsar Timing Array – as well as those of the other international collaborations – do not yet meet that gold-standard. To reach final certainty, the teams plan to merge their data sets into a single, more comprehensive data set under the umbrella of the International Pulsar Timing Array.
This would include observations from more than 100 pulsars, with 13 radio telescopes, and could be sufficient to provide irrefutable proof in the future of the existence of a gravitational wave background – a witness to an important phase in the evolution of the universe.
By combining the already existing radio astronomy faculty of the University of Bonn led by Otto Hachenberg with the new MPG institute the MPG Institute for Radio Astronomy was formed. In 1972 the 100-m radio telescope in Effelsberg was opened. The institute building was enlarged in 1983 and 2002.
The institute was founded in 1966 by the MPG Society as the “MPG Institut für Radioastronomie (MPIfR) (DE)”.
The foundation of the institute was closely linked to plans in the German astronomical community to construct a competitive large radio telescope in (then) West Germany. In 1964, Professors Friedrich Becker, Wolfgang Priester and Otto Hachenberg of the Astronomische Institute der Universität Bonn submitted a proposal to the Stiftung Volkswagenwerk for the construction of a large fully steerable radio telescope.
In the same year the Stiftung Volkswagenwerk approved the funding of the telescope project but with the condition that an organization should be found, which would guarantee the operations. It was clear that the operation of such a large instrument was well beyond the possibilities of a single university institute.
Already in 1965 the MPG Society decided in principle to found the MPG Institut für Radioastronomie. Eventually, after a series of discussions, the institute was officially founded in 1966.
The MPG Institute for Gravitational Physics (Albert Einstein Institute) is a Max Planck Institute whose research is aimed at investigating Albert Einstein’s Theory of General Relativity and beyond: Mathematics; quantum gravity; astrophysical relativity; and gravitational-wave astronomy. The Institute was founded in 1995 and is located in the Potsdam Science Park in Golm, Potsdam and in Hannover where it is closely related to the Leibniz University Hannover [Gottfried Wilhelm Leibniz Universität Hannover](DE). The Potsdam part of the institute is organized in three research departments, while the Hannover part has two departments. Both parts of the institute host a number of independent research groups.
The institute conducts fundamental research in Mathematics; data analysis; Astrophysics and Theoretical Physics; as well as research in Laser Physics; vacuum technology; vibration isolation; and Classical and Quantum Optics.
From 1998 to 2015, the institute has published the open access review journal Living Reviews in Relativity.
History
The newly founded institute started its work in April 1995 and has been located in Potsdam-Golm since 1999.
In 2002 the Institute opened a branch at the Leibniz University Hannover [Gottfried Wilhelm Leibniz Universität Hannover](DE) with a focus on data analysis and the development and operation of gravitational-wave detectors on Earth and in space. The Hannover institute originated from the Institute for Atom and Molecule Physics (AMP) of the Universität Hannover, which was established in 1979 by the Department of Physics.
Research
The research focus of the Institute is in the field of General Relativity. It covers Theoretical and Experimental Gravitational Physics; quantum gravity; Multi-messenger Astrophysics and Cosmology. The Institute has a strong research focus on Gravitational-wave Astronomy: four out of five departments are working on different aspects of this research field. Central research topics are:
Max Planck Partner Groups carry out research in fields overlapping with those of the former host Max Planck institute. They are established to support junior scientists returning to their home country after a research stay at a Max Planck Institute.
The Max Planck Institute for Gravitational Physics has five Max Planck Partner Groups:
MPG Society for the Advancement of Science [MPG Gesellschaft zur Förderung der Wissenschaften e. V.] is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.
According to its primary goal, the MPG Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014) MPG Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.
The MPG Institutes focus on excellence in research. The MPG Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the MPG institutes fifth worldwide in terms of research published in Nature journals (after Harvard University, The Massachusetts Institute of Technology, Stanford University and The National Institutes of Health). In terms of total research volume, the Max Planck Society is only outranked by The Chinese Academy of Sciences [中国科学院](CN), The Russian Academy of Sciences [Росси́йская акаде́мия нау́к](RU) and Harvard University. The Thomson Reuters-Science Watch website placed the MPG Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.
The MPG Society and its predecessor Kaiser Wilhelm Society hosted several renowned scientists in their fields, including Otto Hahn, Werner Heisenberg, and Albert Einstein.
History
The organization was established in 1911 as the Kaiser Wilhelm Society, or Kaiser-Wilhelm-Gesellschaft (KWG), a non-governmental research organization named for the then German emperor. The KWG was one of the world’s leading research organizations; its board of directors included scientists like Walther Bothe, Peter Debye, Albert Einstein, and Fritz Haber. In 1946, Otto Hahn assumed the position of President of KWG, and in 1948, the society was renamed the Max Planck Society (MPG) after its former President (1930–37) Max Planck, who died in 1947.
The MPG Society has a world-leading reputation as a science and technology research organization. In 2006, the Times Higher Education Supplement rankings of non-university research institutions (based on international peer review by academics) placed the MPG Society as No.1 in the world for science research, and No.3 in technology research (behind AT&T Corporation and The DOE’s Argonne National Laboratory.
The domain mpg.de attracted at least 1.7 million visitors annually by 2008 according to a Compete.com study.
MPG Institutes and research groups
The MPG Society consists of over 80 research institutes. In addition, the society funds a number of Max Planck Research Groups (MPRG) and International Max Planck Research Schools (IMPRS). The purpose of establishing independent research groups at various universities is to strengthen the required networking between universities and institutes of the Max Planck Society.
The research units are primarily located across Europe with a few in South Korea and the U.S. In 2007, the Society established its first non-European centre, with an institute on the Jupiter campus of Florida Atlantic University focusing on neuroscience.
The MPG Institutes operate independently from, though in close cooperation with, the universities, and focus on innovative research which does not fit into the university structure due to their interdisciplinary or transdisciplinary nature or which require resources that cannot be met by the state universities.
Internally, MPG Institutes are organized into research departments headed by directors such that each MPI has several directors, a position roughly comparable to anything from full professor to department head at a university. Other core members include Junior and Senior Research Fellows.
In addition, there are several associated institutes:
International Max Planck Research Schools
Together with the Association of Universities and other Education Institutions in Germany, the Max Planck Society established numerous International Max Planck Research Schools (IMPRS) to promote junior scientists:
• Cologne Graduate School of Ageing Research, Cologne
• International Max Planck Research School for Intelligent Systems, at the Max Planck Institute for Intelligent Systems located in Tübingen and Stuttgart
• International Max Planck Research School on Adapting Behavior in a Fundamentally Uncertain World (Uncertainty School), at the Max Planck Institutes for Economics, for Human Development, and/or Research on Collective Goods
• International Max Planck Research School for Analysis, Design and Optimization in Chemical and Biochemical Process Engineering, Magdeburg
• International Max Planck Research School for Astronomy and Cosmic Physics, Heidelberg at the MPI for Astronomy
• International Max Planck Research School for Astrophysics, Garching at the MPI for Astrophysics
• International Max Planck Research School for Complex Surfaces in Material Sciences, Berlin
• International Max Planck Research School for Computer Science, Saarbrücken
• International Max Planck Research School for Earth System Modeling, Hamburg
• International Max Planck Research School for Elementary Particle Physics, Munich, at the MPI for Physics
• International Max Planck Research School for Environmental, Cellular and Molecular Microbiology, Marburg at the Max Planck Institute for Terrestrial Microbiology
• International Max Planck Research School for Evolutionary Biology, Plön at the Max Planck Institute for Evolutionary Biology
• International Max Planck Research School “From Molecules to Organisms”, Tübingen at the Max Planck Institute for Developmental Biology
• International Max Planck Research School for Global Biogeochemical Cycles, Jena at the Max Planck Institute for Biogeochemistry
• International Max Planck Research School on Gravitational Wave Astronomy, Hannover and Potsdam MPI for Gravitational Physics
• International Max Planck Research School for Heart and Lung Research, Bad Nauheim at the Max Planck Institute for Heart and Lung Research
• International Max Planck Research School for Infectious Diseases and Immunity, Berlin at the Max Planck Institute for Infection Biology
• International Max Planck Research School for Language Sciences, Nijmegen
• International Max Planck Research School for Neurosciences, Göttingen
• International Max Planck Research School for Cognitive and Systems Neuroscience, Tübingen
• International Max Planck Research School for Marine Microbiology (MarMic), joint program of the Max Planck Institute for Marine Microbiology in Bremen, the University of Bremen, the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, and the Jacobs University Bremen
• International Max Planck Research School for Maritime Affairs, Hamburg
• International Max Planck Research School for Molecular and Cellular Biology, Freiburg
• International Max Planck Research School for Molecular and Cellular Life Sciences, Munich
• International Max Planck Research School for Molecular Biology, Göttingen
• International Max Planck Research School for Molecular Cell Biology and Bioengineering, Dresden
• International Max Planck Research School Molecular Biomedicine, program combined with the ‘Graduate Programm Cell Dynamics And Disease’ at the University of Münster and the Max Planck Institute for Molecular Biomedicine
• International Max Planck Research School on Multiscale Bio-Systems, Potsdam
• International Max Planck Research School for Organismal Biology, at the University of Konstanz and the Max Planck Institute for Ornithology
• International Max Planck Research School on Reactive Structure Analysis for Chemical Reactions (IMPRS RECHARGE), Mülheim an der Ruhr, at the Max Planck Institute for Chemical Energy Conversion
• International Max Planck Research School for Science and Technology of Nano-Systems, Halle at Max Planck Institute of Microstructure Physics
• International Max Planck Research School for Solar System Science at the University of Göttingen hosted by MPI for Solar System Research
• International Max Planck Research School for Astronomy and Astrophysics, Bonn, at the MPI for Radio Astronomy (formerly the International Max Planck Research School for Radio and Infrared Astronomy)
• International Max Planck Research School for the Social and Political Constitution of the Economy, Cologne
• International Max Planck Research School for Surface and Interface Engineering in Advanced Materials, Düsseldorf at Max Planck Institute for Iron Research GmbH
• International Max Planck Research School for Ultrafast Imaging and Structural Dynamics, Hamburg
Max Planck Schools
• Max Planck School of Cognition
• Max Planck School Matter to Life
• Max Planck School of Photonics
Max Planck Center
• The Max Planck Centre for Attosecond Science (MPC-AS), POSTECH Pohang
• The Max Planck POSTECH Center for Complex Phase Materials, POSTECH Pohang
Max Planck Institutes
Among others:
• Max Planck Institute for Neurobiology of Behavior – caesar, Bonn
• Max Planck Institute for Aeronomics in Katlenburg-Lindau was renamed to Max Planck Institute for Solar System Research in 2004;
• Max Planck Institute for Biology in Tübingen was closed in 2005;
• Max Planck Institute for Cell Biology in Ladenburg b. Heidelberg was closed in 2003;
• Max Planck Institute for Economics in Jena was renamed to the Max Planck Institute for the Science of Human History in 2014;
• Max Planck Institute for Ionospheric Research in Katlenburg-Lindau was renamed to Max Planck Institute for Aeronomics in 1958;
• Max Planck Institute for Metals Research, Stuttgart
• Max Planck Institute of Oceanic Biology in Wilhelmshaven was renamed to Max Planck Institute of Cell Biology in 1968 and moved to Ladenburg 1977;
• Max Planck Institute for Psychological Research in Munich merged into the Max Planck Institute for Human Cognitive and Brain Sciences in 2004;
• Max Planck Institute for Protein and Leather Research in Regensburg moved to Munich 1957 and was united with the Max Planck Institute for Biochemistry in 1977;
• Max Planck Institute for Virus Research in Tübingen was renamed as Max Planck Institute for Developmental Biology in 1985;
• Max Planck Institute for the Study of the Scientific-Technical World in Starnberg (from 1970 until 1981 (closed)) directed by Carl Friedrich von Weizsäcker and Jürgen Habermas.
• Max Planck Institute for Behavioral Physiology
• Max Planck Institute of Experimental Endocrinology
• Max Planck Institute for Foreign and International Social Law
• Max Planck Institute for Physics and Astrophysics
• Max Planck Research Unit for Enzymology of Protein Folding
• Max Planck Institute for Biology of Ageing
When racing to follow up on a new detection of gravitational waves, every second of telescope time is precious. A recent publication describes how a new algorithm for scheduling observations might improve our ability to track down transient events.
Seeking Gravitational Wave Sources
Locations of the observatories that followed up on the detection of the gravitational wave signal GW170817. [LIGO-Virgo]
The search for the source of gravitational wave event GW170817 is an amazing success story. In the days following the initial detection, telescopes across the world pinpointed and monitored the resulting kilonova, leading to a deep understanding of the event — but since then, no other gravitational wave source has been definitively identified.
Searches for gravitational wave sources are challenging because the search areas are often large, telescope time is limited, and the events are transient. How can we track down the causes of gravitational wave signals in a way that makes the most efficient use of the available observing time? In a recent publication, B. Parazin (Northeastern University and University of Minnesota) put a new observation-scheduling algorithm to the test.
Scheduling Telescope Time
Parazin and collaborators tested a new algorithm optimized for the Zwicky Transient Facility (ZTF), which is designed to detect transient events.
The team aimed to maximize the odds of tracking down the source of a new gravitational wave signal while minimizing the amount of observing time needed. They also accounted for factors that are unique to the ZTF, such as the time needed to switch between filters.
In addition to the particulars of the ZTF observing setup, the algorithm takes as an input a map of the sky showing the probable locations of a gravitational wave source, which is released by gravitational wave observatories when a new signal is detected. From there, the algorithm identifies which out of the ZTF telescope’s 1,778 possible pointing directions are appropriate, groups pointings that are continuously observable during a selected length of time, and orders the pointings within each group so as to minimize the amount of time the telescope spends between observations.
Improving Efficiency
Comparison of the probability coverage of the existing algorithm in use by the ZTF (gwemopt) to that of the new algorithm introduced in this work (MUSHROOMS). The new algorithm performs better than the existing algorithm for cases located under the yellow line. [Parazin et al. 2022]
To compare the new algorithm to the one ZTF currently uses, the team scheduled observations with each method for 951 simulated detections of binary neutron star mergers. Under the conditions best suited to compare the two methods, Parazin and coauthors find that their new algorithm improves upon the existing software by 5.8%, on average — in other words, the new observing schedules increased the probability of finding the source. Since the existing algorithm sometimes outperformed the new algorithm, a hybrid approach — running both algorithms and choosing the more efficient solution — was the best, netting an average 8.1% improvement.
A final wrinkle is the fact that transient sources can fade rapidly, making the order in which the observations are carried out important — reach a source too late, and it may have dimmed beyond detection. When testing both algorithms on finding rapidly fading synthetic kilonovae, the team found that 1) once again, the hybrid approach had the best performance, and 2) the new algorithm had an advantage over the existing software when the search area was large.
Citation
Foraging with MUSHROOMS: A Mixed-integer Linear Programming Scheduler for Multimessenger Target of Opportunity Searches with the Zwicky Transient Facility, B. Parazin et al 2022 ApJ 935 87. https://iopscience.iop.org/article/10.3847/1538-4357/ac7fa2/pdf
The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.
The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.
Adopted June 7, 2009
The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.
The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.
In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.
The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.
The upcoming satellite experiment LiteBIRD is expected to probe the physics of the very early Universe if the primordial inflation happened at high energies.
But now, a new paper in Physical Review Letters shows it can also test inflationary scenarios operating at lower energies.
The green line is the lowest signal the LiteBIRD can still observe, so any observable signal should be above that line. The red and black lines are the team’s predictions for two different parameter specifications in their model, showing detection is possible. In contrast, the more standard inflationary models operating at the same energy as the team’s mechanism predict the lower gray (dashed) line, which is below the sensitivity limit of LiteBIRD. (Credit: Cai et al.)
Cosmologists believe that in its very early stages, the Universe underwent a very rapid expansion called “cosmic inflation”.
Alan Guth’s notes: Alan Guth’s original notes on inflation.
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A success story of this hypothesis is that even the simplest inflationary models are able to accurately predict the inhomogeneous distribution of matter in the Universe. During inflation, these vacuum fluctuations were stretched to astronomical scales, becoming the source all the structure in the Universe, including the Cosmic Microwave Background [CMB] anisotropies, distribution of Dark Matter and galaxies.
These gravitational wave propagating ripples of space and time are important for understanding the physics during the inflationary epoch. In general, detecting these gravitational waves is considered determining the energy at which inflation took place. It is also linked to how much the inflation field-or the energy source of inflation-can change during inflation — a relation referred to as the “Lyth bound”.
An artist’s conception of how gravitational waves distort the shape of space and time in the universe (Credit: Kavli IPMU).
The primordial gravitational waves generated from vacuum are extremely weak, and are very difficult to detect, but the JAXA-led LiteBIRD mission might be able to detect them via the polarization measurements of the Cosmic Microwave Background. Because of this, understanding primordial gravitational waves theoretically is gaining interest so any potential detection by LiteBIRD can be interpreted. It is expected LiteBIRD will be able to detect primordial gravitational waves if inflation happened at sufficiently high energies.
Several inflationary models constructed in the framework of quantum gravity often predict very low energy scale for inflation, and so would be untestable by LiteBIRD. However, a new study by researchers, including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), has shown the opposite. The researchers argue such scenarios of fundamental importance can be tested by LiteBIRD, if they are accompanied by additional fields, sourcing gravitational waves.
The researchers suggest an idea, logically very different from the usual.
“Within our framework in addition to the gravitational waves originating from vacuum fluctuations, a large amount of gravitational waves can be sourced by the quantum vacuum fluctuations of additional fields during inflation. Due to this we were able to produce an observable amount of gravitational waves even if inflation takes place at lower energies.
“The quantum fluctuations of scalar fields during inflation are typically small, and such induced gravitational waves are not relevant in standard inflationary scenarios. However, if the fluctuations of the additional fields are enhanced, they can source a significant amount of gravitational waves,” said paper author and Kavli IPMU Project Researcher Valeri Vardanyan.
Other researchers have been working on related ideas, but so far no successful mechanism based on scalar fields alone had been found.
“The main problem is that when you generate gravitational waves from enhanced fluctuations of additional fields, you also simultaneously generate extra curvature fluctuations, which would make the Universe appear more clumpy than it is in reality. We elegantly decoupled the generation of the two types of fluctuations and solved this problem,” said Vardanyan.
In their paper, the researchers proposed a proof-of-concept based on two scalar fields operating during inflation.
“Imagine a car with two engines, corresponding to the two fields of our model. One of the engines is connected to the wheels of the car, while the other one is not. The first one is responsible for moving the car, and, when on a muddy road, for generating all the traces on the road. These represent the seeds of structure in the Universe. The second engine is only producing sound. This represents the gravitational waves, and does not contribute to the movement of the car, or the generation of traces on the road,” said Vardanyan.
The team quantitatively demonstrated their mechanism works, and even calculated the predictions of their model for the upcoming LiteBIRD mission.
The Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at The University of Tokyo [東京大学](JP) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.
The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.
Artistic impression of the merger of two boson stars. Credit: Nicolás Sanchis-Gual and Rocío García Souto.
An international team of scientists led by the Galician Institute of High Energy Physics (IGFAE) and the University of Aveiro [Universidade de Aveiro](PT) shows that the heaviest black hole collision ever observed, produced by the gravitational-wave GW190521, might actually be something even more mysterious: the merger of two boson stars. This would be the first evidence of the existence of these hypothetical objects which are a candidate for dark matter-believed to comprise 27% of the mass in the universe.
Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light. These originate in the most violent events of in the universe, carrying information about their sources. Since 2015, the two LIGO detectors in the U.S. and the Virgo detector in Cascina, Italy, have detected and interpreted gravitational waves.
Caltech/MIT Advanced aLigo at Hanford, WA(US), Livingston, LA(US) and VIRGO Gravitational Wave interferometer, near Pisa(IT).
To date, these detectors have already observed around 50 gravitational-wave signals. All of these originated in the collisions and mergers of black holes and neutron stars, allowing physicists to deepen the knowledge about these objects.
Masses in the Stellar Graveyard GWTC-2 plot v1.0 BY LIGO-Virgo. Credit: Frank Elavsky and Aaron Geller at Northwestern University.
However, the promise of gravitational waves goes much further than this, as these should eventually provide us with evidence for previously unobserved and even unexpected objects, and shed light on current mysteries like the nature of dark matter. The latter may, however, have already happened.
In September 2020, the LIGO and Virgo collaboration (LVC) announced to the world the gravitational-wave signal GW190521. According to their analysis, the signal was consistent with the collision of two heavy black holes, of 85 and 66 times the mass of the sun, which produced a final black hole with 142 solar masses. The resulting black hole was the first of a new, previously unobserved black hole family: intermediate-mass black holes. This discovery is of paramount importance, as such black holes were the missing link between two well-known black-hole families: stellar-mass black holes that form from the collapse of stars, and supermassive black holes that reside in the center of almost every galaxy, including the Milky Way.
In addition, this observation came with an enormous challenge. If what we think we know about how stars live and die is correct, the heaviest of the colliding black holes (85 solar masses) could not form from the collapse of a star at the end of its life, which opens up a range of doubts and possibilities about its origins.
In an article published today in Physical Review Letters, a team of scientists lead by Dr. Juan Calderón Bustillo at the Galician Institute of High Energy Physics (IGFAE), joint center of the University of Santiago de Compostela and Xunta de Galicia, and Dr. Nicolás Sanchis-Gual, a postdoctoral researcher at the University of Aveiro and the Instituto Superior Técnico at University of Lisbon [Universidade de Lisboa](PT] , together with collaborators from University of Valencia [Universitat de València [univeɾsiˈtad de vaˈlensia]](ES), Monash University(AU) and The Chinese University of Hong Kong [香港中文大学; Xiānggǎng zhōngwén dàxué](HK), has proposed an alternative explanation for the origin of the signal GW190521: the collision of two exotic objects known as boson stars, which are one of the most likely candidates to explain dark matter. In their analysis, the team was able to estimate the mass of a new particle constituent of these stars, an ultra-light boson with a mass billions of times smaller than electrons.
The team compared the GW190521 signal to computer simulations of boson-star mergers, and found that these actually explain the data slightly better than the analysis conducted by LIGO and Virgo. The result implies that the source would have different properties than stated earlier. Dr. Calderón Bustillo says, “First, we would not be talking about colliding black holes anymore, which eliminates the issue of dealing with a ‘forbidden’ black hole. Second, because boson star mergers are much weaker, we infer a much closer distance than the one estimated by LIGO and Virgo. This leads to a much larger mass for the final black hole, of about 250 solar masses, so the fact that we have witnessed the formation of an intermediate-mass black hole remains true.”
Dr. Nicolás Sanchis-Gual says, “Boson stars are objects almost as compact as black holes but, unlike them, do not have a ‘no-return’ surface. When they collide, they form a boson star that can become unstable, eventually collapsing to a black hole, and producing a signal consistent with what LIGO and Virgo observed. Unlike regular stars, which are made of what we commonly know as matter, boson stars are made up of what we know as ultralight bosons. These bosons are one of the most appealing candidates for constituting what we know as dark matter.”
The team found that even though the analysis tends to favor the merging black-holes hypothesis, a boson star merger is actually preferred by the data, although in a non-conclusive way. Prof. Jose A. Font from the University of Valencia says, “Our results show that the two scenarios are almost indistinguishable given the data, although the exotic boson star hypothesis is slightly preferred. This is very exciting, since our boson-star model is, as of now, very limited, and subject to major improvements. A more evolved model may lead to even larger evidence for this scenario and would also allow us to study previous gravitational-wave observations under the boson-star merger assumption.”
This result would not only involve the first observation of boson stars but also that of their building block: a new particle known as an ultra-light boson. Prof. Carlos Herdeiro from University of Aveiro says, “One of the most fascinating results is that we can actually measure the mass of this putative new dark-matter particle, and that a value of zero is discarded with high confidence. If confirmed by subsequent analysis of this and other gravitational-wave observations, our result would provide the first observational evidence for a long-sought dark matter candidate.”
Our main goal is to coordinate and foster the scientific and technical research in the field of High Energy Physics, Particle and Nuclear Physics and related areas as Astrophysics, Medical Physics and Instrumentation.
Of primary importance is the planning and promotion of the relation with large experimental facilities, especially with CERN, GSI/FAIR, Pierre Auger Observatory and LIGO at present.
In 2016, IGFAE was accredited “María de Maeztu” Unit of Excellence, integrating the Severo Ochoa and María de Maeztu alliance (SOMMa). This program of the Spanish Ministry of Science, Innovation and Universities identify and promote excellence in existing cutting-edge research institutions.
The IceCube Neutrino Observatory, an array of over 5,000 light sensors embedded in a cubic-kilometer of ice at the South Pole, was built to detect astrophysical neutrinos: mysterious and nearly massless particles that carry information about the most energetic events in the cosmos. Every time IceCube sees something that might be a cosmic neutrino, it sends an alert to a network of telescopes and observatories around the world and in space, telling them to turn and look at that same spot in the sky. These other instruments see the universe in different ways; many detect photons of different wavelengths, from radio waves to gamma rays, while others detect different “messengers” entirely, like gravitational waves or neutrinos. Together, detections from different messengers give us a more complete picture of the cosmos.
The study of the universe with multiple channels—a field known as multimessenger astronomy—is valuable for investigating a number of questions, including learning about the sources of astrophysical neutrinos, one of IceCube’s main scientific goals. So rather than just waiting for neutrinos to come to IceCube, IceCube can also follow up on detections made by other telescopes. And since IceCube can observe the entire sky simultaneously and is “on” more than 99 percent of the time, it can provide unique and valuable insight for other observatories.
Since 2016, the IceCube Collaboration has used a fast-response analysis pipeline to perform follow-up neutrino searches on interesting detections in other messengers that might have neutrino counterparts. As of July 2020, the pipeline led to 58 analyses, none of which found significant neutrino signals but enabled researchers to constrain neutrino emission from some potential sources. The collaboration described their results in a paper recently submitted to The Astrophysical Journal.
Results of IceCube’s follow-up for the gamma-ray burst GRB190114C, one of the only GRBs to ever be detected by a ground-based gamma-ray telescope. This plot shows the flux as a function of energy, where blue tones are results from various wavelengths of light, from X-rays (left) to very high energy gamma rays (right). The upper limit on the high-energy neutrino flux, one of the results reported in the paper, is shown by the solid magenta line. Credit: IceCube Collaboration.
“The motivation for this analysis is to take the idea of neutrino alerts and turn it on its head,” says Alex Pizzuto, a doctoral student at the University of Wisconsin–Madison and a lead on this analysis. “Instead of sending out interesting neutrinos to the community and letting observers follow up on our events, we take interesting events reported in other messengers, like photons, and check to see if there are neutrinos coming from the same object. And we do it all in real time.”
Pizzuto and his collaborators have been doing this since 2016 when they established a fast-response analysis pipeline. The pipeline monitors various channels where astronomers announce interesting observations (such as the Gamma-ray Coordinates Network and the The Astronomer’s Telegram) and identifies potentially interesting detections. Then, IceCube researchers evaluate whether the target is a viable neutrino emitter and whether it would be useful for IceCube to check it out. If yes, the researchers determine a time frame around the event of interest and use the pipeline to rapidly perform a statistical analysis of IceCube data to see if any neutrino candidate events correlate with the target in time and direction. When the analysis is complete, the researchers send out their results via the same channels they were monitoring in the first place.
As of July 2020, the pipeline has led to 58 analyses, none of which found a statistically significant signal of neutrinos. But the researchers were able to use the pipeline to put constraints on some of the source classes they studied, including fast radio bursts, extreme blazar flares, bright gamma-ray bursts, and gravitational waves. Pizzuto says that they are already seeing some of their limits incorporated into models of potential neutrino sources.
“Unlike most telescopes, IceCube observes the entire sky (including both hemispheres), all the time (including both day and night),” according to Justin Vandenbroucke, a UW–Madison physics professor and another lead on the paper. “So whenever a new astrophysical transient event is reported by another observatory, we know IceCube was also looking there then. Our pipeline enables us to rapidly search for neutrinos and report the results. This real-time approach to multimessenger astrophysics has enabled the key discoveries of the field so far, and will continue to in the future.”
Looking ahead, the researchers plan to continue running the pipeline. They hope that this analysis will identify a multimessenger source in the future. In the meantime, they are studying a variety of source classes with this tool. And there is a plan to use this pipeline to search for additional neutrinos coming from the same directions as the high-energy neutrinos that trigger IceCube alerts.
Stem Education Coalition IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.
IceCube neutrino detector interior.IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube CollaborationLunar IcecubeIceCube DeepCore annotated
IceCube PINGU annotated DM-Ice II at IceCube annotated
In the quest for better gravitational wave detectors, scientists are going cold.
An up-and-coming detector called KAGRA aims to spot spacetime ripples by harnessing advanced technological twists: chilling key components to temperatures hovering just above absolute zero, and placing the ultrasensitive setup in an enormous underground cavern.
Scientists with KAGRA, located in Kamioka, Japan, now have results from their first ultrafrigid tests. Those experiments suggest that the detector should be ready to start searching for gravitational waves later in 2019, the team reports January 14 at arXiv.org.
The new detector will join similar observatories in the search for the minute cosmic undulations, which are stirred up by violent events like collisions of black holes. The Laser Interferometer Gravitational-Wave Observatory, LIGO, has two detectors located in Hanford, Wash., and Livingston, La. Another observatory, Virgo, is located near Pisa, Italy.
VIRGO Gravitational Wave interferometer, near Pisa, Italy
Gravitational waves. Credit: MPI for Gravitational Physics/W.BengerESA/eLISA the future of gravitational wave research
Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)
Those detectors sit above ground, and don’t use the cooling technique, making KAGRA the first of its kind.
KAGRA consists of two 3-kilometer-long arms, arranged in an “L” shape. Within each arm, laser light bounces back and forth between two mirrors located at both ends. The light acts like a giant measuring stick, capturing tiny changes in the length of each arm, which can be caused by a passing gravitational wave stretching and squeezing spacetime.
FREEZE UP KAGRA’s mirrors (one shown) are cooled to very low temperatures to prevent jiggling that could hamper the search for gravitational waves.
Because gravitational wave detectors measure length changes tinier than the diameter of a proton, minuscule effects like the jiggling of molecules on the mirrors’ surfaces can interfere with the measurements. Cooling the mirrors to about 20 kelvins (–253° Celsius) limits that jiggling.
In the new tests, performed in spring 2018, researchers cooled only one of KAGRA’s four mirrors, says KAGRA leader Takaaki Kajita of the University of Tokyo. When the detector starts up for real, the others will be chilled too.
Having the detector underground also helps keep the mirrors from vibrating due to activity on Earth’s surface. LIGO is so sensitive that it can be affected by rumbling trucks, a stiff breeze or even mischievous wildlife (SN Online: 4/18/18). KAGRA’s underground lair should be significantly quieter.
Building underground and going cold required years of effort from KAGRA’s researchers. “They’ve taken on these two great challenges, which are both important to the long-term future of the field,” says LIGO spokesperson David Shoemaker of MIT. In the future, even more advanced gravitational wave detectors could build on KAGRA’s techniques.
For now, adding KAGRA to the existing observatories should help scientists improve their studies of where gravitational wiggles come from. Once scientists detect a gravitational wave signal, they alert astronomers, who search for light from the cataclysm that generated the waves in the hope of better understanding the event (SN: 11/11/17, p. 6). Having an additional gravitational wave detector in a different part of the world will help better triangulate wave sources. “This feature is very important,” Kajita says, “because telescopes can only see a small part of the sky at a time.”
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The observatories are also releasing their first catalog of gravitational-wave events.
On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European- based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.
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 being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.
All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.
GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).
The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever 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.
One of the new events, GW170818, which was 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.
Caltech’s Albert Lazzarini, Deputy Director of the LIGO Laboratory, says “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.”
“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,” says 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,” says 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,” says 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 new catalog is another proof of the exemplary international collaboration of the gravitational wave community and an asset for the forthcoming runs and upgrades”, adds EGO Director Stavros Katsanevas.
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.
Laura Cadonati, Deputy Spokesperson for the LIGO Scientific Collaboration, says “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.”
LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (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, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.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 (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) 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 (EGO), 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 http://www.virgo-gw.eu.
Gravitational waves. Credit: MPI for Gravitational Physics/W.BengerESA/eLISA the future of gravitational wave research
Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)
U Wisconsin ICECUBE neutrino detector at the South Pole
IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube CollaborationLunar IcecubeIceCube DeepCore annotated
IceCube PINGU annotated DM-Ice II at IceCube annotated
Artist’s now iconic illustration of two merging neutron stars. The rippling space-time grid represents gravitational waves that travel out from the collision, while the narrow beams show the bursts of gamma rays and neutrinos that are shot out just seconds after the gravitational waves. Image: NSF/LIGO/Sonoma State University/A. Simonnet
Last year was an extraordinary year for multimessenger astrophysics. In August 2017, a gravitational wave and its electromagnetic counterpart emission were detected from a pair of inspiraling neutron stars. Only a month later, a high-energy neutrino was detected at the South Pole and electromagnetic follow-up observations helped identify the first likely source of very high energy neutrinos and cosmic rays.
Since then, the dream of astrophysicists has been to join neutrinos and gravitational waves in the detection of a multimessenger source. According to our understanding of the extreme universe, a possible scenario would be a neutrino created in the relativistic outflows of a merger of binary neutron stars or black holes or the core-collapse of a supernova, all cataclysmic cosmic environments that should also produce gravitational waves.
The IceCube, LIGO, Virgo, and ANTARES collaborations have used data from the first observing period of Advanced LIGO and from the two neutrino detectors to search for coincident neutrino and gravitational wave emission from transient sources.
The goal was to explore the discovery potential of a multimessenger observation, i.e., of a source detection that needs both messengers to confirm its astrophysical origin. Scientists did not find any significant coincidence. The results, recently submitted to The Astrophysical Journal, set a constraint on the density of these sources.
The detection of gravitational waves and neutrinos from a single source would set a new milestone in multimessenger astronomy, allowing the simultaneous study of the inner and outer processes powering high-energy emission from astrophysical objects.
A joint detection would also significantly improve the localization of the source and enable faster and more precise electromagnetic follow-up observations. The scrutiny of an astrophysical source with three different messengers would not only be the next breakthrough in the field but would also confirm that multimessenger astronomy is the only path to a profound understanding of the extreme universe.
Even though the current search was very limited in time, researchers have set a strong constraint for joint emission from core-collapse supernovas, while binary mergers remain secure as potential multimessenger sources of gravitational waves and high-energy neutrinos.
This study used datasets, spanning less than 2.5 months, that are also limited by LIGO’s sensitivity, which will soon improve by a factor of 2. The addition of new LIGO and Virgo data as well as from IceCube and ANTARES will greatly increase the sensitivity of joint searches. In the longer term, future next-generation neutrino and gravitational wave detectors will boost the potential of discovery for these searches.
IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.
Artist’s by now iconic illustration of the merger of two neutron stars, producing a short gamma-ray burst. [NSF/LIGO/Sonoma State University/A. Simonnet]
High-energy radiation released during the merger of two neutron stars last year has left astronomers puzzled. Could a burst of gamma rays from 2015 help us to piece together a coherent picture of both explosions?
A Burst Alone?
When two neutron stars collided last August, forming a distinctive gravitational-wave signal and a burst of radiation detected by telescopes around the world, scientists knew that these observations would change our understanding of short gamma-ray bursts (GRBs).Though we’d previously observed thousands of GRBs, GRB 170817A was the first to have such a broad range of complementary observations — both in gravitational waves and across the electromagnetic spectrum — providing insight into its origin.
Total isotropic-equivalent energies for Fermi-detected gamma-ray bursts with known redshifts. GRB 170817A (pink star) is a factor of ~1,000 dimmer than typical short GRBs (orange points). GRB 170817A and GRB 150101B (green star) are two of the closest detected short GRBs. [Adapted from Burns et al. 2018]
But it quickly became evident that GRB 170817A was not your typical GRB. For starters, this burst was unusually weak, appearing 1,000 times less luminous than a typical short GRB. Additionally, the behavior of this burst was unusual: instead of having only a single component, the ~2-second explosion exhibited two distinct components — first a short, hard (higher-energy) spike, and then a longer, soft (lower-energy) tail.
The peculiarities of GRB 170817A prompted a slew of models explaining its unusual appearance. Ultimately, the question is: can our interpretations of GRB 170817A safely be applied to the general population of gamma-ray bursts? Or must we assume that GRB 170817A is a unique event, not representative of the general population?
New analysis of a GRB from 2015 — presented in a recent study led by Eric Burns (NASA Goddard SFC) — may help to answer this question.
A Matter of Angles
What does a burst from 2015 have to do with the curious case of GRB 170817A? Burns and collaborators have demonstrated that this 2015 burst, GRB 150101B, exhibited the same strange behavior as GRB 170817A: its emission can be broken down into two components consisting of a short, hard spike, followed by a long, soft tail. Unlike GRB 170817A, however, GRB 150101B is not underluminous — and it lasted less than a tenth of the time.
Fermi count rates in different energy ranges showing the short hard spike and the longer soft tail in GRB 150101B. The short hard spike is visible above 50 keV (top and middle panels). The soft tail is visible in the 10–50 keV channel (bottom panel). [Burns et al. 2018]
Intriguingly, these similarities and differences can all be explained by a single model. Burns and collaborators propose that GRB 150101B and GRB 170817A exhibit the exact same two-component behavior, and their differences in luminosity and duration can be explained by quirks of special relativity.
High-speed outflows such as these will have different apparent luminosities and durations depending on whether we view them along their axis or slightly from the side. Burns and collaborators demonstrate that these the two bursts could easily have the same profile — but GRB 150101B was viewed nearly on-axis, whereas GRB 170817A was viewed from an angle.
If this is true, then perhaps more GRBs have hard spikes and soft tails similar to these two; the tails may just be difficult to detect in more distant bursts. While more work remains to be done, the recognition that GRB 170817A may not be unique is an important one for understanding both its behavior and that of other short GRBs.
Gravitational waves. Credit: MPI for Gravitational Physics/W.BengerESA/eLISA the future of gravitational wave research
Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)
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