[RESCEU] Research Center for the Early Universe
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RESCEU Colloquium

RESCEU Colloquium No. 41
Date and Time: September 26, 2019, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kenneth C. Wong
(Kavli IPMU)
A 2.4% Measurement of H0 from Lensed Quasars
Abstract
Abstract: Strong gravitational lens systems with time delays between the multiple images are a powerful probe of cosmology, particularly of the Hubble constant (H0) that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. The H0 Lenses In COSMOGRAIL's Wellspring (H0LiCOW) project has measured H0 from lensed quasars using deep Hubble Space Telescope and AO imaging, precise time delay measurements from the COSMOGRAIL monitoring project, a measurement of the velocity dispersion of the lens galaxies, and a characterization of the mass distribution along the line of sight. Our latest results from a total of six lenses constrains H0 to be 73.3(-1.8,+1.7) km/s/Mpc for a flat Lambda CDM cosmology, which is a measurement to 2.4% precision. These results are consistent with independent determinations of H0 using type Ia supernovae calibrated by the distance ladder method, and are in 3.1-sigma tension with the results of Planck CMB measurements. Combined with the latest distance ladder results from the SH0ES project, we find a 5.3-sigma tension between Planck and late-Universe probes, hinting at possible new physics beyond the standard LCDM model and highlighting the importance of this independent probe.
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RESCEU Colloquium No. 40
Date and Time: August 27, 2019, 13:00-14:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Manami Sasaki
(Dr. Karl Remeis Observatory, Bamberg, Friedrich-Alexander-University Erlangen-Nurnberg)
The eROSITA View of Stellar Endpoints
Abstract
eROSITA (extended ROentgen survey with an Imaging Telescope Array) is an X-ray telescope onboard the Russian Spektrum-RG satellite, which will carry out the first imaging all-sky survey in the X-ray band of 0.2 - 10.0 keV. It will thus bridge the gap between the soft X-ray survey, performed with the German Rontgen Satellite (ROSAT, 0.1-2.4keV), and the hard X-ray to gamma-ray surveys of the Rossi X-ray Timing Explorer Mission (3-20 keV), International Gamma-Ray Astrophysics Laboratory (17-60 keV), or Fermi Gamma-ray Space Telescope (1 GeV). In the soft X-ray band (0.5-2 keV), eRASS will be 20-30 times more sensitive than the ROSAT all-sky survey. I will give an overview of the mission and discuss science objectives of eRASS, in particular focussing on the study of galactic X-ray sources.
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RESCEU Colloquium No. 39
Date and Time: May 30, 2019, 16:45-17:45
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Renyue Cen
(Princeton University)
Computing the Universe: from Intergalactic to Interstellar Medium
Abstract
This talk will highlight some progress made based on our efforts of computing the universe, in order to understand the dynamics of gas in the universe, from intergalactic to interstellar medium. Select observables presented include the cosmic web from redshift zero to z=2-4, and the escape fraction of Lyman continuum photons from galaxies at the epoch of reionization, an essential parameter underlying the feasibility of stellar reionization of the universe.
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RESCEU Colloquium No. 38
Date and Time: April 18, 2019, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Eiichiro Komatsu
(Director of Max Planck Institute for Astrophysics)
Non-Gaussian gravitational waves from inflation
Abstract
It has been widely assumed that detection of primordial gravitational waves from inflation in, for example, B-mode polarisation of the cosmic microwave background, immediately implies discovery of the quantum nature of spacetime. While this statement is true for the vacuum solution (left hand side of Einstein's equation), it does not apply if the gravitational waves originate from the matter fields (right hand side). How can we distinguish between these two origins? The answer is non-Gaussinaity. We show that the gravitational waves from SU(2) gauge fields coupled to a spectator axion field during inflation are highly non-Gaussian with a characteristic shape, whereas those from the vacuum are only weakly non-Gaussian.
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RESCEU Colloquium No. 37
Date and Time: April 04, 2019, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Toshiki Sato
(RIKEN)
The Origin of the X-ray Clumpy Ejecta in Type Ia Supernova Remnants
Abstract
X-ray-emitting clumpy structures are generally observed in young Type Ia supernova remnants although the origin is still obscure. There are two candidates for explaining the formation of clumps; initial clumpiness in ejecta at the explosion (i.e., clumpy ejecta model) or hydrodynamic instabilities made from smooth ejecta profile (i.e., smooth ejecta model). This information should reflect the initial ejecta structure of SNe Ia, so it is important for understanding the Type Ia explosion itself. Our preliminary investigations into constraining the structure of SN Ia remnants using Fourier and wavelet-transform analyses did not turn out to be sufficiently powerful at discriminating the two hydro models and the observed Tycho image from each other. This led us to investigate an approach that would be more sensitive to patterns in the distribution of clumps and holes in the images, such as the "genus statistic".

In this study, for the first time, the genus statistics have been applied to a famous type Ia remnant, Tycho (SN 1572) to understand the formation of the clumps by comparing with hydrodynamical models (Sato et al. 2019, arXiv: 1903.00764). We found the genus curve from Tycho's supernova remnant strongly indicates a skewed non-Gaussian distribution of the ejecta clumps, which is similar to that of a hydrodynamical model for the clumpy ejecta model. In contrast, a hydrodynamical model for the smooth ejecta model has a genus curve that is similar to that of a random Gaussian distribution. Thus, our results support the initial clumpiness in the Type Ia ejecta is more reasonable for the origin of the clumps and demonstrate usefulness of the genus statistics for this field. In addition, we will also discuss the origin of "Fe-rich" ejecta clumps in Type Ia SNRs in this seminar.
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RESCEU Colloquium No. 36
Date and Time: March 13, 2019, 14:00-15:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Tilman Troester
(University of Edinburgh)
Weak gravitational lensing, baryons, and deep learning
Abstract
Baryonic processes that alter the large-scale distribution of gas, and thus the matter power spectrum, such as AGN feedback, are one of the main systematics in current and future weak lensing surveys. Left uncorrected, these effects will bias the inferred properties of dark matter and dark energy that these surveys are designed to measure. Characterising the distribution of gas is thus of vital importance if these surveys are to be exploited to their full potential.

In this talk, I will present ongoing work on joint analyses of weak lensing and tracers of diffuse gas, specifically the tSZ effect. We measure the tomographic cross-correlations between the tSZ effect and preliminary weak lensing data from the KiDS-1000 data set. We model the signal with a new code, based on HMCode, that can jointly predict the matter and pressure distributions and thus fit cosmology and parameters describing baryonic effects, such as the strength of AGN feedback, at the same time. I will then show how a joint analysis of cosmic shear and tSZ cross-correlations breaks degeneracies of the individual probes and can significantly improve the constraints on cosmological parameters compared to cosmic shear alone.

Finally, I will show how we use a class of machine learning methods -- deep generative models -- to augment N-body simulations with gas. Specifically, I will show how conditional variational autoencoders and generative adversarial networks trained on the BAHAMAS hydrodynamical simulations can be used "paint" pressure fields on the SLICS suite of N-body simulations to produce consistent lensing and tSZ maps for use in the estimation of the cross-correlation covariance.
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RESCEU Colloquium No. 35
Date and Time: March 07, 2019, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Anna Lisa Varri
(Dept. of Astronomy, University of Tokyo)
Phase space complexity of star clusters: fresh observables for old and new questions
Abstract
Our traditional paradigm of the internal dynamics of globular clusters has been recently revolutionised by a series of discoveries about their chemical, structural, and kinematic properties. The empirical evidence that their phase space structure is much more complex than usually expected encourages us to use them as refreshingly novel playgrounds for some long-forgotten aspects of collisional gravitational dynamics. Such a realisation, coupled with the discovery that the stars in clusters were not all born at once in a single population, makes them challenging 'chemodynamical' puzzles, with a suite of new questions to be addressed.

This renaissance is stimulated and enabled by significant advancements on the observational side. Precision astrometry now available from Gaia DR2 is complemented by decades-long HST campaigns and recent ESO spectroscopic surveys. The timeline of the forthcoming Gaia data releases is accompanied by the promise of future facilities (such as WEAVE, 4MOST, and MOONS), which will provide crucial spectroscopic follow-ups. And there is much hope that the opportunity to characterise the properties of 'proto-clusters' in the early universe will finally be within reach, thanks to JWST and E-ELT.

In this thriving context, I will discuss our current understanding of the internal dynamics of these collisional stellar systems and present some new theoretical insight emerging from a more realistic description of their phase space, with emphasis on the distinction between signatures resulting from the early formation stage ('primordial features') and from long-term dynamical processes ('evolutionary features'). Specific attention will be given to the interplay between internal rotation and tidal effects, with analogies to spin-orbit coupling in planetary dynamics. The final goal of this synergy between 'remastered' theory and fresh observables will be a deeper understanding of the role of 'small scales' in the assembly of cosmic structures in our universe.
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RESCEU Colloquium No. 34
Date and Time: January 21, 2019, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kenta Hotokezaka
(Princeton Univ.)
Electromagnetic counterparts to GW170817 and astrophysical implications
Abstract
The neutron star merger GW170817 is the first gravitational-wave (GW) event accompanied by electromagnetic radiation: prompt gamma-rays, uv/optical/IR kilonova, and broadband non-thermal afterglow. The signatures of kilonova in GW170817 are consistent with the picture that a substantial amount of material is ejected at merger and the ejecta is composed of r-process nuclei. In particular, the light curve from 0.5 to 70 days after the merger can be explained well with the radioactive power of r-process nuclei. I will discuss what we can learn from this observation about the composition of the ejecta and also discuss the nebular emission of kilonvoae. The second part of my talk, I will focus on the superluminal jet in GW170817 observed by VLBI. Using the afterglow light curve data and VLBI images, the jet's Lorentz factor, kinetic energy, and viewing angle are determined. I will discuss the implication of this jet to short gamma-ray bursts and how these observations can improve the GW distance measurement, which leads to the improvement of the local Hubble constant measurement from the GW-only analysis.
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RESCEU Colloquium No. 33
Date and Time: November 12, 2018, 15:00-16:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Alexei A. Starobinsky
(Landau Institute)
Stochastic dark energy from inflationary quantum fluctuations
Abstract
Late time quantum backreaction from inflationary fluctuations of a very light, non-minimally coupled scalar field which was a spectator one during inflation is studied. It is shown that this quantum field is a viable candidate for the present dark energy. The problem is solved by suitably adapting the stochastic inflationary formalism. This allows to account self-consistently for its potentially large backreaction on the background expansion rate of the present Universe. This framework is equivalent to that of semiclassical gravity in which the matter vacuum fluctuations are included at the one loop level while purely quantum gravitational fluctuations are neglected. The results show that dark energy in this model has a rather specific effective equation of state parameter as a function of redshift. This allows for testing the model using cosmological observational data on the Universe background evolution. (based on D. Glavan, T. Prokopec, and A. A. Starobinsky, Eur. Phys. J. C 78, 371 (2018); arXiv:1710.07824)
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RESCEU Colloquium No. 32
Date and Time: October 22, 2018, 10:30-11:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Yann Alibert
(Univ. of Bern)
A hybrid model for giant planet formation
Abstract
In this talk, I will review the formation of gas giant planets, in particular in the core-accretion framework, assuming core formation by accretion of either large size planetesimals or small size pebbles. In both cases, I will show the success and limitations of the models, using recent results developed in our group. I will in a second part explain how the recent constrain on the growth history of Jupiter can be used to develop a new hybrid formation paradigm that solves some of the shortcomings of planetesimal-based and pebble based formation models.
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RESCEU Colloquium No. 31
Date and Time: October 25, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Yusuke Tsukamoto
(Kagoshima University)
Does disk fragmentation by gravitational instability explain formation of the wide orbit planets?
Abstract
In this talk, I will discuss planet formation via gravitational fragmentation of protoplanetary disk. Recent ALMA observations have found gaps at several tens of AU in protoplanetary disks (e.g., ALMA Partnership 15, Tsukagoshi+16) which are often regarded as a sign of planet formation in the disks (Dipiero+15, Kanagawa+16). Further more, gaseous planets with semi-major axis of several tens AU have been found by direction observations (e.g., HR 8799; Marois+08, GJ504; Kuzuhara+13). However, standard planet formation scenario i.e., core accretion scenario has difficulty to explain such wide-orbit planets. Disk fragmentation by gravitational instability is an alternative and plausible mechanism for formation scenario of planets at several tens of AU because it tends to happen in outer part of disk. In this talk, I will discuss the criterion of disk fragmentation and property of the fragments formed in the protoplanetary disks. Then, I will discuss the whether disk fragmentation can be a preferred mechanism to explain the wide-orbit planets or gaps in the disk.
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RESCEU Colloquium No. 30
Date and Time: July 31, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Magnus Axelsson
(Stockholm Univ.)
Breaking the spectral degeneracies in black hole binaries using rapid variability
Abstract
The spectra of black hole binaries in the low/hard state are complex, with evidence for multiple different Comptonisation regions contributing to the hard X-rays, in addition to a cool disc component. However, it is difficult to constrain the shapes of these components uniquely using spectral data alone. We show how additional information from fast variability can break this degeneracy. In GX 339-4 we focus on the strong variability features known as quasi-periodic oscillations (QPOs), and in Cygnus X-1 we study the broad-band variability. In both sources, the results not only require inhomogeneous Comptonization, but also allow us to constrain the spectral components. We discuss our results in the context of propagating fluctuations through a hot flow, and the implications for our picture of the accretion flow.
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RESCEU Colloquium No. 29
Date and Time: June 21, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Shinsuke Takasao
(Nagoya Univ.)
Accretion from a magnetized disk onto a central star: New accretion mode
Abstract
The accretion process in magnetized disks is a general topic which is relevant for black hole accretion disks and protoplanetary disks, for example. The central region of accretion disks is particularly important for the evolution of central objects. However, since these processes are associated with a global magnetic field configuration and a highly turbulent disk, the detailed physics still remains elusive. To reveal the accretion structure, we performed three-dimensional magnetohydrodynamic simulations of accretion from a disk to a central star, in the context of star formation. Traditionally it has been considered that a fast (>~100 km/s) accretion is an indication of the accretion controlled by a strong stellar magnetic field (magnetospheric accretion), and many studies estimated the accretion rate on the basis of this picture. However, we found that a fast accretion is possible even without a strong stellar field. We will discuss the physics and implication for observations.
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RESCEU Colloquium No. 28
Date and Time: June 13, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Tsuguo Aramaki
(SLAC)
Hunting for Dark Matter with SuperCDMS, GAPS and GRAMS
Abstract
The existence of dark matter has been indicated in many astrophysical phenomena, but the nature of dark matter still remains a great mystery. Complementary dark matter searches with different detection methods are crucial to illuminate the nature and the origin of dark matter. In this talk, I will be presenting my research on both the SuperCDMS (direct dark matter search) and the GAPS (indirect dark matter search) experiments as well as the scientific roles of the projects in the dark matter search. While SuperCDMS measures the dark matter scattering within the detector, GAPS focuses on low-energy antiprotons and antideuterons produced by dark matter annihilation and decay in the dark matter halo. Both projects are funded for a science run/flight and will begin taking data in 2020. I will also be introducing a new project/concept, GRAMS (gamma-ray and antimatter survey) that I have been developing over the past year. GRAMS is the first experiment aiming for both MeV gamma-ray observation and antimatter-based dark matter search using a LAr-TPC detector. Through GRAMS, we can explore astrophysical objects in the MeV energy domain ("MeV gap") while pursuing dark matter.
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RESCEU Colloquium No. 27
Date and Time: May 31, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Stéphane Colombi
(IAP)
Some aspects of Vlasov-Poisson equations
Abstract
Dark matter or stars in galaxies are ensembles of particles that can be approximated with a self-gravitating, collisionless fluid, of which the dynamics is described by Vlasov-Poisson equations. I will study some properties of these equations and how they are solved numerically with the traditional N-body method and direct solvers using “semi-Lagrangian” methods and sophisticated computational geometry techniques. Focusing here on the dynamical evolution of single objects, I will study what happens for various systems, evolving from an initially warm or initially cold state. The concept of mean field limit will be approached through comparisons between N-body and Vlasov codes that will show that it is sometimes difficult if not nearly impossible to disentangle numerical from physical effects. I will discuss as well theoretical predictions, in particular the early evolution of dark matter proto-halos using perturbation theory and “post-collapse” perturbation theory.
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RESCEU Colloquium No. 26
Date and Time: May 21, 2018, 13:00-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kohei Kamada
(IBS-CTPU)
Cosmological Magnetic Fields: a Frontier in Cosmology and Particle Physics
Abstract
Recent observations of gamma-ray from blazars by Fermi-LAT identified the deficit of secondary cascade GeV photons. A natural explanation is intergalactic magnetic fields, which bend the direction of the cascade. This motivates to explore the possibilities that magnetic fields are generated in the early Universe. In particular, helical (hyper)magnetic fields before the electroweak symmetry breaking are interesting objects since they interact with the Standard Model fermions nontrivially through the chiral anomaly. Thus cosmological magnetic fields can be a possible field of study both in cosmology and particle physics. In this talk, I will discuss the impact of the chiral plasma instability that is caused by the chiral magnetic effect on the generation of cosmological magnetic fields and explore their possible connection to the baryon asymmetry of the Universe. I will show that the baryogenesis model from SU(5) Grand Unified Theory, which has been thought not to work, can be an indirect origin of the present baryon asymmetric Universe through these phenomena.
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RESCEU Colloquium No. 25
Date and Time: May 10, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kazuyuki Sugimura
(Tohoku University)
Accretion onto seed BHs: the impacts of radiation anisotropy and gas angular momentum
Abstract
Seed black hole (BH) growth by gas accretion is supposed to play a crucial role in the formation of supermassive BHs. In this talk, I will present the results of our simulations that follow gas accretion onto seed BHs under radiation feedback considering the radiation anisotropy and gas angular momentum. We find that the effects of radiation anisotropy and gas angular momentum can significantly change the accretion rate. I will also discuss the growth of Pop III remnant BHs based on our findings.
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RESCEU Colloquium No. 24
Date and Time: May 17, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kyohei Kawaguchi
(ICRR, Univ. of Tokyo)
Gravitational-wave templates for inspiralling binary neutron stars
Abstract
On 17th of August 2017, three ground-based gravitational-wave detectors, advanced LIGO and advanced Virgo, reported the first detection of gravitational waves from a binary neutron star merger. Gravitational waves from binary neutron stars contain rich information of the neutron stars, in particular, of the equation of state through so-called the tidal deformability. To extract the tidal deformability of neutron stars from the observed gravitational-wave data, an accurate theoretical waveform template is crucial. In this talk, I will present our recent result developing a model for frequency-domain gravitational waveforms from inspiraling binary neutron stars based on the latest numerical-relativity simulations and analytic models, and discuss the measurability of the tidal deformability from gravitational waves from binary neutron stars in future observation.
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RESCEU Colloquium No. 23
Date and Time: April 19, 2018, 13:30-14:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Peter Behroozi
(University of Arizona)
Automated Physics Recovery from Galaxy Observations
Abstract
I discuss new methods that allow computers to recover the underlying physics of galaxy formation using only galaxy observations and dark matter simulations, and show how these methods have already changed our understanding of galaxy formation physics (including why galaxies stop forming stars). Basic extensions to the same techniques allow constraining internal galaxy processes, including coevolution between galaxies and supermassive black holes as well as time delays for supernova / GRB progenitors. Finally, I discuss how these methods will benefit from the enormous amount of upcoming data in widefield (HETDEX, LSST, Euclid, WFIRST) and targeted (JWST, GMT) observations, as well as ways they can benefit observers, including making predictions for future telescopes (especially JWST) and testing which of many possible targeted observations would best constrain galaxy formation physics.
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RESCEU Colloquium No. 22
Date and Time: April 02, 2018, 11:00-12:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Roxanne Ligi
(INAF-Astronomical Observatory of Brera)
Detection and characterization of exoplanetary systems: The contribution of high angular resolution
Abstract
The quest of exoplanets is driven by our search for habitability and our understanding of planetary formation. Whatever the detection method used, the exoplanets parameters are strongly linked to stellar properties. Thus, to know the planet, we have to know the star. However, characterising stars is not an easy task, as direct measurements are limited to bright stars and stellar models meet degeneracies. I will show how high angular resolution can be used both for exoplanetary detection and characterisation. In particular, I will show how interferometry is precious to derive global stellar parameters, and can lead to the determination of internal structure of exoplanets. Finally, direct imaging is a good solution for bringing insights in planetary formation theories.
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RESCEU Colloquium No. 21
Date and Time: March 23, 2018, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Aurélien Crida
(Univ. Côte d'Azur/Obs. Côte d'Azur)
Satellite formation from rings
Abstract
The world of Saturn is fascinating. Cassini's stunning pictures have revealed an extraordinary diversity in the satellites and the rings. However, one intriguing feature appears to link them: the mass of the satellites increases as a power law of their distance to the rings. This can not be explained in the classical model of satellite formation in a gaseous disk around the planet, like a mini-solar system. In this seminar, I will show that Saturn's satellites are actually formed from the spreading of the rings beyond the Roche radius. Starting from basic notions, this model will be explained. In particular, it will be demonstrated how this mechanism explains the mass - distance feature. The history of the evolution of the rings and the satellites can then be revisited. Finally, I will argue that this mechanism can be generalized to all planets of the Solar System (except Jupiter), and that most regular satellites are born from the spreading of massive planetary ring!
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RESCEU Colloquium No. 20
Date and Time: January 18, 2018, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Mark Hindmarsh
(University of Sussex)
Gravitational waves from phase transitions in the early Universe
Abstract
About 10 picoseconds after the beginning of the Universe, the Higgs field turned on. In extensions of the Standard Model of particle physics, this could have been a first order phase transition, with the spontaneously nucleated bubbles of the Higgs phase expanding and colliding at relativistic speeds. I will discuss how sound waves from colliding bubbles generate gravitational radiation, prospects for observing the radiation at the future space-based gravitational wave detector LISA, and outline how LISA complements the LHC as a probe of physics beyond the Standard Model.
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RESCEU Colloquium No. 19
Date and Time: January 10, 2018, 16:30-17:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
George Hobbs
(CSIRO)
Pulsar and transients observations at Parkes and towards the SKA
Abstract
I will describe historical and on-going pulsar observing projects with the Parkes telescope. This will include a discussion on the Parkes Pulsar Timing Array (PPTA) project that aims to use pulsars to detect ultra-low-frequency gravitational waves and the various pulsar search projects that had led to Parkes being used to discover more than half of the known pulsars. I will describe how the SKA will be used to search for and study pulsars and highlight various technical challenges relating to the SKA.
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RESCEU Colloquium No. 18
Date and Time: November 20, 2017, 16:30-18:30
Location: 5F Auditorium in Chemistry Main Building
Kipp Cannon
Masaomi Tanaka
(RESCEU
NAOJ)
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

Electromagnetic Wave Observations of GW170817
Abstract
On August 17, 2017 at 12:41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made the first observation of a compact object collision consistent the the inspiral and merger of a pair of neutron stars. 1.7 s later GRB 170817A was detected by Fermi-GBM, and 10.5 h later supernova SSS17a was identified the 1M2H team using the 1 m Swope Telescope, both in the same part of the sky from which the GWs originated. Many hundreds of observations of the event have followed, marking the dawn of the era of joint gravitational and electromagnetic astronomy. I will present a summary of the gravitational wave discovery and what we have learned from the signal.

The first gravitational wave (GW) observation from a neutron star merger was successfully made for GW170817. The detection triggered electromagnetic (EM) wave observations over the entire wavelength range, which enebled the first identification of an EM counterpart of a GW source. I review EM observations of GW170817 and discuss implications from observations and open questions.
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RESCEU Colloquium No. 17
Date and Time: June 19, 2017, 16:15-17:15
Location: Room 233 on 2nd Floor, Sci. Bldg. 1
Misao Sasaki
(Kyoto University)
Inflationary massive gravity
Abstract
Inflation is a natural platform for modified gravity. Here we present a new massive gravity theory in which the gravitational wave (GW) modes become massive during inflation. Then we discuss its observational signatures, which are particularly intriguing in this coming era of GW physics/astronomy.
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RESCEU Colloquium No. 16
Date and Time: April 20, 2017, 13:00-14:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Kent Yagi
(Princeton University)
Probing Extreme Gravity with Gravitational Waves
Abstract
The binary black hole merger events recently discovered by the LIGO and Virgo Collaboration offer us excellent testbeds for exploring extreme (strong and dynamical-field) gravity that was previously inaccessible. In this talk, I will first review the current status of testing such gravity with GW150914 and GW151226, in particular, explaining how well one can probe various fundamental pillars in General Relativity. I will then describe what comes next in terms of testing gravity with gravitational waves. Regarding black-hole based tests of gravity, I will discuss how one can stack multiple ringdown events to probe black hole no-hair property. Regarding neutron star based tests of gravity, I will use approximate universal relations ("I-Love-Q relations") among certain neutron star observables that are almost insensitive to the unknown stellar internal structure, and describe how one can extract extreme gravity information by combining future gravitational wave and binary pulsar observations. I will conclude with a summary of important future directions.
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RESCEU Colloquium No. 15
Date and Time: March 02, 2017, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Bernard Carr
(Queen Mary University of London)
Primordial black holes as dark matter and seeds for cosmic structure
Abstract
The possibility that the dark matter comprises primordial black holes (PBHs) is considered, with particular emphasis on the currently allowed mass windows at 1016 - 1017g, 1020 - 1024g and 10 - 103 M. The last possibility is of special interest in view of the recent detection of black-hole mergers by LIGO. All relevant constraints (lensing, dynamical, large-scale structure and accretion) are considered and various effects necessary for a precise calculation of the PBH abundance (non-Gaussianity, non-sphericity, critical collapse) are accounted for. It is difficult to put all the dark matter in PBHs if their mass function is monochromatic but this is still possible if the mass function is extended, as expected in many scenarios. A novel procedure for confronting observational constraints with an extended PBH mass spectrum is therefore introduced and this is applied for two inflationary models. Even if PBHs provide only a small fraction of the dark matter, they could generate cosmological structure through either the 'seed' effect on small scales or the 'Poisson' effect on large scales. For example, if supermassive PBHs with much less than the critical density seed galaxies, this naturally explains the proportionality between the mass of the central black hole and the galactic mass. On the other hand, if intermediate mass PBHs provide the dark matter, the first bound clouds of 106 M would form through Poisson fluctuations much earlier than usual. In principle, an extended PBH mass spectrum could permit them to fulfill all of these roles - providing the dark matter, the first bound clouds and galaxies. The gravitational wave background from the PBHs would then extend from the LIGO frequency (due to dark matter black holes) to the LISA frequency (due to galactic nuclei black holes).
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RESCEU Colloquium No. 14
Date and Time: February 20, 2017, 15:30-16:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Alexei Starobinsky
(Landau Institute for Theoretical Physics RAS and RESCEU)
From generic classical curvature singularity in GR and f(R) gravity to inflation
Abstract
I discuss how generic is the onset of inflation from generic classical curvature singularity preceding it in GR and f(R), and which conditions are needed for it. For viable inflationary models in these kinds of gravity theory, the inflaton potential in the Einstein frame is not important near the singularity. Thus, its boundedness in models producing the best fit to observational data does not reduce the degree of generality of inflation. Space-time is asymptotically locally homogeneous near the singularity, despite the absence of causal connection, due to the very structure of field equations. However, an intermediate period when spatial gradients become important may well occur before the beginning of inflation. As a whole it seems that, for inflation to begin inside a patch including the observable part of the Universe, causal connection inside the whole patch is not necessary. However, it becomes obligatory for a graceful exit from inflation in order to have practically the same number of e-folds during inflation inside this patch. Also, the fact that inflation does not "solve" the singularity problem, i.e. it does not remove a curvature singularity preceding it, can be an advantage, not its weakness.
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RESCEU Colloquium No. 13
Date and Time: December 15, 2016, 14:00-15:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Stefan Ballmer
(Syracuse University/LIGO)
What comes next for Gravitational-Wave Astronomy
Abstract
One year ago the Advanced LIGO detectors provided the first observation of gravitational waves from merging black holes. They just started to observe again this fall. I will discuss what we learned from the initial discovery, and where the detector sensitivity stands for the current observation run. Then I will look into the future, describing the next sensitivity upgrades for the detectors, and what we hope to observe with them. I will conclude by looking at possible future gravitational-wave observatories capable of observing binary mergers from an era when the first stars just started to form.
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RESCEU Colloquium No. 12
Date and Time: August 23, 2016, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Gonjie Li
(Harvard University)
Interactions of Planetary Systems with passing Stars and Binaries
Abstract
N/A
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RESCEU Colloquium No. 11
Date and Time: April 21, 2016, 14:00-15:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Surhud More
(Kavli IPMU)
Detection of halo assembly bias and the splashback radius of galaxy clusters
Abstract
Dark matter halos are the basic building blocks that form the large scale structure in the Universe. I will present an overview of our knowledge about the internal structure of these halos, their large scale distribution, and the connection between the two, based on numerical simulations of cold dark matter in the concordance cosmological model. I will talk about some of the recent theoretical developments regarding the physical boundaries of dark matter halos, and their connection to the assembly history of these halos. I will present observational evidence supporting these new developments. In particular, I will highlight the recent detections of halo assembly bias on galaxy cluster scales, and the edges of galaxy clusters, and how these advances will help us to further our understanding of galaxy formation and the challenges they present to cosmological inferences.
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RESCEU Colloquium No. 10
Date and Time: March 17, 2016, 16:00-17:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Krzysztof M. Gorski
(JPL/Kavli IPMU)
The Future of Cosmology with the CMB
Abstract
Observational cosmology has seen a remarkable quarter century of space exploration of the cosmic microwave background with the satellite missions COBE, WMAP, and Planck. I will briefly review the advances that these effort brought about, and discuss current prospects for the future, polarization measurements oriented CMB satellite proposals, including LiteBIRD in Japan, and the forthcoming suborbital CMB projects.
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RESCEU Colloquium No. 9
Date and Time: February 12, 2016, 16:30-18:00
Location: Room 1220 on the 2nd Floor, Sci. Bldg. 4
Kipp Cannon
(RESCEU)
Results From Advanced LIGO's First Science Run
Abstract
In its first 400 hours of operation, Advanced LIGO had already surveyed a larger space-time volume than all previous gravitational-wave detection experiments combined. I will discuss some of the conclusions drawn from this early effort.
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RESCEU Colloquium No. 8
Date and Time: December 08, 2015, 16:30-18:00
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Francois R. Bouchet
(Institut d'Astrophysique de Paris)
Cosmology with the Planck satellite
Abstract
Sketched out in 1992, selected by ESA in 1996, and launched in 2009, the Planck satellite was shut off in 2013, after a measuring mission that exceeded all expectations. The Planck collaboration delivered a first set of cosmological data and results in March 21st 2013, and the full set in February 2015. Part of the data delivery is a "definitive" map of the anisotropies of the Cosmic Microwave Background (CMB), its angular power spectrum together with their full statistical characterisation. The 2015 delivery also includes pioneering polarisation data. The temperature anisotropy map displays minuscule variations as a function of the observing direction, of rms ~100 microK, of the fossil radiation around its mean temperature of 2.725K. Other maps reveal the CMB polarisation. The anisotropies are the imprint of the primordial fluctuations which initiated the growth of the large scale structures of the Universe, as transformed by their evolution, in particular during the first 370 000 years. The polarisation is another imprint whose theoretical implications can then be confronted with those derived from the temperature field. I will describe some of our key results we obtained so far from temperature and polarisation data, both in terms of content of the universe and of characteristics of the primordial fluctuations, in particular concerning precision tests of key hypotheses of the standard model of cosmology, like the flat spatial geometry or Gaussianity, adiabaticity and per cent deviation from scale invariance of the primordial fluctuations.
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RESCEU Colloquium No. 7
Date and Time: November 09, 2015, 16:00-17:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Robert Wittenmyer
(The University of New South Wales)
The great unveiling: a new golden age of exoplanetary science
Abstract
Less than a generation ago, we wondered, as we had for millions of years before, whether there were any other planetary systems at all. Now, we are privileged to be in the first generation of humans to know that many of the points of light dusting our night sky are host to orbiting worlds, some of which may be like our Earth. With that privilege comes the mighty task of our time, to unlock the secrets of the diversity of worlds. I will give an overview of the "discovery revolution" that brought us here. I will then describe the tremendous challenges and opportunities awaiting us in exoplanetary science over the next decade. The next revolution will be one of understanding - a "great unveiling" as we learn the detailed properties of the planetary systems in the Solar neighbourhood.
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RESCEU Colloquium No. 6
Date and Time: July 08, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Giuseppe Bono
(Univ. of Rome Tor Vergata)
On the distribution of neutron capture elements across the Galactic thin disk using Cepheids
Abstract
We present new results concerning the distribution of neutron capture (s-, r-) elements across the Galactic thin disk. We use young (classical Cepheids) stellar tracers for which we collected high spectral resolution, high signal to noise optical spectra with UVES at VLT (ESO). We found that the five (s: Y, La, Ce, Nd; r: Eu) investigated elements show well defined negative gradients when moving from the innermost to the outermost regions. Moreover, we also found that the gradients of the above elements are positive as a function of age/pulsation period. Thus suggesting a trend with age similar to alpha-elements. On the other hand, the slopes of [element/Fe] vs Galactocentric distance are more positive than for alpha-elements. We introduce plausible working hypothesis to take account of the difference, and perform a detailed comparison with similar abundances for dwarf and giant stars available in the literature. Finally, we discuss the abundance ratio between s- and r- elements (La/Eu) and between heavy and light s- elements (La/Y) and outline their impact on the chemical enrichment history of the Galactic thin disk.
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RESCEU Colloquium No. 5
Date and Time: July 03, 2015, 17:00-18:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Samaya Nissanke
(Radboud University Nijmegen, the Netherlands)
Follow the chirp: seeing and listening to the transient Universe
Abstract
The mergers of binary compact objects (black holes, neutron stars, white dwarfs) are amongst some of the most violent events in the Universe. The physics driving these events in strongly curved spacetimes are extremely complex, rich but still remain elusive. These cosmic laboratories present us now with both a challenge and an opportunity. The challenge is to explain the physics at play in strong-field gravity in Universe. The opportunity is to detect the accompanying electromagnetic (EM) and gravitational radiation for the first time with a suite of time-domain telescopes and newly upgraded gravitational wave (GW) detectors.In this pivotal new era of strong-field gravity astronomy, the most compelling astrophysical sources are neutron star binary mergers, which should emit both in electromagnetic and GWs. I will first review the most recent advances in this blossoming field of EM + GW astronomy, which combines two active disciplines: time-domain astronomy and general relativity. I will discuss the promises of this new convergence by illustrating the wealth of astrophysical information that a combined EM+GW measurement would immediately bring. I will then outline the main challenges that lie ahead for this new field in pinpointing the sky location of neutron star mergers using GW detectors and optical and radio wide-field synoptic surveys.
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RESCEU Colloquium No. 4
Date and Time: May 11, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Anupam Mazumdar
(Physics Department, Lancaster University)
Universal laws of Gravity without Singularity
Abstract
I will discuss classical singularity theorem of General relativity, and then construct a general covariant theory of gravity which can avoid cosmological and blackhole singularities in the ultraviolet and reduces to the predictions of Einstein's theory of gravity in the infrared. I will also discuss how such an action may arise from string theory.
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RESCEU Colloquium No. 3
Date and Time: May 13, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Shin'ichiro Ando
(GRAPPA, Univ. of Amsterdam)
Dark matter searches in anisotropic gamma-ray sky
Abstract
As a viable candidate of dark matter, weakly interacting massive particle (WIMP) has been studied. WIMP is considered to annihilate with itself, and as its consequence, to produce high-energy gamma rays. Since dark matter has been annihilating (if ever happens) since the beginning of the structure formation, it gives contributions to the diffuse gamma-ray background measured with the Fermi satellite. The measurement of the gamma-ray background spectrum already gives one of the tightest constraints on the annihilation cross section. Since Fermi already collected more than 5 million photons from the whole sky (above 1 GeV), it is possible to discuss anisotropy* of the gamma-ray background. I will discuss (1) the angular power spectrum, (2) one-point PDF of the gamma-ray flux, and (3) cross correlation with local galaxy catalogs, and prospects on discovering dark matter particles in the near future in the gamma-ray data.
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RESCEU Colloquium No. 2
Date and Time: April 22, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Kipp Cannon
(Canadian Institute for Theoretical Astrophysics / University of Toronto)
Challenges in Gravitational-Wave Astronomy
Abstract
Gravitational radiation promises new knowledge about our world, but all attempts to observe gravitational waves (GWs) have been unsuccessful. There are many challenges to overcome in our quest to detect this elusive form of energy. I will describe how multivariate classifier techniques have been used to combat detector noise in searches for GWs from cosmic strings with LIGO and Virgo, and how the search for binary neutron star collisions has created new techniques for modeling collision waveforms.
Rapid detection of GWs will allow GW antennas like KAGRA to join a larger transient astronomy community and will provide exciting, new, information about the Universe. I will describe the analysis techniques used to achieve the extreme performance required to search for GWs from neutron star collisions with tens of seconds of latency. Finally, I will comment on some challenges that lay ahead for our community, and what might be done to address them.
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RESCEU Colloquium No. 1
Date and Time: April 20, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Pisin Chen
(National Taiwan University)
Radiowave Detection of Ultra High Energy Cosmic Neutrinos and Cosmic Rays
Abstract
There has been tremendous progress in the field of particle astrophysics in recent years, exemplified by the results from the Pierre Auger Observatory in Argentina on ultra high energy cosmic ray (UHECR) detection and the IceCube at the South Pole on PeV cosmic neutrino observation. Here we introduce a novel methodology based on the detection of the radio wave signals emitted by the ultra high energy cosmic neutrinos (UHECN) and cosmic rays. Such radio wave signals can be either triggered by the Askaryan effect or the geosynchrotron effect. In this talk we will review the several projects based on this approach, namely ANITA, ARA, and TAROGE, that have been pursued by the Leung Center for Cosmology and Particle Astrophysics (LeCosPA) at the National Taiwan University. We will first review the science potentials in astrophysics and particle physics through the detection of UHECR and UHECN. We will then report on the history, status and the future prospect of ANITA, ARA, and TAROGE observatories, including their scientific results obtained so far.
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