Research News

2020-02-26

New story released "Let's ask a RIKEN doctor!" (Written in Japanese)

"Let's ask a RIKEN doctor!" is a content that explains the forefront of RIKEN research for children in an easy-to-understand.

2020-02-19

Modeling the insides of a neutron star -- Improvements to a model for the inside of a neutron star make it applicable to neutron star mergers

RIKEN astrophysicists have developed an improved model for the interior structure of neutron stars that agrees well with observations. Unlike previous models, it can be extended to consider what happens when two neutron stars merge. The collapsed remnants of giant stars, neutron stars are fascinating objects. They are a mere 20−30 kilometers in diameter but are nearly 400,000–600,000 times more massive than the Earth, which makes them incredibly dense. Neutron stars are not uniform agglomerations of neutrons—like the astrophysical equivalent of a giant atomic nucleus containing only neutrons. Rather they have an onion-like structure. Theorists have been busy trying to model this internal structure based on quantum mechanics and data from observations.

2019-12-18

Blasts from the past, article on RIKEN Research with reference of iTHEMS Researchers

The evolution of an exploding star begins more haphazardly than previously thought.

2019-11-22

Discovery of teraelectronvolt photons from gamma-ray bursts: A new window for exploring the most luminous explosions in the Universe

On January 14, 2019, TeV gamma rays (photons with energies a trillion times that of visible light) were clearly detected for the very first time from a gamma-ray burst (GRB; dubbed GRB 190114C) by the MAGIC telescopes. The very high energy of the individual photons as well as the high power of the total signal demonstrate that they must be produced by a physical process that is distinct from the previously known afterglow synchrotron radiation. Combined with extensive multiwavelength data obtained by a large number of observatories from the radio to GeV bands, the most likely mechanism is judged to be "inverse Compton” radiation associated with the afterglow, whereby some synchrotron photons are significantly boosted in energy by colliding with high-energy electrons [1]. These findings were reported in two papers published on Nov. 21 in the journal Nature, one authored by the MAGIC Collaboration where Susumu Inoue of iTHEMS is the first corresponding author [2], and the other co-authored by a large team of astronomers including the MAGIC Collaboration [3]. Caption for the figure: Spectra of GRB 190114C in the X-ray to TeV gamma-ray energy range during two time intervals (top: 68-110 seconds after the beginning of the GRB; bottom: 110-180 seconds ibid.). Markers reflect data: white circles are observed MAGIC data; orange circles are MAGIC data corrected for intergalactic propagation effects. Curves are theoretical models: thin solid curves are synchrotron emission and inverse Compton emission shown separately; thick blue curves are their sum; dashed curves are inverse Compton emission when neglecting internal absorption effects.

2019-11-19

Article about iTHEMS on Journal of the Mathematical Society of Japan

Professor Takashi Tsuboi, Deputy Program Director of iTHEMS posted an article about RIKEN iTHEMS on Journal of the Mathematical Society of Japan. See the article in the November issue from the following link.

2019-10-30

The modelling work on supernova remnants made at ABBL & iTHEMS is highlighted in the latest image release from NASA's Chandra observatory

On October 17 the Chandra X-ray Observatory released an updated image of the supernova remnant known as Tycho. Supernova remnants, the aftermath of a stellar explosion, are key to understand how stars end their lives, and how physical elements are synthetized and distributed in the galaxy. The new image, besides being visually striking, contains important clues to understand the explosion physics. Two papers are introduced in the text of the image release. The first paper, Sato et al 2019 (Genus Statistic Applied to the X-ray Remnant of SN 1572: Clues to the Clumpy Ejecta Structure of Type Ia Supernovae), used a new image analysis technique to mathematically characterize the clumpiness of the ejecta. The second paper, Ferrand et al 2019 (From the supernova to the supernova remnant: the three-dimensional imprint of a thermonuclear explosion), presented 3D numerical simulations made from a physically-motivated supernova explosion model. Both works conclude that part of the irregularities visible on the image, at an age of about 450 yr, were actually present from the very beginning. The two teams are now collaborating on the image analysis for the comparison of observations with models. Related work is also on-going with other colleagues at Rikkyo University. The 3D printed model on the photo was made from G. Ferrand's simulations. Credit: RIKEN/G. Ferrand, et al & NASA/CXC/SAO/A. Jubett, N. Wolk & K. Arcand

2019-09-17

Tracking down the origin of photons in gamma-ray bursts, article on RIKEN Research by Drs. S. Nagataki & D. Warren

The photons released by long gamma-ray bursts - the most powerful electromagnetic phenomena in the Universe - originate in the photosphere, the visible portion of the ‘relativistic jet’ emitted by exploding stars, according to simulations by RIKEN researchers.

2019-09-17

The shape of circadian rhythm, article on RIKEN Research by Drs. S. Gibo & G. Kurosawa

The waveforms of circadian cycles in bacteria, flies and mammals become increasingly jagged as the temperature rises, two RIKEN researchers have predicted. This finding is a step toward solving the mystery of how circadian rhythms remain consistent under changing conditions.

2019-09-04

iTHEMS is focused on RIKEN NEWS

iTHEMS is focused on RIKEN NEWS. See the cover and the article on August issue (page 6 from the following link).

2019-08-30

Gilles Ferrand was highlighted in a recent article of RIKEN Research "Supernova remnants used to probe how star explosion took shape"

RIKEN astrophysicists have bridged the gap between studies of supernova and those of their remnants by using the output of a supernova model as the input for a model of a supernova remnant. This approach offers a way to assess the validity of supernova models.

2019-05-15

Masaru Hongo was highlighted in a recent article of RIKEN RESEARCH "Describing the early Universe by simplifying complicated equations"

A powerful mathematical method for simplifying the analysis of highly complex systems has been extended by a RIKEN-led team. This will enhance its usefulness for researchers in a wide range of fields.

2019-05-08

Masaru Hongo and Tatsuhiro Misumi were highlighted in a recent article of RIKEN RESEARCH "A smaller spin system yields its phase diagram"

By employing a clever approximation, three theoretical physicists at RIKEN (Masaru Hongo and Tatsuhiro Misumi of the iTHEMS and Yuya Tanizaki of the RIKEN BNL Research Center) have calculated the phase diagram for an extension of a system proposed over 30 years ago. In addition to advancing the theory of condensed matter physics, this finding could have practical implications for systems made up of particles with the quantum property of spin. This research highlighted in a recent article of RIKEN RESEARCH.

2019-05-08

Review on synthetic dimensions published in Nature Reviews Physics

Nature Reviews Physics is a new journal, just launched this year, focusing on publishing reviews in the area of physics. Dr. Tomoki Ozawa (iTHEMS Senior Research Scientist) together with Dr. Hannah M. Price (University of Birmingham, UK) wrote a review for Nature Reviews Physics on “synthetic dimension,” which is a recently emerging method for simulating high dimensional models using low dimensional platforms making use of non-spatial degrees of freedom as effective dimensions. The review summarizes the current status of the research of synthetic dimensions with a focus on atomic, molecular, and optical physics, where the method is most actively studied. A figure from the review is also adapted for the cover of the May 2019 issue of Nature Reviews Physics.

2019-04-01

Review on Topological Photonics published in RMP

A team of physicists led by Dr. Tomoki Ozawa (iTHEMS Senior Research Scientist) published a review article titled "Topological photonics" in Reviews of Modern Physics. Study of topological phases of matter started in solid-state physics through the discovery of the quantum Hall effect. However, it has been recognized during the past decade that topological band structures, which are at the heart of the phenomenon of the integer quantum Hall effect, are general properties of waves inside medium, and thus are much more ubiquitous. One of the most active fields outside solid-state electron systems where topological physics has been studied is photonics. This review summarizes the current status of the study of topological band structures and topological phases of matter in photonics and related fields. The review is authored by an international collaboration of eleven scientists including both theoretical and experimental researchers from eight different countries.

2019-03-12

Papers soon-to-be published in Nature Communications

A recent paper authored by several iTHEMS members has been accepted for publication in Nature Communications. The authors from iTHEMS include Hirotaka Ito (ABBL /iTHEMS), Shigehiro Nagataki (ABBL/iTHEMS) and Don Warren (iTHEMS). Congratulations! There will be a press release. Here is the explanation on the article by Hirataka Ito: "The photospheric origin of the Yonetoku relation in gamma-ray bursts” by Hirotaka Ito, Jin Matsumoto, Shigehiro Nagataki, Donald C. Warren, Maxim V. Barkov & Daisuke Yonetoku Accepted for publication in Nature Communications. arXiv:1806.00590 Gamma-ray bursts (GRBs), an intense flash of gamma-rays that is observed almost every day, are the brightest event in the Universe. Decades of studies have revealed that they are originating from a relativistic jet launched at the death of massive star. However, exactly how the gamma-rays are emitted from the jet is still veiled in mystery. One unresolved question is the origin of the correlation between the spectral peak energy and peak luminosity discovered in observations. This “Yonetoku relation” is the tightest correlation found in the properties of GRB emission, providing the best diagnostic for the emission mechanism. In this study, we focused on the so-called “photospheric emission” model which is one of the leading models for the emission mechanism of GRBs. To test the validity of the model, global dynamics of relativistic jet and radiation transfer must be taken into account. To tackle this issue, we performed three-dimensional relativistic hydrodynamical simulations and radiation transfer calculations to evaluate photospheric emission from relativistic jet that is breaking out of massive star envelope. Our simulations revealed that the Yonetoku relation is reproduced as a natural consequence of the jet-stellar interactions. This result strongly suggests that photospheric emission is the emission mechanism of GRBs.

2018-12-13

Di-Omega in QCD on the front page of an in-house magazine

Di-Omega in QCD reported in the previous iTHEMS NewsLetter became a front page of the latest news letter of "Science and technology companies pension fund". It is amazing that the pension fund organization is interested in elementary particle physics!

2018-11-08

Susumu Inoue (iTHEMS Research Scientist) was highlighted in a recent article of RIKEN RESEARCH "Highly energetic neutrino traced back to a blazar"

"The spectrum measured by MAGIC strongly points to the neutrino being generated by a high-energy proton in the blazar’s jet interacting with low-energy photons,” says Susumu Inoue of RIKEN’s Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program, who is part of the MAGIC team.

2018-10-11

X-ray telescope reveals the Milky Way’s halo of hot gas is fed by supernovae

The Milky Way is a spiral galaxy up to 100,000 light years across, and our Sun is just one of hundreds of billions of stars within it. The galaxy has a halo, which is partly made up of gas accumulated from the vast expanses of intergalactic space but is also molded and supplemented by matter ejected from the galaxy’s stars. The balance between these two sources is not fully understood, and there is ongoing debate about the halo’s size and shape. RIKEN Researchers have mapped this halo gas using the Suzaku X-ray telescope and revealed how exploding stars have helped to shape this blazing shroud.

2018-09-26

Tightening the noose on neutron star radii

The study by Oliver Just (Nagataki's lab.) and his collaborators in Germany and Greece has added much needed clarity to limiting the neutron star radius, a parameter that provides vital clues about the microphysics of neutron stars and hence also about the microphysics of nuclei on Earth. “Before our study, the radius of a neutron star was only weakly constrained from below,” Just says.

2018-09-10

Book on "Origins of the Gravitational Wave"

Kotaro Kyutoku (Assistant Prof. in KEK and iTHEMS visiting researcher. Former iTHEMS SPDR) has published a book "Origins of the Gravitational Wave" in Japanese with Masaru Shibata (Max Planck Institute and Kyoto Univ.). It contains excellent explanations on general relativity and black holes, structure of neutron stars, supernova explosion, gamma-ray burst, gravitational wave, mergers of black holes and neutron stars, and current/future gravitational wave detectors on earth and space. Everybody who is interested in GW should have one in his/her bookshelf. English translation will be called for.

2018-09-03

The Di-Omega Picture

The image of Di-Omega (an exotic particle with 6 strange quarks) was selected as the front page picture of the August issue of RIKEN NEWS (vol.446, 2018). This is based on the work done by HAL QCD Collaboration composed of 6 institutions (RIKEN Nishina Center, RIKEN iTHEMS, YITP in Kyoto Univ., CCS in Univ. Tsukuba, RCNP in Osaka Univ. and Nihon Univ.).

2018-07-17

High-energy neutrinos from a gamma-ray emitting supermassive black hole: the dawn of the electroweak sector of multi-messenger astronomy

Background: Since 2010, the IceCube Observatory, utilizing a cubic-km volume of ice in Antartica, has been detecting neutrinos with energies exceeding 100 TeV (~10^13 times the energy of a visible photon), which likely originate from astrophysical sources outside of the Milky Way Galaxy. However, their sources remained unknown, mainly due to the limited accuracy of their localizations in the sky. From 2016, IceCube initiated a new, automated alert program that rapidly identifies significant neutrino candidates and widely disseminates their sky positions, so that telescopes around the world can immediately search for potential counterparts at various wavelengths. Result: On September 22, 2017, a neutrino with energy ~300 TeV (dubbed IceCube-170922A) was detected with relatively good sky localization, and was rapidly followed up by numerous telescopes operating across the electromagnetic spectrum. The Fermi-LAT satellite and the MAGIC telescopes identified an object (named TXS 0506+056) shining brightly in gamma-rays (Fig. 1). The object is classified as a “blazar”, a type of supermassive black hole that is actively ejecting “jets" of plasma at relativistic velocities nearly toward us. This is the first time that a likely source of high-energy neutrinos has been identified with reasonable confidence [1]. These results were published in the July 13 issue of Science magazine, in a paper authored by more than 1100 scientits in 16 collaborations, including Susumu Inoue of iTHEMS as a member of the MAGIC Collaboration [2]. Implications: The production of such high-energy neutrinos requires the acceleration of hadrons (proton or nuclei) to extremely high energies. This implies special physical conditions in the jets from supermassive black holes, and offer valuable clues on the formation mechanism of the jets, which is not well understood. This may also be the first step in solving the long-standing mystery of the origin of ultra-high-energy cosmic rays, the highest energy particles known to exist in the Universe [3]. Finally, it may shed new light on the properties of neutrinos at energies far beyond the capability of terrestrial accelerator facilities. Prospects: Following on the heels of GW170817, the binary neutron star merger event discovered in August 2017 in gravitational waves and then identified in electromagnetic waves, this signals the dawn of the “electroweak" sector of multi-messenger astronomy involving neutrinos and photons. Vigorous efforts will continue in the next years, with bright prospects for elucidating the physics of supermassive black holes and their jets, the origin of high-energy neutrinos and cosmic rays, etc. Figure 1: Image of the sky at optical wavelengths of the region of interest. Overlayed are the positional uncertainties of the neutrino IceCube-170922A, and those of the blazar TXS 0506+056 at optical wavelengths and in gamma rays observed by Fermi and MAGIC.

2018-05-11

Shigehiro Nagataki (Deputy Program Director, iTHEMS) was featured in RIKEN NEWS, pp.02-05, No. 443 (2018 May issue) with the title "Why the massive stars explode?"

2017-12-18

An article about ithems was published in the RIKEN NEWS 2017 December p.10-13

2017-10-21

Masato Taki (Senior Research Scientist, iTHEMS) authored a new book on deep learning