Cassiopeia A is the remnant of an exploded star in the Cassiopeia constellation, about 11,000 light years away from us. Light from the explosion should have reached Earth for the first time around 1670. However, there was too much gas and dust around the star for the explosion to be seen with the naked eye or with the then very basic telescopes. The Cassiopeia A explosion nebula is expanding at an average rate of 4000 to 6000 kilometres per second and has a temperature of about 30 million degrees Celsius. The expansion is most likely occurring in gas that was blown out by the star long before the explosion. Cassiopeia A is now about 16 light years across.

## 19 years of data

The researchers, led by GRAPPA member Jacco Vink analysed 19 years of data from the Chandra X-ray Observatory. This is an American X-ray satellite with Dutch spectrometers that orbits the Earth in a high elliptical orbit. The scientists observed that on the western side of Cassiopeia A, the inner regions of the explosion nebula are not expanding, but moving inwards. The researchers also took measurements of the acceleration or deceleration of the outer shock wave. This outer shock wave turned out to accelerate in the west instead of decelerating as was expected.

“The backward movement in the west can mean two things,” says Jacco Vink. “Either there is a hole somewhere, a kind of vacuum, in the supernova material, causing the hot shell to suddenly move inwards locally. Or the nebula has collided with something.” From the models of Vink and his colleagues, a collision appears most likely. The computer models predict that after a collision, the shock first decreases in speed but then accelerates. “Exactly as we have measured,” says Vink.

## Italian group

The collision scenario was also investigated recently by an Italian group with whom Vink collaborates. They suspect that the shock wave collided with a shell of gas particles. This shell would have been created when the unexploded star blew away an irregular wind of gas particles at the end of its life.

The cooperation between Vink and the Italians did not happen out of the blue. The Italian group got to work on preliminary results that Vink showed at a conference in 2019. “When we recently found an acceleration and they predicted just that in their models, the puzzle pieces fell into place,” says Vink.

Cassiopeia A has attracted a lot of attention lately. For example, NASA’s new X-ray satellite IXPE published its first image of the exploded star on Valentine’s Day. And the James Webb Space Telescope will turn its infrared gaze to the supernova remnants later this year.

[Read the prepint](https://arxiv.org/abs/2201.08911).

Ejection nebula of supernova Cassiopeia A does not expand evenly


Astrophysicists and GRAPPA member Jacco Vink has received an NWO Large Investment grant in the amount of 1.5 million euros from the Netherlands Organisation for Scientific Research (NWO). The grant money will enable the Netherlands to develop and manufacture highly specialised cameras for the future southern Cherenkov Telescope Array (CTA), which is scheduled for construction in northern Chile. Jacco Vink will implement this project together with astronomers and physicists from the University of Amsterdam (GRAPPA members Sera Markoff and Christoph Weniger), the University of Groningen (Manuela Vecchi and Andrey Baryshev) and the NOVA lab located at the latter.

The array of 50 telescopes will indirectly measure the gamma-ray photons (particles of light) that enter our atmosphere and then generate a cloud composed mainly of electrons that are moving at close to the speed of light. This causes the electrons to emit a bluish light known as Cherenkov radiation. CTA’s telescopes register this nanosecond-long flashes of blue light and identify the direction in which the electron cloud is moving. In doing so, the CTA actually uses the atmosphere as a detector: the larger the portion of the atmosphere that is being looked at, the more sensitive the CTA is. And when the same flash is detected using multiple telescopes, it is possible to much more accurately determine the direction in which the electron cloud is moving. This, in turn, enables the scientists to more precisely identify the direction of the original gamma-ray photon as well. That is why they use so many telescopes.

Measuring the flash from multiple angles enables them to reconstruct the direction from which the gamma rays came and how much energy the gamma ray photon had. In this way, the location of a gamma ray source can be pinpointed to a precision of 0.1% of the lunar diameter, while images can be made with a pixel size of 10% of the lunar diameter. Known sources of gamma rays include jets created by black holes, the remnants of supernovas and neutron stars, though it might also be emitted when neutron stars merge and set off gravitational waves. Massive particles of dark matter can emit gamma rays as well. CTA hopes to shed new light on the composition of this mysterious and dark component of the universe.

CTA is a European project with international partners including the United States, Japan and Australia. While Dutch astronomers have been involved in the scientific plans for CTA for some time, countries are required to contribute to the array’s construction before they can participate in the CTA observation project. Thanks to the NWO Large grant, the Netherlands will now be able to make such a contribution. The Dutch project will be led from within the UvA, in close cooperation with the University of Groningen and the NOVA lab it hosts, which specialises in the development and construction of astronomical detectors via serial production. This NOVA team will build the detectors for the 50 telescopes that are meant to enable CTA to measure extremely high-energy gamma rays between 10 and 100 tera-electronvolts (TeV). 

More information can be found at [IoP](https://iop.uva.nl/shared/uva/en/news/news/2021/05/jacco-vink-to-use-large-grant-to-seek-out-the-sources-of-gamma-rays.html?origin=LiCYSg5eS82AR0H56Byw2A) and [NOVA](https://www.astronomie.nl/nieuws/jacco-vink-gaat-met-grote-subsidie-op-jacht-naar-de-bronnen-van-gammastraling-2820).

Jacco Vink to use large grant to seek out the sources of gamma rays

GRAPPA member Jacco Vink received an NWO Large Investment grant for €1.5M that will enable the Netherlands to develop and manufacture highly specialised cameras for the future southern Cherenkov Telescope Array (CTA).

Physicist Dr Samaya Nissanke of GRAPPA, the University of Amsterdam and Nikhef will receive the prestigious Suffrage Award for outstanding science, science communication and support of women in STEM. Dr Nissanke and eleven other awardees will be honored at an online celebration on Monday 8 March 2021, the tenth anniversary of the scheme. This will be the fifth Suffrage Science awards for the Engineering and Physical Sciences.

Professor Amina Helmi, University of Groningen, who nominated Dr Samaya Nissanke, University of Amsterdam and Nikhef, said: “Samaya is an excellent researcher focusing on a very hot topic in modern Astrophysics, namely on gravitational waves (Nobel Prize 2017) and how they tell us about the merger of pairs of neutron stars and black holes. She was part of the discovery of the first ever binary neutron star merger that was seen by gravitational waves by the international LIGO and Virgo collaboration in 2017. She was in fact part of the writing team for the discovery paper and was responsible for coordinating the follow-up from many different observatories. Not only is she an outstanding scientist, but she is also a fervent and devoted advocate of diversity and inclusion in science, and beyond. She is the chair of Netherlands Astronomy Equity and Inclusion Committee, which she helped set up.”

On International Woman’s Day in 2011, the inaugural cohort of eleven ‘Suffrage Scientists’ from the life sciences were recognised in a ceremony at the Institute of Contemporary Arts, London. Their awards were hand-crafted items of jewellery created by art students from Central Saint Martins-UAL, who worked with scientists to design pieces inspired by research and by the Suffragette movement. But rather than produce a new set of pieces for the next awards, each holder chose who they would like to pass their award onto, thus generating an extensive ‘family tree’ of incredible scientists and communicators.

Suffrage Science pioneer Professor Fisher said: “We dreamed up the awards scheme to celebrate the contribution that women have made to science, which often gets overlooked. This is as important now as it was ten years ago. This year’s awardees join a community of over 148 women scientists. I’m thrilled that since 2011, the awards have travelled from the UK, across Europe to the USA, Hong Kong, Iran and to Ghana, illustrating the international nature of science and engineering, and the global effort to improve the representation of women in STEM.”

Samaya Nissanke receives Suffrage Science Award

Physicist Dr Samaya Nissanke of GRAPPA, the University of Amsterdam and Nikhef will receive the prestigious Suffrage Award for outstanding science, science communication and support of women in STEM. 

We are pleased to announce two GRAPPA Postdoctoral Fellows who will be starting from fall 2021. They are Lionel London (postdoc at MIT) and Oscar Macias (postdoc at Kavli IPMU). We are very excited and look forward to welcoming and working with them in the very near future!

## Lionel London
![Lionel London](//images.ctfassets.net/g94voriuozkd/sQUP3aamPLSD92Ix6N5mR/e69d594f3b79897566e662405c7b8f3c/LionelLondon-768x769.png)

Lionel London earned his PhD in Physics at the Georgia Institute of Technology under the supervision of Deirdre Shoemaker. There he specialized in using simulations of binary black hole collisions to model gravitational waves from binary black hole mergers. He has since gone on to work as a postdoc at Cardiff University, and at MIT. His research to date has been impactful in tests of gravity as well as the detection and parameter estimation of astrophysical black hole mergers. His work combines General Relativity theory and numerics with insights from computer science and pure maths. 

As a member of the LIGO-Virgo-KAGRA collaboration, London is involved in efforts at the intersection of signal modelling, parameter estimation, and tests of General Relativity.

London says, “I am excited about solving puzzles related to black holes, general relativity, and the fundamental structure and story of the universe. My research aims to tackle some of the big questions in these topics. I want to know if it is possible to understand the nonlinear structure of black hole merger, and whether we use this understanding to learn more about the Universe from exotic theories of gravity to cosmology. During my time at GRAPPA I hope to make progress on these topics and thereby contribute to what we can learn from current Earth based experiments like LIGO, Virgo and KAGRA, as well as future detectors such as the Einstein Telescope and LISA.”

## Oscar Macias
![Oscar Macias](//images.ctfassets.net/g94voriuozkd/I3sBsHVRrbRkR2fS7d8NG/067482c1d927d40055e0fbbffc851e23/OscarMacias-300x200.png)

Oscar Macias currently holds a postdoctoral position at Kavli IPMU. He was previously a postdoctoral researcher in the Center for Neutrino Physics at Virginia Tech for 2015-2018. Before that, he completed his PhD in Physics from University of Canterbury, where he worked with Chris Gordon on dark matter searches with gamma rays.

Macias says, “I study energetic astrophysical phenomena, with a focus on potential signals from dark matter emission. I apply my expertise in analyzing cosmic rays and multiwavelength electromagnetic signals, my experience with numerical simulations, and my rigorous statistical background to probe the inner workings of the Universe. My work informs the current limitations of dark matter models to explain the observations, improves the sensitivity to dark matter searches by producing better background models, and provides precise probes of the high-energy Universe.”

Macias received his undergraduate degree in Civil Engineering from the National University of Colombia, Medellin in 2008, where he also completed his master degree in Physics in 2011. Before moving to Medellin for his undergraduate studies, he lived in a small village — far away from Colombian cities — which was badly affected by the Colombian internal conflict.

Macias adds, “The challenges I faced in the early stages of my educational path have galvanized my passion for equity, diversity and justice in academia. I plan to design and run workshops aimed at increasing the representation of minorities in Physics and Astronomy.”

GRAPPA Postdoctoral Fellows: Lionel London and Oscar Macias

We are pleased to announce two GRAPPA Postdoctoral Fellows who will be starting from fall 2021. They are Lionel London (postdoc at MIT) and Oscar Macias (postdoc at Kavli IPMU).

Astronomers may have found our galaxy’s first example of an unusual 
kind of stellar explosion. This discovery, made with NASA’s Chandra 
X-ray Observatory, adds to the understanding of how some stars shatter 
and seed the universe with elements critical for life on Earth.
This intriguing object, located near the center of the Milky Way, is a
 supernova remnant called Sagittarius A East, or Sgr A East for short. 
Based on Chandra data, astronomers previously classified the object as 
the remains of a massive star that exploded as a supernova, one of many 
kinds of exploded stars that scientists have catalogued. Using longer 
Chandra observations, a team of astronomers has now instead concluded 
that the object is left over from a different type of supernova. It is 
the explosion of a white dwarf, a shrunken stellar ember from a 
fuel-depleted star like our Sun. When a white dwarf pulls too much 
material from a companion star or merges with another white dwarf, the 
white dwarf is destroyed, accompanied by a stunning flash of light.
Astronomers use these “Type Ia supernovae” because most of them mete 
out almost the same amount of light every time no matter where they are 
located. This allows scientists to use them to accurately measure 
distances across space and study the expansion of the universe. Data 
from Chandra have revealed that Sgr A East, however, did not come from 
an ordinary Type Ia. Instead, it appears that it belongs to a special 
group of supernovae that produce different relative amounts of elements 
than traditional Type Ias do, and less powerful explosions. This subset 
is referred to as “Type Iax,” a potentially important member of the 
supernova family.
“While we’ve found Type Iax supernovae in other galaxies, we haven’t 
identified evidence for one in the Milky Way until now,” said Ping Zhou 
of Nanjing University in China, who led the new study while at the 
University of Amsterdam. “This discovery is important for getting a 
handle of the myriad ways white dwarfs explode.”
The explosions of white dwarfs is one of the most important sources 
in the universe of elements like iron, nickel, and chromium. The only 
place that scientists know these elements can be created is inside the 
nuclear furnace of stars or when they explode.

Astronomers are still debating the cause of Type Iax supernova 
explosions, but the leading theory is that they involve thermonuclear 
reactions that travel much more slowly through the star than in Type Ia 
supernovae. This relatively slow walk of the blast leads to weaker 
explosions and, hence, different amounts of elements produced in the 
explosion. It is also possible that part of the white dwarf is left 
behind.
UvA researcher Ping Zhou and GRAPPA member Jacco Vink are co-authors of the [paper](https://arxiv.org/abs/2006.15049), and more details can be found on [Harvard's Chandra website](https://chandra.harvard.edu/photo/2021/sgrae/ "Harvard Chandra website") and [NASA's website](https://www.nasa.gov/mission_pages/chandra/images/rare-blast-s-remains-discovered-in-milky-way-center.html "NASA's Chandra website").

Rare Blast’s Remains Discovered in Milky Way Center

This discovery, made with NASA’s Chandra  X-ray Observatory, adds to the understanding of how some stars shatter  and seed the universe with elements critical for life on Earth.

We are happy to announce a new GRAPPA postdoctoral fellowship position. We invite applications for a GRAPPA Postdoctoral Fellowship position in the areas of Astroparticle Physics, Cosmology, and Gravitation. Established in 2012, GRAPPA Institute strives for revealing fundamental aspects of the universe and laws of physics. The GRAPPA Fellowship has been our flagship postdoctoral program, which fully ensures academic freedom to pursue any theoretical and experimental research subjects that are of relevance to the GRAPPA’s scientific focus.

Deadline for application is 20 December and we encourage applications from people of diverse backgrounds and underrepresented groups.

All details can be [found on the UvA website](https://www.uva.nl/en/content/vacancies/2020/12/20-756-grappa-postdoctoral-fellowship.html).


Opening of GRAPPA Postdoctoral Fellowship!

We are happy to announce a new GRAPPA postdoctoral fellowship position. We invite applications for a GRAPPA Postdoctoral Fellowship position in the areas of Astroparticle Physics, Cosmology, and Gravitation.

The Dutch Black Hole Consortium (DBHC), which includes several GRAPPA members, has been awarded a grant of € 4.9 million by the Dutch Research Council (NWO) as part of the National Science Agenda. This new interdisciplinary consortium aims to further unravel the mysteries surrounding black holes and the wider universe.

Astronomers and physicists are joining forces to make new discoveries about black holes, using the Event Horizon Telescope, the international project that took the first direct image of a black hole last year, and via gravitational waves, where geologists are also ‘delving into the ground’ for the potential underground construction of the planned gravitational wave detector Einstein Telescope. The consortium will work with universities of applied sciences to develop new educational materials aimed at sparking interest in science among people of all backgrounds and especially children. Lead applicant Stefan Vandoren from Utrecht University: ‘This is an excellent project in which we are combining research, technology and the interests of society.’

The Dutch Black Hole Consortium is made up of researchers from the fields of theoretical physics, astronomy and geology, technicians working on the next generation of gravitational wave detectors and researchers of science communication and science history, combined with teacher training courses and museums. The UvA researchers who are part of the consortium are Sera Markoff, Jan de Boer, Franke Linde, Ralph Wijers, Alejandra Castro, Jeroen van Dongen, Erik Verlinde, Alessandro Bertollini, Sarah Caudill and Samaya Nissanke from the Anton Pannekoek Institute (API), Institute of Physics (IOP) and GRAPPA.

Sera Markoff, who sits on the Consortium Board: ‘We are excited to launch this interdisciplinary project in order to enhance our understanding of the nature of black holes, while also conveying our enthusiasm about our discoveries to the public through museums and outreach projects.’

The consortium is made up of 31 applicants from universities and universities of applied sciences and six partners from industry, museums and government. More information can be found on the [UvA news page](https://www.uva.nl/en/shared-content/subsites/anton-pannekoek-instituut-voor-sterrenkunde/en/news/2020/11/black-hole-consortium-granted-49-million-euros-from-nwa.html).


The Dutch Black Hole Consortium receives €4.9 million in funding

The Dutch Black Hole Consortium (DBHC), which includes several GRAPPA members, has been awarded a grant of € 4.9 million by the Dutch Research Council (NWO) as part of the National Science Agenda.


Altair, a project launched by GRAPPA member astronomer Sera Markoff, has been awarded the NWO Diversity Initiative Award. The project introduces primary school children to astronomy and physics. The Diversity Initiative Award is awarded to initiatives that improve diversity in the field. Initiator Prof. Sera Markoff (University of Amsterdam) will receive € 50,000 to help further develop the project.

Markoff wants to use the award to launch Altair+. ‘The idea is to work together with a team of students and volunteers to develop new activities for secondary school pupils, also at the Science Park in Amsterdam. We want to keep in touch with the Altair “graduates”from the primary school by organising annual activities, which also involve other pupils from nearby schools and their parents. This is a step towards a “pre-academic” programme. This will hopefully result in more students with a non-Western background studying at the Science Park!’

The jury was impressed with how the project successfully promotes the sciences to a wide range of communities. Children from various ethnic backgrounds are taught by UvA academics, and their parents are also involved with a range of activities on the university campus. This project reaches 140 children a year. The jury noted that it is remarkable that Markoff launched the initiative alongside her regular work as Professor of Theoretical Astrophysics.

More information can be found on [Sera's personal site](https://www.seramarkoff.com/2020/12/nwo-domain-science-diversity-initiative-award/?fbclid=IwAR26S5LZLLWCudHzsXwSJ0yFvCaliwSmOzFlFjMcPdMUi1LsmulAK_2ptbY) and on the [IOP news](https://www.uva.nl/en/shared-content/subsites/anton-pannekoek-instituut-voor-sterrenkunde/en/news/2020/12/nwo-diversity-initiative.html?origin=cnUSYqO%2BT4OvERocBmGxmw).

Sera Markoff receives Diversity Initiative Award

Altair, a project launched by GRAPPA member astronomer Sera Markoff, has been awarded the NWO Diversity Initiative Award. The project introduces primary school children to astronomy and physics.


Dark matter is even more elusive than thought before. This is the main message of a new study by a group of scientists that includes GRAPPA member Shin’ichiro Ando. The results of the new study were published in Physical Review D Rapid Communications this week.

Revealing the nature of dark matter might be achieved by looking for faint signatures coming from pairs of dark matter particles. These pairs may annihilate each other and turn into gamma-ray light that could be observed. Some of the best targets for such a search strategy, using gamma-ray telescopes such as the Fermi satellite, are dwarf spheroidal galaxies – small satellite galaxies that are trapped in the gravitational pull of our own Milky Way. Dwarf galaxies are full of dark matter but little else, meaning they are nearly pristine laboratories to look for the tell-tale signatures of dark matter annihilation without the pesky complications of other astronomical phenomena.

In order to perform the search, the scientists combined theoretical and observational methods to put together the first ‘end to end’ analysis that models the dwarf galaxies in their cosmic context. Shin’ichiro Ando said: “Our method starts at the big bang, follows the evolution of dark matter and the growth of galaxies across cosmic time, and uses this as the basis to understand how dark matter might be distributed within the individual dwarf galaxies we see in the sky today. This understanding is then used as the basis to search for the gamma-ray signal which reveals information about the microscopic properties of dark matter particles.”

In particular, the team concluded that the expected signal of the dark matter annihilation is much weaker than earlier estimates. Simply put: dark matter is harder to detect using dwarf galaxies than previously expected. Adopting the more holistic analysis therefore implies, counter-intuitively, that the gamma-ray data actually tells scientists less about dark matter than they thought it did previously. One immediate consequence is that there is still a possibility that dark matter annihilation explains one of the great current astronomical mysteries — the anomalous and unexplained gamma-ray glow that we see emerging from the center of our own galaxy. Until now, it was difficult to see how dark matter annihilation could power the galactic center anomaly but avoid generating a similar signal from the dwarf galaxies.

The results strongly call for revising one of the key search strategies towards discovery of dark matter particles and the quest for physics beyond the Standard Model. More information can be found at the [IOP news](https://iop.uva.nl/content/news/2020/09/dark-matter-even-more-elusive-than-previously-thought.html?cb), and the paper can be found at [APS journals](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.061302).

Dark matter even more elusive than previously thought

A consortium of knowledge institutions and public stakeholders, led by UvA physicist Auke Pieter Colijn, was awarded a 1.1 million euro NWA-ORC grant to study so-called ‘relic neutrinos’ that came into existence in the very first second after the Big Bang.

Every second Earth is bombarded with an enormous number of neutrinos from the cosmos. These neutrinos were created in the primordial soup one second after the Big Bang, but they have never been observed. In the proposed research, the consortium will develop an experiment to observe these relic neutrinos by investigating the decay of heavy-hydrogen tritium. The proposed project is called PTOLEMY, and is a new method to measure such low-energy particles. This is particularly difficult because neutrinos hardly interact with ordinary matter, such as a detector. If this is possible with the proposed detector, it will be a groundbreaking result.

Besides the University of Amsterdam, the consortium, for which Auke Pieter Colijn is the coordinator and which also involves UvA physicist Shin’ichiro Ando, consists of the Radboud Universiteit, De Haagse Hogeschool (The Hague University of Applied Sciences), TNO, the Princeton Physics Department, the Laboratorio Nazionale di Gran Sasso (LNGS), the Netherlands’ Physical Society (NNV), Ampulz, and the Karlsruhe Institute of Technology (KIT).

More information can be found at the [IOP news](https://iop.uva.nl/content/news/2020/11/nwa-orc-for-neutrino-observations.html?origin=LiCYSg5eS82AR0H56Byw2A) as well as at the [Nikhef press release](https://www.nikhef.nl/en/news/black-holes-and-the-big-bang-under-scrutiny-in-the-dutch-research-agenda-nwa/).

NWA-ORC for neutrino observations

Pareidolia is a tendency that pushes humans to see shapes in clouds or faces in inanimate objects. The picture shown here is a composition of four cosmic radio sources that can in fact look like a scary monster. To obtain this effect, the sources have been rearranged compared to their original position in the sky but their apparent sizes were preserved.

However, in some sense, these sources are real monsters. Their names are: Cassiopeia A (top left), Taurus A (top right), Cygnus A (center), and Virgo A (bottom). These are the four most powerful radio sources in the northern hemisphere. Historically, the brightest radio sources in the sky were named after the constellation in which they were found followed by a letter starting with an “A”. They were then grouped in the so-called A-team, like the famous TV series from the 80s.

The nature of these four monsters is very diverse. The eyes of the monster (Cassiopeia A and Taurus A) are two supernova remnants: the leftovers of the explosions of two stars in our own Galaxy. The evil pupil that stares at you in Taurus A is the Crab pulsar. The nose of the monster, Cygnus A, is an extremely powerful radio galaxy 600 million light years away, whose two lobes are powered by jets of energetic particles formed near a supermassive black hole. The mouth of the monster (Virgo A) is the extended structure (larger than an entire galaxy) that surrounds the famous supermassive black hole at the centre of the galaxy M87, the same black hole recently imaged by the Event Horizon Telescope.

These four sources are well known to radio astronomers, but this is the first time that they were able to see them in such great detail at the extremely long wavelengths of 5 meters, close to the longest wavelength we can observe with ground instruments. The images used to make the radio monster were obtained with the Low Frequency Array (LOFAR), a pan-European radio telescope made by 52 stations spread across 8 different countries (The Netherlands, Germany, France, UK, Poland, Sweden, Latvia, Ireland, and soon Italy) and coordinated by a supercomputer in Groningen (NL).

GRAPPA member Jacco Vink is one of the co-authors on the paper. [Read the full paper here](https://arxiv.org/pdf/2002.10431.pdf).

LOFAR images cosmic radio monsters

The top prize in high-energy astrophysics, the Bruno Rossi Prize 2020, has been awarded to the Event Horizon Telescope team for the landmark image and analysis of the first shadow of a black hole. The UvA-researchers Sera Markoff, Oliver Porth, Doosoon Yoon and Koushik Chatterjee are part of this team.

The American Astronomical Society awards the Rossi Prize in recognition of significant contributions as well as recent and original work in high-energy astrophysics.

The Event Horizon Telescope, is a planet-scale array of eight ground-based radio telescopes that was designed to capture images of black holes. In April 2019, the EHT collaboration announced that it had successfully taken the first picture of the black hole at the center of the Messier 87 galaxy, with the results published in a series of six papers in the Astrophysical Journal Letters. The image, a bright ring formed by light bending around the black hole, quickly circled the globe, appearing across the front pages of newspapers and throughout social media. The 2020 Rossi Prize recognizes this historic scientific achievement.

The prize is in honor of Professor Bruno Rossi, an authority on cosmic ray physics and a pioneer in the field of X-ray astronomy. The Rossi Prize includes an engraved certificate and a 1,500 dollar award. Dr. Doeleman will give a lecture at the 237th AAS meeting in Phoenix, Arizona, in January 2021.

More information can be found on the [AAS website](https://head.aas.org/PR/2020_Rossi_prize).

Top prize in high-energy awarded to Event Horizon Telescope

Samaya Nissanke has been elected as the new spokesperson for the Gravitation and AstroParticle Physics Amsterdam (GRAPPA) centre of excellence at the University of Amsterdam. Nissanke is the successor of Gianfranco Bertone, who was recently appointed director of EuCAPT.

Nissanke is currently an assistant professor at the University of Amsterdam. She is a joint faculty member at the Anton Pannekoek Institute for Astronomy and the Institute for High Energy Physics, and is already a member of GRAPPA.

Nissanke’s predecessor, Gianfranco Bertone, said: ‘I am sure that thanks to her scientific excellence, enthusiasm and leadership, Samaya will shine in this role. I look forward to seeing GRAPPA further strengthening its scientific impact and establishing its presence at the local, national and international level under her leadership.’

Samaya Nissanke elected GRAPPA spokesperson

On July 10, 2019, a group of leading theoretical physicists active in fields of astroparticle physics and cosmology met with representatives of APPEC and CERN to kick-off EuCAPT (European Consortium for AstroParticle Theory), a new initiative that aims to coordinate and favour theoretical astroparticle and cosmology activities in European centres and institutions.

The steering committee of EuCAPT includes internationally renowned scientists affiliated to leading European institutions: Gianfranco Bertone (U. of Amsterdam), Philippe Brax (CEA Saclay), Vitor Cardoso (IST Lisbon), Gian Giudice (CERN), David Langlois (APC Paris), Silvia Pascoli (U. of Durham), Hiranya Peiris (UCL London & OKC Stockholm) Antonio Riotto (U. of Geneva), Subir Sarkar (U. of Oxford), Piero Ullio (SISSA Trieste), Andrew Taylor (DESY Hamburg), Licia Verde (U. of Barcelona). CERN has agreed to act as central hub for EuCAPT, and committed to provide financial and administrative support to its activities.

GRAPPA Spokesperson Gianfranco Bertone, who has been appointed EuCAPT director, said: “EuCAPT is a bottom-up initiative that aims to be open and inclusive. We will soon reach out to to the scientific community and to the broader society, with an invitation to participate in our exciting programme of scientific and outreach activities. Stay tuned!”.

The first EuCAPT activities will include one annual meeting of the entire theoretical astroparticle community that will take place at CERN starting in 2020, and two topical workshops at other participating institutions. More information on EuCAPT activities will be released in September, when the website of the initiative will be be launched.![eucapt-team](//images.ctfassets.net/g94voriuozkd/UxY3D5kr8fCYpglYxO21s/82787f4e50e9ceb2f92aeaed2289dcdf/201906-190_10-960x540.jpg)

Gianfranco Bertone appointed founding director of EuCAPT

We will welcome Kenny Ng to GRAPPA later this year, who has been awarded, together with ten talented researchers, a Marie Skłodowska-Curie Individual Fellowship to conduct research at the University of Amsterdam (UvA). The awarded projects include research on public support for different interpretations of ‘Social Europe’, the transmission of pathogens from animals to humans and metaphorical narratives in discourses on dementia. The awarded fellowships range from 175,000 to 280,000 euros. The grants are awarded as part of the Marie Skłodowska-Curie Actions, which forms part of the European Union’s Horizon 2020 research and innovation programme. The aim of the fellowship is to equip researchers with the necessary skills and international experience to pursue a successful career.

__Kenny Ng’s research will be on understanding the peculiar gamma-ray emission of the sun.__
With space telescopes, we only recently gained the sensitivity to precisely study the gamma rays from the Sun, presumably caused by energetic cosmic particles (cosmic rays) bombarding the Sun. Surprisingly, many properties of these gamma rays are not yet explained. Kenny Chun Yu Ng plans to understand them through new observational and theoretical investigations, which will ultimately help us better understand the Sun itself and the solar system space environment.

Kenny Ng will collaborate with Dr Shin’ichiro Ando here at GRAPPA.

Kenny Ng to join GRAPPA on a Marie Curie Individual Fellowship

*If upcoming direct searches discover the elusive dark matter in the universe, they may be able to measure the mass of the particle or the way it interacts with ordinary matter, but can only do both if we’re lucky, researchers from the UvA Institute of Physics argue.*

It is one of the great open questions of modern-day physics and astronomy: what is the mysterious dark matter in the universe? Astronomers suspect that the universe contains much more matter than they can see through there telescopes – simply because there is much more gravity than visible matter can account for. So far, however, nobody has been able to find particles that this dark matter can be made of.

## Rare interactions

Yet, many astronomers and particle physicists are optimistic that a dark matter candidate particle can be found soon, in the next generation of experiments and observations. While this may be true, Amsterdam researchers now point out that even if such a new dark matter particle is found, this does not automatically mean that we will immediately know all of its properties.

In their investigation, the researchers looked at planned underground detectors which aim to detect dark matter by looking for its rare interactions with ordinary atomic nuclei. The as yet undiscovered dark matter particle has an unknown mass (how heavy it is) and an unknown cross section (how strongly it interacts with nuclei).

Using new statistical tools, inspired by a concept known as ‘information geometry’ that the same researchers developed earlier this year, the physicists mapped out what a discovery would look like, without assuming a particular dark matter particle mass or cross section – allowing to explore a wide range of these dark matter properties.

## New materials and techniques

It was found that a discovery using multiple different target materials that the dark matter particle can interact with, will substantially improve the measurement of the dark matter properties. However, even with multiple detectors, it will be hard to measure the mass of heavy dark matter particles and at the same time understand their precise interactions. Only over a narrow range of properties can both of these things be measured simultaneously.

This result, which was accepted for publication in Physical Review Letters last week, should spur the dark matter community to explore new detector materials and techniques which will improve the prospects for pinning down the properties of the dark matter particle in the event of a future discovery.

## Reference

[Assessing near-future direct dark matter searches with benchmark-free forecasting](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.181101), Thomas D. P. Edwards, Bradley J. Kavanagh, and Christoph Weniger, Physical Review Letters 2018. ([arXiv preprint](https://arxiv.org/abs/1805.04117)


Mass or interaction, but not both

In a Nature review article published this week, physicists Gianfranco Bertone (GRAPPA, UvA) and Tim Tait (UvA and UC Irvine) discuss the past accomplishments and the current status of dark matter search experiments and how they will shape the future efforts for dark matter searches.

More information can be found at the [IOP news](http://iop.uva.nl/content/news/2018/10/a-new-era-in-the-quest-for-dark-matter.html), [Nature article](https://www.nature.com/articles/s41586-018-0542-z), and
[pre-print version](https://arxiv.org/abs/1810.01668).![Dark Matter cloud](//images.ctfassets.net/g94voriuozkd/6ojL747fXb0a6QJrfrQpNX/f10a98f6a8fa47c4dd54ac5985b9fe35/DM_visual.png)

A new era in the quest for dark matter

Observations of the gamma-ray radiation from the Galactic center region with the Fermi Large Area Telescope have revealed a mysterious diffuse and extended emission. Discovered almost 10 years ago, this emission generated a lot of excitement in the particle physics community, since it had all the characteristics of a long-sought-after signal from the self-annihilation of dark matter particles in the inner Galaxy. Finding such a signal would confirm that dark matter, a substance that so far has only been observed through its gravitational effects on other objects, is made out of new fundamental particles. Moreover, it would help to determine the mass and other properties of these elusive dark matter particles. However, recent studies show that arguably the best astrophysical interpretation of the excess emission is a new population in the Galactic bulge of thousands of rapidly spinning neutron stars called millisecond pulsars, which have escaped observations at other frequencies up to now.

![Dark matter annihilation](//images.ctfassets.net/g94voriuozkd/4XLWlHy1djlVcVKNd9YHcp/f97292f38ac197294854c9a588ea9092/grappa_news1.png)
__Figure 1.__ Observed gamma-ray emission from the Galactic disk, with the bulge region indicated. The insets show the expected profiles of excess radiation coming from dark matter and stars respectively. The researchers were able to show that the stars profile matches the measurements much better than the dark matter profile.

## Where there are stars, there is radiation
‘Understanding in detail the morphology [the location and shape] and spectrum [the combined frequencies] of the excess emission is of vital importance for discriminating between the dark matter and astrophysical interpretations of the Galactic Center excess radiation.’, says Christoph Weniger, one of the researchers that conducted the study. A new study by researchers at the University of Amsterdam and the Laboratoire d’Annecy-le-Vieux de Physique Théorique, a research unit of the French Centre National de la Recherche Scientifique, found strong evidence that the emission actually seems to come from regions where there is also a large amount of stellar mass in the Galactic bulge (the ‘boxy bulge’) and center (the ‘nuclear bulge’). Furthermore, the researchers found that the light-to-mass ratio in the Galactic bulge and center are mutually consistent, so that the gamma-ray GeV emission is a surprisingly accurate tracer of stellar mass in the inner Galaxy – see figure 2. This study was based on a new analysis tool, SkyFACT (Sky Factorization with Adaptive Constrained Templates), developed by the researchers themselves, which combines physical modeling with image analysis.

![Stellar mass and gamma-ray luminosity comparison](//images.ctfassets.net/g94voriuozkd/4mtzHNAsmNbya01E4lChbH/4cafc910b6e75738fd851889350beb63/grappa_news2.png)
__Figure 2.__ Comparison of the stellar mass (horizontal axis) and gamma-ray luminosity (vertical axis) for the “boxy bulge” (in blue) and for the “nuclear bulge” (in green). The prediction for a population of millisecond pulsars in the Galactic disk (in red) and the bulge of the nearby Andromeda galaxy (M31, in pink) are also shown. Stellar mass and luminosity are proportional to each other in the inner Galaxy (dashed line), which shows that the mysterious excess radiation very likely has a stellar origin and is not coming from dark matter.

The findings support the millisecond pulsar interpretation of the excess emission, since neither a dark matter signal nor other astrophysical interpretations are expected to show such a correlation. ‘The results will help guide upcoming radio searches for this hidden population of millisecond pulsars in the Galactic bulge with MeerKAT and the future Square Kilometre Array’, said Francesca Calore, another of the paper’s authors. ‘This makes these upcoming searches even more promising.’

### Reference

R. Bartels, E. Storm, C. Weniger and F. Calore, The Fermi-LAT GeV excess traces stellar mass in the Galactic bulge, Nature Astronomy 2018.


Another blow for the dark matter interpretation of the Galactic Center Excess

In January 2018, UvA-IoP/GRAPPA researchers Shin’ichiro Ando and Bradley Kavanagh led a team of 9 bachelors students to investigate radiative neutrino decay and its impact on the cosmic microwave background. They set precise constraints on the neutrino lifetime, which was found to be orders of magnitude longer than the age of the universe. More information can be found at the [IOP news][1].

[1]: http://iop.uva.nl/content/news/2018/07/bachelor-workshop-results-in-publication-on-neutrino-decay.html?origin=%2BmF538O4Qz6cnSjy3y%2FYlA

Bachelor workshop results in publication on neutrino decay

UvA-IoP/GRAPPA researchers Shin’ichiro Ando and Bradley Kavanagh led a team of 9 bachelors students to investigate radiative neutrino decay and its impact on the cosmic microwave background.

We are delighted to welcome [Samaya Nissanke](https://samayanissanke.wordpress.com/) as a faculty member at GRAPPA, shared between [IHEF](http://iop.uva.nl/ihef/ihef.html) and [API](http://api.uva.nl/). Samaya’s current research focuses on the detection, measurement and interpretation of gravitational waves, the astrophysics of compact object (black holes, neutron stars and white dwarfs) binaries, and general relativity.
Samaya expressed her excitement by stating, “I am very excited to be joining the GRAPPA department and building a new dynamic gravitational wave and multi-messenger astrophysics group here. It is an incredible time to be working in strong-field gravity astrophysics thanks to the recent gravitational wave detections, time-domain electromagnetic surveys and astroparticle experiments, and recent advances in cosmology and computational astrophysics. I am greatly looking forward to the many scientific adventures here, and working with the excellent students, postdocs and staff members in both the physics and astronomy departments at UvA, as well as the nearby Nikhef institute.”
Samaya will start her first day at GRAPPA on June 15. We look forward to her contributions to our intellectual community for many years to come.

Welcome, Samaya Nissanke!

We are delighted to welcome Samaya Nissanke as a faculty member at GRAPPA, shared between IHEF and API.

This year’s TeVPA will be hosted in Berlin, Germany from 27 – 31 August, 2018. TeVPA is a five day conference which aims to bring together leading scientists in the field to discuss recent advances in Astroparticle Physics. Early bird registration closes on July 7, 2018.

TeVPA 2018

This year’s TeVPA, a five-day conference, will be hosted in Berlin, Germany from 27 – 31 August, 2018.

News

Jacco Vink to use large grant to seek out the sources of gamma rays