The Science Case for CTA
Presented by: Prof. Werner Hofmann, CTA Spokesperson and Director, Max Planck Institute for Nuclear Physics, Heidelberg
As the project to build CTA nears the pre-production phase, more than 1,350 scientists from 32 countries in CTA’s Consortium have been working to fine-tune CTA’s scientific goals and performance expectations. The result is the highly-anticipated publication of the CTA science case: “Science with CTA.” With an expected release date in the coming weeks, this will be the first public presentation of CTA’s science goals and expected performance since a collection of 24 publications was published in a special CTA edition of the Journal of Astroparticle Physics in 2013.
Ground-based gamma-ray astronomy is a young field with enormous scientific potential, as demonstrated by the current generation of instruments. With its superior performance, the prospects for CTA combine the in-depth understanding of known objects with the anticipated detection of new classes of gamma-ray emitters and a great potential for fundamentally new discoveries. CTA will transform our understanding of the high-energy Universe by seeking to address a wide range of questions in astrophysics and fundamental physics. These questions fall under three major study themes:
1. Understanding the origin and role of relativistic particles
2. Probing extreme environments
3. Exploring frontiers in physics
In our own Galaxy, CTA will look for the remnants of supernova explosions, wind nebulae produced by rapidly spinning pulsars and for stars in binary systems or in large clusters. Beyond our Galaxy, CTA will detect star-forming galaxies and galaxies with supermassive black holes at their centres (active galactic nuclei) and, possibly, whole clusters of galaxies. The gamma rays detected with CTA may also provide a direct signature of dark matter, evidence for deviations from Einstein’s theory of special relativity and more definitive answers to the contents of cosmic voids.
Prof. Hofmann will present a brief background on CTA and highlight some of the discoveries expected as detailed in the science case.
CTA is a global initiative to build the world’s largest and most sensitive high-energy gamma-ray observatory. More than 1,350 scientists and engineers from 32 countries are engaged in the scientific and technical development of CTA. The Observatory will be constructed by the CTAO gGmbH, which is governed by Shareholders and Associate Members from a growing number of countries.
CTA will serve as an open observatory to the world-wide physics and astrophysics communities. The CTA Observatory will detect high-energy radiation with unprecedented accuracy and approximately 10 times better sensitivity than current instruments, providing novel insights into the most extreme events in the Universe.
The project to build CTA is well advanced: working prototypes exist or are under construction for all the proposed telescope designs and significant site characterization has been undertaken. The southern hemisphere site will be located close to the existing European Southern Observatory site at Paranal, Chile. The northern array will be located at the Roque de los Muchachos astronomical observatory on the island of La Palma. Construction is set to begin in 2019.
Two members of the European Astronomical Society (EAS) have been awarded prizes this week during the European Week of Astronomy and Space Science (EWASS2017) in Prague, Czech Republic, in part to acknowledge their involvement in the emergence of curved detectors: The Tycho Brahe Prize for Bernard Delabre from the European Southern Observatory (ESO), and the New Technologies MERAC prize for Emmanuel Hugot from the Laboratoire d’Astrophysique de Marseille, who is leading an ERC programme on these developments.
The small world of curved detectors, either CCD or CMOS-like, starts to be very competitive, preparing a tremendous revolution in the field of wide field imaging systems. By directly correcting the field curvature in the focal plane, curved detectors help saving about one third of the optics, usually used as field flatteners, and then avoids undesirable distortion effect either in the image and also on the optical properties across the field of view.
After ten years of effort to convince the astronomical community about the benefits offered by curved focal planes, the activity is now ongoing around the world, with academic developments at ESO, Stanford, MIT, but also at the industrial level with recent realizations from Sony and Microsoft.
In terms of technologies, this is the dawn of a new era for astronomical instrumentation, with the access to wider fields and exquisite homogeneity of the optical properties across the images, and faster systems not possible with classical flat foal planes. Also, fewer components are needed, and the remaining ones are less complex.
ESA and ESO already expressed their interest in having dedicated programs focused on the maturity level increase of these new devices. Hugot has high expectations of these new devices: “Soon to be off-the-shelf components for civil applications (cameras, bio-medical) these breakthrough components will blossom in the focal planes of any telescope in the future.”
The MERAC Prize for Theoretical Astrophysics went to Selma the Mink (University of Amsterdam, The Netherlands) for her major contributions to our understanding of the role of binarity as one of the dominant physical parameters for massive stars. The MERAC Prize in Observational Astrophysics was awarded to Kevin Schawinski, ETH-Zurich, Switzerland, for his groundbreaking work on the galaxy/black hole connection and innovative use of citizen science in astrophysics.
The MERAC Prize consists of 20,000 euros, the Tycho Brahe Prize is worth 6,000 euros.
An international team of researchers has shown that the hot diffuse gas that fills the space between the galaxies has the same concentration of iron in all galaxy clusters that were studied in sufficient detail by the Japanese Suzaku satellite. It seems that most of the iron inside the intergalactic gas arose long before the first clusters of galaxies were formed. The results will be presented this Friday at the annual meeting of the European Astronomical Society, EWASS2017, in Prague, Czech Republic by Norbert Werner, leader of the MTA-Eötvös University Lendület “Hot Universe” research group in Budapest, Hungary and associate professor at the Masaryk University in the Czech Republic and Hiroshima University in Japan.
The team studied the hot gas permeating ten nearby clusters of galaxies and showed that the concentration of chemical elements is about the same in all of them – a third of that observed in our Sun.
These results confirm earlier indications, which suggested that most of the iron in the Universe was produced and spread throughout intergalactic space before galaxy clusters formed, more than 10 billion years ago. The iron, and many other elements, was blown out of galaxies by the combined energy of billions of supernovae, as well as outbursts from growing supermassive black holes.
Only hydrogen, helium, and trace amounts of lithium were produced during the big bang. Most of the elements that we are made of were forged inside stars and released by stellar explosions called supernovae. How well are the elements spread through the intergalactic space has long been an open question.
“If these elements were produced relatively recently, astronomically speaking, then we would expect a different concentration of iron from cluster to cluster. The fact that the distribution of iron appears so homogeneous, indicates that it has been produced by some of the first stars and galaxies that formed after the big bang,” says Ondrej Urban, the first author of the study who has been a PhD student at Stanford University when he performed the extensive data analysis presented in the study.
“The remarkably uniform distribution of iron also means that the combined energy of many supernovae and the jets and winds of accreting supermassive black holes were able to mix the elements thoroughly across the Universe,” says the corresponding author of the study, Norbert Werner.
The results are accepted for publication in the Monthly Notices of the Royal Astronomical Society.
The SKA project is nearing the end of pre-construction phase. Ahead of construction, the international scientific community is getting organised and looking at possible synergies and collaborations with other facilities. In this press briefing we will highlight three promising areas of research where the SKA is expected to bring a crucial contribution.
Ms. Manisha Caleb
The Fast Radio Burst phenomenon
In April of this year, Ms Manisha Caleb from the Australian National University and Swinburne University published results from the discovery of 3 new Fast Radio Bursts (FRB) using the Molonglo radio telescope in Australia, an SKA pathfinder. These were the first discovery of FRBs using an interferometer, providing scientists with greater accuracy to identify their origin and paving the way for their study with the SKA.
Fast Radio Bursts (FRBs) are intense millisecond-duration bursts of radio waves believed to originate beyond our own galaxy, and whose source is unknown. Until now, FRBs had been detected exclusively using single dish antennas, and only after the event by sifting through data. Due to the limited resolution of individual dishes, their localisation in the sky is not accurate, making it difficult to figure out their origin.
Ms. Caleb will briefly introduce these results and relate them to the future research on FRBs in the era of the SKA.
Prof. Alberto Vecchio
The synergies between SKA and gravitational wave observatories
The discovery of gravitational waves by LIGO last year proved a groundbreaking moment for fundamental physics, finally proving a long-standing theory. Three weeks ago, LIGO confirmed for the third time a detection of gravitational waves, triggered by the cataclysmic merger of two black holes about 3 billion years ago and only last week, the LISA mission was selected by ESA.
With this third detection, scientists are beginning to close in on their goal of using gravitational waves as a way of observing ancient events that would otherwise be invisible, opening a new chapter of astronomy.
Prof. Vecchio will summarise the latest LIGO results and looking forward, will explain how the SKA will complement gravitational wave observatories.
Dr. Steve Croft
The Breakthrough Listen Search for Extraterrestrial Intelligence
Breakthrough Listen is the largest ever scientific research program aimed at finding evidence of civilizations beyond Earth. The scope and power of the search are on an unprecedented scale.
The program includes a survey of the 1,000,000 closest stars to Earth. It scans the center of our galaxy and the entire galactic plane. Beyond the Milky Way, it listens for messages from the 100 closest galaxies to ours. The initiative will span 10 years and commit a total of $100,000,000.
The radio telescopes currently used include the 100m Green Bank Telescope in the US and the 64m Parkes Telescope in Australia, an SKA Pathfinder instrument, and Breakthrough have also signed agreements to collaborate with the 500m FAST telescope in China and the 76m Lovell Telescope at Jodrell Bank Observatory where the SKA Headquarters is located.
Dr. Croft will describe the goals of Breakthrough Listen, discuss the latest developments and the future of Breakthrough with the SKA.
About the SKA
The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, led by the SKA Organisation based at the Jodrell Bank Observatory near Manchester. The SKA will conduct transformational science to improve our understanding of the Universe and the laws of fundamental physics, monitoring the sky in unprecedented detail and mapping it hundreds of times faster than any current facility.
The SKA is not a single telescope, but a collection of telescopes or instruments, called an array, to be spread over long distances. The SKA is to be constructed in two phases: Phase 1 (called SKA1) in South Africa and Australia; Phase 2 (called SKA2) expanding into other African countries, with the component in Australia also being expanded.
Already supported by 10 member countries – Australia, Canada, China, India, Italy, New Zealand, South Africa, Sweden, The Netherlands and the United Kingdom – the SKA Organisation has brought together some of the world’s finest scientists, engineers and policy makers and more than 100 companies and research institutions across 20 countries in the design and development of the telescope. Construction of the SKA is set to start in 2019, with early science observations in the early 2020s.
With the help of software that mimics a human brain, ESA’s Gaia satellite spotted six stars zipping at high speed from the centre of our Galaxy to its outskirts. This could provide key information about some of the most obscure regions of the Milky Way. The results were presented today at the annual meeting of the European Astronomical Society, EWASS2017, in Prague, Czech Republic.
Our galactic home, the Milky Way, houses more than a hundred billion stars, all kept together by gravity. Most are located in a flattened structure – the Galactic disc – with a bulge at its centre, while the remaining stars are distributed in a wider spherical halo extending out to about 650 000 light-years from the centre.
Stars are not motionless in the Galaxy but move around its centre with a variety of velocities depending on their location – for example, the Sun orbits at about 220 km/s, while the average in the halo is of about 150 km/s.
Occasionally, a few stars exceed these already quite impressive velocities. Some are accelerated by a close stellar encounter or the supernova explosion of a stellar companion, resulting in runaway stars with speeds up to a few hundred km/s above the average.
A new class of high-speed stars was discovered just over a decade ago. Swooping through the Galaxy at several hundred of km/s, they are the result of past interactions with the supermassive black hole that sits at the centre of the Milky Way and, with a mass of four million Suns, governs the orbits of stars in its vicinity.
“These hypervelocity stars are extremely important to study the overall structure of our Milky Way,” says Elena Maria Rossi from Leiden University in the Netherlands, who presented Gaia’s discovery of six new such stars today at the European Week of Astronomy and Space Science in Prague, Czech Republic.
“These are stars that have travelled great distances through the Galaxy but can be traced back to its core – an area so dense and obscured by interstellar gas and dust that it is normally very difficult to observe – so they yield crucial information about the gravitational field of the Milky Way from the centre to its outskirts.”
Unfortunately, fast-moving stars are extremely difficult to find in the stellar haystack of the Milky Way, as current surveys list the speed of at most a few hundred thousand stars.
To find them, scientists have been looking for young, massive stars that would stand out as interlopers in the old stellar population of the Galactic halo. Given away by their out-of-place age, these stars are likely to have received an extra kick to reach the halo. Further measurements of their speeds and estimates of their past paths can confirm if they are indeed hypervelocity stars that were shoved away from the centre of the Milky Way.
So far, only 20 such stars have been spotted. Owing to the specific selection of this method, these are all young stars with a mass 2.5 to 4 times that of the Sun. However, scientists believe that many more stars of other ages or masses are speeding through the Galaxy but remain unrevealed by this type of search.
The billion-star census being performed by Gaia offers a unique opportunity, so Elena and her collaborators started wondering how to use such a vast dataset to optimise the search for fast-moving stars.
After testing various methods, they turned to software through which the computer learns from previous experience.
“In the end, we chose to use an artificial neural network, which is software designed to mimic how our brain works,” explains Tommaso Marchetti, PhD student at Leiden University and lead author of the paper describing the results published in Monthly Notices of the Royal Astronomical Society.
“After proper ‘training’, it can learn how to recognise certain objects or patterns in a huge dataset. In our case, we taught it to spot hypervelocity stars in a stellar catalogue like the one compiled with Gaia.”
As part of Elena’s research project to study these stars, the team started developing and training this program in the first half of 2016, in order to be ready for the first release of Gaia data a few months later, on 14 September.
Besides a map of over a billion stellar positions, this first release included a smaller catalogue with distances and motions for two million stars, combining observations from Gaia’s first year with those from ESA’s Hipparcos mission, which charted the sky more than two decades ago. Referred to as the Tycho–Gaia Astrometric Solution, or TGAS, this resource is a taster for future catalogues that will be based solely on Gaia data.
“On the day of the data release, we ran our brand new algorithm on the two million stars of TGAS,” says Elena.
“In just one hour, the artificial brain had already reduced the dataset to some 20 000 potential high-speed stars, reducing its size to about 1%.
“A further selection including only measurements above a certain precision in distance and motion brought this down to 80 candidate stars.”
The team looked at these 80 stars in further detail. Since only information on the star’s motion across the sky are included in the TGAS data, they had to find additional clues to infer their velocity, looking at previous stellar catalogues or performing new observations.
“Combining all these data, we found that six stars can be traced back to the Galactic Centre, all with velocities above 360 km/s,” says Tommaso.
Most importantly, the scientists succeeded at probing a different population from the 20 stars that were already known: the newly identified stars all have lower masses, similar to the mass of our Sun.
One of the six stars seems to be speeding so fast, at over 500 km/s, that it is no longer bound by the gravity of the Galaxy and will eventually leave. But the other, slightly slower stars, are perhaps even more fascinating, as scientists are eager to learn what slowed them down – the invisible dark matter that is thought to pervade the Milky Way might also have played a role.
While the new program was optimised to search for stars that were accelerated at the centre of the Galaxy, it also identified five of the more traditional runaway stars, which owe their high speeds to stellar encounters elsewhere in the Milky Way.
“This result showcases the great potential of Gaia opening up new avenues to investigate the structure and dynamics of our Galaxy,” says Anthony Brown from Leiden University, a co-author on the study and chair of the Gaia Data Processing and Analysis Consortium.
The scientists are looking forward to using data from the next Gaia release, which is planned for April 2018 and will include distances and motions on the sky for over a billion stars, as well as velocities for a subset.
Dealing with a billion stars, rather than the two million explored so far, is an enormous challenge, so the team is busy upgrading their program to handle such a huge catalogue and to uncover the many speeding stars that will be lurking in the data.
“The sheer number of stars probed by Gaia is an exciting but also challenging opportunity for astronomers, and we are glad to see that they are happily embracing the challenge,” says Timo Prusti, Gaia project scientist at ESA.
The European Week of Astronomy and Space Science (EWASS) 2017 will be held in Prague, Czech Republic, from 26-30 June. The conference is the annual meeting of the European Astronomical Society (EAS).
As the largest conference for European Astronomy, it expects to welcome more than 1000 astrophysicists from all over Europe and beyond. Researchers will present their latest results in plenary talks and sessions, covering a wide range of topics.
Media representatives are invited to attend the conference and can apply for a free registration. (See contact information below.)
A wide variety of topics will be covered during the 5-day gathering: (exo)planets, gravitational waves, star formation, astrometry, stars & spectroscopy, star / galaxy clusters, strong gravity & high energy, cosmology, software & big data, and ground based & space instruments.
During the conference, there will be activities for the general public as well:
Exhibition AD INFINITUM – Look into the Depths of the Universe. Gallery of Science and Arts in the building of the Czech Academy of Sciences, Mo-Fri 10 a.m.–6 p.m. Address: Národní 3, Praha 1.
Outdoor exhibition Universe – yours to discover. It consists of twenty 2mx2m panels with interesting images of the Universe made by a variety of telescopes. The exhibition will be located in front of the Rudolfinum where the Concert and Conference dinner will take place on Thursday June 29.
Two public lectures in the building of the Czech Academy of Sciences with translation into Czech:
The Greedy Super-Massive Black Holes, Francoise Combes (Observatoire de Paris), Wednesday, June 28 4 p.m. – 6 p.m.
The Best Space Images from NASA’s Astronomy Picture of the Day, Robert Nemiroff (Michigan Technological University) Friday, June 30 4 p.m. – 6 p.m. EWASS 2017 is organized by the European Astronomical Society in collaboration with the Czech Astronomical Society (CzAS). The conference will be held at the Faculty of Law of the Charles University.