The International Astronomical Union (IAU) today announced the 32nd General Assembly of the IAU in 2024 will be hosted by Cape Town, South Africa. This will be the first time in the 105 year history of the IAU that the General Assembly will be held on the African continent. The award recognises the incredible strides that African astronomy has taken in recent years.
The South African astronomical community in collaboration with the Academy of Science of South Africa (ASSAf), and with strong support from the South African Government and astronomy stakeholders across the African continent, last week formally invited the IAU to Africa at the 30th IAU GA currently being held in Vienna, Austria.
Africa has a long and rich relationship with astronomy, dating back millennia. The world recognized the unique geographical importance of Africa in global astronomy almost two centuries ago with the establishment of the Royal Observatory, Cape of Good Hope in 1820. Since then Africa’s contributions to global human knowledge have both independently and collaboratively grown from strength to strength.
The beginning of the 21st century has seen a renewal of Africa’s strong heritage of astronomical excellence. The IAU has held Middle East and Africa Regional Meetings since 2008. The Entoto Observatory in Ethiopia, has been operating as an independent research centre since 2013.
Since the establishment of the IAU’s global Office of Astronomy for Development (OAD) in 2011, Africa has become the home of three such regional offices coordinating activities across East Africa from Ethiopia, West Africa from Nigeria, and Southern Africa from Zambia. The mandate of the regional offices is to ensure that the region benefits maximally from the practice of astronomy. In 2017, the 1-metre Marly telescope was installed in Burkina Faso as a research telescope as part of the University of Ouagadougou.
Africa is also host to the world-renowned HESS telescope in Namibia. The continent is developing the very exciting African Very Long Baseline Interferometry Network (AVN), and a number of countries are rapidly developing their own astronomy programmes and instruments. At the General Assembly currently underway in Vienna, Algeria, Ghana, Madagascar, Morocco and Mozambique all became new national members of the IAU.
Today, Africa is home to the largest optical telescope in the southern hemisphere (SALT), the largest and most powerful radio telescope in the southern hemisphere (MeerKAT) and will play host to a large part of the international Square Kilometre Array (SKA) Project, whose African partnership includes Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, South Africa and Zambia.
The winning bid is particularly timeous as the SKA telescope is expected to start conducting science observations in the mid-2020s.
“The support for the bid from not only astronomers but also industry, academic institutions and government have been phenomenal, and its success is a testament to what we can accomplish through our united efforts. For astronomers, this is like winning the bid to host a Football World Cup or the Olympics. It’s time for Africa! We are excited and look forward to welcoming our colleagues from around the world to the first of hopefully many IAU General Assemblies on African soil.” says Dr Shazrene Mohamed, member of the bid committee, an astronomer at the South African Astronomical Observatory and the University of Cape Town.
The General Assembly in Cape Town in 2024 is an occasion to give voice to Africa in the global astronomical endeavour and will bring attention to the excellent science and education conducted on the continent. It is expected that the opportunity for many African astronomers to take part in one of the world’s biggest astronomy meetings will contribute to an enduring legacy of astronomy on the continent.
Pluto is an interesting object located in the outer region of our Solar System. Although only 2376 km in diameter, it hosts five moons and a thin atmosphere. As shown in Figure 1, Pluto has a high orbital inclination (17 deg) and eccentricity (0.25), and it requires 248 years to travel once around the Sun. At 120 deg., Pluto has unusually high obliquity, which is the angle between the rotational pole and the orbital plane. Thus Pluto’s north pole (as defined by the right-hand rule) lies 40 deg. below the orbital plane. This combination of high orbital eccentricity and obliquity results in extreme seasons: Pluto’s most distant location from the Sun is nearly twice as far away as the closest, and each pole is exposed to the Sun for more than a century at a time. This geometry is expected to strongly affect the atmosphere.
Figure 1: Schematic plot of Pluto’s orbit in our Solar System. In 2018, Pluto crossed the ecliptic plane and is moving away from the Sun. Pluto was at perihelion in 1990 and won’t be there again for more than two hundred years. Credit: A. Verbiscer; earthsky.org
Pluto’s micro-bar atmosphere was first definitively detected in 1988. In 2002, measurements showed that the atmosphere had expanded, even though Pluto was moving away from the Sun. By 2015, when NASA’s New Horizons spacecraft [https://www.nasa.gov/mission_pages/newhorizons/main/index.html] flew through the Pluto system, the atmosphere was roughly the same size it had been in recent years. However, the story gets more intriguing: models of the mass and distribution of surface ice, which include thermal inertia, predict that Pluto’s atmosphere could collapse out completely. For these reasons, continued observations of Pluto are important.
Figure 2: Image from NASA’s New Horizons spacecraft of Pluto and Charon. This image was taken in July 2015, while the spacecraft was 5.4 million km from the bodies. The colours are approximately those that would be seen by the human eye: it is obvious that Pluto and Charon have very differently-coloured surfaces. Credit: NASA/JHU APL/SwRI.
In August of 2017, researchers from the South African Astronomical Observatory (SAAO) and the Massachusetts Institute of Technology (MIT) observed a relatively rare event, a stellar occultation by the dwarf planet Pluto. The stellar occultation technique requires accurate measurements of the positions of a distant star and a foreground body, in order to predict exactly when and where on Earth a shadow will fall. In this case, Pluto was predicted to occult a star of approximately 15th visible magnitude, with the moderately-sized shadow path (less than 1/3 the diameter of Earth) falling over the northern Pacific Ocean. The event was observed remotely from Cape Town, using NASA’s 3-m IRTF (Infrared Telescope Facility [http://irtfweb.ifa.hawaii.edu/]) with the high-speed, accurately-timed, visible-wavelength instrument MORIS (MIT Optical Rapid Imaging System). Figure 3 contains Images taken before and after the occultation, which show Pluto and it’s largest satellite, Charon, as they approach the star and then after they pass by.
Figure 3: Animated images of the Pluto system moving up to, and then past, the occultation star on 07 August 2017. Charon is clearly discernible from Pluto, with a separation of approximately 0.8 arcsec. These 60-sec images are subframes of an unfiltered dataset taken on NASA’s 3-m IRTF with MORIS. Discrete jumps occur between separate data cubes as well as during the occultation, when separate data were taken at significantly faster cadence. Credit: A. Sickafoose; N. Erasmus; SAAO
These data show that Pluto’s atmosphere still existed in late 2017. They are currently being analyzed, along with additional occultation measurements from 2018, to determine the most recent measurements of Pluto’s atmospheric characteristics. Results will be presented at the 2018 American Astronomical Society’s Division of Planetary Sciences meeting [https://aas.org/meetings/dps50] in October
The South African Astronomical Observatory(SAAO) will play host to the next generation of asteroid-hunting telescopes as part of the NASA funded Asteroid Terrestrial-Impact Last Alert System (ATLAS). On 13 August NASA confirmed that it will fund two asteroid-hunting observatories in the Southern Hemisphere at a cost of US$3.8 million, SAAO will host the first with the location of the second still to be decided.
In 2013, NASA announced the Asteroid Grand Challenge (AGC) “to find all asteroid threats to human populations and know what to do about them.” The 2013 meteor strike in Chelyabinsk, Russia in which a 20m rock exploded mid-air injuring numerous people was a clear reminder of the busy neighbourhood in which we live and of the destructive potential of asteroids.
The ATLAS project was designed to address these concerns and two telescopes are currently operational on the islands of Maui and Hawaii, run by the University of Hawaii. Since it began operations in 2015 ATLAS has discovered over 300 asteroids which pass near the Earth’s orbit. However, since these telescopes are located in the Northern Hemisphere they are blind to roughly 30% of the southern sky and therefore to any asteroids in that region.
The new telescope in Sutherland will aid in the detection, tracking and characterization of near-Earth objects (NEOs) and address the current gaps in sky coverage by imaging the entire sky twice per night. This will be performed using a fully robotic 50-cm diameter telescope with a 110 MP CCD Camera.
The ATLAS system also has software which is optimized to detect fast-moving objects. In early June, the system assisted in providing data on the trajectory of a 1.8-metre asteroid called 2018 LA that entered the atmosphere over Southern Africa. Fragments of this asteroid were found in Botswana using this information.
The telescope will be able to detect a 100-meter diameter asteroid at a distance of 40 million kilometres (~ 3 weeks warning) and a 10-meter diameter asteroid at a distance of 4 million kilometres (~2 days warning). Newly discovered NEOs can then be followed up using SALT and other SAAO telescopes to determine the type, rotation rate, and other important information.
SAAO’s involvement in the ATLAS project offers an excellent opportunity for South African staff, scientists and students to collaborate with NASA and share valuable technology and expertise.
During the evening of Friday, 27 July, one of nature’s grandest spectacles will be on display across southern Africa as the full Moon slips into the Earth’s shadow, a total lunar eclipse.
Professional astronomers from the South African Astronomical Observatory (SAAO) alongside members of the Astronomical Society of Southern Africa (ASSA), an association of amateur astronomers, will be offering the public a free viewing with an array of telescopes along the V&A Waterfront.
In addition, the SAAO will be hosting a free public viewing in Sutherland at the Roggeveld Primary School.
A composite image of the full progression of a Lunar Eclipse
“This spectacle will capture the attention of millions, and we are especially fortunate here to have what are front-row seats to it,” said Eddy Nijeboer, President of the ASSA. “This extraordinary event will not come again to the region until 2029. Families with children are especially encouraged to attend what will be both an enjoyable and educational experience.”
The evening’s observing programme will begin at sunset (18:00) with a tour of the Solar System with numerous instruments as large as 250mm in diameter. The planets Venus, Jupiter, Saturn and Mars will be visible for telescopic viewing, weather allowing. The full Moon first begins to darken as it enters the earth’s shadow at 19:15, with totality beginning at 21:30. The duration of total eclipse will be nearly two hours. The sight of the Moon in total eclipse will be striking with or without a visual aide.
The event will be the longest total lunar eclipse of the 21st century and in addition, Mars will be at its brightest for many years. Mars, the Earth, and the Sun will be roughly lined up on 27 July. Mars is on the opposite side of the Earth to the Sun, and hence the alignment is known as opposition. This coincides with the time when the planet is near its closest point to the Earth, and that night it will be about 57.7 million kilometres away. This means that Mars also appears near its largest apparent size in a telescope and is close to its maximum apparent brightness.
“For those new to astronomy, the evening may prove to be a mesmerizing introduction to core scientific principles,” said Dr Daniel Cunnama, Science Engagement Astronomer at the SAAO. “For experienced observers, the sight of the eclipse continues to be mesmerizing even when witnessed repeatedly. Young visitors will be entertained and perhaps be inspired to an interest in the wonders of nature and science.”
The event is hosted by the V & A Waterfront, part of its ongoing astronomy observing programme with the ASSA and SAAO.
Event Details(Cape Town):
Time: 18:00 – 24:00
Location: V&A Waterfront, Flagpole Terrace(alongside the amphitheatre)
Cost: Free
Event Details(Sutherland):
Time: 19:00 – 23:00
Location: Roggeveld Primary School in Sutherland
Cost: Free
For more details on the Eclipse see the following:
The Southern African Large Telescope (SALT) at the South African Astronomical Observatory (SAAO) in Sutherland has discovered a binary star system in The Hourglass Nebula, one of the most famous nebulae captured by the Hubble Space Telescope.
The Hourglass Nebula consists of two hourglass-shaped lobes of gas and what appears to be an eye staring right back at us. Shells of gas form the eye surrounding the hot central star that illuminates the nebula like a neon sign. Astronomers have long suspected the peculiar nebula to be formed by two interacting stars in a binary system, but until now no one could prove it. The SALT discovery of two stars orbiting each other every 18.15 days in The Hourglass Nebula firmly settles the matter and gives new insights into how a wide variety of close binary stars and hourglass-shaped nebulae may form.
An international team of astronomers, led by SALT Astronomer Dr Brent Miszalski at the SAAO, used SALT to peer into the “sparkle” of the eye of the Hourglass Nebula – its central star.
Dr Miszalski says, “A total of 26 SALT measurements were taken that detected the small movements of the central star towards or away from us caused by the gravity of a second companion star. This Doppler or “wobble” method, that can also be used to find planets around other stars, revealed a hidden companion orbiting the central star every 18.15 days.”
Co-author of the study, Mr Rajeev Manick, formerly a Masters student at SAAO and The University of Cape Town, and now completing his PhD at The Katholieke Universiteit Leuven in Belgium, analysed the SALT measurements and found that the companion must be a small, cool star about 5 times lighter than the Sun.
Another surprise came with the binary – the relatively wide separation between the two stars is remarkable. Co-author Professor Joanna Mikołajewska of the Nicolaus Copernicus Astronomical Center in Warsaw, Poland, a major partner in SALT, Prof. Mikołajewska says, “Previous authors have suggested that a nova explosion could explain many aspects of The Hourglass Nebula, but curiously we found the stars were too far apart for this to have ever been possible.”
Instead of a nova explosion, the orbital period indicates the Hourglass Nebula formed through an interaction that many close binary stars experience – a so-called common-envelope stage. In this scenario, the cooler companion spirals into the atmosphere of its larger companion and helps ejects the shared atmosphere which we now see as the nebula. The Hourglass Nebula is one of very few such examples to show an orbital period above 10 days, making it helpful to improve our understanding of this brief phase that many types of binary stars experience during their lifetime.
While astronomers still do not quite understand how hourglass-shaped nebulae form, the discovery of a binary in The Hourglass Nebula considerably strengthens the long suspected, but difficult to prove, connection between binary stars and hourglass-shaped nebulae. A famous example is the nebular remnant of Supernova 1987A that is often compared against The Hourglass Nebula because of its very similar shape. It is thought to have resulted from the merger of two massive stars before the supernova event. This process shares similarities with that which formed The Hourglass Nebula, hinting at some shared physics resulting in two of the most unusual nebulae in the sky.
Dr Miszalski says, “The combination of SALT’s enormous 11-metre mirror, highly sensitive instrumentation and flexible queue-scheduled operations was fundamental to making this difficult, cutting-edge discovery. We will continue searching other nebulae for new binary systems to gain more insights into their complex origins.”
The study entitled “SALT HRS discovery of the binary nucleus of the Etched Hourglass Nebula MyCn 18” was recently accepted for publication in the Publications of the Astronomical Society of Australia (PASA) journal and is available fromhttps://arxiv.org/abs/1805.07602. The work is the result of a collaboration between astronomers at SAAO and SALT in South Africa, the Nicolaus Copernicus Astronomical Center in Poland, and The Katholieke Universiteit Leuven in Belgium.
Historical background:
The Hourglass Nebula was discovered by Margaret Walton Mayall and Annie Jump Cannon from photographs taken during 1938-1939 with telescopes located in Bloemfontein, South Africa. Its enigmatic beauty was only revealed much later by the Hubble Space Telescope in 1995 and soon drew widespread attention amongst the wider public, gracing the covers of the April 1997 issue of National Geographic and Pearl Jam’s 2000 album Binaural (Fig. 1). Now in 2018, the Southern African Large Telescope has finally proved the long suspected binary nature of its central star.
On Friday May 25 – Africa Day 2018 – a new telescope has been inaugurated at the South African Astronomical Observatory (SAAO), near Sutherland, that will be an “eye of the MeerKAT radio array”, the country’s precursor to the Square Kilometre Array (SKA)
MeerLICHT, which means “more light” in Dutch, is an optical telescope that will simultaneously scan the Southern Skies together with MeerKAT. This creates a truly unique combination where astronomers will always be studying stars and galaxies in two parts of the spectrum at the same time.
The project is a Dutch – South African – United Kingdom collaboration involving researchers from six different institutes from the respective partner countries. It was decided to launch it on Africa Day to recognise and celebrate both our incredible African skies and the important partnerships between Europe and Africa that have led to this innovation.
MeerLICHT is a good example of projects aligned to the objective of the Multi-wavelength Astronomy (MWA) strategy, which was approved by the Department of Science and Technology (DST) in 2015.
The aim of the MWA strategy is to forge closer ties between radio, optical and gamma-ray astronomy communities and facilities to work together to achieve common scientific objectives and develop human capital.
Speaking at the inauguration of the telescope on Friday, the DST Director-General, Dr Phil Mjwara, said South Africa had chosen astronomy as the field of science to show its abilities in research on a global scale, to bolster technological development in the fields of telecommunication, Big Data and large-scale computing, and as the field best able to bring science to the people.
“MeerLICHT is also foreseen to play an important role in the astronomical education of people in southern Africa. The project team also hopes that the MeerLICHT project can grow into a stepping stone to allow other southern African countries to share in humanity’s fascination of the night sky,’ said Dr Mjwara.
Among the chief scientific goals of MeerLICHT is the study of stellar explosions, which need to be investigated intensely before they fade away again. “The study of exploding stars across the Universe will gain a whole new dimension”, states University of Cape Town Prof. Patrick Woudt, co-principal investigator of the MeerLICHT telescope.
The MeerLICHT telescope was purpose-built to combine excellent resolution with a wide field of view. It sees more than 13x the Full Moon while being able to see objects one million times fainter than is possible with the naked eye.
The telescope achieves this amazing combination by coupling a 65cm diameter main mirror with a single 100 megapixel detector, which is a full 10cm x 10cm in size. This camera uses the largest single detector used in optical astronomy anywhere in the world. The telescope was designed and built in the Netherlands, and then shipped to South Africa.
“We started work on the technical definition of this telescope back in 2012, and it is fantastic to see what amazing views it produces”, adds Radboud University Prof. Paul Groot, co-principal investigator.
The link with the MeerKAT radio array has astronomers across the world excited about the new combination. “For us, it was the reason to join this consortium. Flashes of radio emission known as Fast Radio Bursts may now be ‘caught in the act’ by both MeerKAT and MeerLICHT”, explains University of Manchester’s Prof. Ben Stappers, MeerLICHT collaborator, and leader of the MeerTRAP project. “ Hopefully we can finally determine the origin of these enigmatic flashes”.
Prof. Rob Fender, of the Universities of Oxford and Cape Town, co-principal investigator of the telescope, was excited about the inauguration and beginning of operations of the telescope. “This is the beginning of a new phase of coordinated multi-wavelength research into the most extreme astrophysical events” , he said.
“Besides extreme astrophysics, typically associated with black holes and neutron stars, we will also study normal stars, in particular those that produce strong flares” adds Prof. Rudy Wijnands of the University of Amsterdam, “The simultaneous optical-radio monitoring of these stars will allow us to investigate the impact of such flares on the habitability of the planets around them.”
The MeerLICHT telescope will be housed at the Sutherland Observatory, run by the South African Astronomical Observatory. “MeerLICHT directly links the whole optical observatory, and especially our 10 meter SALT telescope, to the MeerKAT array. It fits perfectly in our strategy to turn the Sutherland Observatory into an efficient transient machine to study the dynamic Universe”, adds Dr. David Buckley of the South African Astronomical Observatory.
MeerLICHT is a South African – Netherlands – United Kingdom collaboration involving researchers from six different institutes from the respective (SKA) partner countries. The MeerLICHT consortium is a partnership between Radboud University Nijmegen, the University of Cape Town, the Netherlands Organisation for Scientific Research (NWO), the South African Astronomical Observatory (SAAO), the University of Oxford, the University of Manchester and the University of Amsterdam, in association with the South African Radio Astronomy Observatory (SARAO), the European Research Council and the Netherlands Research School for Astronomy (NOVA). The SAAO and SARAO are National Facilities of the National Research Foundation (NRF). The detector’s cryostat was built at the KU Leuven, Belgium.
On a regular basis, various space debris, including sometimes threatening asteroids, comes close to or impacts the Earth. For example, in October 2017 asteroid 2012 TC4 passed by the Earth approximately 1/8th the distance between us and the moon. While this event did not present a threat, because there was no impact and because 2012 TC4 was only about 10 meters in diameter so would have burnt up in the atmosphere if it did enter, questions arise as to how to deal with asteroids that are more menacing and pose a risk of great harm. Dr. Nicolas Erasmus, an astronomer here at the South African Astronomical Observatory (SAAO), is co-author of a recently published paper that tries to address this problem.
In July 2016 Dr. Erasmus attended the Frontier Development Lab hosted by NASA’s Ames Research Center and SETI in Mountain View, California. The six-week workshop brought together planetary scientists and machine-learning experts to tackle various challenges that involve asteroids. As part of a team of four, Dr. Erasmus and his fellow team members were posed the following dilemma: “Could mankind deflect a hazardous asteroid on a crash course with Earth and if so which method would give us the best chance?”. To answer this, the team worked together to create a machine-learning algorithm called the “Deflector Selector”, which can be used to study a given population of potentially hazardous objects and then determine which technology has the best chance of deflecting them from Earth’s path.
To train the algorithm, a simulation of millions of hypothetical asteroids with the potential to hit the Earth was created. For each hypothetical impact, they simulated how far in advance of the collision it could be detected and the velocity change to the asteroid which would be required to avoid the collision with Earth. With the aid of this information, the team reviewed the capability of three technologies to induce this velocity change: a nuclear detonation, a kinetic impactor, and a gravity tractor. The technologies each work differently and present different challenges. Nuclear detonations release an explosive force that can impart momentum, which while effective, carries with it the dangers associated with launching nuclear warheads into space. The somewhat less effective kinetic impactor causes a change in momentum by crashing a spacecraft into the asteroid and is technologically the easiest method. Gravity tractors are more subtle and involve hovering a spacecraft near an asteroid, allowing its gravitational pull to nudge the asteroid in a different direction. The latter two technologies currently offer less potent results but have more predictable outcomes. Their effectiveness can also be enhanced with earlier detection and therefore longer lead times.
The benefit of using a machine learning algorithm to solve this dilemma is that while it takes a long time to generate the training data and train the algorithm with this data, it can provide clear answers extremely quickly when given a new unknown impact scenario which mankind might one day face.
A publication describing this work has been accepted by Acta Astronautica journal, and an open-access version of the paper can be downloaded from arXiv.org.
Following on from the major global announcement in October 2017 on the discovery of the first electromagnetic counterpart of a gravitational wave source, named GW170817, this new paper has just been published on observations undertaken at the South African Astronomical Observatory (SAAO), which are compared to the latest model predictions. On 16 October 2017,the SAAO, together with many other observatories world-wide, announced the important discovery of the first gravitational wave source counterpart (see: http://www.saao.ac.za/press-release/salt-and-saao-telescopes-investigate-the-origin-of-the-first-detection-of-gravitational-waves-produced-by-two-colliding-neutron-stars/). The preliminary results from the Southern African Large Telescope (SALT) and other telescopes at the SAAO were featured in a number of multi-institutional investigations utilizing a range of global facilities.
This recent paper brings together various observations made at the South African Astronomical Observatory (SAAO) to improve upon the original estimates of the luminosity of the remnant kilonova and compares the observations with recent models developed by a Japanese team. Lead author, Dr David Buckley, explains: “Our SALT spectroscopic results were improved upon by using simultaneous observations of the kilonova’s brightness at three different wavelengths using the MASTER-SAAO facility.”
The MASTER-SAAO is a southern hemisphere node of a global network of small robotic telescopes, operated from Russia, used to discover and observe “transient” events in the Universe. These include counterparts to gravitational wave sources and gamma ray bursts. The MASTER-SAAO observations were used to more accurately estimate the flux measurements made by SALT. These were then compared to recently published models. “It was fortuitous that only a matter of a few months before the observations, a preprint of a new paper on kilonova models was posted. I contacted the lead author, Professor Masaomi Tanaka of the National Astronomical Observatory of Japan (NAOJ), who kindly shared the detailed results in order for us to compare our results with these models”, says Buckley.
This allowed a direct comparison with the observations made in the optical with SALT and MASTER-SAAO and in the infrared with the Japanese Infrared Survey Facility (IRSF), also situated at the SAAO observatory site, near Sutherland. The results were very interesting, showing that the kilonova evolved rapidly, over a matter of days, from a very blue to a red object, pretty much as the models predicted. “I was quite struck by the matching of the observations to the predictions in the blue part of the spectrum”, explained Buckley, “using the just the known distance of the host galaxy. No other parameters needed tweaking.”
This initial blue component, which disappeared after about two days, was consistent with ultraviolet observations made at an earlier time by the Swift satellite. The South African Astronomical Observatory (SAAO) observations, taken over a period of about nine days, showed broad agreement with the predictions of the new kilonova models. These show a rapid reddening of the spectra over timescales of days. The results confirmed the conclusions of other investigators that the kilonova explosion, resulting from the rapid (less than a minute) merger of two neutron stars in orbit about each other, resulted in the ejection of a fast (5% to 10% the speed of light) outflow of material, which was observed at a high angle to the orbital plane of the neutron stars.
It was only through good fortune that the SALT observations were able to be undertaken. The information on the position of the optical counterpart to GW170817, crucial for any SALT follow-up, was only received several hours before the telescope could observe, from the US and Australian co-authors. As Dr Petri Väisänen, also one of the papers co-authors and the SALT astronomer observing that night commented, “After a flurry of messages and emails that afternoon in Sutherland, I finally got the coordinates in time to make the observation, which was only just reachable by SALT during the twilight. The Southern African Large Telescope was only the third observatory worldwide to provide a spectrum of the target, showing the anomalous behaviour and proving that this was no run-of-the-mill transient event.”
Once the target position had been determined a SALT target-of-opportunity observation was then undertaken using Director’s Discretionary Time. The first SALT observation was taken one and half days after the initial gravitational wave trigger. This delay was due to the time it took other imaging telescopes to survey the large area where the event occurred in order to locate its optical counterpart. SALT was able to take one more observation, on 19 August, before it was well and truly lost as the kilonova faded rapidly and was overwhelmed by the bright twilight sky.
“We were really fortunate that the event did not happen two days later, otherwise we would never have had the opportunity to observe it with SALT”, says Väisänen. The SAAO and SALT had been poised for some time to make such an observation, since the original discovery of the first gravitational wave event in September 2015. Dr Stephen Potter, the SAAO astronomer with responsibility for attempting follow-up observations of gravitational wave sources expressed his delight at the results, “I had heard from one of our Chinese collaborators about the event and was in contact with David Buckley, who is principal investigator of the SALT transient programme, about triggering a SALT observation, once an accurate position was determined. We were getting rather desperate at the prospects of getting a precise enough position in time for a SALT observation. But in the end it came in the nick of time and we did it”
As it happened, Buckley was attending a conference on transients in Russia, when the news arrived of the detection of GW170817. However, it was only the following day, when he was travelling home, that the final all-important positional information became available. Other co-authors were able to ensure that the observations were undertaken and the data reduced quickly. Owing to the quick response of SALT and other SAAO telescopes, crucial information on the nature of the gravitational wave source was obtained. These have resulted in the publication of 8 refereed papers containing observations conducted at the South African Astronomical Observatory with the three different telescopes (SALT, MASTER-SAAO and IRSF), including the paper which is the subject of this press release.
The detection of an electromagnetic counterpart to a gravitational wave source, coming only two years after the first gravitational wave detection, bodes well for the study of future gravitational wave neutron star merger events. The ability of SALT to respond promptly and appropriately to transient alerts, in this case the GW170817 event, is one reason for the success of the observations reported here and will hopefully result in similar successes in the future.
[This Saturday, 27 January at 20h00, Dr David Buckley will be delivering a public lecture titled “Gravitational Waves: the new frontier in Astronomy”.]
A Canadian-led international team of astronomers recently discovered for the first time observational evidence in how some features at the surface of the hot massive supergiant star Zeta Puppis induce the formation of fundamental structures in its wind. The research team used the network of nano satellites of the BRIght Target Explorer (BRITE) mission to […]
SALT and SAAO telescopes partake in an unprecedented international collaboration to investigate the origin of the first detection of gravitational waves produced by two colliding neutron stars.
The discovery marks the birth of a new era in astrophysics, the first cosmic event observed in both gravitational waves and light. SALT and other SAAO telescopes have provided some of the very first data in what is turning out to be one of the most-studied astrophysical events ever.
The South African Astronomical Observatory (SAAO) and the Southern African Large Telescope (SALT) are among the 70 ground- and space-based observatories that observed the cataclysmic explosion of two colliding neutron stars, immediately after their gravitational shock waves were detected by the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector.
Neutron stars are the smallest, densest stars known. They are the remains of massive stars which exploded as supernovae. In this particular event, dubbed GW170817, two such neutron stars spiralled inwards and then collided, emitting gravitational waves that were detectable for about 100 seconds. The collision also resulted in a kilonova explosion of light, initially in the form of gamma rays which were detected by space-based telescopes. The gamma rays were then followed by X-rays, ultraviolet, optical, infrared, and radio waves.
This allowed astronomers to localise the event within hours and launch follow-up observations by SALT and numerous other telescopes in South Africa and around the world. South African activities also included the first observations contributing to published scientific results by the MeerKAT radio telescope under construction in the Karoo.
Gravitational waves from colliding black holes were first detected only two years ago, and have been detected three more times since then, leading to the 2017 Nobel Prize in Physics being awarded to three US scientists. Black hole collisions, however, are not expected to emit light. GW170817 is the first time light and gravitational waves from the same event have been observed.
The significance of the present event lies in the combination of the gravitational waves and light. “Imagine you have only one sense”, explains Petri Vaisanen, Head of SALT Astronomy Operations, who was the observer at SALT during the frantic search for the counterpart for the gravitational wave event. “All your life you have merely looked at the world. Two years ago you heard something, voices coming from somewhere around you. But then, suddenly, you actually see someone talking. How much more will you understand about how the world works when you put those together? Immensely more. That to me sums up the momentous discovery, and hints at the possibilities going forward.”
August 18, 2017, the day and night following the LIGO detection and the initial successful searches in Chile for the counterpart, was a busy day for observational astronomers. “After a flurry of messages and emails that afternoon in Sutherland, I finally got thecoordinates”, continues Vaisanen. “There was a new object, which had caused the whole of space-time to ripple, sitting at the outskirts of the galaxy NGC 4993 some 130 million light-years away. I knew that everyone with a working telescope in the Southern Hemisphere was scrambling to get data on it. We decided to drop all other plans for that evening, and went for a spectral observation with SALT, since you need a large telescope for such observations breaking up the light into all its colours. It was a difficult observation since we had to do it in twilight, before it got properly dark. I’m very proud of the whole team, SALT was only the third observatory to provide a spectrum of the target, and the first spectrum that clearly started showing anomalous behaviour proving that this was no run-of-the-mill transient event”.
The significance of getting early observations stems from the afterglow of the collision changing very rapidly. Piecing together the new science from the event requires combining observations spanning the first hours, days and weeks after the merger. The first SALT spectrum has a very prestigious spot in the combined scientific paper, with thousands of authors and hundreds of institutions. In addition, several, more detailed scientific papers have also been written based on SALT, SAAO and other Sutherland observations.
“Finally, the irony of the moment for me, anxiously sitting at the telescope that evening looking at the new object, was that just three weeks before I had attended a meeting discussing the future of optical searches of gravitational waves and the SAAO part in it. There were arguments that it could be decades before we are able to localise such events well enough for observations, and it would probably not be worth expending the effort. It’s amazing how quickly things change.”
Sutherland telescopes reveal the details of the neutron star merger
Theorists have predicted that what follows the initial collision is a “kilonova” explosion— a phenomenon by which the material that is left over from the neutron star collision, which glows with light, is blown out of the immediate region, far out into space. The light-based observations from other large international telescopes show that heavy elements, such as lead and gold, are created in these collisions and subsequently distributed throughout the universe – confirming the theory that a major source for the creation of elements heavier than iron does, indeed, results from these neutron star mergers.
MASTER-Net full frame composite of GW170817 (Credit: MASTER-Net/NRF/SAAO)
The early SALT observations showed that the explosion was relatively bright and blue. Only two or three days later, further observations by SALT, SAAO and other major international telescopes showed that the light was rapidly fading and turning red, due to the dusty debris blocking the bluer light, as predicted by the theory of the evolution of a kilonova explosion. Simultaneously, MASTER (a joint Russian-South African optical telescope located in Sutherland) and IRSF (Infra-Red Survey Facility; a joint Japanese-South African infrared telescope also in Sutherland) continued to monitor GW170817 for two weeks, showing that it gradually faded in the visible light but brightened in the infrared, consistent with the final stages of the afterglow from the surrounding debris.
The results of this unprecedented event have demonstrated the importance of collaborative multi-messenger observations and mark a new era in astronomy.“The ability of SALT and SAAO telescopes to respond rapidly to unexpected discoveries is a major reason for the success of these observations and will ensure similar successes in the future”, says Dr Stephen Potter, Head of Astronomy at the SAAO. “We are very proud to have played a major role in such a historical event thanks to the sterling efforts and expertise of SAAO and SALT staff who ensure that our observatory is at the forefront of world-class scientific endeavours.”
The South African Astronomical Observatory is funded by the National Research Foundation. For more information about SAAO : www.saao.ac.za
About the NRF: The National Research Foundation (NRF) was established on 1 April 1999 as an independent statutory body in accordance with the National Research Foundation Act. The NRF is a key public entity responsible for supporting the development of human resources for research and innovation in all fields of science and technology. The organisation is one of the major players in educating and training a new generation of scientists able to deal with South African and African needs. The organisation encourages public awareness and appreciation of science, engineering and technology, and facilitates dialogue between science and society. Its vision is to contribute to a prosperous South Africa based on a knowledge economy. For more information on the operations and programs within the NRF please visitwww.nrf.ac.za
About SALT: The Southern African Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere and among the largest in the world. It has a hexagonal primary mirror array 11 metres across, comprising 91 individual 1m hexagonal mirrors. For more information about SALT please visit www.salt.ac.za
