The Culture Institute of Barcelona conferred the 2013 Barcelona City Award in the category of Experimental Sciences and Technology to the group of scientists who collaborated in the project Gaia of the University of Barcelona, composed by researchers of the Department of Astronomy and Meteorology and members of the Institute of Sciences of the Cosmos (ICCUB) and the Institute of Space Studies of Catalonia (IEEC). The award ceremony takes place on 11 February at the Saló de Cent of Barcelona City Council.

The jury emphasises that Gaia UB Group (ICCUB/IECC) is awarded “for their remarkable contribution to the design of Gaia, the satellite that was successfully launched on 19 December 2013 and will created the most complete 3D map of the Milky Way. They have played a major role in defining and designing instruments and performing simulations to prepare the data processing system”. The jury of the category was composed by Josep Amat, David Jou, Víctor Puntes, David Serrat and Fernando Albericio.

The Barcelona City Council confers the Barcelona City Awards every year. The objective is to honour the creation, research and good quality cultural production done by Barcelonese individuals or groups and institutions or organizations which promote and develop this type of activities.

Gaia is considered the cornerstone mission of the European Space Agency (ESA) not only for its ability to revolution future astrophysics —thanks to the unprecedented accuracy of its astrometric observations—, but also for the technological challenge it means. In addition, the project constitutes the maximum exponent of a technology that places Europe in a leading position in the field of astrometry.

Gaia UB Group (ICCUB/IEEC) has been involved in Gaia mission since the very early phases. It has played a major role in the scientific and technological design of the instrumentation, database prototypes and data simulation. It has also developed a calibration algorithm of photometric data, and the system that will enable to daily process satellite’s data and store them in a database to later extract the first scientific results. Parallelly, the group is developing tools for scientific exploitation, by means of data got from the Earth in order to complement the one provided by Gaia. It leads the development of the catalogues of the mission, the intermediate ones and the final one.

Spanish scientists have discovered the first binary system ever known to consist of a black hole and a ‘spinning’ star —or more accurately, a Be-type star. Although predicted by theory, none had previously been found. The observations that led to the discovery were performed with the Liverpool and Mercator telescopes at the Observatorio del Roque de los Muchachos (Canary Islands, Spain). The discovery is published today in Nature.

Be-type stars are quite common across the Universe. In our Galaxy alone more than 80 of them are known in binary systems together with neutron stars. “Their distinctive property is their strong centrifugal force: they rotate very fast, close to their break-up speed. It is like they were cosmic spinning tops” says Jorge Casares from the Instituto de Astrofísica de Canarias (IAC) and La Laguna University (ULL). Casares is the lead author and an expert in stellar-mass black holes (he presented the first solid proof of their existence back in 1992).

The newly discovered black hole orbits the Be star known as MWC 656, located in the constellation Lacerta (the Lizard) —8,500 light years from Earth. The Be star rotates so fast that its surface speed exceeds 1 million kilometres per hour. “We started studying this star back in 2010, when space telescopes detected transient gamma-ray emission coming from its direction”, explains Marc Ribó, from the Institute for Sciences of the Cosmos of the University of Barcelona (ICCUB/IEEC-UB). “No more gamma-ray emission has subsequently been detected, but we found that the star was part of a binary system”, he adds.

A detailed analysis of its spectrum allowed scientists to infer the characteristics of its companion. “It turned out to be an object with a mass between 3.8 and 6.9 solar masses. An object like that, invisible to telescopes and with such large mass, can only be a black hole, because no neutron star with more than three solar masses can exist”, states Ignasi Ribas, CSIC researcher at the Institute of Space Sciences (IEEC-CSIC).

The black hole orbits the Be star and is fed by matter ejected from the latter. “The high rotation speed of the Be star causes matter to be ejected into an equatorial disc. This matter is attracted by the black hole and falls on to it, forming another disc —called an accretion disc”. “By studying the emission from the accretion disc we could analyse the motion of the black hole and measure its mass”, comments Ignacio Negueruela, researcher at the University of Alicante (UA).

Scientists believe this object to be a nearby member of a hidden population of Be stars paired with black holes. “We think these systems are much more common than previously thought, but they are difficult to detect because their black holes are fed from gas ejected by Be stars without producing much radiation, in a ‘silent’ way”, Casares highlights. Experts hope to detect other similar binary systems in the Milky Way and other nearby galaxies by using bigger telescopes, such as the Gran Telescopio Canarias (GTC).

Also participating in the study with Jorge Casares, Ignacio Negueruela, Marc Ribó and Ignasi Ribas are Josep M. Paredes, from the Institute for Scinces of the Cosmos of the University of Barcelona (ICC/IECC-UB), and Artemio Herrero and Sergio Simón, both from IAC and ULL. ICCUB and ICE researchers are also members of the Institute for Space Studies of Catalonia (IEEC).

UB researchers, Marc Ribó and Josep M. Paredes, belong to the Group High Energy Astrophysics (HEAUB); their activity is focused on gamma-rays sources in the Milky Way. They are experts on multi-wavelength observations and theoretical modelling. Their research has been published on prestigious journals, for instance they published an article on Science in 2000 that won Josep M. Paredes, ICREA Academia awardee and leader of the group, the City of Barcelona Award for scientific research. Both researchers are members of the international collaboration MAGIC and the project Cherenkov Telescope Array (CTA) to build the next generation very high energy gamma-ray instrument. Ribó is the main research of the project at UB.

Black holes, an ongoing challenge

The detection of black holes has been a challenge since their existence was first surmised by John Michell and Pierre Laplace in the 18th century. Given that they are invisible —their enormous gravitational force prevents light from escaping—, telescopes cannot detect them. However, black holes can occasionally trigger high energy radiation from the environment surrounding them and can thus be traced by X-ray satellites. This is the case with active black holes, fed by matter transferred from a nearby star. If violent X-ray emission is detected from a place where nothing but a normal star is seen, a black hole might be hiding there.

Thanks to this method, researchers have discovered 55 potential black holes over the last 50 years. Seventeen of them have what astronomers call a ‘dynamic confirmation’: the feeding star has been localised, allowing for the mass of its invisible companion to be measured. If it is above three solar masses, then it is considered to be a black hole.

The biggest problem is put forth by ‘dormant’ black holes, such as the one found by the Spanish researchers: “Their X-ray emission is almost absent, so it is very unlikely that our attention would be drawn to them”, Casares explains. Researchers believe there are thousands of black hole binary systems across the Milky Way, some of them also with Be-type stellar companions.

Reference article

J.Casares, I.Negueruela, M.Ribó, I.Ribas, J.M.Paredes, A.Herrero, S.Simón-Díaz. “A Be-type star with a black-hole companion”.Nature, January 2014. DOI: 10.1038/nature12916

This year: "Astronomy in our day to day"

Peter Goldreich, Emeritus Professor at the Institute for Advanced Studies, Princeton, and Emeritus Lee A. DuBridge Professor of Astrophysics and Planetary Physics at the California Institute of Technology, will visit the Institute of Sciences of the Cosmos at the University of Barcelona, on Monday, October 28, 2013.

He will give a colloquium entitled “Reading the Record of Ancient Impacts”, at the Aula Magna of the Faculty of Physics of the UB, at 12:00.

Professor Goldreich is well known for his pioneering work on the origin of planetesimals, the alleged precursors to fully-fledged planets. He also studies the important problem of the migration of planets. The Kepler satellite is discovering thousands of extrasolar planets, with a rich variety of properties, often drastically different from those of the solar system planets, and in contradiction of basic ideas about planet formation. An important example is the existence of so-called "hotJupiters’’, very massive planets found to orbit extremely close to their star. Models of planet migration, as those proposed by Professor Goldreich, address these challenging problems presented by the Kepler’s ever growing sample of extrasolar planets. Professor Goldreich’s most recent research turns to Earth to look for a new kind of evidence of the process of formation of the solar system: impact spherules. The main topic of his colloquium, impact spherules are the leftovers of asteroid impacts on Earth. When a fragment of an asteroid hits the Earth, the impact vaporizes ambient rocks generating a vapor plume,also known as a fireball. The cooling of the fireball results in the formation of nearly spherical droplets of molten rock, known as impact spherules. Theoretical physicists, like Professor Goldreich, develop models that allow them to derive the size of the asteroid (from the thickness of the spherule layer deposits) and the velocity of the impact (from the size of the spherules).

Professor Goldreich is one of the most accomplished and diverse theoretical astrophysicists. He is the recipient of the 2007 Shaw Prize, also known as the "Nobel Prize of the East’’, for his achievements on theoretical astrophysics and planetary sciences. Earning his PhD from Cornell University in 1963, he was an Assistant Professor of Astronomy and Geophysics at the University of California, Los Angeles, between 1964 and 1966, and became Associate Professor at the California Institute of Technology in 1966, and then Full Professor in 1969. He has also been a professor at the prestigious Institute for Advanced Studies at Princeton since 2005. His work has led to profound contributions in our understanding of the rotation of planets, the dynamics of planetary rings and planet satellites, the spiral arms of galaxies, the oscillations of the sun and white dwarfs, the nature of pulsars, the physics of turbulence in magnetized fluids, and the origin of planets.