Gr@v researchers have found that there are only two equilibrium possibilities for the spin of black hole binaries, and that they are similar to the equilibria observed for the spin of the Moon, which was identified by Giovanni Domenico Cassini in 1693. The results were published this week in MNRAS Letters.
Abstract: The study of configurations where the orbital motions are in synchrony (resonances) is important to understand the formation and evolution of the solar-system and other planetary systems. In particular, dissipative forces acting on small bodies (e.g. gas drag in early stages of the planetary system) cause slow orbital decay until capture in a resonance with a planet occurs. Previous studies of capture in resonance have been restricted to coplanar or nearly coplanar configurations. However, small bodies can have orbits which are significantly inclined with respect to the planet's orbital plane. I will present results of simulations of resonance capture in a three-dimensional model which includes prograde and retrograde orbits (respectively, inclined by less or more than 90 degrees with respect to the planet's orbit). I will show that the probability of capture in resonance has a strong dependence on inclination. In particular, retrograde orbits are more likely to be captured in resonance than prograde orbits. This study has been published in Namouni & Morais, MNRAS, 446, 1998–2009, 2015.
To celebrate the centenial of General Relativity and simulataneously celebrate five years of the Gravitation Group at the University of Aveiro (Gr@v), established in the Fall 2010, Gr@v will organize a two days event, on 25-26 November 2015. This event will also mark the closing of the "Numerical Relativity and High Energy Physics" Marie Curie IRSES action, an international partnership which was coordinated by our group that ran over the period 2012-2015. Finally, the event will also be integrated in the IDPASC doctoral programme.
The chaotic rotation of Pluto's small moons has been explained by Gr@v researchers as a natural consequence of the gravitational dynamics in Pluto's system (A&A Letter).
C. Herdeiro was the guest interviewee of Porto Canal's "Mentes que Brilham". Watch and listen to the conversation with interviewer Cláudia Fonseca about black holes and some of the research work made at Gr@v in this area.
Abstract: Transiting exoplanets, that cross their stellar disk, are of special interest because their allow the determination of their bulk density by measuring both their radius and mass. Characterising transiting exoplanets is very important since it provides unique constraints to the theories of planet formation, migration and evolution. However, the planets that have been detected by the CoRoT and Kepler space missions transits relatively faint stars. The characterisation of the mass of those exoplanets is therefore challenging, especially in the low-mass regime. Those planets have a measured radius, but very poor constraints on their mass. In this seminar, I will present the objective of the search for transiting exoplanets and the methods to characterise them. Then, I will discuss the limitation of those techniques and finally, I will present the perspectives for the future exploration of the planet density's diversity.
Abstract: Coorbital bodies are observed around the Sun sharing their orbits with the planets, but also in some pairs of satellites around Saturn. The existence of coorbital planets around other stars has also been proposed. For close-in planets and satellites, the rotation slowly evolves until some kind of equilibrium is reached. When the orbits are nearly circular, the rotation period is believed to always end synchronous with the orbital period (as it happens for the Moon). Here we demonstrate that for coorbital bodies in quasi-circular orbits, stable non-synchronous rotation is possible for a wide range of mass ratios and body shapes. We further show that the rotation becomes chaotic when the natural rotational libration frequency has the same magnitude as the orbital libration frequency.
Abstract: The discovery of more than 900 planets orbiting other stars than our Sun makes this period very exciting. Our knowledge which was based on the Solar System has been challenged by new planetary systems which are very different from our system. Some of them are much more compact than the Solar System. Some planets are located extremely close-in from their star, within the orbital distance of Mercury, in a region where tidal effects are important. Understanding the structure of the known exoplanetary systems and the future ones requires to take into account the physics of tidal evolution.
I will talk about the dynamical and tidal evolution of planetary systems orbiting evolving brown dwarfs. Close-in planets orbiting brown dwarfs are very interesting to study because they are influenced by tides and they can be in the habitable zone: the region around a star where a planet with an atmosphere can have water on its surface. I will show that tides are important for these systems because it has an effect on the possible habitability of planets.
Abstract: Since long time ago that it is been argued about a possible connection between the planets orbital motions in the solar system and the cycles of the activity of the Sun. These discussions have been based, often, on presumed correlations between the position of the planets and the occurrence of the solar maximum/minimum, but with no real physical explanation. However, very recently, Abreu et al. (2012) proposed that the planets dynamics can have an influence in the solar tachocline (a thin layer separating the solar radiative and convective regions) and, by consequence, in the activity of the Sun. Following that, several articles have been published with pro and con arguments (cf. Cameron & Schüssler 2013) . Thus, the subject is becoming particularly interesting. This talk will give a review of the current status of the discussion.
Our group coordinated the "Numerical Relativity and High Energy Physics" IRSES network (2012-2015). Here is a list of the global network meetings organized:
