To date (2020 March 23rd) there are 4141 confirmed exoplanets in 3072 planetary systems, plus 5075 candidate exoplanets that still await to be confirmed (data from https://exoplanets.nasa.gov/). The number of known exoplanets is large enough to allow astronomers to study their global properties such as mass distribution, orbital parameters, planets dimension and composition, and to put them in relation with the
Cepheids are pulsating giant stars, whose luminosity varies periodically. This is an important class of stars for several reasons. For instance, the period of their pulsations is related to their intrinsic luminosity. This makes cepheids a class of astronomical “standard candles”, e.g. sources whose intrinsic luminosity can be estimated, allowing us to estimate their distances by comparing intrinsic and observed
A supernova exploded on 1987 February 23rd in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. Being at a distance of “only” 170000 light years from us, this supernova, named SN 1987 A, is the closest supernova exploded in the modern era, and thus it is a template to understand the physics of supernova explosions and the
The “Ultra-Short Period” (USP) exoplanets have very close orbits and orbital periods shorter than one day. These planets typically have a radius smaller than 2 Earth radii and a terrestrial composition, sometime with an excess of iron. Four hypotheses have been made to explain the formation and evolution of USP planets. The main hypothesis is that these planets originate
The development of numerical models is a powerful method to explore properties and evolution of astrophysical objects, mainly for remote objects or when the necessary spatial details are higher than the resolution of modern telescopes. These models can be both hydrodynamical or magneto-hydrodynamical, depending on the importance of the effects related to the magnetic fields. In the last years, the
When a massive star explodes as a supernova, its atmosphere is ejected forming an expanding nebula called “supernova remnant“. Very often, supernova remnants impact pre-existing clouds, which can be made of material ejected by the star before the explosion (circumstellar material) or clouds that happen to be nearby the star (interstellar material). The interaction between the expanding supernova remnant and
“Super-Earths” are rocky exoplanets with a mass between that of Earth and Uranus. Some of these planets may also have a close orbit around the parent star. For instance, the super-Earth 55 Cancri e has a mass of 8.6 Earth masses and it orbits at a distance of 0.016 AU (Astronomical Unit, which is the average distance between Earth and
At a distance of about 160 light years, the stellar association TW Hydrae is a benchmark for the study of pre-main sequence stars and their protoplanetary disks. Pre-main sequence stars are a few million years old stars, still gravitationally contracting and not powered yet by the thermonuclear reactions. They are often surrounded by disks of dust and gas called “protoplanetary
Solar corona is made of plasma at million degrees. The mechanism responsible for the heating of the corona, which is the outer part of the solar atmosphere, is still one of the unsolved problems of solar physics. For comparison, the plasma in the photosphere is on average at about 5600 degrees. It is widely accepted that the responsible for heating
To date (October 2019), 4073 exoplanets have been confirmed, while 4495 are still candidates. The vast majority of these exoplanets have been discovered with two techniques: the analysis of transits (e.g.: measuring the decline of stellar luminosity during the passage of the planets in across the stellar disk) and radial velocity (by detecting, thanks to the Doppler effect and spectroscopic
