Turbulence is a common chaotic phenomenon that everyone has certainly experienced: you witness the development of turbulence when you stir a coffee too vigorously or watch the smoke of a cigarette or feel the aeroplane going up and down. What makes turbulence often spectacular is the presence of several vortices which are indeed seen in many atmospheric phenomena from the magnificent tornadoes and hurricanes to the tiny dust devils. Such vortices have a certain life-time that is set by the amount of energy that sustains them and that works against viscosity, which tries to re-establish the calm and quietness of the flow.
We know that black holes exist in Nature with at least two different sizes: super-massive black holes, that live in the centre of galaxies and stellar-mass black holes. The origin and evolution of these two types of black holes are very different. The millions of stellar mass black holes that populate our galaxy are mostly formed during the gravitational collapse of a massive star. The formation of super-massive black holes is much less well understood. Continue reading
Neutron stars are few kilometres sized objects that come to life when a massive star dies in a devastating supernova explosion. A few months ago a very peculiar neutron star has been discovered in an even more peculiar location of our Galaxy. A magnetar is neutron star surrounded by a magnetic field so intense that it is billion of times stronger than the strongest magnetic field ever produced in a physics lab on Earth. Place yourself in such a strong magnetic field and you won’t survive a whole second.One such magnetar has been discovered in the Galactic Center, very close to the supermassive black hole that exists there. Continue reading
Imagine to have a black hole spinnig around a normal companion star like our Sun. At some point of the evolution the black hole can start removing and devouring matter from the outer layers of its companion star, in a process known as accretion. During this phase the matter becomes so hot that it shines X-rays that are detectable from X-ray space telescopes orbiting around the Earth.