black hole tagged posts

In principle, nothing that enters a black hole can leave the black hole. This has considerably complicated the study of these mysterious bodies on which generations of physicists have debated ever since 1916, the year their existence was hypothesized as a direct consequence of Einstein’s Theory of Relativity. There is, however, some consensus in the scientific community on the fact that black holes possess an entropy, because their existence would otherwise violate the second law of thermodynamics. In particular, Jacob Bekenstein and Stephen Hawking have suggested that the entropy – a measure of the inner disorder of a physical system – of a black hole is proportional to its area and not to its volume, as would be more intuitive...

This is a simulation of gravitational waves from a collapsing Neutron star. Credit: Luciano Rezzolla

Astrophysicists have found a simple formula for the maximum mass of a rotating neutron star and hence answered a question that had been open for decades. Neutron stars are the most extreme and fascinating objects known to exist in our universe: Such a star has a mass that is up to twice that of the sun but a radius of only a dozen kilometres: hence it has an enormous density, thousands of billions of times that of the densest element on Earth.

An important property of neutron stars, distinguishing them from normal stars, is their mass cannot grow without bound. Indeed, if a nonrotating star increases its mass, also its density will increase...

Image shows an artist’s impression of a black hole, similar to V404 Cyg, devouring material from an orbiting companion star. Credit: ESO/L. Calçada

Violent red flashes, lasting just fractions of a second, have been observed during one of the brightest black hole outbursts in recent years. June 2015, a black hole called V404 Cygni underwent dramatic brightening for about 2 weeks, as it devoured material that it had stripped off an orbiting companion star. V404 Cygni, which is ~7,800 light years from Earth, was the first definitive black hole to be identified in our Galaxy and can appear extremely bright when it is actively devouring material.

The astronomers associated the red colour with fast-moving jets of matter that were ejected from close to the black hole...

As part of the first observations with the new GRAVITY instrument the team looked closely at the bright, young stars known as the Trapezium Cluster, located in the heart of the Orion star-forming region. Already, from these first data, GRAVITY made a discovery: one of the components of the cluster (Theta1 Orionis F) was found to be a double star for the first time. The brighter double star Theta1 Orionis C is also well seen. The background image comes from the ISAAC instrument on ESO’s Very Large Telescope. The views of two of the stars from GRAVITY, shown as inserts, reveal far finer detail than could be detected with the NASA/ESA Hubble Space Telescope. Credit: ESO/GRAVITY consortium/NASA/ESA/M. McCaughrean

GRAVITY at ESO’s VLT successfully combined starlight using all 4 Auxiliary Telesc...