What Black Holes Are

Black holes are the places of the most dense environment in our Universe. They are places where the matter has become condensed to the point that not even light, with its speed of 671 million miles per hour (300,000 km/s), may escape from them. The main tendency now, emerging from the studies of black holes, is to think that there might be 3 kinds of them. Galactic, stellar, and intermediate mass ones

It's now well-established that supermassive black holes, the orbit of Mercury in size and in the range of multimillion solar masses, are lurking in the center of each galaxy, our included. How they formed there is still a mystery. Such black holes are active, that is that they are still swallowing matter -and in some cases, stars. They may produce polar jets either side, which may reach up to about 1 million light-years of distance. The supermassive black holes are thought to rotate at highly excessive speeds, at about the limit of the light's speed and that's those high speeds which are a the origin of the jets. As far as stellar black holes are concerned, they mostly result from the collapse of one star, following a supernova event. Such black holes are small in size, about 10 solar masses. Intermediate mass black holes, at last, might be, like the name, intermediate-sized black holes, in the order of the 10,000 solar masses, resulting from the merger of several stellar class ones in the heart of a star cluster (like evidenced, for example, in April 2008), or being the central black holes of diminutive galaxies in the process of being absorbed by larger ones. Late studies are showing that intermediate mass black holes are to be found too in the turbulent environment inside globular clusters, this pointing to that stellar black holes there accrete together and reach a mass sufficient to withdraw the powerful gravitational interaction in the cluster

A recent, 2005 study by NASA's Chandra Telescope is showing that a mass between 25 and 40 Sun might be the condition for a massive star to eventually turn into a black hole. More massive stars than that would turn into a neutron star due to that they blow off mass more effectively during their lives. Other factors like the star’s chemical composition, its rotation rate, or whether it is part of a double star system, may play a role in determining whether a massive star leaves behind a neutron star or a black hole

All black holes are characterized by an accretion disk, surrounding them, which is where the infalling matter is orbiting before being definitively swallowed. The activity of the black hole is generating too two polar jets. Generally, black holes are spotted by dedicated tools, like the Chandra X-Ray Observatory, this space telescope operating in the X-ray, as their activity is mostly yielding in this wavelengths range. Galactic black holes, which are usually 'dormant' and quiet, may -about once every 10,000 years- swallow a passing star. The fact emits X-rays flares until that the star has been eventually swallowed. As far as our Milky Way Galaxy's black hole is concerned, studies by the NASA in spring 2008 have shown that the last episode of activity of it occurred about 300 years ago, with a giant star exploding nearby and sweeping gas into the black hole, leading to a temporary feeding frenzy that awoke the black hole from its slumber. When it comes to assumptions, black holes are believed to be the place of interconnection with places where the laws of physics might be completely different, or where it might be possible to travel in time. One thing is certain however. Should you venture for a long space journey, never approach a black hole of any kind. You would never be back!