### location | region:

Black hole
* All black holes are entities that produce a tremendous amount of gravity
  - contain a horizon, which is the surface of the black hole
* Many black holes acquire an envelope of gas and dust called an accretion disk.
* Most black holes are hot
  - bear an accretion disk of super-heated plasma
  - originate from a collapsing star
  - tend to be in a consistent spinning motion as a result of the gravitational waves
* Some black holes are also responsible for quasars
  - perfectly spherical - like a ball
  - the end product for massive stars as they evolve
* Some black holes have a large star such as an O or B star as the companion
  - companion stars whose gases they pull off
  - masses several times the mass of the Earth's Sun
  - strong gravity
  - such strong gravity
* are a key to understanding the early evolution of the universe
  - also singularities, and singularities make scientists nervous
* are areas of intense gravitational attraction
  - pressure
  - astronomical objects
  - basically large masses that have collapsed onto themselves
  - believed to form from massive stars at the end of their life times
  - big
* are black because gravity is so strong
  - for the same reason
  - blackness
  - compact, dense powerhouses at the core of galaxies
  - deep wells in the fabric of space and time
  - even smaller than neutron stars
  - extremely compact objects
  - fairly small on a universal scale
  - fantastic sources of very strong gravitational fields
  - films
* are formed by dying super-massive stars
  - the collapse of massive stars, stars many times the size of our own sun
  - when massive stars die
  - heavenly bodies
  - huge, containing as much material as millions or billions of suns
* are incredibly massive objects that suck nearly all nearby matter inward
  - massive, but cover only a small region
  - like bottomless pits from which nothing escapes
* are located in space
  - universes
* are massive objects that only flare with light when they engulf nearby stars
  - star-like objects that only flare with light when they engulf nearby stars
  - no different than planets or stars except in power and strength
  - one type of compact object
  - perhaps the most fascinating and bizarre of all the objects in space
  - points in space that are extraordinarily dense
  - predicted by the theory of general relativity
  - probably the weirdest objects in space
  - really just the final step of the life cycle of a massive star
  - roller coasters
  - so massive that their escape velocity is faster than the speed of light
  - some of the strangest and most fascinating objects found in outer space
  - stars that have collapsed into one very small point
* are the densest objects in the universe
  - end point of gravitational clumping, the highest entropy state of matter
  - energy engines for AGNs
  - final stage of a star's development
  - result of burned out stars that have collapsed on themselves
  - vacuum cleaners of the solar system
  - tremendously powerful, and the field it generates is also powerful
  - truly black
  - ubiquitous in the universe, and their intense gravity can be explored
* are usually in the center of quasars and characteristically have accretion disks
  - small in size
* are very compact and yet contain phenomenal amounts of mass
  - voracious, but proceed slowly
  - vortex drains returning matter back to empty space
  - where god divides by zero
* arise in general relativity, a classical theory of gravity.
* can also be quiet.
* can be almost any size, from a few miles to as large as the solar system
  - dangerous
  - come in many sizes
  - even increase their mass by absorbing gas and stars in their environment
  - form form astronomical objects by gravitational collapse
  - provide extreme amounts of energy
* can, theoretically, come in any size.
* come in different sizes
  - sizes from stellar to galactic
* do and can get small
  - exist
  - release a slight bit of light as they evaporate, as postulated by Hawking
* emit no light.
* evaporate slowly by radiation.
* excites astronomers.
* exert a tremendous gravitational pull.
* exist in space, and mark the edge of space and time.
* have a boundary of no return
  - very intense gravitational field
  - an image problem
  - large, dark masses concentrated in small volumes
  - mass, which makes the presence of a black hole felt by any object near it
  - tremendous gravitational forces
* move around the same way any other mass does.
* occur when stars of a certain size use up all of their nuclear fuel.
* represent the most extreme form of matter in the universe.
+ A Brief History of Time, Summary, Chapter 6: 1988 books :: Science books
  * Black holes are talked about in this chapter. Black holes are stars that have collapsed into one very small point. This small point is called a 'singularity'. Black holes suck things into its center because its gravity is very strong. Some of the things it can suck in are light and stars. Only very large stars, called 'supergiants', are big enough to become a black hole. The star must be one and a half times the mass of the sun or larger to turn into a black hole.
  * Black holes can be shaped differently. Some black holes are perfectly spherical - like a ball. Other black holes bulge in the middle. Black holes will be spherical if they do not rotate. Black holes will bulge in the middle if they rotate.
+ Black hole, Formation of black holes, Explanation: Stars :: Astrophysics
  * Some black holes are also responsible for quasars. A quasar occurs when a black hole consumes all the gas surrounding it. As the gas gets close to the black hole itself, it heats up from friction, and glows so brightly that this light can be seen on the other side of the Universe. It is often brighter than the whole galaxy the quasar is in. When astronomers first found quasars, they thought they had found objects close to us. After using a measuring technique called red shift, they discovered these quasars were actually very far away in the universe.