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Kerr Black Holes

By Amigos IAS

Why is it in the news?

  • Rotating black holes, also known as Kerr black holes, exhibit a distinct region outside their outer event horizon known as the
About Black Holes

·       Black holes are formed when massive stars collapse under their own gravity at the end of their life cycle. The collapse results in the formation of a singularity, a point of infinite density where the laws of physics, as we currently understand them, break down.

·       Black holes are broadly classified into two main categories based on their mass: stellar mass black holes and supermassive black holes.  Stellar mass black holes have masses ranging from 5 to tens of times that of the Sun, while supermassive black holes have masses ranging from hundreds of thousands to billions of times that of the Sun.

·       As objects approach the event horizon of a black hole, they experience extreme gravitational forces. This can lead to a phenomenon known as spaghettification, where objects are vertically stretched and horizontally compressed as they are pulled towards the black hole.

·       Sagittarius A* (Sgr A*) is the closest known supermassive black hole to Earth, located at the centre of our Milky Way galaxy in the constellation of Sagittarius. It has an estimated mass millions of times that of the Sun and is the focus of extensive research by astronomers.

 About Kerr black holes

  • Kerr black holes are a type of black hole characterized by their angular momentum or rotation.
  • Like all black holes, Kerr black holes are formed from the gravitational collapse of massive stars. When a massive star exhausts its nuclear fuel, it undergoes a supernova explosion, leaving behind a dense core. If this core is massive enough, it collapses into a black hole.
  • One of the distinctive features of Kerr black holes is the presence of an ergosphere, which is a region of spacetime surrounding the black hole but outside its outer event horizon.
  • The outer event horizon is the boundary beyond which nothing, not even light, can escape the gravitational pull of the black hole. Inside the outer event horizon lies the ergosphere.
  • Kerr black holes have two event horizons – an outer and an inner one. The space between these two horizons constitutes the ergosphere.

Properties of the Ergosphere

  • In the ergosphere, spacetime itself is dragged along with the rotation of the black hole. This dragging of spacetime creates a region where objects cannot remain stationary but are forced to rotate with the black hole.
  • Despite the strong gravitational pull of the black hole, objects within the ergosphere still have the potential to escape if they have sufficient velocity.
  • The presence of the ergosphere in Kerr black holes has significant scientific implications. It provides a mechanism for extracting rotational energy from the black hole.
  • Objects or particles entering the ergosphere can be split into two parts, with one part falling into the black hole and the other escaping with increased energy due to the black hole’s rotation. This process allows for the extraction of rotational energy from the black hole itself.

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