what makes a black hole

Question: what makes a black hole
- Keywords:
- Click on a keyword to find out more on the RSC site:
  
  black hole
Asked by craigis to Angus, Catherine, Jenni, Melissa, Waqar on 22 Jun 2016. This question was also asked by charlie, Deez Nutz, pie.
- Melissa Ladyman answered on 22 Jun 2016:
  
  First of all lets think about what a black hole actually is: It’s a region of space that has such strong gravity that nothing can escape from inside it- not even light! To have such a strong gravitational force the mass inside of a black hole has to be huge. But that’s not all, because some stars have a huge mass, a black hole is special because of the massive density, essentially the mass of a giant star is squeezed into a tiny space.
  
  So how does that happen? Black holes are created from dying stars- ones much, much bigger than our own sun. In the prime of their life stars are burning hot and furiously- creating lots of energy, but eventually even stars run out of fuel and the really massive stars might explode in a supernova.
  
  If the star is big enough, after the supernova there will still be a lot of mass left over- but because it is so huge it can no longer support its own weight and begins to collapse. The core gets smaller and smaller, until it practically has no volume- but still has all of the same mass. When this happens you’d need to be travelling faster than the speed of light to escape the gravity of the black hole.
  
  There are other black holes which scientists think are created at the same time as the galaxies they are in- but they don’t know as much about those ones.
- Angus Cook answered on 22 Jun 2016:
  
  Gravity!
  
  The mass of an object tells you how strong its gravity is. The more massive the object then the stronger its gravity.
  
  Compare the Earth and the Sun. The Earth is big enough to hold the Moon in orbit around it, through its gravitational attraction.
  Now think of the Sun. The Sun is so much bigger than the Earth, and so can hold 8 whole planets in orbit (and dwarf planets, and asteroids, and comets, etc…). This is because it’s got a much stronger gravitational field (the fancy phrase we use to talk about the force of gravity reaching out from a mass).
  
  Now the stronger something’s gravitational field is, the more difficult it is to get away from it (because it’s pulling on you more and more). If we put a spaceship a million miles from Earth, and one a million miles from the Sun, the one by the Sun would be tugged toward the Sun more than the one near the Earth was tugged toward the Earth.
  
  Now imagine someone’s on the outside of the Earth spaceship, and they want to throw a stone away from the Earth. They want to throw it so hard that it will never get attracted back to Earth by its gravity. To do this they need to throw the stone faster than the ‘Escape Velocity’ of the Earth at that point. If they throw it faster than this they the stone will be able to fly off out of the Earth’s gravity. If they throw it slower then the stone will eventually slow down and tumble back toward the Earth, it has not managed to escape.
  
  If you wanted to do the same thing from the Sun spaceship then you’d need to throw the stone EVEN FASTER, because the gravity pulling back on the stone is EVEN STRONGER.
  Imagine we can do the same thing around bigger and bigger objects. As the mass of the object increases, so does the strength of its gravity. This means that we’d need to throw the stone faster and faster to be able to get it to escape.
  BUT we eventually get to a limit. The fastest speed in the universe is the speed of light. Nothing can go faster than this (we think at least). So imagine that instead of a stone we’re sending light out from our spaceship. If the force of gravity is so strong that even LIGHT (the fastest thing we know) can’t make it out of the gravitational field of the object, then that object is a Black Hole. It’s an object that’s SO MASSIVE, and its gravity is SO STRONG that even light can’t go fast enough to escape it.

Question: what makes a black hole

Comments