Once objects are sucked inside the event horizon, however, there is no return.Īfter the black hole forms, it can grow by absorbing mass from its surroundings, such as other stars and other black holes w2. Objects outside the event horizon still feel the black hole’s gravity, and will be attracted towards it, but they can be seen and can potentially escape falling in. This boundary is called the event horizon. (It is not actually a hole, though: there is a lot in there, although we cannot see it.)Īt a certain distance from the singularity, gravity is weak enough to allow light to escape, thus objects beyond this distance are visible. The escape velocity would need to be higher than the speed of light – so not even light can escape, which is why the black hole is black. An image of the galaxy NGCĬlose to the singularity, gravity is so strong that nothing can escape. If the dying star is very massive, gravity will pull on the gas and cause the star to become smaller and smaller until its density reaches infinity at a single point, which is called a singularity (figure 2). When the star runs out of fuel in its core, however, it is unable to support these heavy outer layers of gas. The heat created in this process exerts an outward pressure, which counteracts the force of gravity pulling the gas towards the centre of the star and gives the star its large size. In the core of the star, lighter elements such as hydrogen and helium are joined together by thermonuclear fusion to form heavier elements such as metals. Black holes Figure 2: A black hole: theīlack holes form during the death of very massive stars (at least several times the mass of our Sun).Ī star consists of a hot core surrounded by many layers of gas w1. Each activity should take about an hour both are suitable for pupils aged 10-14 (although note that the reviewer suggests using the activities with students aged 10-19). In this article, therefore, I briefly introduce black holes and then describe two simple activities to help school students to visualise what is happening. That is how a black hole gets its name: it is a point in space that does not emit any light (figure 1). Many young people have heard of black holes and understand that if something falls into one, it cannot get out again – even light cannot escape. Having difficulties explaining black holes to your students? Why not try these simple activities in the classroom? Figure 1: An artist’s