How to Make a Black Hole When really massive stars burn out, they turn into black holes. To understand how this happens – and what black holes really are, you need to remember a little bit about atoms and gravity…

The protons and neutrons are stuck together in the center of the atom; this center is called the nucleus. PNPNNP The basic parts of an atom EPN Neutron (0) Proton (+) Electron (-) There is a lot of space between electrons and the nucleus. The electrons spin around the outside of the nucleus. Key EEE

P NP N N P In fact, there is so much empty space between an atom’s electrons and nucleus that even this diagram is misleading EEE Really far apart!

To keep things simple, let’s use this diagram for an atom P N P N N P E E E

Gravity is an attractive force (like a magnet) between 2 objects; the acceleration of an object due to gravity depends on its mass Object 1: Many Atoms Object 2: Few Atoms Because Object 2 has fewer atoms than Object 1, Object 2 moves more than Object 1 P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E

P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E A simple diagram of Earth Warning: This diagram is NOT to scale! The Earth is made of a lot more atoms than you are. If you could jump really fast (7 miles per second), you could escape from Earth’s gravity – but you cannot jump that fast… …however, a rocket can “jump” that fast! USAUSA

As stars burn out, the electrons collapse toward the center of the nucleus of each atom Stars are always battling 2 forces: nuclear fusion releases energy that makes the star want to expand, gravity makes the star want to collapse. After a star runs out of fuel with which to make nuclear fusion, gravity wins this battle. PNP N NPEEE

After all the star’s atoms have collapsed, it is called a “white dwarf” A white dwarf is about the size of Earth but much more dense. Because it is so dense, it has a greater gravitational force. Our rocket must go 3000 miles per second to escape. 7 miles per second is too slow to escape 3000 miles per second is fast enough USAUSA USAUSA A teaspoon of a white dwarf would weigh more than a car! A white dwarf is not made of ordinary atoms. Gravity has crushed the atoms’ electrons and nuclei together into a mixture (called “degenerate matter”).

star (such as our sun) A white dwarf is a lot smaller than the star it comes from white dwarf

White dwarf A white dwarf is about the size of Earth Hi, Mom!

PNP N NPEEE In really big white dwarfs, gravity’s enormous pressure fuses electrons with protons to become neutrons NNN

Really big white dwarfs collapse into neutron stars

A neutron star is just a big bunch of neutrons stuck together. It contains no electrons or protons. It is incredibly dense – and has an enormous gravitational force miles per second is too slow to escape 83,000 miles per second is fast enough A simple diagram of a neutron star USAUSA USAUSA A teaspoon of a neutron star would weigh more than a 100 million cars!

A neutron star is about the size of a large city Neutron Star

Gigantic stars don’t stop collapsing after they become neutron stars – the gravitational force is so strong that neutrons collapse into each other, forming a single point – a “Black Hole” Really big neutron stars collapse into black holes

Light moves at 186,000 miles per second (we call this “light speed”). In other words, light speed is 669,600,000 miles per hour. Even this speed is too slow to escape a black hole’s incredibly powerful gravity. Nothing can go fast enough to escape from a black hole 83,000 miles per second is too slow to escape So, imagine you are standing on a black hole with a flashlight (this would be impossible to actually do). If you pointed the flashlight up, this is what would happen to the light… That’s why we call these objects “black holes” – “black” because light cannot escape from them; they are invisible – “holes” because anything (including the energy of light) that gets too close to a black hole falls into it because of its super strong gravity. USAUSA

Don’t get too close to black holes! USAUSA

Black holes really exist! Consider the evidence: scientists observe stars being sucked into nothingness Star being pulled into a black hole Black hole

There’s even more evidence of black holes – scientists have seen stars orbiting nothing Probably a black hole here

An artist’s picture of a black hole

Star White Dwarf Neutron Star Black Hole Weak Gravity Strong Gravity Summary: the family history of a black hole P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E P N P N N P E E E 1,000,000 km 10,000 km 10 km Smaller than cm

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