Childrens Illustrated Encyclopedia

77

gravitational well

if the gravity of empty space is like a flat plane, then a

black hole’s gravity is like a funnel-shaped well. any

object that strays within the

area of the dent will

probably spiral toward

the middle. eventually,

it swirls down the

“gravitational well,”

into a region from

which even light

cannot escape.

when a giant star explodes and collapses,

it can create an object of incredibly high density.

this object has such massive gravitational pull that

nothing can escape, not even light. it is called

a stellar black hole. things pulled very close to the

black hole become invisible. its presence is betrayed

by spirals of matter swirling into it, rather like water

going down the drain. Black holes may also develop

at the center of galaxies from clouds of gas, rather

than from the remains of giant stars. these are

called supermassive black holes and can have up

to hundreds of thousands of times the mass of

our sun. the gravitational force is so immense that thousands of

stars may be dragged into the vortex. as they

become squeezed together, they form a

whirlpool concentration of gas, dust, and

smashed stars that flares with brilliant light.

Inside a

large star,

nuclear fusion

converts hydrogen

into helium. As it runs low on

hydrogen, the star expands

into a “red giant.”

Black holes

accretion disK

Matter spiraling into

a black hole is known

as an accretion disk.

it may contain stars

and planets as well as

debris and gases. You

can’t see black holes, but

the material falling into

them causes them to give

out enormous amounts

of radiation.

Gas drawn

from nearby

blue supergiant

star

astronomy

einstein, albert

gravity

stars

Eventually, it

becomes part

of the mass of

the black hole.

The star finally dies

in an explosion that

is called a supernova.

star cYcle

astronomers believe that many

massive stars end as black

holes. as it uses up the last of

its fuel, a large star expands

to become an even bigger

“supergiant” star. eventually, it

explodes as a supernova. the

center then collapses to

become a neutron star, or

a black hole.

supernova reMnant

the cloud of debris and gas created by a

supernova is called a supernova remnant. at the

center sits a black hole or a neutron star. when

the mass of the original star is not enough to create

a black hole, the result may be a neutron star. this

spins rapidly, emitting electromagnetic radiation.

If enough debris falls

back on to the stellar

core it can become a

black hole.

An object

is drawn

by gravity

toward

the black

hole.

The accretion disk swirling

into the black hole

Once the object has

plunged into the

vortex, there is

no escape.

alBert einstein

physicist albert einstein

(1879-1955) proposed

a general relativity theory

showing that light is bent

by gravity, so it can be

trapped inside a black hole.

Find out more

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