Black holes

Black holes

 Black holes are areas in the universe where gravity pulls in everything, even light. Nothing can get out and all objects are squeezed into a tiny space.  Because there is no light in black holes we cannot see them.  But scientists can detect the immense gravity and radiation around them. They are the most mysterious objects in astronomy. Scientists think that the first black holes were formed when the universe began about 13 billion of years ago.

Albert Einstein was the first scientist to predict that black holes existed. But it was in 1971 that the first black hole was actually discovered.

Black holes can have various sizes, some may be even as small as an atom. But they all have one thing in common – a very large mass.

There are three kinds of black holes :

A stellar occurs when very large stars burn away the rest of the fuel that they have and collapse. It is so massive that several of our suns could fit in it. Our sun, however, could never become a stellar because it is too small.

Supermassives are the largest and most dominating black holes in our universe. They have masses of a million or more suns put together. Every galaxy has a supermassive in its centre. As they become larger and larger they pull in more material. The black hole at the centre of our Milky Way is four million times as massive as our sun and surrounded by very hot gas.

Intermediate mass black holes have not been found yet, but scientists think they probably exist. They have the mass of between a hundred and a thousand suns.  

 A black hole consists of three parts:

The outer event horizon is the farthest away from the centre. Gravity here is not so strong and you would be able to escape from it.

The inner event horizon is the middle part of a black hole. In this area an object would be slowly pulled to the centre.

The singularity is the centre of a black hole, where gravity is strongest.

Madnets and magnetism.

Madnets and magnetism.

 A magnet is a piece of rock or metal that can pull other metals towards it. The force of magnets is called magnetism. Together with gravity and electricity it is a basic force of nature. Early humans discovered magnets and magnetism thousands of years ago. They found out that certain types of rock, called loadstone, pulled iron and other metal objects towards it. After some time they found out that thin pieces of such a rock would always point in one direction if you hung it on a piece of thread . The ends of such a metal are the poles of a magnet. All magnets have a magnetic field around them, the force between the two poles.

Magnets attract or repel other metals. This is because every magnet has two poles: a north and a south pole. North and south poles attract each other but two north poles or two south poles push each other apart.

Our planet is also a big magnet with a North and a South Pole. But the Earth’s magnetic poles are not in the same place as the geographic poles. The magnetic North Pole, for example, is in northern Canada. Compasses always point to the magnetic poles, not to the geographic ones.

Magnetism comes from electrons , the tiny particles that fly around the nucleus of an atom. They are negatively charged and produce a very weak magnetic field. When many of these electrons point towards the same direction they can pull metals to them.

It is also possible to make a magnet by taking an existing one and rubbing another piece of metal with it. If you keep rubbing the new piece of metal in the same direction its electrons will start to point in that direction , thus creating a new magnet.

If a magnet keeps its magnetic field all the time we call it a permanent magnet. However , not all magnets are permanent . Some objects become magnets only when electricity passes through them. They are called electromagnets. There are many examples of such electromagnets in everyday life: car motors, railway signals, loudspeakers .

Magnetism and electricity

In the 1700s scientists discovered that magnetism and electricity had similar features. Just like magnets have two poles, electricity has positive and negative charges . A positive and a negative charge attract each other and two negative or two positive charges repel each other.

After they had found this out they started making useful tools and machines with the help of electricity and magnetism. The Danish physicist Oersted sent electricity through a wire and put a compass near it. To his surprise the compass needle moved. Soon after that the first electromagnet was made by making a wire into a coil and sending electricity through it.

Use of magnets

The first magnetic instruments were compasses which sailors used to guide them on their journeys . Today, magnets can be found in many areas of everyday life. They are in washing machines, hold doors shut and work in generators and electric motors. Credit cards have magnetic strips on them that give you financial information. Magnetic audio and videotapes as well as disks have many tiny magnetic particles which are used to store sounds, pictures and other information.

In medicine a magnetic resonance imaging machine (MRI) can create exact pictures of organs and bones inside the human body . It is much better and more exact than x-rays .

Powerful electromagnets are attached to big cranes that can move iron and steel. In some parts of the world trains travel on tracks that are magnetized . These trains, called maglev, are lifted above the tracks and do not have any contact with them. They travel at speeds of up to 480 km an hour.

Magnets in animals

Scientists have also discovered that some animals, like pigeons , dolphins and turtles may have some magnetic particles in their body. They are able to detect the Earth’s magnetic field and find out their location.

 

 

X-rays

X-rays

 X-rays are high energy waves that are invisible. They are useful because they can pass through many things that normal light cannot. For example, doctors can see inside the human body and security guards at airports can see inside your handba

Discovery

In 1895, a German scientist, Wilhelm Roentgen, discovered X-rays by accident. He called them X-rays because he hadn’t seen such a form of energy before. In mathematics X means something unknown. Roentgen took his first X-ray pictures of the bones of his hand. In 1901 he received the first Nobel Prize for Physics for his discovery.

X-Rays in Medicine

X-rays are valuable in medicine because they can see through certain parts of the body. Doctors can take pictures of bones, teeth and tissue. They use these pictures to see which bones are broken or to find out which teeth have holes in them.

To produce X-ray pictures you need two things: a special plate that can capture X-rays is placed behind a part of a person’s body. A machine that produces X-rays is put in front of the person.

The X-rays are strong enough to pass through the skin and muscles but they cannot pass through hard objects like bones. In the picture you see hard objects, like bones, as white areas. Objects that X-rays go through are dark.

There are some situations in which X-rays cannot give you a clear picture. Some organs, for example, may block X-rays from showing a broken bone. For this reason computed tomography (CT) was invented. A person is put inside a scanner, which is a large tube-shaped machine. Then he is X-rayed from all sides. A computer puts together all of these images and can show doctors more than a normal X-ray can. CTs are used for brain diseases and head injuries.

X-rays, however, can also do harm to your body. Patients must wear special protection for the parts of their body that are not X-rayed. Doctors and helpers who work with X-ray machines must wear lead aprons and stand behind screens.

X-rays are sometimes used to in the fight against cancer. Doctors often beam X-rays at cancer cells in order to destroy them.

X-rays in science

Scientists often use X-rays to study the structure of other organisms or minerals that are in rock. By bombarding material with X-rays you can tell how old an object is.

Since the 1970s X-rays have been used to study stars and galaxies that are very far away. X-ray telescopes are put on board satellites that orbit far above the earth’s surface. They can see things that telescopes on earth cannot detect, because X-rays are absorbed by the earth’s atmosphere.

Other uses

Factories use X-rays to find cracks in machines or in metal objects. At airports X-ray machines scan millions of handbags and suitcases for weapons like bombs, guns or knives.