Galaxies

The Hubble space telescope has photographed closeup images,

of what NASA refers to as the universe's brightest infrared galaxies.

The galaxy images is magnified through a phenomena called gravitational lensing.

The images have exotic patterns such as rings and arcs.

The unusual forms may have been produced by spectacular collisions between distant galaxies.

These galaxies are producing more than 10000 new stars a year.

Their glow is so bright in the infrared range, that they shine with the intensity of 10 to 100 trillion suns.

Galaxies range in different sizes and shapes, and include billions or trillions of stars.

Scientists try to estimate how many galaxies are there in the universe.

On a dark night we can see the milky way as a band of light.

For a long time we thought that the milky way is the only galaxy in the universe.

This thinking changed only in 1924.

Edwin Hubble discovered stars in several spiral Nebulae.

He calculated that these stars were far to distant to belong to our milky way galaxy.

He realised that these stars were members of other galaxies, outside the milky way.

Now scientists wondered how many galaxies were there in the universe.

The first estimate, could be made only in 1995 when the Hubble Deep Field was observed.

This was the first deep observation that was made, and it revealed hundreds of galaxies,

that were never seen before.

Further observations were made with Hubble and others.

From these observations, scientists estimated that there was a total of 120 billion galaxies.

These are the galaxies within the so called observable universe.

These are galaxies which can be observed with space telescopes like Hubble.

These are galaxies from which light had time to reach us since the beginning of the universe.

This limit is called the cosmological horizon.

The universe continues beyond this.

How far it goes is yet an unanswered question.

Now astronomers think that 90% of the galaxies are too distant and too faint to be observed with current telescopes.

Estimates now have to be made based on mathematical modelling and calculations.

Using these models they have looked back as far as 13 billion years, into the past.

This is close to the beginning of the universe, which is 14 billion years old.

At that time the density of galaxies was much higher.

These galaxies were relatively small.

These results prove that galaxies grew and evolved throughout the history of the universe.

With 90% of the galaxies yet to be observed, there is much more to be discovered,

using the upcoming James Webb space telescope, and others.

Scientist think that the Hubble space telescope will find close to trillion galaxies within our visible universe.

Future telescopes will discover trillions of more galaxies.

Each galaxy could have billions or trillions of stars.

Each star in the galaxy would have at least one planet.

We can try to imagine how many planets are there in the universe.

Is it possible that some of them have life?