03Feb2012

Countless Trillions Of  Orbs Illuminate The Universe.

Have you ever wondered how many stars there are in space? This question has fascinated not only astronomers but also other scientists as well as philosophers, musicians and dreamers throughout the ages. They have also fascinated all of us, ordinary people all over the world who occasionally look at the stars.

Look into the sky on a clear night, out of the glare of streetlights, and you will see a few thousand individual stars with your naked eyes. With even a modest amateur telescope, millions more will come into view. So, how many stars are there in the Universe? It is easy to ask this question, but difficult for scientists to give a fair answer!

Stars are not scattered randomly through space, they are gathered together into vast groups known as galaxies. It is possible for astronomers to guess the quantity of stars. Astronomers estimate there are about 100 thousand million stars in the Milky Way alone.

It has been said that counting the stars in the Universe is like trying to count the number of sand grains on a beach on Earth. We might do that by measuring the surface area of the beach, and determining the average depth of the sand layer.

If we count the number of grains in a small representative volume of sand, by multiplication we can estimate the number of grains on the whole beach.

The nearby dwarf galaxy NGC 1569 is a ‘hotbed’ of vigorous star birth activity which blows huge bubbles and super-bubbles that riddle the main body of the galaxy. The galaxy’s vigorous ‘star factories’ are also manufacturing brilliant blue star clusters. This galaxy had a sudden and relatively recent onset of star birth 25 million years ago, which subsided about the time the very earliest human ancestors appeared on Earth. In this new image, taken with the NASA/ESA Hubble Space Telescope, the bubble structure is sculpted by the galactic super-winds and outflows caused by a colossal input of energy from collective supernova explosions that are linked with a massive episode of star birth.

The bubble-like structures seen in this image are made of hydrogen gas that glows when hit by the fierce winds and radiation from hot young stars and is racked by supernovae shocks. The first supernovae blew up when the most massive stars reached the end of their lifetimes roughly 20-25 million years ago. The environment in NGC 1569 is still turbulent and the supernovae may not only deliver the gaseous raw material needed for the formation of further stars and star clusters, but also actually trigger their birth in the tortured swirls of gas. Credits: ESA, NASA and Peter Anders (Göttingen University Galaxy Evolution Group, Germany)

For the Universe, the galaxies are our small representative volumes, and there are something like 1011 to 1012 stars in our galaxy, and there are perhaps something like 1011 or 1012 galaxies.

With this simple calculation you get something like 1022 to 1024 stars in the Universe. This is only a rough number, as obviously not all galaxies are the same, just like on a beach the depth of sand will not be the same in different places.

No one would try to count stars individually, instead we measure integrated quantitites like the number and luminosity of galaxies. ESA’s infrared space observatory Herschel, to be launched in 2007, will make an important contribution by ‘counting’ galaxies in the infrared, and measuring their luminosity in this range – something never before attempted.

Knowing how fast stars form can bring more certainty to calculations. Herschel will also chart the ‘formation rate’ of stars throughout cosmic history. If you can estimate the rate at which stars have formed, you will be able to estimate how many stars there are in the Universe today.

The famous 1995 image of the Hubble Deep Field. By analysing the galaxies revealed here, astronomers made their first estimates of the history of star formation in the Universe. However, there are many stars that cannot be seen on this image because dust clouds hide them from view. ESA’s Herschel mission will see them, providing a more accurate determination of the amounts of stars that have formed in the Universe. Credits: R. Williams (STScI), the Hubble Deep Field Team/NASA/ESA

In 1995, an image from the Hubble Space Telescope (HST) suggested that star formation had reached a peak at roughly seven thousand million years ago. Recently, however, astronomers have thought again.

The Hubble Deep Field image was taken at optical wavelengths and there is now some evidence that a lot of early star formation was hidden by thick dust clouds. Dust clouds block the stars from view and convert their light into infrared radiation, making them invisible to the HST.

Herschel is designed to view exactly the time in the evolution of the Universe, at the right wavelengths where it is thought the majority of the obscured star formation can be seen. So with Herschel, astronomers will see many more stars than before. We will be one step closer to provide a more reliable estimate to that question asked so often in the past – “How many stars are there?”

While you think about the number of the stars in the Universe, you might also want to see some of the Best Universe Photos Taken By Herschel Space Observatory

Source: Message to Eagle.Com