In most of the galaxy , the stars are not uniformly distributed , but instead are arranged in certain patterns. The most frequent ones are spiral galaxies .The center of such galaxies is thick with several old , red shining stars. A flat disc stretcher all around this centre in wich the individual arms of the spiral are present. It has a thickness of just about 100 light years, which is very thin as compared to the size of a galaxy. The spiral arms contain a lot of young bright blue stars. If a sprial galaxy . other types of galaxies are the egg-shaped “elliptical galaxies ” and the irregular galaxies , which are completely disordered.
OTHER GALAXIES NEAR MILKY WAY
There are more than 30 other galaxies near the milky way alone.the largest of them is the Andromeda galaxy. Earlier it was known as Andromeda galaxy cold because only an unclear cloudy pitcher of it could be seen. But now with good telescope , the individual stars can be observed.In 1780 , a french astronomer, CHARLES MESSIER,prepared a catalogue with 110 such starry clusters and clouds and he called it Andromeda M31. In 1888 , a new catalogue was published called new general catalogue , which included 8000 objects. It is also included unusual galaxies like those which were deformed upon a collision or had lost one of their arms.
THE DARK MATTER
The physicists calculated the total mass available in the universe by different method. The first method is to measure the movement of the galaxies,which arises as result of the force of attraction between them. Science this , in turn , depends on the mass of the galaxies, the researchers can determine the mass of the galaxies from their movement. The second method is to measure the luminosity of the star, and from this determine the mass of the objects in the universe. Both the methods give different result and the missing mass is known as the ‘DARK MATTER ‘. There is at least five times as much dark matter as the ‘VISIBLE’ matter and no one knows what it is.
Scientists are confronted by the embarrassing fact that they don’t know just how much energy, dark or otherwise, space contains. When quantum theorists try to calculate how much energy resides in, say, a quart of seemingly empty space, they get a big number. But astronomers calculating the same quantity from their dark energy observations get a small number. The difference between the two numbers is staggering: It’s ten to the 121st power, a one followed by 121 zeroes, an amount far exceeding the number of stars in the observable universe or grains of sand on the planet. That’s the largest disparity between theory and observation in the entire history of science. Clearly something fundamentally important about space—and therefore about everything, since galaxies, stars, planets, and people are made mostly of space—remains to be learned.
Yet just such conundrums have opened the doors of discovery before. Einstein’s general relativity theory was invented in part to solve tiny discrepancies between the predicted and the observed orbits of the planet Mercury. Quantum physics sprang in part from little puzzlement about how heat is radiated. How much may be learned, then, by resolving today’s much deeper confusions about dark matter and dark energy? As the physicist Niels Bohr used to say, “No paradox, no progress.”