Question

Describe the life cycle of stars.

Include information related to how scientists can determine how far away a star is.

The required deliverable length (3-4 Paragraphs)

Answer 1

(a).The life cycle of a star is determined from its mass. The amount of mass in a star is determined from the substance available there in the nebulae from where the star actually originated. A nebulae is a cloud of gas -expecially hydrogen , Helium and dust, It is found that larger the mass of the star shorter the life of the star shorter the mass larger the life cycle.

The hydrogen gas available there will pulled together by gravity and will start to spin creating a large temparature at the core of the gas cloud which will initiate the nuclear fusion reaction. In this process hydrogen will be converted in to helium by emitting huge amount of energy which will glow brightly. For massive stars this process will continue only up to few hundred thousand s years only. But for smaller stars like sun it will go up to several billion years.

As the fuel of the stars burns out sequence of events happens.For a big star they will transforms to red gaints they are having diameters from 10-100 times that of sun.They have cool surfaces, Very big stars transforms to super red gaints. they have diameters 1000 times that of the sun.

But smaller stars will undergo relatively slow death. It is observed that they pass through a planetary nebulae phase and finally becomes a white dwarf. It consists of degenerate mass with very high density due to gravity, They have the mass as that os sun but with very small diameter. Finally this will cools down to a brown dwarf or a black dwarf

Massive stars on the other handwill have more energetic and violent end.They will remain scattered in the cosmosin a supernova explosion.They emittes light of 100 million suns in seconds. Once the dust from it clears out it will be known as a neutron star. While the supernova explodes electrons and protons will combine together to form neutron stars . They are highly dense and are having masses 3 times that of the sun concentrated in a diameter of 20km. If its mass is much greater then its gravitaional pull will be more and will form black holes.A spinning neutron star is known us a Pulsar.

Massive stars ends up in a black hole which is the last stage in a stars life cycle. The gravitational pull inside a blackhole is so high such that nothing can escape from it. Black holes curve sthe space surrounding it and it can eat even stars lying very close to it due to the enormous gravity.

(b). Astronomers uses two different methods to measure how far a star is.One method is known us method of triangulation. This method uses the fact that the earths orbits around the sun is 186 million miles. so observing the star today and observing the star after six month will make a difference in its viewing angle. different angles yield a distance which can be obtained with little trignometry . This method is not applicable to stars lying 400 light years away from earth.

So for such cases Astronomers uses a different method the brightness measurement method. Stars color spectrum gives an idea about its brightness. Astronomers look at a distant star and find out its color spectrum. From the color spectrum they obtain the brightness. Once they obtain the brightness they compare it with the apparent brightness- how dim the star has become once it s light reached earth- they can measure the distance to the star.