Question

I know that the type 1A Supernova stars are ideal to measure distances and to prove that the universe is accelerating.

They are standard candles type of stars. Their luminosity will decline after explosion.  They shine as brightly as an entire galaxy for a few weeks or months then gradually fade away.

By analyse the velocity obtained by the redshift and the distance the star is from us we can assume that the universe is accelerating.  But if I know the velocity and the distance, still how can I conclude the universe is accelerating? Plus, what this has to do with dark matter? And is the Universe gonna stop expending eventually?

I hope someone can help me with a clear explanation.

Answer 1

Red shift occurs when the wavelength of the light waves are stretched. The wavelength of the light from the object going away is redshifted but, the key challenge for astronomers is to check if the light they observe has been stretched by the expansion in space. In order to accomplish this, astronomers use a source which produces a constant source of light, a source for which they can measure the observed spectrum against a already known spectrum. Supernova 1a are best suited for this purpose. Supernova are explosions caused when massive stars collapse under their own gravity. The light produce from these explosions can outshine a whole galaxy for several weeks or months. Type 1a supernovae always release the same amount of light with the same amount of intensity. By observing the spectrum of a type 1a supernova the astronomers can compare this with the known spectrum at the time of the explosion. This is because the astronomers know the elements involved in the explosion and their associated spectrum. By measuring the difference in the spectrum the astronomers can measure the amount of red shift and thus the amount of expansion of the universe, which eventually proves that the universe is expanding.

Dark matter is not a normal matter, it helps to the galaxies to form the shapes they have today. It provides attractive force to the normal matter as the amount of normal matter is not enough to provide the gravitational attractive force to keep the stars in the orbit around the center of the galaxy. It is opposite to the dark energy, the energy that helps in accelerating the expansion in the universe.  

Scientists believe that one fine day, the universe will be ripped apart by ever expanding space.