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What is a star?

Geography | 7-14 yrs | Interactive

A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth, during the night.

If a star has a planetary system, it maybe referred to as a sun.

There are millions of stars in the universe and astronomers are constantly discovering new heavenly bodies, including new stars and planets.

How are stars formed?

  • Stars are formed in the densest regions of the interstellar medium, called molecular clouds. Molecular clouds are perfect star forming regions because the combination of these atoms into molecules is much more likely in dense regions. Stars are born as clumps within gigantic gas clouds that collapse in on themselves!
  • When a molecular cloud collapses under its own gravity, it forms a denser core which is sustained by nuclear fusion. Nuclear fusion reactions, which take place in the star’s core, support the star against gravity and also produces photons and heat, as well as small amounts of heavier elements.
  • As the cloud’s material heats up, it falls inward under the force of its own gravity. This process goes on for millions of years. As the gases within the star get exhausted, the star starts to cool down slowly and dies eventually.

How do stars die?

Due to its high temperature and intensity, a star is constantly creating materials including helium, silicon, oxygen. As it continues creating, it will eventually start creating iron. When the core turns to iron, it will start to die, as iron is not combustible. It will slowly collapse on itself.

What is the biggest star in the Universe?

R136a1 is the biggest(heaviest) star in the Universe right now! The facts keep changing because of the changing mass of a star or a new discovery!

The R136a1 is a huge star. It’s a member of a star cluster within the Tarantula Nebula, an immense star formation factory located in the Large Magellanic Cloud. It’s believed that the R136a1 contains anything from 265 – 320 solar masses, making it the biggest star known. But it is believed that R136a1 is a star that will probably collapse into itself in a million years.

The other stars that are also big are the Eta Carinae, UY Scuti and NML Cygni.

What is the smallest star in the Universe?

EBLM J0555–57Ab, has been discovered to be the smallest star ever found. Its size is slightly larger than Saturn and it’s about 600 light years away from Earth. It is a part of a binary star system.

The gravity pull of EBLM J0555–57Ab, is 300 times of Earth with a radius of 49,000 kms, 80 percent the size of Jupiter and 85 times the mass of Jupiter. The temperature is lesser than exoplanets discovered. If its size were smaller, it wouldn’t be possible for it to have nuclear fusion reaction required for it to be a star.

What do stars look like?

  • Looking at stars, from earth, it’s impossible to judge what stars look like. Because of a star’s distance and earth’s dense atmosphere, stars appear to twinkle.
  • A star’s colour is based on their age and heat intensity. The hottest stars are blue, and the next hottest are white. Yellow stars are next in heat intensity and red stars are the coolest. Our sun is a green star.
  • Blackholes are stars who have finished being stars and they trap light, instead of emitting it.
  • Sometimes a star shines brighter, simply because it is closer to earth than the other stars.

What are the well known stars and constellations?

  • Polaris, also known as North Star has been a guide for navigation for centuries.
  • Sirius, also known as the Dog Star, has been used by different early civilisations to herald changes in seasons and navigation.
  • Alpha Centauri System is the closest star system to earth.
  • Betelgeuse is 650 light years from Earth. It is also known as the Alpha Orionis and is part of the Orion constellation. It’s a star that is expected to go supernova soon, althought its exact date is not known. And we might be able to see this spectacular event!

9 Interesting facts about stars

  1. Did you know there are runaway stars? Stars that encounter one or two heavier siblings in a massive, dense cluster are pushed out from the cluster by the larger ones. Sometimes, a star may experience being pushed away due to a stellar explosion.
  2. Total number of stars visible to the naked eye are only about 6000.
  3. The Sun is the closest star to us.
  4. Most stars come in multiples and form constellations.
  5. There are between 200-400 stars in our galaxy and that there maybe 500 billion galaxies in the Universe. That’s a lot of stars!
  6. 99 percent of our Solar System is the mass of the sun.
  7. The most massive stars are short lived.
  8. In 185 AD Chinese astronomers were the first to record a supernova, this is now classified as SN 185.
  9. Most stars travel the galaxy with companions or in clusters. But not all stars do that; our Sun, for example, moves through the galaxy without a stellar companion.
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