DARK SKIES: The birth and death of stars
SINCE the deployment of the Hubble Space Telescope and other specialised orbiting telescopes, astronomers have found out how and why stars are formed and how they die.
What are stars? Simply put, a typical star (like our Sun) is a huge glowing ball of hot gas - Hydrogen fusing into Helium at 600 tons a second.
Hot, blue/white stars like Sirius - Alpha Canis Majoris aka 'The Dog Star' and Rigel - Beta Orionis, fuses more Hydrogen into Helium per second, than all of humankind could produce in a million years, using nuclear, ballistic, thermal, solar and wind energy.
Blue/white stars are also the hottest, smallest and have the shortest life span of a few billion years, as opposed to reddish stars like Betelgeuse, Regulus and Antares, that live for tens of billions of years.
How many stars are created in our Milky Way Galaxy?
Astronomers observing stars in the UV, Visual, IR and X-ray modes, have concluded that our Milky Way Galaxy that represents an average type of galaxy, create roughly 150 billion stars born per year in the entire visible Universe.
This corresponds to about 400 million stars born per day or 4800 stars per second!
How are stars born? Like people, stars are born, they grow old and they die.
Their birth places are huge, cold clouds of gas and dust, known as 'nebulas'.
The most famous of these is the Orion nebula, which is just visible with the unaided eye.
These clouds start to shrink under their own gravity.
As the cloud gets smaller, it breaks into clumps.
Each clump eventually becomes so hot and dense that nuclear reactions begin.
When the temperature reaches 10 million degrees Celsius, the clump becomes a new star.
After their birth, most young stars lie at the centre of a flat disc of gas and dust.
Most of this material is eventually blown away by the star's radiation.
Before this happens, planets may form around the central star.
How do stars die? When the star's Hydrogen is used up and the energy flow from the core of the star stops, nuclear reactions outside the core cause the dying star to expand outward into the "red giant” phase like Betelgeuse, before it begins its inevitable collapse.
If the star is about the same mass as the Sun, it will turn into a white dwarf star and when its core finally cools, it turns into a black dwarf.
This is what happens when a normal-sized star dies.
If a really huge star dies, it has so much mass that after the helium is used up, it still has enough carbon to fuse it into heavy elements like iron.
When the core turns to iron, it no longer burns, as iron absorbs energy.
If you have a Space question or want to book a stargazing night at the Observatory, email email@example.com or phone James on 0427 961 391.
Next week: Binary Stars.