BIG BOOM: The Andromeda galaxy on the left will collide with our Milky Way galaxy 3 billion years from now.
BIG BOOM: The Andromeda galaxy on the left will collide with our Milky Way galaxy 3 billion years from now. Contributed

DARK SKIES: How big can a star really get?

SINCE humans have been looking up into a dark, starry sky, no one, least of all early astronomers, knew how far away stars were or how big they were.

Now, with the aid of super-fast computers, orbiting space telescopes, CCD and other sophisticated cameras, modern-day astronomers can not only measure the stellar distance, size, density, volume and age, they can also tell how much hydrogen is left in that star, that is fused into helium, at 40 million degrees centigrade.

Stars, like planets, are born in huge dust gas clouds, called nebula.

While it takes millions of years for a star to mature, astronomers have recently found our Milky Way galaxy is producing about 5000 stars a second and at this rate our galaxy will be twice what it is currently 1 billion years from now.

Just recently, the Hubble Space Telescope estimated the Andromeda galaxy 2.2million light years away will collide with ours in about 3 billion years' time.

This impact will merge them into one gigantic galaxy unprecedented in size and mass.

Colliding galaxies are ongoing. What astronomers have found of colliding galaxies is that all of this happened tens of billions of years ago.

The size of stars are based on their colour. Blue-white stars like Rigel Orionis Canopus in Carina and Sirius in Canis Majoris, to name a few, are also called Blue Supergiants as opposed to Red Supergiants.

Blue-white stars are extremely hot, young and feisty by stellar standards.

Yellow stars like our sun and Alpha Centauri are smaller "middle-age” stars and red stars like Betelgeuse in Orion, Antares in Scorpio and Regulus in Leo are huge, dying stars from lack of hydrogen and old age.

For size comparison, let's shrink our sun down to a golf ball.

To begin, Rigel Orionis (the top bright star of Orion) is a Pilates gym ball, Canopus a beach ball and Sirius is a cricket ball.

A yellow star like Alpha Centauri is about the same, while Betelgeuse - the largest naked-eye star - is a 4m ball.

Antares and Regulus could easily fit into the former.

But wait, there's more.

In the constellation of Scutum is UY Scuti, so massive its size is a 3km ball, while VY Canis Majoris is 2km - and all this is just within 1000 light years from the sun.

So how big can stars get? Good question.

While we have only scratched the cosmic surface of the universe, there is no reason why stars should not be larger. Astrophysicists believe there are stars even larger than what they've found in our galaxy.

The older a star gets, its star's core increases in size from expanding molecules of gas to a point where its volume is so large, the core suddenly collapses and one of three things happen.

We will look into that in another weekly column here in the South Burnett Times.

If you want to book a stargazing night at the observatory, email mao123@bigpond.com, phone 0427 961 391 or visit the website, www.kingaroy observatory.com.