Tag Archives: Canis Major

[COSMIC BODIES] – SuperStars

6 Nov Sizes of Stars

The stars… the givers of light, the givers of warmth, the givers of life…

These huge fiery furnaces have been burning brightly for billions of years and they will continue to light up the universe for many more to come. Our Sun is just one prime example of an ordinary, middle-aged star but stellar systems come in all shapes and sizes. In this issue we will uncover super massive stars and witness some of the most luminous objects in the universe.

The Sun, at the centre of our solar system, was integral to that of human existence, to large and our planet would be to hot for liquid water to form, to small and the energy emitted would not be enough to support the staples we rely upon. Our star is at exactly the right size and distance, 93 million miles away, for humans to bathe in its brilliant glory and prosper from its energy. The Sun is known as a ‘Yellow Dwarf’ star, it is at the middle of its life cycle or ‘Main Sequence’, the point of a stars life were it starts to burn its reserves in a bid to fight against the inevitable gravitational forces that will one day collapse it into a much smaller ‘White Dwarf’ star.

The sheer size of the Sun leaves our planet basking in the warmth of the radiation discharged from nuclear reactions going on under its surface. A super heated core converts hydrogen into helium at the temperature of 15 million degrees Celsius, compare that to the hottest Earth temperature of 70.7 degrees recorded in Libya and we can count ourselves lucky we are at the perfect distance. It is said that a million Earths could fit in the sun and that it is 750 times the size of all the masses of all the planets combined.

At this moment the star’s approximate size is thought to be near to 1,000,000 miles in diameter as it grows older it will start to expand outwards, past the orbits of Mercury, Venus, Earth and Mars as it uses up the last of its energy. Even at this inconceivable magnitude the star is still dwarfed by our next specimen 8,000 light years away.

Eta Carinae is a binary system, consisting of at least two stars orbiting each other, surrounded by a huge cloud nebula ejected from one of these stars in a mass explosion in the past. One of the stars is a smaller Wolf-Rayet star which burns slower and at a lesser temperature than its oversized blue neighbour. This star managed to stay stable for the time being but will be subject to a super or hypernova explosion in the near future, approximately in the next 10,000 to 20,000 years.

Supernova and hypernova explosions occur once a star has finished nuclear fusions and has exhausted its last reserves, this will lead to an eruption and total destruction, once gravity loses the battle, of the matter once holding it together. The size and class of the star determines what type of explosion it will endure.

This massive blue star, Eta Carinae, is 120 times the volume of the sun, which means if it was at the centre of our system it would extend beyond the distance of Jupiter, past the four inner planets and far beyond the asteroid belt that separates those rocky bodies from the outer gas giants.

Eta Carinae is a ‘Luminous Blue Variable’ (LBV), meaning its luminosity differs due to it pulsating irregularly; this aside this giant still burns at the brightness of 4 million suns. Although this star is younger than ours it is much larger, meaning these class of stars are able to produce an iron core at their centre, this is thought to one day cause Eta Carinae to go hypernova.

Another example of stellar behemoths that has its future yet to be determined is Betelgeuse(Beetlejuice) or Alpha Orionis. A red supergiant that is 300 times bigger than Eta Carinae and 500 times that of the sun. Placed at the centre of our solar system and the surface would reach out to twice the orbit of the planet Mars. Betelgeuse, due to its size, is the 10th largest star and its furnace is 14,000 hotter than our own. Sitting on the shoulder of Orion in this popular constellation, Betelgeuse has an uncertain future ahead of it. Running low on energy Betelgeuse is sure to explode into a supernova. When…? No one knows. It could happen in the next million years, it could happen this decade.

Betelgeuse (top left)

It is unlikely for this star to explode any time soon but it is not impossible, when it inevitably does happen Betelgeuse will appear as a second sun to us. Rivaling that of our own during the day and out shining the moon during the night. This will conclude in either the explosion slowly dimming out over the course of a few months, or turning into a gamma ray emitting pulsar sure to reign for thousands of years.

Finally we have our last remaining stars the brightest, Sirius and the largest VY Canis Majoris who both belong to the constellation Canis Major.

Sirius is also a binary star system like Eta Carinae but its major star Sirius A is our point of interest as it is the brightest of all the stars in the night sky. Sirius A is 23 times more luminous than our sun and double its size, quite small in comparison to some of the other stars featured above. Sirius used to be of huge significance to ancient civilizations that depended on the night sky for their survival. As time has moved on it held less importance due to technology helping us pinpoint ourselves on this planet but Sirius has still remained the brightest star ever discovered.

Sharing the same constellation as Sirius is VY Canis Majoris, of which this section of the night sky is named. It is massive, truly gigantic and is a bit of an anomaly. Being the biggest it is also one of the brightest, surprisingly unlike most other giant stars this is a single star system, consisting of just one red hypergiant, much like Betelgeuse but significantly larger.

If the Earth were to represent 1cm on a ruler then VY Canis Majoris would correspond to 2.3km.

If, like the others, it were placed in the middle of the solar system we call home. This star would end far beyond the orbit of the planet Saturn.

It is one billion times the size of the sun.

Much like Betelgeuse VY Canis Majoris will meet a violent end. Thought to occur in the next 100,000 years both of these red supergiants are expected to go supernova causing beautiful but dangerous eruptions that will eventually be recycled into new, possibly even bigger stars.

Example of a Hypernova