BIG STARS AND LITTLE STARS

When looking up at the stars, you probably wouldn't give them a second thought as to exactly what they are, but they are much more amazing than you could imagine. 

when you look up at a star you are not actually looking at the star itself, but looking at the light that it emits.  If you were standing on a hillside looking at the light of a torch in the distance, you wouldn't be able to see the bulb that makes the light, would you?

Stars come in all sorts of colours, temperatures and sizes, ranging from hot white dwarf planet size stars, to cool red giant stars the size of planetary orbits.  On this page I will show the two extremes of the scale.  The largest known stars - and possibly the smallest main-sequence star in the galaxy.

Big stars

The star imaged below is one of the largest stars in the Milkyway galaxy.  It is called Eta Carina in the southern constellation of Carina.

This star is the bright object at the centre of the two lobes of ejected gas.  Large amounts of condensed gas are also visible silhouetted against the bright background light.  It is about 8,000 light years away (192 thousand trillion miles), yet structures as small as 1 billion miles in size are seen.  150 years ago this was one of the brightest stars in the southern hemisphere, when a huge event took place giving out as much light as a supernova.  The star did not quite self-destruct, and today lies on the limit of naked eye visibility.

The two lobes and equatorial disc are moving through space at about 1.5million mph.  They surround the seemingly small star which is actually 100 times the size of the sun, and radiates 5 million times as much energy.  This star is still expected to go supernova in the next few million years.

Betelgeuse is another monster of a star.  Below shows the position, colour and enormous size of this star in Orion.

To get an idea of just how big this star is, the diameter of Earth's orbit is 186 million miles, while Jupiter's is near to 1 billion miles.  The sun is only 864,000 miles wide.  If the sun were to be drawn to scale on the above left hand image, it would be smaller than 1 pixel in size.

The big one.....

If the above two stars were not big enough, then this will astonish you.

In a star system 2,000 light years away lies a pair of stars in orbit about each other, an eclipsing binary.  They have an very long orbital period of over 20 years and consist of a red supergiant (VV Cephei A, spectral type M2) and a blue star (VV Cephei B, spectral type B0).  The larger of the two stars...A... is coming to the end of its life, and has swelled up as it rapidly consumes elements in its core.  The star has reached epic proportions, Its radius is believed to be about 1,900-2,000 times that of the sun and therefore has a volume of around 8 billion times that of the Sun.

VV Cephei, Digital Sky Survey        Click on the image to see a comparison to the sun

And then there are the small stars

The star in question is the one on the right of the below image.  Called Gliese 623b, it is 10 times smaller than the sun just 86,400 miles in diameter, this star is barely 10 times the size of Earth.  The star is 25 light years away in the constellation Hercules.  The Separation between the two stars is only twice that of the Earth to the Sun.

Possibly the smallest star yet discovered is OGLE-TR-122b.  It was discovered by the OGLE (THE OPTICAL GRAVITATIONAL LENSING EXPERIMENT) when it eclipsed OGLE-TR-122 and reduced the luminosity by 1.5%.  After much research it was determined that OGLE-TR-122b is just 16% larger than Jupiter, and only 96 times heavier, very close to the 75 Jupiter mass threshold for an official star.