Page 84 - BBC Focus - August 2017

How do

stars die?

LESLIE GRIFFIN, MALVERN

Stars die because they exhaust their
nuclear fuel. The events at the end of
a star’s life depend on its mass.
Really massive stars use up their
hydrogen fuel quickly, but are hot
enough to fuse heavier elements
such as helium and carbon. Once
there is no fuel left, the star
Does holding your breath make you stronger? collapses and the outer layers
explode as a ‘supernova’. What’s left
PAD SCANLON, LONDON
over after a supernova explosion is a
‘neutron star’ – the collapsed core of
It won’t make you stronger in the sense you need to exhale normally and hold the star – or, if there’s sufficient
of building muscle in your heart or your breath when your lungs are empty, mass, a black hole.
diaphragm, but holding your breath rather than taking a big breath in and Average-sized stars (up to about
while training for certain sports has holding that. There are significant 1.4 times the mass of the Sun) will
been shown to improve the ability of risks, though. die less dramatically. As their
your muscles to cope with short, intense A 2009 study found that free divers hydrogen is used up, they swell to
exertions. This works by increasing who regularly held their breath for become red giants, fusing helium in
the concentration of bicarbonate in the several minutes had elevated levels of their cores, before shedding their
blood, which helps to neutralise the a protein called S100B in their blood, outer layers, often forming a
lactic acid produced during anaerobic which is an indication of long-term ‘planetary nebula’. The star’s core
exercise. For this technique to work, brain damage. LV remains as a ‘white dwarf’, which
cools off over billions of years.
The tiniest stars, known as ‘red
WHAT’S IN… dwarfs’, burn their nuclear fuel so
slowly that they might live to be 100
billion years old – much older than
...HAND CREAM the current age of the Universe. AGu

There are two ways that hand creams act to moisturise your skin. Occlusive agents form a barrier
that traps water, while humectants attract more water to your skin. The problem is that the
humectants are water soluble, while the occlusive agents dissolve in oil. So to get them to mix in
an easy-to-use formulation, the creams also need an emulsification system. ML

FATS AND OILS
WATER 7 per cent
80 per cent Coconut oil, petroleum jelly or lanolin
(a waxy substance secreted by
Gives the cream volume and
woolly animals such as sheep) might
dissolves some ingredients.
be used as occlusive agents that form
a barrier to block escaping water.
GLYCERINE
3 per cent EMUSIFIER
Is a typical humectant used to draw 2.5 per cent
water in from the atmosphere. Glyceryl stearate and stearic
acid help to stabilise the oil/ PHOTOS: ESA/HUBBLE/NASA, GETTY X3 ILLUSTRATIONS: RAJA LOCKEY
water mixture.
THICKENERS
5 per cent
PEG or polyacrylic acid (which may PRESERVATIVES
appear as carbomer on the label) are AND FRAGRANCE
long polymer molecules that 2.5 per cent
increase the viscosity of the cream, These improve the product’s shelf life
making it easier to apply. and make it smell nice.

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