people drink tea in the
UK every day48
million
of an apple’s volume is air,
which is why they float25
per cent
Do stars have a size limit?
Astronomers reckon that stars probably can’t survive
above a mass of about 150 solar masses. This is
because the enormous radiation pressure and mass
loss from the star would disrupt its gravitational
stability. Although more massive stars have been
discovered, such as the 265-solar-mass star R136a1,
these are likely to form by the merger of two or more
stars. But mass and physical size are not simply
related, particularly for giant stars. The best candidate
for the largest known star is UY Scuti which, although
it is only about 30 solar masses, has a radius 1,700
times that of the Sun. Giant stars such as UY Scuti are
known to swell up due to changes in their internal
structure as they evolve. But there is no clear-cut
equation that determines how big a star can get since
it depends not only on mass, but composition,
evolutionary history and the strength of its stellar wind.
For giant stars, such as UY Scuti, the outer
atmosphere can continue to puff up and grow
essentially without limit. But at some point the diffuse
gas of its outer layers become merged with the
interstellar medium and cannot really be regarded as
the stellar surface. AGWhat effect does
drinking too
much water have
on your body?
If you drink more water than your
kidneys can remove
(approximately one litre an hour),
the concentration of sodium and
other electrolytes in your blood
begins to drop. Beyond a certain
point, your cells will uncontrollably
absorb water by osmosis and swell
up. In the brain this increases the
pressure against your skull, which
leads to headache, confusion,
vomiting and (ironically) thirst. If it
isn’t treated promptly, this
progresses to seizures, brain
damage and death. LVOur Sun (tiny yellow dot)
compared to largest
known star UY ScutiPHOTOS: ISTOCK, ALAMY, GETTY X3, SCIENCE PHOTO LIBRARY X2
IN NUMBERS