The next supernova
How do stars explode?
Stunning supernovae explosions can come
from very different stellar systems
2AFindingtherightstars
Theseoccurwhena whitedwarf,
liketheoneourSunwillleave
behindafteritsdeath,isfoundina
binarypairwithanotherstar.3ASqueezingdown
Thisaccretionofmatterfromits
companionaddsextramass.The
additionalgravitationalforces
compressthealreadyhighly
pressurisedcoreofthewhitedwarf.5ALimitedgains
However,whitedwarfscanonly
getsomassivethroughaccretion.
TheChandrasekharlimitputstheir
maximumsizeatabout1.4times
themassofourSun.4AAstarreborn
Asthestarapproachesthe
Chandrasekharlimit,the
dyingstarcomestolife
againandundergoes
fusioninitscentre.6AOutward
pressure
Thistimethestar
cannotexpandto
accommodatethe
outwardpressure
ofitsnewlykindled
fusionburning.Instead
expansiveforcesbuild,
eventuallycreatinga
violentsupernova.1AMattertransfer
Occasionallythetwostarswill
orbitcloseenoughtoeach
otherthatmatterwilltransfer
fromthecompanionontothe
whitedwarfstarina process
calledaccretion.Type Ia supernovae
Type II supernovae
1BOutofgas
SupergiantslikeBetelgeuse
willeventuallyrunoutof
hydrogenandheliumfuel,
thenuclearburningofwhich
preventsthemcollapsingin
onthemselves.4BBurningfuels
Forstarsthissize,theirmass
andcompressionalforcesat
theircoreallowthemtofuse
heavierelementsinorder
tomaintaintheoutward
pressurethatholdsoffgravity.2BAnelementalonion
Graduallyheavierelements
buildupatthestar’scentre,
whichbecomeslayeredlikean
onion,withlighterelements
towardstheoutsideofthestar.3BResistance
isfutile
Thisactof
resistanceholds
untilthestar’s
innermostcoreis
composedofiron,
whichrefusesto
fuse.Gravityfinally
winsoutandthe
star’souterlayers
collapseinwards.5BShockwave
rebound
Thisinward
implosionbounces
backoffthecoreas
a reboundingshock
wavethatblowsthe
wholeatmospheric
envelopeoffthe
star,creating
thespectacular
supernova.© Nicholas Forder1A
1B
3A
3B
5A
5B
2A
2B
4A
4B
6A