modelexplainingthe
Perseusobservationswould
onlybepossibleifSun-
likestarsarebornwitha
companion.“Weshowedthat
probablyallstarslikeoursform
withcompanions,”hetellsus,“but
thatmost,includingtheSun,thenlose
thosecompanionswithinthenextmillionyears.”
TheworkbuiltonthatofPavelKroupaof
theUniversityofBonn,whosecomputer
simulationsin 2011 ledhimtoconcludethatall
starsarebornasbinaries.“Starsgenerallydonot
forminisolationbutareborntogetheringroups
withincloudsofgasanddustornebulae,”Kroupa
wrote.“Thesestellarlabourroomsproducebinary
starsystems,whichmeansthatvirtuallyall
newbornstarshavea companion.Mostofthese
groupsofstarsdispersequicklysothattheir
membersbecomepartofthegalaxy.”
InthecaseofNemesis– oratleastinthecase
ofSadavoyandStahler'sversionofa companion
Sun– theSun'ssiblingescapedandmingledwith
otherstarsintheMilkyWay.Stahlersayshedoesn't
subscribetotheviewthatitthencausedstrong
cometactivityintheOortCloud.“20yearsago
astronomersthoughtso,butfewpeoplebelievethat
now,”heaffirms.Neitherdoeshebelievethatthe
Sunhasanyinf luenceoveritscompanion.
“Muller'stheoryisdifferent,”heexplains.“He
postulatedthattheSuncurrentlyhasa companion
onaneccentricorbitbut,despitea lotofeffort,
thiscompanionhasneverbeenfound.”Stahleris
unsurprisedthata formofNemesishasneverbeen
discovered,though.“WethinktheSun'scompanion
driftedawaybillionsofyearsago,withina million
yearsaftertheSunanditscompanionformed,”hesays.“Itcouldnowbeonthe
othersideofthegalaxy."
Suchfindingshavewide
implications,andtheygo
totheheartoftheoriginsof
galaxies.InthecaseofPerseus
therewere 45 single-starsystems,
yetallbutfiveofthe 55 youngstarsin 24
multiple-starsystemswerebinary.Morethanthat,
allofthewidelyseparatedbinarysystems– which
arethosewithstarsseparatedbymorethan 500
AU– wereyoungsystems.
“Ourfindingthatmoststarsarebornwith
companionsisinterestingforthoseofuswhothink
aboutstellarbirth,”Stahlersays.“Apparentlyour
Sun,andalsotheSolarSystem,wasbornfroman
elongatedgascloudthatformedanotherstar– and
perhapsanotherplanetarysystem– aswell.Wesee
lotsofsuchclouds,sostudyingthemwilltellusthe
conditionsunderwhichweformed.”
It'sthemostcompellingevidencethatourSun
wasoncepartofa binarystarsystem,butthe
emphasison‘once’cannotbestressedenough.
Asforthefigureof 26 millionyears,well,that
tooisindoubt,withAdrianMelottandRichard
Bambachhavingarguedintheirpaper,Nemesis
Reconsidered, that“theorbitofa distantcompanion
totheSunisexpectedtobeperturbedbythe
galactictidalfieldandencounterswithpassing
stars,whichwillinducevariationintheperiod”.
WhatallofthismeansisthattheSun'spotential
twinisoffthehookwithregardstoitbeinga
mass-murderer,butthereisgreatweighttoMuller's
assertionthattheSunwasbornwitha companion.
Unfortunatelyit'llbesofarawaynowthatwe're
unlikelytoeverseeit,it'shistoryperhapsforever
keepingusinthedark.Left:
Sarah Sadavoy
and Steven
Stahler say
low-mass stars
are always
born with a
companion
but are likely
to split, like
the Sun
Right:
The cold dwarf
planet Sedna
is said reside
at the outer
edges of the
known Solar
System from
where the Sun
appears as
an extremely
bright star
Below:
It was thought
that the Sun's
hypothesised
twin, Nemesis,
caused
disruption
to icy rocks
in the Oort
Cloud, causing
chaos on Earth
© Getty© NASA/JPL-CaltechNemesis