mysteriouscosmiceventmight
haveeversoslightlystretchedand
squeezedourplanet.On 14 January
astronomersdetecteda split-second
burstofgravitationalwaves,distortionsinspace-
time– butresearchersdon’tknowwherethisburst
camefrom.Thesignal,pickedupbytheLaser
InterferometerGravitational-WaveObservatory
(LIGO)andtheVirgointerferometer,lastedonly 14
milliseconds,andastronomershaven’tyetbeenable
topinpointtheburst’scauseordeterminewhether
itwasjusta blipinthedetectors.
Gravitationalwavescanbecausedbythe
collisionofmassiveobjects,suchastwoblackholes
ortwoneutronstars.Astronomersdetectedsuch
gravitationalwavesfroma neutronstarcollisionin
2017 andfromoneinAprilof2019.Butgravitational
wavesfromcollisionsofsuchmassiveobjects
typicallylastlongerandmanifestinthedataasa
seriesofwavesthatchangeinfrequencyovertime
asthetwoorbitingobjectsmoveclosertoeach
other,saidAndyHowell,a staffscientistatLos
CumbresObservatoryGlobalTelescopeNetwork
andanadjunctfacultymemberinphysicsatthe
UniversityofCalifornia,SantaBarbara,whowasnot
partoftheLIGOresearch.
Thenewsignalwasnota seriesofwavesbut
a burst.Onemorelikelypossibilityisthatthis
short-livedburstofgravitationalwavescomes
A
“Waves from
collisions of such
massive objects
typically last longer”
Left: Ripples
in space-time
travel out from
the collision
of massive
© Mark Garlick/Science Photo Libraryobjectsfroma moretransientevent,suchasa supernova
explosion,thecatastrophicendingtoa star’slife.
Indeed,someastronomershavehypothesised
thatthiscouldhavebeena signalfromBetelgeuse,
whichmysteriouslydimmedrecentlyandis
expectedtoundergoa supernovaexplosion.But
Betelgeuseisstillthere,soit’snotthatscenario.It’s
alsounlikelytobeanothersupernovabecausethey
happeninourgalaxyonlyaboutonceevery 100
years,Howelladded.
What’smore,theburststill“seemsa littletoo
shortforwhatweexpectfromthecollapseofa
massivestar,”hesaid.“Ontheotherhand,we’ve
neverseena starblowingupingravitationalwaves
before,sowedon’treallyknowwhatitwouldlook
like.”Inaddition,theastronomersdidn’tdetect
anyneutrinos,tinysubatomicparticlesthatcarry
nocharge,whichsupernovaeareknowntorelease.
Anotherpossibilityisthatthemergingoftwo
intermediate-massblackholescausedthesignal,
Howellsaid.Mergingneutronstarsproducewaves
thatlastlonger– around 30 seconds– thanthis
newsignal,whilemergingblackholesmightmore
closelyresembleburststhatlastfora coupleof
seconds.However,intermediateblackholemergers
mightalsoreleasea seriesofwavesthatchange
infrequency.
LIGOcameacrossthissignalwhilespecifically
lookingforsuchbursts.But“thatdoesn’tmeanGravitational waves
that what it found is an intermediate-mass black
hole merger,” Howell explained. “We don’t know
what they found,” especially since LIGO hasn’t yet
released the exact structure of the signal, he added.
It’s also possible this signal was just noise in the
data from the detector, Howell said. But this burst
of gravitational waves was found by all three LIGO
detectors: one in Washington state, one in Louisiana
and one in Italy. The probability of the LIGO
detectors finding this signal by chance is once
every 25.84 years, which “gives us some indication
that this is a pretty good signal,” Howell said.
There could be other explanations for this
mysterious burst, too. For example, a supernova
could have directly collapsed into a black hole
without producing neutrinos, though such an
occurrence is very speculative.
Astronomers are now pointing their telescopes
to that region to try to pinpoint the source of the
waves. “The universe always surprises us,” Howell
added. “There could be totally new astronomical
events out there that produce gravitational waves
that we haven’t really thought about.”