BBC Focus - 04.2020_

COSMIC LENS

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GRAVITATIONALLENSING

Galaxyclustersareoneofthemostmassiveobjects
intheUniverse.Theyaresoheavythattheywarpthe
fabricofspace-time,tothepointthatlightgetsbent
asit passesby.Undertherightconditions,this
bendingcanactasa lens,magnifyinggalaxies
locatedbillionsoflight-yearsbehindthem,aneffect
knownasgravitationallensing.
Intheleft-handpictureabove,youcanseeseveral
brightbluegalaxieswhichhavebeenlensed,though
theprocesshasdistortedthemintocurvedarc
shapes.Suchimagesarevitalintrackingoneofthe
mostmysterioussubstancesintheUniverse,dark
matter.“Mostofthematterina clusteris dark
matter,”explainsWiseman.“Wedon’tknowwhat
darkmatteris,butthroughHubble’sobservationsof
lensingwecantellhowit’sdistributedandthe
historyofhowdarkmatterevolvedthroughoutthe
historyoftheUniverse.”
Afterstudyingthepatternofdistortedgalaxies,
astronomershavecreateda mapofdarkmatter
withinthiscluster, shown in the right-hand
image, in blue.

FE ATURE

WHEN GALAXIES COLLIDE

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GALAXIESCOLLIDING

Twogalaxiescollidingintoeachothersoundslikeit

shouldbehazardous,if notfatal,to theobjects

involved.Inreality,it is themainwaythesestellar

collectivesgrowandevolve.Whentheycrash

together,orevenjustpasscloseby,theresultingchaos

stirsupthegaswithinthem,creatingknotsof material

whichgoonto formstellarnurseries.

Here,weseetwoseparategalaxiesthathave

recentlypassedcloseenoughthatthey’vepulled

eachother’sspiralarmsoutof shape.Hubble’s

ultravioletcamerashavebeenableto pickoutregions

wherehot,youngstarsarebusilyforming.Theseare

thebrightblueclumpsclusteredaroundthegalaxies’

distortedarms,wheretheinteractionwouldcreatethe

mostturbulence.

Hubble’sunparalleledsharpnessandabilityto see

intheultravioletis oneof thekeywaysinwhichit

differsfromitsEarth-boundcounterparts.Our

atmospheresoaksupmostof theultravioletradiation

thatarrivesatourplanet,andsoHubble’sviewabove

theatmospheregivesusa unique view of the Universe

at these wavelengths of light.

byDRELIZABETH

PEARSON(@E z z y P)

Elizabethis a space

journalistandnewseditor

atBBCSkyAtNight

magazine.

HUBBLE’S HIDDEN GEMS