Astronomershavediscovereda thindiscofmaterial
spirallingintoa supermassiveblackholeina veryfaint
galaxy– anunexpectedfindingthatmayprovidefurther
cluestothedynamicprocessessurroundingblackholes.
UsingtheHubbleSpaceTelescope,astronomersobserved
theblackholeatthecentreofthespiralgalaxyNGC3147,
whichislocatedaround 130 millionlightyearsawayinthe
Dracoconstellation.Blackholesinlow-luminositygalaxies
likeNGC 3147 usuallylacksufficientmaterialcaptured
bythegalaxy'sgravitytofeedfrom,andaretherefore
considered‘starving’.
Theresearchersweresurprisedtofinda thindisc
encirclingtheblackholeatthecentreofthisgalaxybecause
thedisclookssimilartothekindsofaccretiondiscsthat
typicallyencircleblackholesfoundinextremelyactive,and
muchbrightergalaxies.
"Thetypeofdiscweseeisa scaled-downquasar[a
luminousgalacticnucleus]thatwedidnotexpecttoexist,"
StefanoBianchi,anastrophysicsprofessoratRomaTre
UniversityinItalyandleadauthorofthestudy,saidina
statement."It'sthesametypeofdiscweseeinobjectsthat
are1,000oreven100,000-timesmoreluminous."
Thediscissodeeplyembeddedintheblackhole's
gravitationalfieldthatthelightbeingemittedfromthe
gasdiscisalteredbytheintensegravitationalpull.Hubble
measuredthediscspinningaroundtheblackholeatmore
thantenpercentofthespeedoflight,causingittobrighten
asitmovestowardsEarthanddimwhenitmovesaway
fromourplanet.Scientistscanusetheseobservationstotest
AlbertEinstein'stheoriesofrelativity.
"Thepredictionsofcurrentmodelsforveryfaintactive
galaxiesclearlyfailed,"Bianchisaid.Scientistshadpreviously
proposedtheendearingterm
‘moonmoons’todescribe
moonsthatmayorbitother
moonsindistantsystems.Now,
anotherteamofresearchershas
coinedthemelodiousnickname
‘ploonet’formoonsofgiant
planetsorbitinghotstars;under
certaincircumstances,these
moonsabandonthoseorbits,
becomingsatellitesofthehost
star.Theformermoonisthen
‘unbound’andhasanorbitlike
a planet's– ergo,a ploonet.
Ploonetshaveyettobe
detected,butploonetsmay
producelightsignaturesthat
planet-huntingtelescopescould
identify,researchersreportedin
a newstudy.
Forthestudythescientists
createdcomputermodels
totestscenariosthatmight
transforma planet-orbiting
moonintoa star-orbiting
ploonet.Theresearchers
foundthatifa mooniscircling
a type of exoplanet known
as a ‘hot Jupiter’ – a massive
gas giant close to a star –
the gravitational tug of war
between star and planet could
be powerful enough to wrest
the moon from its planetary
orbit and send the object
circling around the star instead.
However, most ploonets
would likely be relatively
short-lived. The majority of
the objects disappeared within
a million years and never
became planets; instead, they
disintegrated during collisions
with their former host planets,
were gobbled up by stars in
acts of ‘planetary cannibalism’
or were ejected from orbit.Outerspaceisa notoriouslyharshenvironment,exposing
astronauts to high levels of radiation. And radiation
exposure can increase cancer and heart disease rates in
earthbound humans. But a new study has some good
news: space radiation doesn't seem to increase astronauts'
risk of death from cancer or heart disease, at least not at
the doses they experienced during historical missions. Still,
longer missions – such as a mission to Mars – will likely
come with much greater radiation doses that could pose
larger health risks.
Space travel exposes the body to higher levels
ofionising radiation than those typically
experienced on Earth. At high dosesthat
radiation has been tied not just to
cancer and heart disease, but to a
host of other health problems.
The new study analysed
information from 418 space
travellers, including 301 NASA
astronauts, who had travelled to
space at least once since 1959.Duringthistime, 89 oftheparticipantsdied.Among
the 53 NASA astronauts who died, 30 per cent died
from cancer and 15 per cent from heart disease, while
among the 36 Russian or Soviet cosmonauts, 50 per cent
died from heart disease and 28 per cent from cancer.
"If ionising radiation is impacting the risk of death due
to cancer and cardiovascular disease, the effect is not
dramatic," the authors wrote in their study, published 4 July
in the journal Scientific Reports.
Still, the study cannot determine whether longer
missions would pose different risks. "It
isimportant to note that future
missions of deep-space exploration
willlikely offer much greater
doses of space radiation than
have historical doses, which
will lead to a different risk
profile for future astronauts
and cosmonauts," the
authors said.Exomoonshavea newnameAstronaut cancer deathsnot
caused by space radiation
Runaway
exomoons
nowknown
asploonets
This monster black hole’s
disc shouldn’t exist
LAUNCH PAD
YOUR FIRST CONTACT WITH THE UNIVERSEININCOOPERATIONCOOPERATIONWITHWITHWords by Passant RabieWords by Rachael RettnerWords by Mindy WeisbergerNGC 3147's black
hole has a larger disc
than expected© ESA© NASA/ESA© NASA