Views Columnist
C1landa Frescod-Vlkilsterl
is an assistant professor of
physics and aslrOl'IO~and
a ccrefacultymember in
women's studies at the
University of New Han1:lstft.
Her research In theoretical
physics focuses on msmology,
neutron stars and particles
be1ond the standard modelChanda's week
Wball':mreadlfll
I am m:ited to dig
lntofeBow scientist
Bl'luldon Taylor'•
debut novel Real life.
Whatl':mwakldDg
I am really happy
that NeNe and Porsha
made up an The Real
Housewives of Atlanta.
Wball':mwmldnian
Worting during a
pandemic is hard, but
I am starting some new
wort involving machine
learning, and that is fun.
ThiS c:aUnn appears
monthly. Up next week:
Graham L..awtcn.. I lfftrldllllllt I 11.Maa'Cluiom
Pielclnotel from spac:e-tlme
Hubble In crisis The universe is expanding, but sums at the heart
of the process don't seem to add up. What we learn next may alter
our view of the cosmos, writes ChandaP.n!scocl·WeimtelnI T1Snearly1ooyean since we a powerful tool because they are disagreementassummgtheyare
amfinned that the universe- found in other galaxies. Hubble taking all of the right physics into
space-time-is expanding. took advantage oftbat, leading account comc:tl.y.
Butwe are still struggling with to his finding that galaxies move As wonderful as Cepheids are,
a basic fact: what is the rate of away from us at a velocity directly because they aie:young stars, they
theapansion7Dependmgon proportional to their distance tend to be sunoundecl by dust.
hawwemeuureacrudalnumber from us. The proportionality This is a problem because it can
that sets this value, we seem to constant ofthis relationship ls obscure measurements, making
get cliff'emlt answers. The fallout knownastheHubblecollBtaDt them inaccunde. It means there
of this question could chastically Ninety years after Leavitt maybe errors In Cepheid-baaed
change our understanding of disooverecl her law, astronomers calibrations oftype la supemova
the cosmos. were making distance distances, leading to an error in
In1929,astmnomer Edwin measurements using exploding the distances calc:ulated from
Hubble used observations of stanknownastypelasupemovae. obsenationsofthem.
galaxies to show that there was a Theyirundsomethingunexpecll!d: Inmct. the Panchromatic
correlation between their velocity not only is space-time expanding. Hubble Andromeda Treasury
and their distance from us. The but that expansion is acceleiating, collaboration (PHAT) has since
furtherawaytheywere,thefaster found that Riess and his team
they seemed to be receding from "Thedlscovmy of may have the wrong calibrations
our galaxy. Gen.enl relativity, cosmkaccelemtlon fortheirCepheids and this may
which at that point bad only been netted three of be partly due to their use of
around fora decade and a halt; had
theasb'ollomenground-hued telescopes as
aclearthemeticalexplanationfor opposed to something in space
thisflndlng:s~timeim'tstatic. Involved a likePHATuses. Th.ecalhmations
It expands, c:arrylng galaxies Nobel prize" also suft'erfromcrowding-the
alonglilce a raft on a river. possibiliqrthatwbatlooblike one
Hubblewasabletomake lib a river current picking star is actually several-and this
this radical dlsooveJY because up speed. The discovery of effect can get worse with distance.
of something we now call cosmic acxeleradon, as this In July .a019, astronomer
Leavitt's law. Discovered by phenomenon is known.netted Wendy Freedman said these
Henrietta Leavitt in1908, the three ofthe astronomers involved inoonsistendes are "what keeps
law conc:ems young stars called a Nobel pm.e. [her] up at night". She is leading
Cepheid variables. These sbUs For a time, discussions of a team that is using another type
are called variable because their expansion focused primarlly of starto:meumetheHubble
brightness and sJze vuy. on the problem of exp]aining constant: those in the so-called
While working as a computer cosmic acceleration. But now tip ofthe red giant branch, known
at Harvanl College Obsemttoiy. astronomers are spending a lot as TRGBs. These stars are maybe
Leavitt noticed that Cepheid1 had oftimeargumgovertheexact half the mass of the sun, and are
a pattern: the power of their light value of Hubble's constant. at a later stage of their lives when!
emission-absolute magnitude, AdamBiess, one of the cosmic heliumbumJnghasbegunmtheir
to astronomers-conelates with acceleJationNobel. laureates, bas cores, after all of their hydrogen
the fn!quency ofthe pulsations. been leading a team that used type has burned up. Earlier this :year,
In other words, by observing Ia supernova to find a value for the Freedman's team published a
these, one could calculate their Hubble mnstantthatis12 per cent paper saying thatcablnatingtype
absolute magnitude, whk:h largerthanoneproducedby a Ia supernovae with TRGBsleads to
we could then use to calrulate different method involving the aHubblevaluetbatissomewhere
howfa.rwe are from an object. cosmic microwave background between that suggested byCMB
Leavitt'slaw c:n!ated a rung (CMB) radiation, the leftover measurements and whatRiess's
on what we call the cosmological radiation from the big bang. team has found
distance ladder, which.is a This difference is much larger Whyarethesevaluesso
collection of different ways that than the margin of er.rm involved. different? We just don'tknow-
we measure distances to objects which means that the two and not knowing ii part of what
in the sty. Cepheids proved to be measurements appearto be in makes science so fun. I