10 | New Scientist | 31 August 2019KOALAS in Australia may find
settling into a new habitat easier
after a faecal transplant.
In 2013, a population of koalas
grew so large that the animals ate
enough leaves from their preferred
type of eucalyptus tree, the manna
gum (Eucalyptus viminalis) to kill
many of the trees. This resulted in
starvation and the death of more
than 70 per cent of the koalas.
Surviving animals were moved
to a new area, but they had little
interest in feeding on a similar
tree, the messmate (Eucalyptus
obliqua), despite other koalas
living off it exclusively.
Michaela Blyton at the University
of Queensland, Australia, found that
giving the relocated koalas a faecal
transplant from the local population
helped them to adapt. The process
changed the koalas’ natural mix
of bacteria, which began to
resemble that of the donors (Animal
Microbiome, doi.org/c9nx). ❚AnimalsCOSMOLOGISTS can’t agree on
how fast the universe is expanding
because the two methods they use
to find out give distinctly different
results. Now a third method
involving gravitational waves
could help break the deadlock.
Gravitational waves are the
ripples in space-time whose
existence was confirmed in 2015
by the Laser Interferometer
Gravitational-Wave Observatory
(LIGO). They are produced when
massive objects like black holes
or neutron stars smash together
(more on page 13).
To calculate the Hubble constant,
which quantifies the expansion
rate of the universe, astronomers
usually look at distant objects andfind out two things: how far away
they are and their redshift, which
is the degree to which the object’s
light has stretched as it passed
through expanding space on its
way towards us.
The Hubble constant is usually
calculated either by looking at
certain supernovae or at the
cosmic microwave background,
often called the big bang’s
afterglow. But these methods
result in different numbers.
It is possible that this discrepancy
is caused by errors, but some
astronomers believe that it is
evidence of unknown physics.
The events that make
gravitational waves don’t always
produce light. Even if they do, itcan be hard to spot. But in 2017,
LIGO researchers showed that if
they could catch some light from
the source of a gravitational wave,
they could measure the redshift.
The gravitational wave itself gives
the distance, so the Hubble
constant could be calculated.Now the LIGO team has
extended its work to black hole
mergers, which don’t emit light.
The group instead used galaxy
catalogues to identify the most
likely place that the gravitationalwaves came from. Then they
used the galaxy’s redshift in
their calculations (arxiv.org/
abs/1908.06060v1).
The new method is important
because it is independent of
the other two, but it can’t yet
provide a definitive answer. The
10 detections made so far are too
few to provide a precise estimate
of the constant.
“At the moment, our method
is like Switzerland, completely
neutral,” says Patricia Schmidt
at the University of Birmingham,
UK, and a member of the LIGO
consortium. As more detections
are made, the estimate should
get more precise. ❚CosmologyLIGO could solve space expansion mystery
Ruby Prosser ScullyKoala microbiome shift
Faecal transplants help the marsupials change their diets
JOUAN&^ RIUS/NATURE
PL
.COMNews
“ The two methods we
use to find out how fast the
universe is expanding give
distinctly different results”Stuart Clark