New_Scientist_3_08_2019

18 | New Scientist | 3 August 2019

Aerodynamics

Tree stump kept alive

by nearby trees

A TREE stump that should

have died is being kept alive by

neighbouring trees, which are

funnelling water to it via their

roots. The finding adds weight to

the idea that organisms can work

together for the benefit of a forest.

Sebastian Leuzinger and Martin

Bader at the Auckland University

of Technology in New Zealand saw

a tree stump near Auckland with

living tissue growing from it.

Hurtling star proves

Einstein right again

EVEN at the centre of the

Milky Way, Einstein’s laws rule.

Measurements of light from

a star that orbits close to our

galaxy’s central supermassive

black hole can’t be explained

by classical views of gravity

and instead require Einstein’s

general relativity.

General relativity predicts that

starlight should lose some energy

as it travels through the powerful

gravitational field of a black hole.

That energy loss is expected to

stretch the wavelength of light

from stars near huge black holes,

making them look more red.

Standard, or Newtonian,

gravitational theory doesn’t

predict this. No one really

expects Einstein’s theory to

be wrong at this scale, but if its

predictions were off by even

a little bit, it might point the

way towards new physics.

Astrophysics^ Ecology

HAVING dark feathers may help

birds fly more efficiently as

sunlight heats their wings and the

surrounding air, increasing airflow.

Svana Rogalla at Ghent University

in Belgium and her team thermally

imaged an osprey (pictured) and

saw that its dark feathers get

warmer than light ones, probably

because they reflect less light.

To see how this might affect

flight, the team put stuffed wings of

ospreys, gannets and back-blacked

gulls in a wind tunnel. These were

then heated with infrared light

bulbs similar in intensity to being

outdoors on sunny and cloudy days.

They exposed the wings to wind

speeds of 6, 12 and 18 metres

per second, similar to the birds’

natural flight speeds. “We wanted

to simulate flight under realistic

conditions,” says Rogalla.

Darker feathers heated up

much  more than light feathers

(Journal of the Royal Society

Interface, doi.org/c8t4). “We found

temperature differences of about

9 degrees between black and

white,” says Rogalla. “We would

even find these temperature

differences in the same wing.”

The finding suggests that a

common wing pattern – white

feathers where the wing attaches to

the body and black feathers at the

tip – could increase lift while flying.

The temperature difference

between the light and dark

feathers creates convective

currents in the air above the wing

that move from the cooler base of

the wing to the darker tips, says

Rogalla. This boosts the airflow

over the wing, which may make

flight more efficient. Donna Lu

Dark feathers give birds

a lift when they heat up

Wondering how it could survive

without foliage, they put water

monitors in the kauri (Agathis

australis, pictured) stump and

in two nearby trees of the same

species. In healthy trees, water

flow is largely driven by

evaporation through their leaves.

Over the following weeks, they

saw a pattern in the water flow in

the trees. When the neighbouring

trees evaporated water through

their leaves during the day, water

movement in the stump remained

low. But when the trees were

dormant in the evening, water

circulated through the stump

(iScience, doi.org/c8t2).

Without leaves, the stump’s

water flow was bound by the

movements of its neighbours.

Combined with the fact that

fungi and trees exchange

nutrients, this finding undermines

the idea of trees as individuals.

“That dramatically changes

our view of forest ecosystems

as ‘superorganisms’,” says

Leuzinger.  Ruby Prosser Scully

Tuan Do at the University of

California, Los Angeles, and his

colleagues used 24 years of

observations of a star called S0-2,

which orbits relatively close to

our galaxy’s central supermassive

black hole, Sagittarius A*. The data

included measurements of the

star’s colour and position, and

the team calculated its velocity

from measurements of its

position over time.

“When the star becomes

redder, it also looks like it’s

moving away from us faster

than it would without this

gravitational redshift,” says Do.

The team needed 24 years’

worth of data to nail down the

star’s orbit and make sure this

wasn’t tainting the colour

measurements.

Do and his colleagues found

that S0-2 appeared significantly

redder than we would expect if

its light wasn’t being stretched

by relativistic effects (Science,

doi.org/c8tt). “Einstein was right,

for now,” says Do. Leah Crane

HARRY COLLINS/ALAMY STOCK PHOTO

BADER AND LEUZINGER

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