12 October 2019 | New Scientist | 15Astronomy Engineering
Chelsea Whyte Donna Lu
STRANGE blasts of radiation from
space called fast radio bursts (FRBs)
may sometimes be sparked when
two stars collide and then vibrate
in reverberating aftershocks.
The origins of FRBs have puzzled
astronomers for years. Most of the
nearly 100 FRBs we have detected
consist of a single burst, but a few of
them flash repeatedly, which makes
it easier to find where they are
coming from and determine what
might be causing them.
One such source, known as
FRB 171019, was first detected
in 2017, when a bright burst was
seen with the Australian Square
Kilometre Array Pathfinder. It was
followed by three more flashes over
a year, some of which were nearly
600 times fainter than the first.
Jinchen Jiang at Peking University
in China and his colleagues have
now created a model to account
for the successively dimmer bursts
seen from FRB 171019. They
suggest that the first bright burst
may have been created when
two neutron stars collided (arxiv.
org/abs/1909.10961).
Neutron stars are extremely
dense objects. When two spin
closer and eventually collide,
the result can be a more massive
neutron star, which would
potentially have different rates
of rotation in its layers. This could
create powerful oscillations in the
body of the star – starquakes –
that would throw out radiation
that we see as faint bursts.
“This is one of many proposals for
how FRBs form,” says Bing Zhang at
the University of Nevada, Las Vegas.
“Personally, I wouldn’t bet on it,
but it’s a possibility of course.”
Zhang says he is sceptical
because FRB 171019 has only
been observed for a few years.
“Suppose in the future, there is
another brighter burst detected
from this source. In that case,
this model is dead,” he says. ❚
Mystery space
signals could come
from starquakes
AIRSHIPS were once considered
the future of flight. Now, they
are being touted as a greener
method of transport. A solar-
powered craft being built by
UK-based firm Varialift Airships
could eventually be used as a
low-emissions way to freight
cargo internationally.
On a transatlantic flight
between the UK and the US,
the airship would use 8 per cent
of the fuel of a conventional jet
aeroplane, says Varialift CEO
Alan Handley.
Airships – lighter-than-air
vehicles that rely on gas to lift
them into flight – were common
until the 1940s, when they
were supplanted by jet engine
aeroplanes.
The advantage of airships
is that they don’t require
dedicated runways to take
off and land, meaning they
can travel to areas with poor
infrastructure. “We can take
it from point A to point B
where it’s required, without
any transfer from aircraft to
lorries,” says Handley.
They are, however, far slower
than jet engines. Handley saysthe Varialift airship would travel
at roughly half the speed of a
Boeing 747, which has a cruising
speed of around 900 kilometres
per hour. Made from a solid
aluminium exterior, it could
carry 50 tonnes of cargo.
The airship will contain tanks
filled with compressed helium,
which it will use for buoyancy.
When the helium is transferred
from the tanks into a larger
chamber, it will expand and
push air out, generating lift.
Once the airship reached a
height of around 10,000 metres,
it would be propelled forward
by a combination of two solar-
powered and two conventional
jet engines. Because there would
be no on-board battery, the
solar-powered engines would
be limited to daylight hours.
At an airfield near
Châteaudun, France, Varialift is
building a prototype for training
pilots that is 140 metres long,
26 metres wide and 26 metres
high. It is set to be completed
in the next nine months.
Manoeuvring an airship
of this size poses significant
challenges, says Robert Hewsonat Imperial College London.
Elsewhere, UK manufacturer
Hybrid Air Vehicles has been
developing Airlander, a hybrid
airship combining lighter-
than-air lift and aerodynamic
lift (pictured). It uses four
diesel engine-powered
propellers. Global aerospace
firm Lockheed Martin has
also been developing a hybrid
airship for several years, but
hasn’t yet started production.A team at the University
of the Highlands and Islands,
UK, has developed a solar-
powered aircraft that
is propelled by changes
in buoyancy. The aircraft
alternates its buoyancy
between positive and
negative, propelling itself
forward on each descent
by compressing air.
For the moment, airships
remain a niche industry, says
Hewson. They may be useful
for transporting oversized cargo
and large structures, such as gas
turbines and nuclear reactors,
to inaccessible places, he says.
Surveillance and broadcasting
are two other possible uses.
But it is unlikely that we
will see the return of airships
as a means of transporting
passengers on commercial
flights. The significant speed
disadvantage would be a
deterrent, says Hewson.
“It would take days to fly to
Australia, for example,” he says.
“I think it’s just not feasible.” ❚Solar-powered airship
could make freight green
HYBR
ID^
AIRVEHICLE
SAirlander is a diesel-
powered airship under
development“ The airship would
use 8 per cent of the
fuel of a conventional
jet aeroplane”