Page 13 - BBC Sky at Night - September 2017 UK

Þ Material is being drawn off the white dwarf into the BULLETIN SEPTEMBER 13
black hole, but it’s thought the star will survive all the same

NEWS IN
Super-Earths excite at Tau Ceti
BRIEF
Four exciting new worlds have been found, two in the habitable zone
Four potentially habitable planets have been but their diminutive size suggests that they are
found around Tau Ceti, the closest Sun-like star to on the edge of what can be observed.
Earth at a mere 12 lightyears away. Two of them “Our detection of such weak wobbles is a
are in the star’s habitable zone, the region where milestone in the search for Earth analogues
water could exist as a liquid. and the understanding of the Earth’s habitability
With masses as low as 1.7 times that of Earth, through comparison with these,” says Fabo BEPICOLUMBO
they are the smallest planets ever detected around Feng from the University of Hertfordshire, IN FINAL TESTS
a Sun-like star. They were found by observing the who led the study. The Mercury spacecraft
wobbles they create in the movement of the star, www.herts.ac.uk BepiColumbo passed
one of its last sets of
tests in early July. The
0.5 AU 1 AU 1.5 AU 2 AU
craft was configured
Tau Ceti
as it will be for launch
– with both orbiters, one
built by Japan, the other
by ESA, stacked on top
of each other – then
subjected to extreme
vibrations and noise to
ensure it will survive
the beginning of its
g h e f
7.2-year journey to the
innermost planet.
BepiColumbo will now
undergo final thermal
tests before being
transported to French
Guiana for launch in
October 2018.
Two of the exoplanets (e and f) are thought to exist in the star’s habitable zone, where water would be a liquid

The Milky Way’s hidden masses

As many as 100 billion brown dwarfs may be hiding makes them difficult to spot as they don’t emit DARK MATTER
within the Milky Way, according to observations much radiation. MAPPED
made with ESO’s Very Large Telescope. A study of star cluster RCW 38 conducted in The most accurate map
It’s thought that brown dwarfs form in much 2016 determined that it contained around one of dark matter has
the same way as stars, but lack the mass needed brown dwarf for every two stars. The finding been released, helping
to kick start hydrogen fusion in their cores. This corroborates previous observations from another to explain how the
cluster, one with a much substance has shaped
lower density of massive our Universe. It was
stars, suggesting that the created by analysing
number of brown dwarfs is the light of 26 million
independent of the type of galaxies using the first
cluster they grew up in. year of data from the
“We’ve found a lot of Dark Energy Survey,
brown dwarfs in these a five-year project to
clusters,” says Aleks Scholz investigate the role
from the University of St of dark matter and
Andrews. “Whatever the energy in the cosmos.
cluster type, the brown Where previous dark
dwarfs are really common. matter studies looked
Brown dwarfs form alongside back to 380,000 years
stars in clusters, so our work after the Big Bang, this
suggests there are a huge one observed how
number of brown dwarfs galaxies have changed
out there.” over the past seven
Þ The central 1.5 lightyears of RCW 38 and (inset) some of its faintest brown dwarfs www.eso.org billion years.

skyatnightmagazine.com 2017