Sky and Telescope - August 2016 - 12

News Notes

Y. HEZAVEH (STANFORD UNIV.) / ALMA (NRAO / ESO /
NAOJ) / NASA / ESA / HUBBLE SPACE TELESCOPE

GALACTIC I Distant Dwarf Discovered with ALMA

This composite, false-color image shows
a massive elliptical galaxy called SDP.81
(center, from Hubble Space Telescope)
surrounded by the light from a distant
background galaxy (red, imaged by
ALMA) that's been gravitationally lensed
by SDP.81. The ring is 3 arcseconds
across. When Yashar Hezaveh (Stanford
University) and others employed the Blue

Waters supercomputer to analyze the
ALMA ring, they found a dwarf galaxy
hidden within the depths of the background galaxy's distorted image. (It's
marked by the white dot near the left
arc in the image.) The dwarf, a neighbor
of the elliptical, contains the mass of a
billion Suns. Although it doesn't emit
observable light itself, the dwarf nevertheless has enough mass to add its own distortion to the background galaxy's image.
The researchers report in an upcoming
Astrophysical Journal that they also found
hints of even smaller clumps, presumably
dominated by dark matter as this dwarf
is, ﬂoating in SDP.81's halo. All together,
the clumps match what's expected from
simulations modeling the evolution of the
universe in the presence of dark matter
(see page 11). The elliptical and its dwarf
are roughly 4 billion light-years away.

August 2016 sky & telescope

$100M for Probes to
Alpha Centauri

consuming observations of the smallest,
faintest stars - until the robotic 0.6meter TRAPPIST (Transiting Planets and
Planetesimals Small Telescope) began its
work in 2010 at La Silla in Chile.
In the May 12th issue of Nature, the
authors report 11 signals of objects passing in front of a star, called TRAPPIST-1.
Two planets, TRAPPIST-1b and TRAPPIST-1c, made nine of the 11 transits,
orbiting their star every 1.5 and 2.4 days,
respectively. The two planets are so close
to the star that they're probably tidally
locked with it.
The last two transit signals might be
from a third planet, 1d. The team couldn't
pin down its exact orbit.
Planets 1b and 1c aren't in their star's
habitable zone. The third planet might
lie in the habitable zone, or beyond it -
there isn't enough information on its
orbit yet to tell. Regardless, the planets
could be a great chance to study exo-Earth
atmospheres, previously out of reach.

The Russian billionaire Yuri Milner,
who last summer committed $100 million to boost SETI searches to a new level
(S&T: Nov. 2015, p. 10), announced on
April 12th a second, far more ambitious
$100 million project. Breakthrough
Starshot will conduct research and development toward accelerating gram-scale
interstellar probes to 20% of the speed
of light, using lightsail technology and a
100-gigawatt laser array on Earth.
The laser array would boost the
probe out of Earth orbit by aiming at the
probe's super-reﬂective lightsail and,
with radiation pressure, accelerating it
to one-ﬁfth the speed of light in the two
minutes the mini craft is within laser
range. It will have to do this without
vaporizing the sail or probe. The lasers
would then take a day to recharge their
batteries (from a dedicated power plant),
before sending oﬀ the next probe.
The nanoprobes would take only 20
years to get to Alpha Centauri, if they
survive both the laser blast and the trip.
In theory, as each zips through the star
system, a tiny camera and atmosphere
analyzer would grab pictures and data on
any planets there. Then it would transmit these data 4.3 light-years back to
Earth using a "compact laser." The total
mass of each probe, including power
supply, camera, sensors, processors, ﬁnenavigation thrusters, and that amazing
transmitter, is to be just a few grams.
If you think this sounds impossible,
you're in good company. But for years
now, blue-sky engineering analyses
have concluded that while this technology is rather beyond us at present, it
could come into reach if Moore's Law
continues, if materials science and
ultra-micro manufacturing develop
as hoped, and if lasers keep getting
cheaper and more powerful. Milner's
$100 million will go toward investigating whether all of this can happen.

■ MONICA YOUNG

■ ALAN MACROBERT

■ MONICA YOUNG

EXOPLANETS I Nearby Earth-size Planets
Forty light-years away, a star just
one-tenth the size of the Sun holds three
Earth-size planets in orbit, where none
was expected. Although the worlds probably aren't habitable, their proximity to
Earth makes them excellent targets for
attempts to observe any atmosphere they
might have.
The star is an M8 red dwarf, containing only 8% of the Sun's mass and emitting only 5% of its luminosity. It's what's
known as an ultracool dwarf, a class of
objects with eﬀective temperatures less
than half that of the Sun. (Technically,
the term also includes brown dwarfs.)
Some scientists suspected that such
small stars might not host planets.
Smaller stars should form with smaller
planet-forming disks around them, and
ultracool dwarfs might have such small
disks that they wouldn't be able to form
even tiny, rocky planets. According to
Michaël Gillon (University of Liège,
Belgium), who led the new study, the
controversy was enough to dissuade time-

SCIENCE & SOCIETY

Sky and Telescope - August 2016

Table of Contents for the Digital Edition of Sky and Telescope - August 2016