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This false-colour image of the
Lagoon Nebula (M8) in Sagittarius
in the southern Milky Way shows
starbirth in a cloud of gas and
dust. Red indicates hydrogen,
green shows ionized sulphur and
blue picks out infrared radiation.
Argentinean astronomers Julia
Arias (Universidad de La Serena)
and Rodolfo Barbá (Universidad
de La Serena and ICATE-CONICET)
used the Gemini Multi-Object
Spectrograph to explore the
relationship between newborn stars
and Herbig–Haro (HH) objects. Most
of the newborn stars are in the tips
of thick dusty clouds which look like
bright-rimmed pillars. Abundant
fast-moving gas from the HH objects
ploughs into the surrounding
nebula, producing bright shock
fronts. They found a dozen of these
HH objects in the image, between
a few thousand astronomical units
across and 1.4 parsecs.
http://www.gemini.edu/node/11631
Super-heavy
superearth
Predictions about the orbit of an
exoplanet came good when observations pinned down the properties
of 55 Cancri e, to show it was both
hotter, denser and closer to its star
than had been thought.
This planet was discovered by the
radial velocity method, which uses
regular wobbles in the position of a
star to indicate an orbiting planet. In
this case, gaps in the data introduced
systematic errors into the estimate of
its orbital period at 2.8 days. Harvard graduate student Rebekah Dawson (Harvard-Smithsonian Center
for Astrophysics) worked with Daniel Fabrycky (now at the University
of California, Santa Cruz) and found
that 55 Cancri e was much closer to
its star, orbiting in less than 18 hours
– and that the chances of seeing a
transit were good. Jaymie Matthews
(University of British Columbia) led
an international team that scheduled
observations with Canada’s MOST
(Microvariability & Oscillations of
STars) satellite. They found transits
every 17 hours and 41 minutes, just
as Dawson and Fabrycky predicted.
And the new data show that
55 Cancri e is only 60% larger in
diameter than Earth but eight times
as massive, making it the densest
solid planet known, almost as dense
as lead. Its close orbit around its star
means that it is extremely hot, about
3000 K. It is also the closest transiting planet known.
http://www.cfa.harvard.edu/news/2011/
pr201112.html
http://www.science.ubc.ca/news/539
3.6
Preparing for asteroid 2005 YU55 at close quarters
The usual way to get a close-up of
an asteroid is to fly a spacecraft
there and have a look. But this is
never going to be a routine means
of studying the smaller members
of the solar system, and space missions don’t exactly come cheap. So
when an asteroid heads close to
Earth, the obvious thing to do is to
take a close look.
That is what will happen in
November this year, when asteroid
2005 YU55, a lump of rock some
400 m across, will make a close
approach to Earth, 325 000 km away
at its closest. Instruments on Earth
now could get radar images of the
asteroid at resolutions comparable
to the best fly-by images.
“Using the Goldstone radar operating with the software and hardware
upgrades, the resulting images of
YU55 could come in with resolution as fine as 4 m per pixel,” said
Jet Propulsion Laboratory radar
astronomer Lance Benner. “We’re
talking about getting down to the
kind of surface detail you dream of
when you have a spacecraft fly by one
of these targets.” Radar images are
especially valuable because they give
astronomers data that can be used to
produce a 3D model of the body, as
well as indicating by the quality of
the reflections how rough or smooth
the surface is.
In April 2010, Mike Nolan and colleagues at the Arecibo Observatory in
Puerto Rico generated some ghostly
images of YU55 when the asteroid
was about 2.3 million km (1.5 million
miles) from Earth. The best resolution of those images was 7.5 m per
pixel. Banner hopes to do a lot better
this year: “The asteroid will be seven
times closer. We’re expecting some
very detailed radar images.”
http://deepspace.jpl.nasa.gov/dsn
Gravity probe shows Einstein got it right again
Gravity Probe B, the NASA mission
to carry out the most sensitive test
yet of general relativity, has concluded that Einstein was right. The
team measured the predicted distortion of spacetime around Earth
from the mass of the planet, and
demonstrated that the rotation of
the Earth does indeed twist spacetime, causing frame dragging.
Gravity Probe B was launched in
2004 to orbit Earth for 16 months
carrying sensitive gyroscopes aligned
with a distant guide star. In free fall,
the gyroscope should continue to
point at the reference star, unless
spacetime is distorted in the way
that general relativity predicts. The
probe measured the misalignment
of the gyroscope spin axis and the
reference star, to a startling precision
of 0.0005 arc­sec, the equivalent of
measuring the thickness of a sheet of
paper edge-on from 160 km away.
“We measured a geodetic precession
of 6.600±0.017 arcsec and a frame
dragging effect of 0.039±0.007 arcsec,” said Francis Everitt of Stanford
University, principal investigator of
Gravity Probe B. These measurements represent accuracies of 0.28%
and 19% respectively. The results
confirm Einstein’s predictions about
spacetime around the Earth and may
in future come to be seen as a classic experiment, albeit one requiring
considerable new technology.
Gravity Probe B required considerable technological development,
becasue the effects that the researchers were hoping to see were beyond
measurement at the time the project
began. The gyroscopes, for example,
use rotating balls of fused quartz
coated with niobium, less than 4 cm
across, that vary from a perfect
sphere by less than 40 atomic layers.
They feature in the Guinness World
Records as the most perfect spheres
manufactured; only neutron stars are
considered more perfect spheres.
This is one of NASA’s longest
running projects, with initial funding coming in 1963, although the
idea was first proposed in 1959 – a
career-long project for Everitt and
colleagues. Technology developed
for this mission was used in the Cosmic Background Explorer mission,
among others, and is used in commercial applications such as the GPS
system that allows planes to land
unaided. More than 100 postgraduate and 350 undergraduate students
have worked on the project, including the astronaut Sally Ride and 2001
Nobel Prize Laureate Eric Cornell.
http://www.nasa.gov/mission_pages/gpb
http://einstein.stanford.edu
A&G • June 2011 • Vol. 52