SkyNews – September 2019

(Barré) #1


rocky worlds near the Sun and giant
gas planets scattered across its outer realms.
But the very first exoplanets discovered re-
versed this trend—giant planets were found
skimming extremely close to their stars.
Most exoplanets have been detected via in-
direct methods, which can probe just the
central regions of planetary systems. “Given

what we and other surveys have seen so far,
our solar system doesn’t look like other solar
systems,” remarks Bruce Macintosh of Stan-
ford University, the principal investigator of
a recently concluded five-year search for
giant worlds in the distant reaches of more
than 500 stellar neighbourhoods.
The search involved the 8-metre Gemini
South telescope, located in Chile, and the
Gemini Planet Imager (GPI), a sensitive in-
frared detector. When combined with adap-
tive optics and advanced image processing,
the GPI allowed researchers to photograph-
ically search for Jupiter-like exoplanets and
brown dwarf stars up to a million times
fainter than the host sun. An interim report
reveals that the GPI survey of 300 stars has
yielded six planets and three brown dwarfs.

This is a surprise; astronomers expected to
find at least a dozen giant planets. Another
striking result: All hosts of the newly detected
planets are high-mass stars. Researchers
have concluded that large planets may be
present around only a minority of small stars
such as our own. “The fact that giant planets
are more common around stars more mas-
sive than Sun-like stars is an interesting puz-
zle,” says team member Eugene Chiang of
the University of California, Berkeley.
The team is currently following up on
the remaining planet candidates to deter-
mine which are truly planets and which are
distant background stars impersonating
giant worlds. Later, the GPI survey will
begin again, this time using the 8-metre
Gemini North telescope, in Hawaii.




FTER A 26-YEAR-LONGslumber,
the binary star system known as V
Cygni woke up for two weeks in 2015 to
become, for a short time, the brightest
high-energy X-ray object in the sky. When
James Miller-Jones of Australia’s Interna-
tional Centre for Radio Astronomy Re-
search studied the black hole, he and his
team saw its jets behaving in a way never
seen before. Jets are usually thought to
shoot straight out from the poles of a black
hole, but these jets were firing in different
directions at different times. And they were changing direction
very quickly, over no more than a couple of hours.
Coauthor Alexandra Tetarenko, a recent University of Alberta
graduate now at the East Asian Observatory, in Hawaii, notes that
the speed at which the jets were changing direction meant scientists
had to use a very different approach to their radio observations.
“Typically, radio telescopes produce a single image from several
hours of observation,” she explains. “These jets were changing so
fast that in a four-hour image, we just saw a blur.” To solve this chal-
lenge, the researchers took a series of 103 images, each about 70
seconds long. Miller-Jones and Tetarenko then led the effort to

combine those images into a continuous video. “It was only by
doing this,” says Tetarenko, “that we were able to see these changes
over a very short time period.”
“What’s different in V404 Cygni is, we think the disc of material
and the black hole are misaligned,” says Miller-Jones. “The inner
part of the accretion disc was precessing and effectively pulling the
jets around with it.” To understand such rapid precession requires
applying an aspect of Einstein’s general theory of relativity, which
states that massive objects like black holes distort space and time.
“This is the only mechanism we can think of,” adds Miller-Jones,
“that can explain the rapid precession we see in V404 Cygni.”



SPRAYING JETSV404 Cygni, a binary consisting of a normal star orbiting a black hole, is shown
in this illustration. Star-stuff pulled toward the black hole spirals inward, forming an accretion disc.
Jets are launched from the disc’s inner regions. The “water-sprinkler” effect of the jets is likely due to
the accretion disc’s core being tilted with respect to the rest of the system.ILLUSTRATION COURTESY ICRAR

A NEW WORLD GLOWINGThis is an artist’s rendering of exoplanet 51 Eridani b, the lowest-
mass planet ever directly imaged. Discovered in 2014 during the Gemini Planet Imager survey,
this giant is a mere 20 million years old and about three times the mass of Jupiter.


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