This fact makes the latest ALMA image of a a dust ring around Fomalhaut even more incredible.
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that planets orbiting the star Fomalhaut
must be much smaller than originally thought. This is the first published science result from ALMA in its first period of
open observations for astronomers worldwide.
The discovery was made possible by exceptionally sharp ALMA images of a disc, or ring, of dust orbiting Fomalhaut, which lies about
25 light-years from Earth. It helps resolve a controversy among earlier observers of the system. The ALMA images show that both
the inner and outer edges of the thin, dusty disc have very sharp edges.
That fact, combined with computer simulations, led the scientists to conclude that the dust particles in the disc are kept within
the disc by the gravitational effect of two planets — one closer to the star than the disc and one more distant.
Their calculations also indicated the probable size of the planets — larger than Mars but no larger than a few times
the size of the Earth. This is much smaller than astronomers had previously thought.
In 2008, a NASA/ESA Hubble Space
Telescope image had revealed the inner planet, then thought to be larger than Saturn, the second largest planet in our Solar System. However,
later observations with infrared telescopes failed to detect the planet.
That failure led some astronomers to doubt the existence of the planet in the Hubble image. Also, the Hubble
visible-light image detected very small dust grains that are pushed outward by the star's radiation,
thus blurring the structure of the dusty disc.
The ALMA observations, at wavelengths longer than those
of visible light, traced larger dust grains — about 1 millimetre in diameter — that are not moved by the star's radiation.
They clearly reveal the disc's sharp edges and ringlike structure, which indicate the gravitational effect of two planets.
"Combining ALMA observations of the ring's shape with computer models, we can place very tight limits on the mass
and orbit of any planet near the ring," said Aaron Boley (a Sagan Fellow at the University of Florida, USA) who was leader of the study.
"The masses of these planets must be small; otherwise the planets would destroy the ring," he added. The small sizes of the planets
explain why the earlier infrared observations failed to detect them, the scientists said.
The ALMA research shows that the ring's width is about 16 times the distance from the Sun to the Earth, and is only one-seventh as thick
as it is wide.
This view shows a new picture of the dust ring around the bright star Fomalhaut from the Atacama Large Millimeter/submillimeter Array (ALMA). T
he underlying blue picture shows an earlier picture obtained by the NASA/ESA Hubble Space Telescope.
The new ALMA image has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable
clues about how such systems form and evolve. Note that ALMA has so far only observed a part of the ring. Credit: ALMA (ESO/NAOJ/NRAO)
"The ring is even more narrow and thinner than previously thought," said Matthew Payne of the University of Florida.
The ring is about 140 times the Sun-Earth distance from the star. In our own Solar System, Pluto is about 40 times more distant from the Sun than the Earth.
"Because of the small size of the planets near this ring and their large distance from their host star, they are among the
coldest planets yet found orbiting a normal star," added Aaron Boley.
The scientists observed the Fomalhaut system in September and October of 2011, when only about a quarter of ALMA's planned
66 antennas were available. When construction is completed next year, the full system will be much more capable.
Even in this Early Science phase, though, ALMA was powerful enough to reveal the telltale structure that had eluded earlier millimetre-wave observers.
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Direct imaging of exoplanets has been a field in rapid development over the past few years, with detections of several planets and low-mass brown-dwarfs.
Among these discoveries, one claimed planet detection that stands out as peculiar in many ways is that of Fomalhaut b.
Is Fomalhaut b a planet? New observations suggest this question will probably be debated for a while from now on.
A team of astrophysicists from Germany, France and Italy have discovered in the constellation Leo is an old star.
The star's existence raised at once many questions for scientists.
The object is definitely not as its "contemporaries" that appeared immediately after the Big Bang event.
Though the universe is filled with billions upon billions of stars, the discovery of a single variable star in 1923 altered the
course of modern astronomy. And, at least one famous astronomer of the time lamented that the discovery had shattered his world view.
The coldest class of stars have temperatures as cool as the human body.
Astronomers hunted these dark orbs, termed Y dwarfs, for more than a decade without success.
When viewed with a visible-light telescope, they are nearly impossible to see.
Twenty five years ago, on 1987 February 23, the brightest supernova of modern times was observed in the Large Magellanic Cloud.
Appearently we still have a lot to learn about the stars in the Milky Way.
Something strange has been noticed about the stars in our galaxy.
Rather than moving in circles around the center of the Milky Way, all the stars in our Galaxy are travelling along different paths,
moving away from the Galactic center.
An object obscured by dust, and buried in a two-star system enshrouded by dense gas, is not easy to find.
NGC 5907 is sometimes called the "Splinter" or Knife Edge Galaxy because of its unusual appearance.
It is a spiral galaxy lying in the Dragon constellation,
about 40 million light-years from Earth that could have been formed through a gigantic collision of galaxies, 8 to 9 billion years ago.