The Aldebaran – Chronicles of the Stars Pilgrim

Conundrum of Astronomy, particularly in South East Asia

Then There is a Vision of a Planet on Fomalhaut

It is a wonderful first magnitude star for the southern hemisphere, its name means ‘the mouth of the (southern) fish’, derived from the Arabic, (فم الحوت ); representing a mouth of a fish lying on its back, drinking in the waters pouring from the jars of Aquarius. The lying fish is well known as constellation Piscis Austrinus, and the bright one on its mouth is known as Fomalhaut. Fomalhaut is well noted as one of the brightest star in the southern hemisphere.

Fomalhaut - personal collection

Piscis Austrinis - Image from

Piscis Austrinis - Image from

Since the ancient time, Fomalhaut has play cultural significance for many observers around the globe. One well known name is Lonely Star of Autumn, because it is the only first-magnitude star in the autumn sky of mid-northern latitudes. For the Persians, Fomalhaut is one of the four ‘royal stars’, that is ‘The Watcher of the North’. Not just for the ancient, Fomalhaut still play major roles for human endeavor in the sky until the modern time. So, what about now?

With the distance of 7.7 parsecs (25 light-years, 1 ly = 9.461×1012 km – for further information on transformation between system measurement can be found from here) from our Solar System, that is quiet close to observe & test bed for many modern astronomy activities, supported by modern astronomy equipment.

On November, 13th, 2008, a team of astronomers using NASA’s Hubble Space Telescope announced that they had obtained the first visible-light image of a giant planet orbiting Fomalhaut! This new found planet is called Fomalhaut b.

How certain is this finding? Is it true, that is a planet? How did they know where to find the planet? What is the planet looks like? Now that is intriguing.

Fomalhaut is a white main sequence star, A3V, estimated around 2.3 times mass of our Sun, 1.7 times the diameter, around 16 times luminosity of our Sun, still bigger and hotter than our Sun, with the age about 200 to 300 million years old, yet has one billion years left before turn into red giant or Cepheid variable and blown away the outer layers to left the inner core as white dwarf. Okay, that is far from close to our Sun. But, let us go back to around 1983, an orbiting satellite, called IRAS (Infra Red Astronomy Satellite) belongs to NASA observed the sky.

During the observation, IRAS discovered the excessive infrared radiation coming from Fomalhaut, far more expected for small interstellar dust grain found around young, early-type stars. The radiation is coming from a huge disk of matter of around 370 AUs in diameter (nearly five times the dimension of the Solar System) that surrounds the star. The disk is thought to be made of icy dust particles that have been warmed by the star. In short, if our Solar System in its infant time looks like this, there is a possibility that there is a planet in Fomalhaut. So the planet hunting began on Fomalhaut.

In 2005, the coronagraph in the High Resolution Camera on Hubble’s Advanced Camera for Surveys produced the first-ever resolved visible-light image of a large dust belt surrounding Fomalhaut. It clearly showed that this structure is in fact a ring of proto-planetary debris approximately 21.5 billion miles across with a sharp inner edge.

Fomalhaut Debris Ring - Hubble image

Fomalhaut Debris Ring - Hubble image

According to Hubble astronomer Paul Kalas, (University of California at Berkeley), and the team proposed that the ring was being gravitationally modified by a planet lying between the star and the ring’s inner edge. And the long hard laboring process begun to verified the existence of the planet.

The Coronagraphic observations with the HST in 2004 produced the first optical image of Fomalhaut’s dust belt and detected several faint sources near Fomalhaut. To make sure that the faint sources are also the member of Fomalhaut, so the observation of common proper motion has to be taken into account. By the observation using Keck II 10-m telescope in 2005, HST in 2006. Then by the May 2008, the comprehensive data analysis revelaed that there is one object that is physically associated with the star and diplays orbital motion. This faint object is located near the faint half of the belt seen in stellar light backscattered by dust grains. Therefore, it lies behind the sky plane (the Earth–Fomalhaut–Fomalhaut b angle is 126°), at ~51° past conjunction as it orbits counterclockwise.

Fomalhaut b, observed on 2004 & 2006 - Hubble image

Fomalhaut b, observed on 2004 & 2006 - Hubble image

Not just from the observational derivation, there is a long rigorous working conducted on the modeling of planet-belt interaction. To model the mass , the astronomers constrained the mass of object by modeling its gravitational influence on the dust belt, reproducing properties of the belt inferred from the HST scattered-light images. The model assumes that the object is solely responsible for the observed belt morphology. From the model, they derived that the mass of the object is < 3 times the mass of Jupiter and the least the mass of Neptune

All in all, and to put things in brief, after long & hard labour, the astronomers finally came to conclusions, yes, there is a possibility that a planet exist in the Fomalhaut, because it is observed visually, and this candidate of exoplanet officially called Fomalhaut b. In the plane of the belt, Fomalhaut b lies about 119 astronomical units (AU) from the star and within 18 AU of the dust belt. Hubble Space Telescope observations separated by 1.73 years reveal counterclockwise orbital motion. Dynamical models of the interaction between the planet and the belt indicate that the planet’s mass is at most 3 times that of Jupiter; a higher mass would lead to gravitational disruption of the belt. .However, Fomalhaut b is 1 billion times fainter than the star.

Prior to this found, astronomeres inferred the presence of planets by detecting an unseen world’s gravitational ‘distortion’ on its host star or waiting for the planet to transit in front of its star and then detecting a tiny dim in the star’s light.  While these methods have identified more than 300 extrasolar planets to date, astronomers still struggled to actually make a direct image of such planets if exist. And this found on Fomalhaut has open a new chapter on extra solar planet.

Disregard that Fomalhaut will have shorter lifetime compare to our Sun, which mean little opportunity for advance life to evolve on any habitable worlds might exist, but this finding has open new frontier on searching the extra solar planet. If with current technology, the astronomers could found a planet with such 1 billion times fainter than the host star, who know, next generation of instrumentation could reveal more and more, and maybe earth-like planets on stars. Maybe we have to wait until 2013 when NASA will send the James Webb Space Telescope to give us more clear perspective on our universe.

From many sources, and all the image are belong to the respected owner.

November 16, 2008 - Posted by | Astronomy, Humanity, Nature | , , , , , , , , , , , , ,

1 Komentar »

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