ALMA, the highest observatory on Earth, has produced a remarkable and detailed image of a ring of debris from colliding comets encircling a young star, Fomalhaut, that lies only 25 light-years away.
The ring shows as a bright band as seen by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. It is thought to be made up of gas and rubble left by as countless comets collided.
Fomalhaut is one of the brightest stars in the sky, and you can spot it easily, shining at first magnitude in the constellation of Pisces Austrinus, the southern fish.
It has long fascinated astronomers because it is only about 440 million years old, which is a tenth the Sun’s age of around 4.5 billion years. This is allowing space scientists to observe another solar system in the process of forming.
The advanced array of dishes, high in the Atacama desert, had previously detected around a half of the debris disk in 2012 when it was still being constructed. The bright band of icy material, which is about 2 billion kilometres wide, lies about 20 billion kilometres from Fomalhaut.
The telescope’s latest observations suggest that the glowing band has similar chemical properties to those found in comets in our own Solar System. The alien comets are termed exocomets, in the same way that planets of other stars are known as exoplanets.
Using the same data, the astronomers detected vast stores of carbon monoxide gas in precisely the same location as the debris disk.
Luca Matrà, of the University of Cambridge, UK, who is lead author on the team’s second paper, said: “These data allowed us to determine that the relative abundance of carbon monoxide plus carbon dioxide around Fomalhaut is about the same as found in comets in our own solar system.
“This chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own.”
Matrà and his colleagues believe this gas is either released from continuous comet collisions or the result of a single, large impact between supercomets hundreds of times more massive than the greatest seen back home.
Astronomer Meredith MacGregor, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., is lead author of one of two papers describing the latest observations, and accepted for publication in the Astrophysical Journal.
She said in a statement: “ALMA has given us this staggeringly clear image of a fully formed debris disk. We can finally see the well-defined shape of the disk, which may tell us a great deal about the underlying planetary system responsible for its highly distinctive appearance.”
ALMA’s study of Fomalhaut’s debris disk suggest that it is experiencing a similar event to the Late Heavy Bombardment in our own Solar System. This was a period around 4 billion years ago when the Earth and other planets were being battered by swarms of asteroids and comets left over from the formation of our Solar System.
Debris left over from these collisions absorbs light from Fomalhaut and reradiates that energy as a faint millimeter-wavelength glow that can be studied with ALMA.
Using the new ALMA data and detailed computer modelling, the researchers were able to calculate the precise location, width, and geometry of the disk. MacGregor says that these parameters confirm that such a narrow ring is probably produced through the gravitational influence of planets in the system.
Astronomers hope that advanced technology will soon help them to detect planets orbiting Fomalhaut. One has been suggested before but never confirmed, and observations with NASA’s Spitzer Space Telescope suggest it is actually an accumulation of rubble.
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