A complete observation of the great ring around the star Fomalhaut

The Fomalhaut system seen by ALMA and Hubble (Image ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF))
The Fomalhaut system seen by ALMA and Hubble (Image ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF))

Two articles to be published in “The Astrophysical Journal” describe two studies concerning the ring of debris surrounding the star Fomalhaut. An international team of astronomers used the ALMA radio telescope to get the first complete image of those debris, which are probably the product of a series of collisions among comets near the outer edges of that solar system. Carbon monoxide and carbon dioxide have also been found in abundance.

Fomalhaut is actually a multiple system that until recently was considered binary but a few years ago a third star was identified. The main star, also called Fomalhaut A, is young, although a 2012 study estimates an age of around 440 million years for this star, much more than previous estimates that gave it between 100 and 300 million years, and has a mass that is about twice the Sun’s. Its distance from the Sun is about 25 light years so it’s in the neighborhood in astronomical terms and yet it keeps on giving surprises.

Traces of various disks have been detected over the years around Fomalhaut A and in 2012 the first studies started with the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, at that time still incomplete and therefore able to make limited observations. ALMA was inaugurated in March 2013 and its array of antennas completed after a few months, so subsequently it was possible to make new observations of the Fomalhaut system and in particular a ring of debris and gas detected only partially in 2012.

Exploiting ALMA’s full power and sensibility, astronomers were able to gather much more information about that huge ring about 2 billion kilometers wide and about 20 billion kilometers away from the center of the system. Meredith MacGregor, an astronomer from the Harrar-Smithsonian Center for Astrophysics and the lead author of one of the articles, stated that it’s now possible to see the well-defined shape of the ring, which can tell us a lot about that planetary system.

Astronomers speculated that there are many exocomets that often clash against each other producing abundant debris or that there was a single clash among supercomets hundreds of times more massive than the ones we’re used to. According to Luca Matrà of the British University of Cambridge and first author of the other article, the detection of a large amount of carbon monoxide and carbon dioxide suggests a similarity with the comets existing in the solar system that might also concern their formation’s conditions.

If the hypothesis of multiple collisions among many comets is the correct one, it’s possible that the Fomalhaut system is going through the period called Late Heavy Bombardment. In the solar system, it happened between 4.1 and 3.8 billion years ago and the inner planets, including the Earth, were struck by asteroids and comets far more often than in any other period of their history.

There are various differences between the solar system and Fomalhaut’s system but the observations are also revealing the various similarities. For this reason, observing what’s happening around that star can give us new information about what happened a few billion years ago in the solar system.


    1. Assembling photos taken by different instruments – in this case ALMA and Hubble – they can obtain great pictures!


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