Fomalhaut's Stellar Sister's Comets: Exoplanet Goldmine?
Artist’s impression of the Fomalhaut system. The newly discovered comet belt around Fomalhaut C is shown to the right. The comet belt around Fomalhaut A is in the distance to the left. The belt around Fomalhaut A is offset slightly, a signature of the elliptical orbits in the belt, which may have been caused by past interactions with the star Fomalhaut C.
On April 29, the European Space Agency announced that its premier infrared space observatory had run out of coolant and the mission had come to an end. Observing the cosmos in far-infrared wavelengths, the space telescope has given us some of the most striking views of cool nebulae, star forming regions, comets being pulverized around nearby stars, even asteroids buzzing around our own solar system. As we say goodbye to the historic mission, and astronomers continue to analyze the huge wealth of data Herschel has left us with, it's time to have a look back at some of the mission's most spectacular observations.
In this picture, embryonic stars feed on the gas and dust clouds deep inside the Orion Nebula. This image combines far-infrared data by Herschel and mid-infrared data by NASA's Spitzer space telescope.
ESA/Herschel/PACS & SPIRE Consortium, O. Krause, HSC, H. Linz
The Andromeda galaxy in infrared -- Herschel took this portrait of the famous spiral galaxy, picking out the fine detail from gas and dust running through its structure.
ESA/PACS & SPIRE consortia, A. Rivera-Ingraham & P.G. Martin, Univ. Toronto, HOBYS Key Programme (F. Motte)
This three-color image of the W3 giant molecular cloud combines Herschel's 70 μm (blue), 160 μm (green) and 250 μm (red) filters. W3 is located about 6200 light-years away and is a hub of intense star formation. Filaments of gas and dust cocooning protostars (yellow dots) can be seen.
ESA/Herschel/PACS/L. Decin et al
The star Betelgeuse is observed in infrared by Herschel as it rapidly approaches a "barrier" of interstellar gas. The bow shock of the star's stellar winds can easily be seen.
ESA/Bonsor et al (2013)
The star Kappa Coronae Borealis is captured in this infrared observation by Herschel. The star itself is blocked out whereas the ring of debris (likely from asteroid/comet impacts) glows bright.
ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium
The infrared emissions from dust produced by a huge number of cometary collisions surrounding the famous star Fomalhaut glows in bright blue in Herschel's eye. At least one exoplanet is known to orbit within this ring of dust.
Herschel: Q. Nguyen Luong & F. Motte, HOBYS Key Program consortium, Herschel SPIRE/PACS/ESA consortia. XMM-Newton: ESA/XMM-Newton
Supernova remnant W44 is the focus of this observation created by combining data from ESA's Herschel and XMM-Newton space observatories.
ESA and SPIRE & PACS consortia, Ph. André (CEA Saclay) for Gould’s Belt Key Programme Consortia
Herschel picks out 600 newly forming stars inside the W40 nebula cradle of stars -- located 1,000 light-years away in the constellation Aquila.
ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss (Konkoly Observatory)
Herschel could also study solar system objects with ease. In this observation, asteroid Apophis was captured during its approach to Earth on 5/6 January 2013. This image shows the asteroid in Herschel’s three PACS wavelengths: 70, 100 and 160 microns, respectively.
ESA/Herschel/PACS, SPIRE/N. Schneider, Ph. André, V. Könyves (CEA Saclay, France) for the “Gould Belt survey” Key Programme
This striking image complemented Hubble's 23rd anniversary optical view of the Horsehead Nebula. Herschel's infrared observation of the Orion Molecular Cloud complex (including the Horsehead Nebula -- visible far right of image) provided a unique perspective on this astronomical favorite.
Astronomers scoping-out the vicinity of the famous star Fomalhaut have discovered that its mysterious stellar sister is also sporting a rather attractive ring of comets.
This news is brought to you by the recently-defunct Herschel space observatory, a European-led infrared mission, that was especially fond of probing the infrared signals being emitted by cool nebulae, the gas in distant galaxies and, in this case, vast icy debris fields surrounding young stars. Sadly, the orbiting telescope was lost earlier this year as it ran out cryogenic coolant, but its legacy lives on.
Located 25 light-years away in the constellation Piscis Austrinus, Fomalhaut A is one of the brightest stars in Southern Hemisphere skies. The bright blue giant is notable in that it hosts a gigantic ring of cometary debris and dust. Embedded within this ring is the infamous Fomalhaut Ab, a massive exoplanet that has been the cause of much debate.
But this new research, published in the journal Monthly Notices of the Royal Astronomical Society, doesn’t focus on the stellar “Eye of Sauron,” it is actually centered around Fomalhaut’s less famous sibling, Fomalhaut C.
Fomalhaut C is a red dwarf star and was only confirmed to be gravitationally bound Fomalhaut A and Fomalhaut B in October. Fomalhaut is therefore a triple, or trinary, star system. The small red dwarf star may be the proverbial runt of the Fomalhaut stellar litter, but it appears to share some common ground with its larger sibling.
“It’s very rare to find two comet belts in one system, and with the two stars 2.5 light years apart this is one of the most widely separated star systems we know of,” said astronomer Grant Kennedy, of the University of Cambridge and lead researcher of this work. “It made us wonder why both Fomalhaut A and C have comet belts, and whether the belts are related in some way.” Interestingly, Fomalhaut B doesn't appear to have such a belt.
Astronomers have noted that both cometary belts around Fomalhaut A and C are bright and elliptical, indicating that gravitational perturbations may be destabilizing comets’ orbits, causing collisions and close encounters with the central stars. As Comet ISON dramatically demonstrated last month, stellar near-misses can result in disintegration, flinging huge quantities of ice, dust and gas around star systems. Scale that activity up in a younger star system and you have huge debris belts like the ones found around Fomalhaut A and C.
So what’s causing this activity? The researchers point out that Fomalhaut A already has a known exoplanet mixing things up from deep inside the dusty ring. Also, gravitational interactions between Fomalhaut A and C could be a huge factor.
“We thought that the Fomalhaut A system was disturbed by a planet on the inside — but now it looks like a small star from the outside could also influence the system. A good test of this hypothesis is to measure (Fomalhaut C’s) exact orbit over the next few years,” said Paul Kalas, of the University of California.
The relationship between Fomalhaut A and C could go beyond their gravitational interplay, Fomalhaut C could also have hidden exoplanets in tow, jostling the comets from the inside.
This research is fascinating as it demonstrates how young, widely spaced stars interact with one another — an ideal test to see how star systems mold each other’s planetary destiny.
Publication: Discovery of the Fomalhaut C debris disc, Kennedy et al., MNRAS, 2013. doi:10.1093/mnrasl/slt168