Image of a Planet around Fomalhaut

That image is incredible. I wonder how much of the apparent "shape" of the supposed planet is intrinsic to the planet, as opposed to noise in the image.

Well there goes the "ring shepherds" idea I guess... fireworks due in 2032 maybe.

Fomalhaut b's eccentric orbit and main belt structure: Evidence for other Fomalhaut planets?
https://webcast.astrosci.ca/1/watch/284.aspx

Video lecture. New 2012 detection of the object. Still appears to be in a ring-crossing orbit.

STIS Coronagraphic Imaging of Fomalhaut: Main Belt Structure and the Orbit of Fomalhaut b
http://arxiv.org/abs/1305.2222

Lots going on in this one, quite a large number of possibilities seem to be in play.

Not directly related to the planetary system, but it seems that Fomalhaut may actually be a triple star system.

Mamajek et al. "The Solar Neighborhood XXX: Fomalhaut C"
http://arxiv.org/abs/1310.0764

The M4 star LP 876-10 appears to be part of the Fomalhaut system, making it the second known companion star (the first being TW PsA, Fomalhaut B). The system therefore seems to be a very wide multiple.

Whether the triple nature of the system would have an effect on the planetary/debris disc system is for future studies to determine...

Quote :

The existence of both Fomalhaut C (LP 876-10) and B (TW PsA) should be considered for future dynamical calculations trying to explain the unusual offset (~13 AU) between Fomalhaut A and its debris disk (Kalas et al. 2005), and the eccentric orbit for the planet candidate Fomalhaut Ab (Kalas et al. 2013).

Beust et al. "An independent determination of Fomalhaut b's orbit and the dynamical effects on the outer dust belt"
http://arxiv.org/abs/1311.5035

Confirms the high eccentricity of the orbit of Fomalhaut b, and arrives at the conclusion that Fom b is likely a low-mass planet that is not responsible for sculpting the belt.

SciTech Daily: Herschel Discovers a Comet Belt around Fomalhaut C

Two stars in the same system with debris discs is quite rare.

If, as they suggest, Fomalhaut C is on a highly eccentric orbit and is perturbing the Fomalhaut A disk, wouldn't that make the Fomalhaut star system unstable? The orbit would have to cross (or go interior to, at least) Fomalhaut B.

Now on arXiv.

Kennedy et al. "Discovery of the Fomalhaut C debris disc"
http://arxiv.org/abs/1312.5315

No (detectable) debris around TW PsA, huh? Aww. Though you've got to wonder what could have happened to its protoplanetary disk…

Sirius_Alpha wrote:

If, as they suggest, Fomalhaut C is on a highly eccentric orbit and is perturbing the Fomalhaut A disk, wouldn't that make the Fomalhaut star system unstable? The orbit would have to cross (or go interior to, at least) Fomalhaut B.

In theory, yes, but in practice the enormous orbital periods (Gyr-scale) of the stars mean that dynamical stability is not a particularly important factor over the age of the system (440 Myr/0.44 Gyr). However, though, it seems a bit thoughtless to assume that the two disks are so likely related when they could have very easily come about independently…

Orbital periods of gigayears? I estimate ~40 million years based on Kepler's laws for a 0.77 parsec separation, which matches the estimates in the paper (~10-100 Myr), though as noted the galactic environment may play a large role in the dynamics.

Still, that is sufficiently long compared to the age of the system that it is certainly believable that the dynamics are a long way from being settled down.

Consequences of an Eccentric Orbit for Fomalhaut b
http://arxiv.org/abs/1312.7020

Attempting to figure out a scenario that explains the eccentricity of the dust ring together with the observational constraints on the orbit of Fom b.

From the abstract:

Quote :

I argue that the scenario best able to match the observational constraints is a super-Earth Fomalhaut b surrounded by a vast cloud of dust that is generated by a population of irregular satellites, with an undetected ~Saturn-mass planet orbiting interior to the disk and driving the secular dynamics.

Return of the planetless dust cloud hypothesis.

Lawler, Greenstreet and Gladman "Fomalhaut b as a Dust Cloud: Frequent Collisions within the Fomalhaut Disk"
http://arxiv.org/abs/1412.1129

So the next question is whether the dust cloud expands substantially over the next few decades.

Cataldi et al. "Constraints on the gas content of the Fomalhaut debris belt; Can gas-dust interactions explain the belt's morphology?"
http://arxiv.org/abs/1412.5785

Turns out that the Fomalhaut debris disc is gas poor, suggesting that the belt morphology is not due to gas-dust interaction. The likely explanation is either a shepherding planet "Fomalhaut c" or the result of stellar interactions - see Shannon et al. (2014) for details of evolutionary scenarios for the Fomalhaut system and the possible results in terms of coherent eccentricities in the system's debris discs.

So I'm not sure what to make of this.

Neuhäuser et al. "The companion candidate near Fomalhaut - a background neutron star?"
http://arxiv.org/abs/1501.07083

Apparently the available data for Fomalhaut b is compatible with the object being a neutron star at a distance of ~11 parsecs (a few parsecs beyond Fomalhaut itself). If so, this would be by far the closest known neutron star to the solar system. They do seem to do a decent job of considering the various objections to such a hypothesis but I'm not familiar enough with the observational properties of neutron stars to really tell.

I was definitely perplexed as well, but this is clearly written by neutron star experts so I would not doubt that they knew what they were talking about.

I suppose it is a significant problem that the linear motion of Fomalhaut b is not incompatible with an unbound object. This neutron star model would certainly allow the objects spectrum to make sense.

…What is the field neutron star density (i.e rate of incidence)? I imagine it's a few orders of magnitude less than the white dwarf density. That would mean the probability of this line-up occurring would be small, but not zero. So, what further observations are needed to determine whether the companion is a NS or not? Observations in the high-energy wavelengths?

Constraints on the neutron star hypothesis from X-ray nondetection. If Fomalhaut b is a neutron star then its temperature must be below 90000 K, which would make it by far the coldest neutron star detected.

Quote :

However, it is still noteworthy that this would be the most near-by and coldest neutron star known, i.e. even with a neutron star explanation for Fomalhaut b’s surprising colours, we would be facing a very unusual scenario for detected neutrino [sic] stars. It is worth pointing out that in general one can expect old and cool neutron stars to be quite common from supernova occurrence rates in the Milky Way (see for example Camenzind 2007 p.269). However, since they are dim objects at all wavelengths, detecting those old and cool neutron stars is extremely challenging; if Fomalhaut b truly is a neutron star, it would be the coldest one detected so far.

Distinguishing between the cool neutron star scenario and reflected light from a large disc/ring system looks like it will be tricky, as there are no telescopes operating at the wavelengths where this would be easiest.

Poppenhaeger, Auchettl & Wolf "A Test of the Neutron Star Hypothesis for Fomalhaut b"
https://arxiv.org/abs/1703.03279

A Complete ALMA Map of the Fomalhaut Debris Disk
https://arxiv.org/abs/1705.05867

None of the structures or gaps reported earlier show up in the ALMA image.

Also on arXiv,

Detection of exocometary CO within the 440 Myr-old Fomalhaut belt: a similar CO+CO2 ice abundance in exocomets and Solar System comets
https://arxiv.org/abs/1705.05868

An investigation whether the eccentricity of the belt around Fomalhaut A can be induced by the stellar companions:

Kaib, White & Izidoro "Simulations of the Fomalhaut System Within Its Local Galactic Environment"
https://arxiv.org/abs/1709.07006

Close encounters between Fomalhaut A and B (TW Piscis Austrini) seem to be possible, and a small (but not vanishingly rare) fraction seem to be capable of inducing the observed properties of the belt. So maybe a ring-shepherd planet (Fomalhaut "c") is not required after all.

NASA Press Release.
Exoplanet Apparently Disappears in Latest Hubble Observations
https://www.nasa.gov/feature/goddard/2020/exoplanet-apparently-disappears-in-latest-hubble-observations

This seems to be in line with what the evidence has been pointing toward for some time now

Here's the abstract of the actual paper
https://www.pnas.org/content/early/2020/04/15/1912506117.short?rss=1

Quote :

The apparent detection of an exoplanet orbiting Fomalhaut was announced in 2008. However, subsequent observations of Fomalhaut b raised questions about its status: Unlike other exoplanets, it is bright in the optical and nondetected in the infrared, and its orbit appears to cross the debris ring around the star without the expected gravitational perturbations. We revisit previously published data and analyze additional Hubble Space Telescope (HST) data, finding that the source is likely on a radial trajectory and has faded and become extended. Dynamical and collisional modeling of a recently produced dust cloud yields results consistent with the observations. Fomalhaut b appears to be a directly imaged catastrophic collision between two large planetesimals in an extrasolar planetary system. Similar events should be very rare in quiescent planetary systems of the age of Fomalhaut, suggesting that we are possibly witnessing the effects of gravitational stirring due to the orbital evolution of hypothetical planet(s) around the star.

Now on arXiv:
New HST data and modeling reveal a massive planetesimal collision around Fomalhaut
https://arxiv.org/abs/2004.08736

So can we now rename it to Da-gone?

*ducks tomatoes*

I'm interested to see what the reaction to this is among exoplanet astronomers.