The exoplanet apparently disappears in the latest Hubble observations

(Nanowerk News) Now you see it, now you don’t see it.

What astronomers thought was a planet beyond our solar system has now apparently disappeared from view. Although this happens in science fiction, like the explosion of the planet Krypton from Superman, astronomers are looking for a plausible explanation.

One interpretation is that, instead of being a full-size planetary object, which was first photographed in 2004, it could be a large expanding dust cloud produced in a collision between two large bodies orbiting the nearby bright star. Fomalhaut (PNAS, “New HST data and models reveal a massive planetesimal collision around Fomalhaut”). Possible follow-up observations could confirm this extraordinary conclusion. This diagram simulates what astronomers, studying the Hubble Space Telescope observations, taken over several years, consider evidence of the first detection of the aftermath of a titanic planetary collision in another star system. The color-tinted Hubble image on the left is of a vast ring of icy rubble surrounding the star Fomalhaut, located 25 light-years away. The star is so bright that a black masking disc is used to block its glare and be able to photograph the dust ring. In 2008, astronomers saw what they thought was the first direct image of a planet in orbit away from the star. However, by 2014, the candidate planet faded below Hubble’s detection. The best interpretation is that the object was never a fully formed planet, but an expanding dust cloud from a collision between two smaller bodies, each about 125 kilometers wide. The diagram on the right is based on a simulation of the expanding and fading cloud. The cloud, made of very fine dust particles, is currently estimated to be over 200 million miles wide. Smashups like this are estimated to happen around Fomalhaut once every 200,000 years. Therefore, Hubble was searching for the right place at the right time to capture this transient event. (Image :: NASA, ESA and A. Gspr and G. Rieke (University of Arizona) (click image to enlarge)

“These collisions are extremely rare, so it’s a big problem that we can actually see one,” said Andrs Gspr of the University of Arizona, Tucson. “We believe we were in the right place at the right time to have witnessed such an unlikely event with NASA’s Hubble Space Telescope.”

“The Fomalhaut system is the definitive testing laboratory for all of our ideas about how exoplanets and star systems evolve,” added George Rieke of the Steward Observatory at the University of Arizona. “We have evidence of such collisions in other systems, but nothing of this magnitude has been observed in our solar system. This is a model of how planets destroy each other.”

Called Fomalhaut b, the object was first announced in 2008, based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it to be a moving point. Until then, evidence for exoplanets had been inferred primarily through indirect detection methods, such as subtle round-trip stellar oscillations and shadows of planets passing in front of their stars.

However, unlike other exoplanets with direct images, the puzzles arose with Fomalhaut b from the beginning. The object was unusually bright in visible light, but had no detectable infrared heat signature. Astronomers surmised that the additional brightness came from a large shell or ring of dust surrounding the planet that could possibly have been related to a collision. Fomalhaut b’s orbit also seemed unusual, possibly very eccentric.

“Our study, which analyzed all available Hubble archival data on Fomalhaut, revealed several features that together paint a picture that the planet-sized object might never have existed in the first place,” said Gspr.

The team emphasizes that the final nail in the coffin came when their data analysis of Hubble images taken in 2014 showed that the object had disappeared, to their disbelief. Adding to the mystery, the above images showed that the object continually fades over time, they say. “Clearly, Fomalhaut b was doing things that a bona fide planet should not be doing,” said Gspr.

The interpretation is that Fomalhaut b is slowly expanding from the smashup that launched a cloud of dust into space. Taking all available data into account, Gspr and Rieke think that the collision occurred not long before the first observations taken in 2004. At this time, the debris cloud, consisting of dust particles of about 1 micron (1 / 50 of the diameter of a human hair), is below the Hubble detection limit. The dust cloud is estimated to have expanded to a size larger than Earth’s orbit around our Sun.

Equally confusing is that the team reports that the object is more likely in an escape path, rather than in an elliptical orbit, as expected for planets. This is based on the researchers adding later observations to the earlier data path graphs. “A recently created massive dust cloud, experiencing considerable radiation forces from the central star Fomalhaut, would be placed on that path,” said Gspr. “Our model is naturally capable of explaining all the observable independent parameters of the system: its expansion rate, its fading and its trajectory.”

Because Fomalhaut b is currently inside a vast ring of icy debris surrounding the star, the colliding bodies would likely be a mixture of ice and dust, like the comets that exist in the Kuiper belt on the periphery of our solar system. . Gspr and Rieke estimate that each of these kite-shaped bodies measured approximately 200 kilometers (125 miles) across (approximately half the size of the asteroid Vesta).

According to the authors, their model explains all the observed characteristics of Fomalhaut b. Sophisticated dynamic dust modeling performed on a computer group at the University of Arizona shows that such a model is able to fit all observations quantitatively. According to the author’s calculations, the Fomalhaut system, located about 25 light years from Earth, can experience one of these events only every 200,000 years.

Gspr and Rieke, along with other members of an extended team, will also observe the Fomalhaut system with NASA’s upcoming James Webb Space Telescope in its first year of scientific operations. The team will take images directly of the system’s warm internal regions, spatially solving the elusive component of the asteroid belt of an extrasolar planetary system. The team will also search for bona fide planets orbiting Fomalhaut that may be gravitationally sculpting the outer disk. They will also analyze the chemical composition of the disc.