A vortex in the turbulent dust disk surrounding a young star named AB Aurigae was revealed in high resolution and too much fanfare in the astronomy community last week. Such a characteristic disorder, according to the researchers, could be the signature of a baby exoplanet that is currently being formed.
Although this baby exoplanet has been widely referred to as an undeniable interpretation of the data by many retail outlets, this “could” is the key. A new paper now shows exactly why: A separate team of researchers has found that the swirling dust can be caused by another object – an emerging star, a binary companion of AB Aurigae.
The new interpretation was in one Monthly communications from the Royal Astronomical Societyand is waiting for the final assessment by colleagues.
“AB Aurigae is a compendium of interesting features,”
“We have a huge central cavity, including spirals and dusty clumps. The planetary scenario has been proposed to explain some of these features.
“It is true that a planet can explain the dusty lumps, but not the huge cavity, and it is true that it can explain spirals, but not the spirals that we observe in AB Aurigae,” added Poblete. “In contrast, a stellar binary scenario can easily explain all of these features.”
AB Aurigae is one of the next stars of its kind. It is very young, only about 4 million years old (the sun is about 4.6 billion years old) and still surrounded by a thick, complex protoplanetary disk – the material that is produced by the star formation is left.
Such stars are of great interest and importance because we believe they can show how exoplanets are formed from leftover star dust. And AB Aurigae in particular is very interesting. In 2017, the Atacama Large Millimeter / Submillimeter Array (ALMA) in Chile revealed a gap in the dust cloud that contained apparently rippling spiral features.
“AB Aurigae belongs to a class of discs called” transition discs “, which are” discs with holes in the middle, “said Monash University astronomer Daniel Price, co-author of the latest paper ScienceAlert.
“There was one amount Speculation about what creates these central cavities (or ‘holes’) – whether double stars or planets, or dust cleaning by some other mechanism. “
Exoplanets were the explanation that was proposed in the work of astronomer Anthony Boccaletti from the Observatoire de Paris in France last week. His team’s modeling suggested that the swirling spirals in the AB Aurigae cloud may have been created by an exoplanet that was between four and thirteen times the mass of Jupiter.
But not everyone agrees. “A planet alone would not be massive enough to create the strong spiral arms and cleared central void seen in AB Aurigae,” Price told ScienceAlert.
A binary companion, on the other hand, could match the observed features. And it’s not a wild idea. Binary stars are extremely common – up to 85 percent of all stars could be in multi-star systems, and there are indications that all stars are born in pairs and some later lose their companions (like the long-lost twin of the sun).
In a binary formation model, the circumstellar disk collapses around a young star, and part of it gravitationally collapses into itself to form a second star, with the surrounding material being pulled around in a second, smaller disk within the larger disk .
In the model proposed by Poblete and his team, the spiral observed in the AB Aurigae dust cave could have been created from a small star, about half the solar mass, to the two AB Aurigae solar masses – if the binary companion was at a high level is an inclined orbit between 60 and 90 degrees around the poles of AB Aurigae and with a high eccentricity of the orbit.
This is not as strange as it sounds. As Price notes, star formation is a chaotic process that can lead to a strange orbit.
“We expect to find a ‘strange’ configuration in the early stages of binary star formation,” said Poblete.
“We know that stars are formed in a huge gas cloud. This cloud is a factory of stars. When stars are born, they always interact with others, and in some cases, two or more stars can [become] bound in a multiple system. “
“All of this happens when the stars are still absorbing gas from an accretion disk. That’s why you can get [secondary] Discs eccentric and tilted in relation to such discs, “added Poblete.” A binary system will also tend to have an unstable stable configuration; then the binary file becomes more and more stable over time. “
The observed spiral arms in the disk of AB Aurigae, according to the team at work, are similar to those that are found in other forming binary systems such as e.g. [BHB2007] 11 and FS Tau A, the latter having a web inclination between 35 and 60 degrees.
However, since we can’t see the object – which isn’t really strange given the brightness of AB Aurigae and the amount of material swirling around – the presence of a binary companion is still hypothetical.
The exoplanet cannot therefore be excluded. As Boccaletti ScienceAlert explained, his team had access to more information, although the Poblete team model is more complex than his own team’s work.
“We have new data from SPHERE,” Boccaletti told ScienceAlert, referring to the adaptive optics system that is connected to the Very Large Telescope in Chile.
“ALMA and SPHERE do not observe the same light and are not sensitive to the same component. SPHERE is sensitive to the light scattered by the dust from the star. It is also very sensitive to the stars themselves.”
“Although we used different information,” he added, “there is a good chance that a star companion responsible for the spiral would have been an obvious signal in the SPHERE image, unless the gas and dust obscuration is big.” “”
None of the teams is currently claiming to be discovered. We just don’t have enough data. Neither an exoplanet nor a protostar is recognized – only waves in the gas that could be interpreted as one or the other, depending on the model and data set used.
“We cannot claim a discovery based on modeling paper,” Price said. “What we can say is that the protoplanet we claim is implausible because of our modeling, because we think that there is something much bigger (and not at the suggested location). This does not mean that our claims are correct, it is only one healthy debate. “
This is how science works at its best. Observations are made. Scientists interpret the data and suggest explanations. This is where we are right now. The next step is further observations that can shed more light on the phenomenon and contribute to a more solid conclusion.
Both teams are working towards this goal. According to Price, a binary companion AB Aurigae would easily displace into the sky. If so, this shift should be noticeable the next time data is released from the Gaia satellite that maps the Milky Way.
In the meantime, the Boccaletti team is requesting further data from SPHERE to determine whether closer inspection of the system can solve AB Aurigae’s identity crisis.
“AB Aurigae is definitely a very interesting system to understand planet formation and there is still a lot to do,” said Boccaletti.
The new research was made to the Monthly communications from the Royal Astronomical Society and is available on arXiv.