The study, involving NPF researcher Johan Olofsson, concludes that this may have been caused by an event similar to the one that led to the formation of our natural satellite.
About 20% of stars have a debris disk orbiting around them. Its presence means that there are tiny dust grains, about the size of a micrometer, orbiting the star. These small grains cannot survive for long, which means that there must be a replenishment mechanism.
It is believed that the replenishment of these dust grains in the disks is due to the presence of planetesimals, kilometer-sized bodies, which, upon colliding with each other, continuously release these grains. Unfortunately, these planetesimals cannot be observed directly, so very little is known about the outcome of these collisions.
Recently, an international team of astrophysicists led by Dr. Carl Melis of San Diego Astrophysics and Space Science Center, and including Johan Olofsson, a research associate of the Nucleus Millennium of Planetary Formation, investigated one of these debris disk stars, called TYC 8830 410 1, because they detected a peculiar variability in it. The scientific paper detailing this research was published in the scientific journal AAS (American Astronomical Society).
The researchers made photometric observations of TYC 8830 410 1 over a long period of time. Given the resolution of these observations, it was not possible to detect the disk, so only the total brightness of the star and the disk could be measured. With these data, the scientists noticed an interesting change in brightness as a function of time.
“The first conjecture would be that there is a planet orbiting around the star (this how thousands of exoplanets have been detected in the recent years), which explains why it becomes fainter. But this is not the case for TYC 8830 410 1 because these events are too long, and the shape of the eclipse is irregular,” notes Olofsson, who also leads the Max Planck MPIA-UV Tandem group and member of the Instituto de Física y Astronomía at Universidad de Valparaíso. “Unfortunately, we don’t have a very regular sampling of the photometric observations, so it is very difficult to estimate whether there is any periodicity in the eclipses we saw,” he adds.
The team concluded that the best explanation is that the brightness decrease is due to dust clouds transiting in front of the star. “If we imagine that we see the disk from the side – just as we see the Milky Way – as the clouds are orbiting around the star, they can pass in front of it, which makes it fainter, and then move away, which makes the star brighter. As these clumps are not necessarily homogeneous, this may also explain the irregular shape of the eclipses we detect,” Olofsson says.
For astronomers, it is surprising that the debris disk has clumps, since they expected something more homogeneous, like Saturn’s rings. The best explanation is that there could have been a large collision, which could be comparable to what we think happened when a body the size of Mars collided with the Earth and formed the Moon. In this case, what scientists see are fragments colliding with each other. Probably, they indicate, more than one minor collision occurred, since they have found no clear periodicity for the events.
“Such detections are overall very rare, making TYC 8803 410 1 an extremely interesting system to study, as it provides an indirect way to constrain the results for collisions between planetesimals,” Olofsson stresses.
In general, explains the research team, it is in the early stages of debris disk evolution that rocky planets are expected to form through such collisions. Finding a way to characterize the outcome of these collisions opens the possibility to better understand how rocky planets form.
Johan Olofsson comments that more observations are needed to know if there is indeed any periodicity in the events. Currently, researchers are observing the system with robotic telescopes installed in Chile and around the world.
In addition, scientists are investigating the “color” of the eclipse. “When we see the Sun through clouds, the clouds are gray or white. But when there is fire or smoke in the air, suddenly the light becomes redder. This is because the particle size of the smoke is larger. So, if we can observe eclipses around TYC 8830 410 1 at different wavelengths, we can determine the color of the clouds passing in front of the star. And this might tell us something about the typical size of those dust particles, which are passing in front of the star 520 light-years away from us!”, Olofsson stresses.
“Astronomy in the time domain is a fantastic thing. In my work, I always assume that stars and disks are ‘static’, that they don’t change from day to day, or year to year. Most of the time this is a reasonable assumption, but there is a lot to discover by studying the time component,” concludes the scientist.
Image credit: ESA/NASA, M. Kornmesser