The dust cloud is believed to have been created by a catastrophic collision between two dwarf planets.

Astronomers write that in the magazine The Astrophysical Journal† As mentioned, they are based on data collected by the Spitzer telescope that will be decommissioned in 2020. The researchers used the telescope to observe the young star HD 166191 more than 100 times between 2015 and 2019. They had a clear goal in mind; they hoped to encounter a large cloud of dust.

planetesimals

Young stars are surrounded by a huge gas and dust disk in which planets can form. These planets are formed because material in the gas and dust disk clumps together. Also called planetesimals, these clumped objects are separated from each other by gas early in the life of their parent star. However, there comes a time when that gas is gone. And that’s when catastrophic collisions between the planetesimals will become much more frequent. These collisions cause the planetesimals to grow at an accelerated rate – because they clump together with other fairly large planetesimals – or, on the contrary, to disintegrate into much smaller objects.

Dust clouds

In the past, indications of such collisions have been spotted by the Spitzer space telescope. For example, in 2014 the telescope encountered a huge cloud of dust around a young star. It was suspected that the dust was released by a collision between planetesimals. But the observations provided little further insight into the nature of the collision. For example, it remained unclear how large the colliding objects had been before their unfortunate crash.

To change that, scientists turned to HD 166191. The star is about 10 million years old and therefore at an age at which surrounding planetesimals can gradually start colliding with each other. Several years in a row, scientists aimed the Spitzer telescope at HD 166191. And in 2018 it hit the mark. The infrared telescope saw the system brighten significantly, indicating that quite a bit of debris had been generated. This was subsequently confirmed by the actual observation of a dust cloud moving in front of the star.

Elongated, huge dust cloud

By combining Spitzer’s observations with those from ground-based telescopes, the researchers were able to estimate the size of that dust cloud. The observations suggested that a rather elongated dust cloud had formed around the star. And based solely on what the researchers saw moving in front of the star, that dust cloud would cover an area at least three times the size of the star’s area. Spitzer’s infrared observations, however, suggested that the cloud’s size was actually much larger; Spitzer saw the system become so much brighter in infrared that the cloud must be hundreds of times larger than the star. It is therefore suspected that only a small part of that gigantic cloud – seen from Earth – moved in front of the star.

Dwarf Planets

In order to create such a huge cloud of dust, two quite large objects have to be collapsed on top of each other. The researchers think that these are dwarf planets that can measure themselves in size with Vesta (a dwarf planet in our own solar system with a diameter of about 530 kilometers). Enough energy and heat would have been released during the collision to vaporize at least some of the material that made up the two colliding objects. Most of the dust was created by the remaining material then clapping onto surrounding planetesimals.

The researchers watched the dust cloud grow and thin over the next few months, indicating that the dust was spreading throughout the young star system. By 2019, the cloud the researchers had seen moving in front of the star was no longer visible, but the system still contained twice as much dust as it had before the collision.

The research not only provides more insight into the processes that take place in young, distant star systems and the way in which they influence the formation of exoplanets. The research also has implications for our understanding of our own solar system. Our own planet and moon would also have taken shape through agglomeration and collisions. “By looking at discs of dust around young stars, we are actually looking back in time and seeing the processes that may have shaped our own solar system,” said study researcher Kate Su. “And by learning more about the outcome of collisions in these systems, we can also get a better idea of ​​how often rocky planets form around other stars.”