(ORDO NEWS) — Astronomers have discovered a cloud of dust the size of an entire star at a distance of 330 light-years from us. His reason? A colossal collision of two exoplanets that were just forming.
We know this because astronomers have analyzed the infrared glow of this dust cloud, as well as changes in the light of the host star, periodically fading due to debris orbiting it.
Thanks to this data, we now know the size of the objects involved and other key details of the collision.
This could provide insight into the formation of our solar system – and perhaps even shed light on stars with unusual dimness patterns like KIC 8462852 or Boyadjian’s star, providing more information about how quickly such debris clouds dissipate.
“For the first time,” says astronomer Everett Shlavin of the University of Arizona’s Steward Observatory, “we have captured both the infrared glow of dust and the nebula that dust creates when a cloud passes in front of a star.”
The star, called HD 166191, is a small child that is only 10 million years old. Since it was formed very recently, it is still surrounded by quite a lot of material left over from the formation process.
Stars form from a dense knot in a cloud of gas that collapses under its own mass; as the star rotates, it grows, adding more and more material from the surrounding cloud, and the latter forms a disk that feeds the star, like water descending into a sewer.
After star formation is complete, whatever is left in the disk can move on to form other elements of the planetary system. The clumps of material stick together, being attracted first electrostatically and then gravitationally.
As you can imagine, it’s a messy process with lots of collisions. Eventually, enough material sticks together to form first a planet seed, or planetesimal, and then eventually a planet.
Collisions between bodies can direct this process. For example, our Moon is believed to have formed when another planetary body crashed into the Earth during the solar system’s youth. But it is not a fact that after each collision there will be survivors.
Led by astronomer Keith Su of the Steward Observatory, a team of researchers used the now-defunct Spitzer Space Telescope to make infrared observations of HD 166191.
These wavelengths allow you to penetrate dust clouds and see what happens in heavily shrouded environments. In addition, starlight absorbed and re-emitted by the dust glows brightly in the infrared.
Between 2015 and 2019, the researchers collected 126 data from the star, specifically looking for orbital dust clouds that could be the result of planetary collisions.
In 2018, the signal they were looking for showed up: an infrared boost indicating an increase in dust, and a dimming indicating blockage of the star’s light.
The same event was recorded by a ground-based telescope in the optical wavelength range – and a similar dimming was recorded 142 days earlier, during a gap in Spitzer’s observations.
Multi-wavelength transit data confirmed this: The signal was generated by the interiors of two planetesimals that crashed into each other and spewing dust everywhere.
An earlier observation from a ground based telescope showed an orbital period of 142 days, giving an orbital distance from the star of 0.62 astronomical units. This is the distance at which rocky planets are expected to form.
Having data on multiple transits also allowed the team to observe the evolution of the cloud. It quickly changed from the first to the second transit, swelling, becoming wider, more opaque and elongated, occupying an area at least three times the size of the star.
But the Spitzer data show that only a small part of the cloud passed between us and the star. This suggests that the cloud was actually much, much larger, perhaps hundreds of times larger than the star.
To create this amount of dust, according to experts, the collision had to occur between two bodies the size of a dwarf planet, with a diameter of 400 to 600 kilometers (250 to 470 miles).
The initial collision must have generated such intense heat that some of the material evaporated; the remainder shattered into fragments that continued to ricochet and collide with each other, as well as other rocks in the area, creating more dust.
By the time the third transit was due to fly, very little trace of the original cloud remained.
However, the environment around the star has become twice as dusty as it was before the collision. This suggests that the debris from the collision rather quickly dispersed through the protoplanetary disk around the star.
This not only suggests that clumpy dust clouds may not be suitable for explaining the peculiar dimness of stars, but also helps to clarify the processes that occur during the formation of a full-fledged planetary system, including ours.
“By looking at the dust disks around young stars, we can look into the past and see the processes that may have shaped our solar system,” Su said.
“By studying the results of collisions in these systems, we can also get a better idea of how often rocky planets form around other stars.”
The team will continue to monitor HD 166191 to see if they can spot any more interesting changes to its dusty shroud.
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