With the recent story of the star with a debris ring potentially being a sign of extraterrestrial life (spoiler alert, it’s not aliens), I had to talk a bit more about debris rings in general around other stars. How can they exist? When we start to look at the number of worlds and the variability of objects and stars, it would be no surprise to find strange systems where recent interactions have produced all kinds of fascinating patterns. It’s another example of finding art in nature.
A group of astronomers from the university of Warwick have directly imaged a debris ring around a white dwarf star, resulting from a close encounter with an asteroid. The strong tidal forces of the star shredded the asteroid and led to a ring of material forming in orbit.
Christopher Manser of the University of Warwick’s Astrophysics Group describes the ring, saying “The diameter of the gap inside of the debris ring is 700,000 kilometres, approximately half the size of the Sun and the same space could fit both Saturn and its rings, which are only around 270,000 km across. At the same time, the white dwarf is seven times smaller than Saturn but weighs 2500 times more.”
Even though debris rings have been found around other stars, this is the first time a ring has been directly imaged, giving us new insights into what happens during and after these types of interactions, and how we can identify this kind of scenario when looking at more distant stars.
“We knew about these debris disks around white dwarfs for over twenty years, but have only now been able to obtain the first image of one of these disks,” says Manser.
The image uses a technique called Doppler tomography, which is quite similar to computed tomography (CT) scans that a patient gets in a hospital. Both methods use a series of scans from different angles to compute a final image. In CT, the scanner moves around the patient, but with the Doppler method, the team has to take a series of images over a period of 12 years.
Following the results, Manser says, “The image we get from the processed data shows us that these systems are truly disc-like, and reveal many structures that we cannot detect in a single snapshot. The image shows a spiral-like structure which we think is related to collisions between dust grains in the debris disc.”
Objects are torn apart due to the tidal force. Since the strength of the gravitational force varies with the square of the distance from an object, a large object can feel a stronger gravitational force on one side, and a weaker force on the opposite side. This creates a shearing force, which can be tolerated by the strength of a space rock. But when a rock comes closer to a strong source of gravity, the tidal force increases rapidly, and can create such large shearing forces that an object can no longer be held together. Even small objects can be shredded by tidal forces if they come close enough. I’m often asked what happens if a person could fall into a black hole. The answer is that the tidal forces would ‘spaghettify’ you once you came close enough.
Long story short, debris disks can form easily, we haven’t found aliens, and tidal forces can kill.