- CfA/Mark A. Garlick
In the first observation of its kind, astronomers have discovered an Earth-sized dead star in the process of feeding on a small planetoid.
The discovery could solve a long-standing mystery about these stars and their chemical composition that have puzzled experts for the last decade.
While the idea of a dead star gorging itself sounds slightly disturbing, the process is a natural consequence of basic physics.
Dead stars are a colloquial term for a type of star astronomers refer to as white dwarfs, which are the residual cores left behind after stars like our sun deplete their main energy source of hydrogen into helium.
These stars cram the mass of our sun into an Earth-sized volume, and are therefore extremely dense with a tremendous gravitational grip on the space around them: A teaspoon’s worth of a white dwarf weighs nearly 11,000 pounds.
In theory, white dwarfs should consist mostly of carbon and oxygen, but numerous observations have revealed other elements inside them like calcium, silicon, magnesium, and iron.
For years, astronomers pondered over the existence of these bizarre elements because the star itself could not have possibly made them. Therefore, they must have come from the residual guts of objects that orbited too close to the dead star and were eventually disintegrated by its powerful gravitation and searing heat.
However, there were no observations to back this theory – until now.
Using an upgraded version of the planet-hunting space telescope, Kepler – now called K2 – an international team of scientists detected a periodic dimming of starlight coming from the white dwarf WD 1145+017, which floats in space 570 light years from Earth. They published their results in Nature.
By mapping how the dimming changed over time, in what experts call a light curve, the team determined that the object could not be your average run-of-the-mill planet. The light curve was too elongated, as shown in the light curve the scientists took shown below:
- CfA/A. Vanderburg
The object’s characteristic light curve was more indicative of a comet because of its elongated tail.
“The eureka moment of discovery came on the last night of observation wth a sudden realization of what was going around the white dwarf,” Andrew Vanderburg, who led the study and is a graduate student from the Harvard-Smithsonian Center for Astrophysics said in a NASA report. “The shape and changing depth of the transit were undeniable signatures.”
After the object fell into the powerful gravitational claws of the white dwarf, the dead star’s gravity began ripping the object apart while its heat vaporized the object, generating the tail that produced the characteristic light curve you see above.
“For the last decade we’ve suspected that white dwarf stars were feeding on the remains of rocky objects, and this result may be the smoking gun we’re looking for,” Fergal Mullally, who is the staff scientists of K2, said in the NASA report. “However, there’s still a lot more work to be done figuring out the history of this system.”
By developing a better understanding ot the system’s history, the team will be better able to determine whether times of feeding do, in fact, resolve the issue behind dead stars’ mysterious chemical compositions.