The object is located “only” 400 light-years from Earth. According to the WM Keck Observatory in Hawaii, CWISE J1249 is the closest known hypervelocity star to our planet.
The mass is also a surprising feature for researchers. CWISE J1249 is the first object found with a mass similar to or less than that of a small star. The low mass makes classification difficult, according to the study. “It could be a low-mass star, or if it is not continuously fusing hydrogen in its core, it would be considered a brown dwarf, placing it between a gas giant planet and a star,” the paper explains.
Brown dwarfs are objects that are more massive than planets, but not massive enough to be considered stars. According to the Institute of Physics of the University of the South Pacific (University of São Paulo), the mass of a brown dwarf is between 13 and 80 times that of Jupiter, which in turn is 316 times heavier than Earth, the largest planet in the solar system. On the surface of a brown dwarf, the temperature generally ranges between -173 and 3400 degrees Celsius. To the naked eye, the hottest brown dwarfs are orange or red in color, while the cooler brown dwarfs are purple in color.
The object’s composition is unique. According to data from the WM Keck Observatory, CWISE J1249 contains lower amounts of iron and other metals than other stars and brown dwarfs.
This unusual composition suggests that CWISE J1249 is very old, and probably comes from one of the first generations of stars in our galaxy. Excerpt from the study describing the discovery of the object.
Why does the body move so fast?
There are two hypotheses for this. One is that it originally formed from a binary system, with a white dwarf, and went supernova (a star explosion) by absorbing a lot of material from the other body in the system. See below the simulations made by UCLA for this scenario:
