Astronomers have come across something of a rare find: a binary system consisting of a failed star and a dead star.
Failed stars are more commonly known as brown dwarfs. Brown dwarfs are too big to be planets, but they are not massive enough to have the atomic fusion that characterizes a star. Thus, a brown dwarf is something in between a star and a planet and are thus fascinating objects in themselves.
The other half of this very rare binary system, meanwhile, is a white dwarf star. When stars similar to the sun run out of their energy and eventually die, they turn into white dwarfs. These stars will turn into red giants after they lose the hydrogen in their core. Then, the red giant will turn into a planetary nebula that has a white dwarf in its center. Eventually, our sun will turn into a white dwarf.
When astronomers found the system with a brown and white dwarf, they found something remarkable. The brown dwarf orbits around the white dwarf in just 71.2 minutes. This single detail leads us to many other fascinating details about the system.
An orbital period of 71.2 minutes indicates that the brown dwarf moves quite quickly. This means that the stars in the binary system orbit each other at a speed of about 100 kilometers per second. If we traveled this quickly, we'd be able to cross the Atlantic in under a minute.
A team of astronomers from multiple countries used five telescopes in three continents to study the system. They found that the brown dwarf has a mass equivalent to just 6.7 % the mass of the Sun. Meanwhile, the white dwarf, identified as WD1202-024, has a mass equivalent to 40% the mass of the sun.
The team also figured that the brown dwarf likely didn't form with an orbit of just 71.2 minutes around the white dwarf. Through the use of computer simulations, the team discovered that the brown dwarf possibly spiraled into the red giant that the white dwarf had been. As the brown dwarf spiraled closer to the core, it dispelled the red giant's mass. Eventually, the core cooled down and turned into the white dwarf it is today.
Calculations say that the binary system is about three billion years old. Its future, however, is of some interest. Astronomers estimate that the white dwarf will engulf the brown dwarf in 250 million years or less. The brown dwarf will orbit closer and closer to the white dwarf, and the white dwarf will soon begin consuming its satellite.
When the white dwarf finally engulfs the brown dwarf, it will turn into a cataclysmic variable. Cataclysmic variable stars have a brightness that flickers between irregular periods of an increase in brightness, and periods of low brightness.
This binary system isn't just a rare discovery, but an extremely interesting one as well. We won't be around to see it, but we know that when that brown dwarf goes, it'll go out with a bang.
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