An artist’s illustration shows a white dwarf and a larger, sun-like star forming a “cataclysmic” binary system. (M.Weiss, Center for Astrophysics, Harvard and Smithsonian via Reuters)
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WASHINGTON – Unlike the sun itself, about half of the stars in our Milky Way Milky Way are committed to another star for a long time, orbiting each other in a celestial marriage called a binary system.
Researchers this week stumbled upon one of these marriages — two that are on the extreme border, with the twins orbiting each other every 51 minutes in the fastest such orbital period known for the rare class of binary stars. As part of the drama, one star eats his companion.
The two stars are located about 3,000 light-years from Earth in the direction of the constellation Hercules. A light year is the distance of light in a year, 5.9 trillion miles.
The system belongs to a class of binary stars known as “cataclysmic variables,” in which a star similar to our Sun orbits near what is called a white dwarf, basically the hot, compact core of a burned-out star. Variable just means that their combined brightness varies over time as viewed from Earth. It looks cataclysmic because this luminosity changes dramatically – by a factor of 10,000 or more in some cases.
Over millions of years the distance between these two stars has narrowed to the point that they are now closer than the moon to Earth.
“Imagine if the moon traveled across the sky 10 times per night. We’re talking about that kind of speed,” said Massachusetts Institute of Technology astrophysicist Kevin Burdge, lead author of the study published this week in the journal Nature.
Relative does not mean that they are nice to each other, but – the white dwarf is siphoning material mercilessly from his partner.
This massive star is about the same temperature as the sun, but is stripped down to about 10% of the sun’s diameter—leaving it about the size of Jupiter, our solar system’s largest planet. The white dwarf has about 56% the mass of our Sun, but is densely packed, with a diameter about 1.5 times that of Earth.
“It’s an old pair of stars where one of the two is moving — the stars die as they get older and become white dwarfs — but then the remnants start eating their companion,” Burdge said.
“Individually, they are connected for 8 billion years in a binary orbit. And now, before the second, it can end its stellar life cycle, and they become white dwarfs in the way that stars usually do – evolving into a type of star. He called red giants – the remnants of white dwarfs, the remnants of the first star the end of the count’s life was interrupted and slowly began to consume,” Burdge said.
The researchers used data from the Palomar Observatory in California and telescopes in Hawaii and the Canary Islands.
Most stars are composed primarily of hydrogen, with smaller amounts of helium and other elements. The larger of the two stars in this binary—already aging—is unusually rich in helium, not only because it has shed some of its hydrogen from its outer layers, but because it has a lot of this element in its core through a slow process of infusion. hydrogen atoms into helium in its thermonuclear furnace.
This binary system periodically brightens and recedes in part because the larger star is physically deformed into a teardrop shape, rather than a sphere, by the gravitational pull of the white dwarf.
More than a thousand cataclysmic variables are known, although only a dozen have orbital periods under 75 minutes. While this binary system is 51 minutes faster, it is not a record compared to other binary types. The fastest known orbital period between binaries is only 5 minutes and 21 seconds, with two white dwarfs orbiting each other.
“There are tons of wild animals going on in the area,” Burdge said.
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