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Busy Binary

A star system in the unicorn stays busy. An old, puffy star pours gas onto a small, dead companion. That forms a bright disk, high-speed jets, and powerful outbursts — with perhaps a much bigger outburst in the system’s future.

MWC 560 is in Monoceros, the unicorn, which follows bright Orion across the sky.

The “dead” star is a white dwarf — the hot, dense core of a once normal star. The other star is a red giant — a star at the end of its life. It’s puffed up to giant proportions, so its grip on the gas at its surface isn’t very strong. That allows the gravity of the white dwarf to pull some of its gas away.

The gas forms a wide, thin disk around the white dwarf. Some of the gas falls onto the white dwarf, making the star heavier. But some of it shoots back out into space in skinny jets. They reach speeds of millions of miles per hour. Earth lines up directly in the path of one of the jets.

MWC 560 has grown much brighter several times in the last few decades. The most recent outburst started in 2016, and it took a while to fade. The companion probably was dumping more gas onto the white dwarf. As a result, the jet that faces Earth got thicker and faster, carrying a lot more material away from the white dwarf.

It’s possible that the white dwarf could become a nova later in this century. That would blow its outer layers into space, making it shine thousands of times brighter — a powerful eruption from a busy star system.

Script by Damond Benningfield

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