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Sakurai’s Star

February 24, 2021

Some stars just don’t know how to stay dead. Consider Sakurai’s Object. It had already “died.” But 25 years ago this week, an amateur astronomer in Japan reported that the star had flared back to life. This “rebirth” won’t last long, though — the star is already back on its earlier track.

Originally, Sakurai’s star probably was several times the mass of the Sun. It aged quickly, and puffed up to form a giant. About 8,000 years ago, it expelled its outer layers into space. Today, those layers form a faint red bubble around the star.

The expulsion left only the star’s core — a dense ball of carbon and oxygen topped by a thin layer of hydrogen and helium. It no longer produced nuclear reactions. But it was extremely hot, and a hundred times brighter than the Sun.

The core was cooling and fading, so it was on track to become a white dwarf — the final phase of life for many stars. But a quarter of a century ago, it flared up. The helium at its surface basically caught fire — nuclear fire. The helium fused to make heavier elements, causing the “dead” star to briefly flare back to life.

The outburst expelled a lot of gas into space. Some of the gas cooled and condensed to form grains of dust. For a while, the dust was so thick that it completely hid the star. But it’s thinned out, allowing astronomers to watch Sakurai’s Object settle down once more, probably for good — and complete its evolution into a white dwarf.

Script by Damond Benningfield

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