Billions of years from now, as our Sun approaches the end of its life and helium cores begin fusing into its core, it will swell dramatically and transform into what is known as a red giant star. After swallowing Mercury, Venus, and Earth with the difficulty of burping, it would grow so large that it could no longer hold its outer layers of gas and dust.
In a glorious finale, these layers will blast out into space to form a beautiful veil of light, which will glow like a neon sign for thousands of years before fading out.
The galaxy is studded with thousands of these jewel-like monuments, known as planetary nebulae. It is the natural end stage of stars ranging from half the mass of the Sun to eight times its mass. (Most massive stars have a more violent end, an explosion called a supernova.) Planetary nebulae come in a dizzying variety of shapes, as suggested by names like Southern Crab, Cat’s Eye, and Butterfly. But despite its beauty, it has also been a mystery to astronomers. How does a cosmic butterfly emerge from the seemingly featureless round cocoon of a red giant star?
Observations and computer models now point to an explanation that would have seemed strange 30 years ago: Most red giants have a much smaller companion star hiding in the arms of gravity. This second star forms the transformation into a planetary nebula, just as a potter forms a bowl on a potter’s wheel.
The prevailing theory of planetary nebula formation previously included only one star – the red giant itself. With only a weak gravitational force on its outer layers, it loses mass very quickly near the end of its life, losing up to 1 percent every century. It also comes out like a pot of boiling water below the surface, causing the outer layers to pulsate in and out. Astronomers hypothesized that these pulses produce shock waves that explode Gas and dust in space, creating the so-called stellar wind. However, it would require a great deal of energy to completely expel this matter without it falling back into the star. Can not be any gentle exhale, this wind; You need the power of a missile blast.
After the star’s outer layer escapes, the much smaller inner layer collapses into a white dwarf. This star, much hotter and brighter than the red giant it came from, lights up and warms the escaping gas, until the gas begins to glow on its own—and we see a planetary nebula. The whole process is very fast by astronomical standards but slow by human standards, usually taking centuries to thousands of years.
Until the launch of the Hubble Space Telescope in 1990, “we were sure we were on the right track” toward understanding the process, says Bruce Balick, an astronomer at the University of Washington. Then he and colleague Adam Frank, of the University of Rochester in New York, were at a conference in Austria and saw the first Hubble images of planetary nebulae. “We went out for coffee, saw the pictures, and knew the game had changed,” Balik says.
Astronomers assumed that the red giants were spherically symmetric, and that the round star should produce a planetary circular nebula. But that’s not what Hubble saw — not even close to it. “It is becoming clear that many planetary nebulae have asymmetrical, centered structures,” says Joel Kastner, an astronomer at Rochester Institute of Technology. Hubble revealed remarkable lobes, wings, and other structures that weren’t round but were symmetrical about the nebula’s main axis, as if they were spinning around a potter’s wheel.
In early images from ground-based observatories, the Southern Crab Nebula appeared to have four “legs” curved like a crab. But detailed images from the Hubble Space Telescope show that these legs are the sides of two bubbles that roughly form an hourglass shape. In the center of the bubbles are two streams of gas, with “knots” that may light up when you encounter interstellar gas. Southern Cancer, located several thousand light-years from Earth in the constellation Centaurus, appears to have experienced two gas-releasing events. About 5,500 years ago she devised the outer “hourglass”, and a similar event 2,300 years ago created the much smaller indoor event.
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