IC 1295

The glowing green planetary nebula IC 1295 surrounds a dim and dying star. It is located about 3300 light-years away in the constellation of Scutum (The Shield). The white dwarf star is softly shedding its outer layers, like an unfolding flower in space. It will continue this process for a few tens of thousands of years.

Image Credit: ESO

NGC 2440

Hubble reveals NGC 2440This Hubble Space Telescope image shows the colorful end of a star like the Sun. This star is casting off its outer layers of gas, which formed a cocoon around the star’s remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, a white dwarf, is the white dot in the center. Our Sun will eventually burn out and surround itself with stellar debris, but that’s not expected for another 5 billion years or so.

The galaxy is filled with these stellar relics called planetary nebulae. (They have nothing to do with planets. 18th- and 19th-century astronomers used that name because through small telescopes the nebulae resembled the disks of the planets Uranus and Neptune.) This planetary nebula in this image is named NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of more than 200,000°C. The nebula’s chaotic structure suggests that the star shed its mass in multiple stages. During each outburst, the star blew off material in a different direction, resulting in the two bowtie-shaped lobes.

The material expelled by the star glows with different colors depending on its composition, its density and how close it is to the hot central star. Blue samples helium; blue-green oxygen, and red nitrogen and hydrogen.

Image Credit: NASA / ESA

The Case of the Hungry Dwarf

disintegrating_asteroid smallThe K2 mission using the repurposed Kepler Space Telescope has uncovered strong evidence of a tiny, rocky object being torn apart as it spirals around a white dwarf star. (That’s an artist’s concept of it above.) This discovery supports the theory that a white dwarf is capable of cannibalizing any planets that have survived within its solar system. As stars like our Sun age, they first swell into red giants and then gradually lose about half their mass, shrinking down to 1/100th of their original size (roughly the size of Earth). This dense star remnant is called a white dwarf.

During a series of observations last year, K2 was used to measure the minuscule change in brightness of  distant white dwarf known as. WD 1145+017. When an object passes in front of a star from our vantage point, a dip in the starlight can be detected. A periodic dimming indicates the presence of an object in orbit around the star. The object found around WD 1145+017 was the first found orbiting a white dwarf. It’s orbital period is only 4.5 hours, placing extremely close to the white dwarf and its searing heat and shearing gravitational force.

comparetotransit2While there was a prominent dip in brightness every 4.5 hours, the transit signal of the tiny planet did not exhibit a normal symmetric U-shaped pattern. The data (shown as the black dots) displayed an asymmetric elongated slope pattern that indicated the presence of a comet-like tail. Together these features indicated a ring of dusty debris circling the white dwarf. That could be the signature of the small planet being vaporized.

In addition to the strangely shaped transits, other data shows signs of heavier elements polluting the atmosphere of WD 1145+017. Because of their intense gravity, white dwarfs are expected to have chemically pure surfaces and be covered only with the light elements helium and hydrogen. For years, researchers have found evidence that some white dwarf atmospheres are polluted with traces of heavier elements such as calcium, silicon, magnesium, and iron, and scientists have long suspected that the source of such pollution could come from a planet being torn apart. It looks as if they found one.

Image Credits: CfA / A. Vandenberg