A White Dwarf and Its Nebula

This is the planetary nebula NGC 3918, a brilliant cloud of colorful gas in the constellation of Centaurus, roughly 4,900 light-years from Earth. In the center of the cloud of gas lies a tiny star, the dying remnant of a red giant. When such a star dies, huge clouds of gas are ejected from its surface before collapses to become a white dwarf. Intense ultraviolet radiation from the tiny remnant star causes the surrounding gas cloud to glow.

NGC 3918 has a distinctive eye-like shape with a bright inner shell of gas and a more diffuse outer shell that extends far from the nebula and looks as if it could be the result of two separate irruptions of gas. However, studies of the object suggest that the two cloud components were formed at the same time but are being blown from the star at different speeds. The powerful jets of gas emerging from the ends of the large structure are estimated to be shooting away from the star at speeds of up to 350,000 km/h/

Image Credit: ESA / NASA

An Eye in Space?

Sauron in SpaceEven though it looks like it belongs atop the Dark Tower of Barad-dûr, this fiery swirl is actually a planetary nebula known as ESO 456-67. It lies in the constellation of Sagittarius (The Archer) in the southern sky.

It is possible to see in this image of the nebula the various layers of material expelled by the central star. Each appears in a different color—red, orange, yellow, and green-tinted bands of gas are visible, with clear patches of at the center. Astronomers don’t fully understood how planetary nebulae form such a wide variety of shapes and structures. Some are spherical, some elliptical, others shoot material in waves from their polar regions, some look like hourglasses or figures of eight, and others resemble large, messy stellar explosions.

Image Credit: NASA

A Dying Star

he2-47This Hubble image is of the planetary nebula He 2-47, the remnant of a dying star. These gaseous clouds are created when stars in the last stages of life cast off their outer layers of material into space. Hen 2-47’s six lobes of gas and dust that suggest that the central star of the nebula ejected material at least three times in different directions. During each ejection, the paired jets of gas pointed in opposite directions, eventually giving the nebula it’s present shape.

Image Credit: NASA

A Fading Nebula

Data from the Hubble Space Telescope reveal that the nebula Hen 3-1357 (aka the Stingray Nebula) has faded dramatically over the past two decades. These two strikingly different images of the nebula were captured 20 years apart. The image on the left was taken in March, 1996, and shows the nebula’s central star in the final stages of its life. The gas being puffed off by the dying star is much brighter than the gas photographed in January, 2016. It’s very rare to see a nebula change so quickly.

Image Credits: NASA / ESA / B. Balick (University of Washington), M. Guerrero (Instituto de Astrofísica de Andalucía), and G. Ramos-Larios (Universidad de Guadalajara)

A Possible Future

Stars like our Sun end their lives by casting off their outer layers, briefly forming a spectacular “planetary nebula” like the Helix Nebula. In 5 billion years or so, our Sun will probably go through a similar blowout.

This brief video fades between images taken at different wavelengths which show different aspects of the nebula. Optical: Hot gas ejected from a dying star glows. Near-Infrared: Near-infrared light reveals cooler material. Mid-far-Infrared: Warm dust is identified in mid-infrared light. Infrared-Ultraviolet: The ultraviolet light traces the hot gas being expelled from the dying star.

Video Credit: STScI

A Ring of Fire

Fine Ring NebulaThis rather unusual planetary nebula is the Fine Ring Nebula. Planetary nebulae form from dying stars when they have expanded into a red giant phase and then eject a shell of gas as they evolve into the next phase of their stellar evolution, white dwarfs. Most planetary nebulae are either spherical or elliptical in shape, or are bipolar (featuring two symmetric lobes of material), but the Fine Ring Nebula looks like an almost perfectly circular ring. Astronomers believe that this unusually shaped planetary nebula was formed from a binary system. The interaction between the primary star and its orbiting companion shapes the ejected material.

The stellar object at the center of the Fine Ring Nebula does appear to be a binary system, orbiting with a period of 2.9 days. Observations suggest that the binary pair is almost perfectly face-on from our vantage point, implying that the planetary nebula’s structure is aligned in the same way. Our point of view looks down on the torus (doughnut shape) of ejected material, leading to the strikingly circular ring shape in the image.

Image Credit: ESO

A Ghost Ring Sight

NGC 6369 is a planetary nebula also known as the Little Ghost Nebula. Planetary nebulae aren’t related to planets. They’re gaseous shrouds created at the end of a Sun-like star’s life as the dying star’s outer layers expand while its core shrinks to become a white dwarf. The white dwarf radiates strongly at ultraviolet wavelengths, powering the expanding nebula’s glow. NGC 636’s main round structure is about a light-year across, and the glow from its ionized oxygen, hydrogen, and nitrogen atoms are colored blue, green, and red respectively. The Little Ghost Nebula offers a glimpse of the likely fate of our Sun which could produce its own planetary nebula about 5 billion years from now.

Image Credit: NASA / ESA

Hubble Versus My Backyard Telescope

ngc7027N7027lredsgNGC 7027 is one of the brightest nebulae in the sky, but it has never been given a common name. In a 6-in telescope at around 50x it appears as a relatively bright bluish star. I didn’t take the picture on the right, but it’s the sort of view I get with my backyard telescope. The Hubble image above shows a bit more detail.

Before being studied via Hubble, NGC 7027 was thought to be a proto-planetary nebula with the central star too cool to ionize any of the gas. It is now known to be a planetary nebula in the earliest stage of its development with a central star is believed to have been about 3 to 4 times the mass of the Sun.

Image Credit: NASA

NGC 7027

NGC 7027 is a very young and dense planetary nebula about 3,000 light-years from Earth in the constellation Cygnus Only a few hundred years old, it’s a tiny infant. Indeed, it’s one of the smallest planetary nebulae, only 0.2 by 0.1 light-year. Most planetary nebulae are around 1 light-year across. NGC 7027 has a very complex structure, consisting of inner elliptical region of ionized gas inside of a large cloud of neutral gas.

The white dwarf at the core of the nebula has a mass about 70 percent of the Sun’s. The expanding halo has roughly three times the mass of the Sun.

Image Credit: NASA / ESA

A Shell in a Fish

supernova_shellThese thin wisps of gas are an object known as SNR 0519. The blood-red clouds are the remains from a violent explosion of a star as a supernova seen about 600 years ago. The star that exploded is known to have been a white dwarf star—a Sun-like star in the final stages of its life.

SNR 0519 is over 150 000 light-years from Earth in the southern constellation of Dorado (The Dolphinfish), a constellation that also contains most of our neighboring galaxy the Large Magellanic Cloud, a region of the sky is full of intriguing and beautiful deep sky objects. The Large Magellanic Cloud orbits the Milky Way galaxy as a satellite and is the fourth largest in our group of galaxies.

Image Credit: NASA / ESA

A Celestial Diamond Ring

Celestial Diamond RingESO’s Very Large Telescope in Chile captured this eye-catching image of planetary nebula PN A66 33 (aka Abell 33). This beautiful blue bubble in space was created when an aging star blew off its outer layers, and it is, by chance, aligned with a foreground star. From the Earth’s point of view the pair bears an uncanny resemblance to a diamond engagement ring.

Image Credit: ESO

The Helix Nebula

The Helix Nebula (aka NGC 7293) is a large planetary nebula located in the constellation Aquarius. It’s about 700 light-years away. The Helix Nebula has sometimes been referred to as the “Eye of God.” Tolkien fans have occasionally called it the “Eye of Sauron”

This animation of a 3-D model was created from Hubble Space Telescope and ground-based data of the Helix Nebula.

Credit: NASA, ESA, and G. Bacon (STScI)

Caldwell 90

Caldwell 90 is a planetary nebula formed in the late stages of the life of a Sun-like star. Initially, the star’s energy was derived by fusing hydrogen into helium. When the supply of hydrogen ran low, it produced less energy, so the force of gravity caused it to contract. Eventually, that contraction increased the pressure in the star’s core and triggered fusion of the heavier element carbon. That process caused the star to expand into a red giant. Finally, the red giant’s outer layers were eject to form the nebula and the star collapsed again into a small, dense star whose intense radiation continues to push the nebula boundaries outward.

The Sun will probably go through a similar process in 4 or 5 billion years.

Image Credit: NASA / ESA

NGC 6153

A nitrogen-rich nebula This is NGC 6153. The faint blue haze is what remains of a star like the sun after it had depleted most of its fuel. When that happened, the outer layers of the star were ejected and then ionized by the ultraviolet light from hot core of the star, forming the nebula.

NGC 6153 is a planetary nebula which contains large amounts of neon, argon, oxygen, carbon and chlorine—up to three times more than can be found in our solar system. It contains five times more nitrogen than our sun! It could be that the star developed higher levels of these elements as it grew and evolved, but it is more likely that the star originally formed from a cloud of material that already contained an abundance of those elements.

Image Credit: ESA / NASA

The Oyster Nebula

A hazy nebulaThis is a false color image from Hubble’s Wide Field Planetary Camera 2 of NGC 1501, a complex planetary nebula located in the constellation of Camelopardalis (The Giraffe). NGC 1501 is a planetary nebula that is just under 5,000 light-years away from us. It has a central star shining brightly from within the nebula’s cloud. This bright pearl embedded in its glowing shell gives rise to the nebula’s popular nickname—the Oyster Nebula.

While NGC 1501’s central star blasted off its outer shell long ago, it still remains very hot and luminous, but it can be difficult to spot through modest telescopes. The star seems to be pulsating, varying quite significantly in brightness over a timescale of just half an hour. While variable stars are not unusual, it is unusual to find one at the heart of a planetary nebula.

Image Credit: ESA / NASA

NGC 2371/2

When astronomers first studied this object, they thought they were seeing two, so the two lobes of this planetary nebula were cataloged as NGC 2371 and NGC 2372. Now, the object is often called NGC 2371/2. NGC 2371/2 formed when a Sun-like star reached the end of its life and blew off its outer layers, shedding gas and dust and pushing material out into space to leave a dying, superheated star. That remnant is the bright star between the two lobes at the middle of the image.

Image Credit: NASA / ESA

The Fine Ring Nebula

Fine Ring NebulaThis is the Fine Ring Nebula, an unusual planetary nebula. Planetary nebulae form after some dying stars that have expanded into a red giant phase eject a shell of gas as they evolve into the next phase of their stellar evolution, white dwarfs. Most planetary nebulae are either spherical or elliptical in shape, or bipolar (featuring two symmetric lobes of material), but the Fine Ring Nebula looks like an almost perfectly circular ring. Astronomers believe that this unusually shaped planetary nebula was formed from a binary system. The interaction between the primary star and its orbiting companion shapes the ejected material.

The stellar object at the center of the Fine Ring Nebula does appear to be a binary system, orbiting with a period of 2.9 days. Observations suggest that the binary pair is almost perfectly face-on from our vantage point, implying that the planetary nebula’s structure is aligned in the same way. Our point of view looks down on the torus (doughnut shape) of ejected material, leading to the strikingly circular ring shape in the image.

Image Credit: ESO

Making a White Dwarf

NGC 40 is one of a class of objects called planetary nebulas, so-called because they look like the disk of a planet when viewed with a small telescope. This composite X-ray (blue)/optical (red) image of the nebula NGC 40 shows that it is a bubble of hot gas around a dying Sun-like star. In another 30,000 years or so, the nebula will dissipate, leaving behind a smallt, ultradense white dwarf star about the size of Earth.

Image Credit: X-ray—NASA / CXC  / RIT / J.Kastner & R.Montez.; Optical—NSF / AURA / NOAO / WIYN