Posts Tagged ‘white dwarf’

Death Throes

Credit: NASA/JPL-Caltech/ J. Hora (Harvard-Smithsonian CfA)

Comet collisions may be kicking up dust in the Helix Nebula in this image from NASA‘s Spitzer Space Telescope.

Resembling a giant, shimmering eye, the Helix Nebula was a star much like our Sun. When a star like our Sun burn all of the hydrogen that fuels nuclear fusion in their cores, the star begins to shed its outer layers, puffing them out into space as giant bubbles. Astronomers call these cosmic beauties planetary nebula. Radiation from the dead star’s white hot core, called a white dwarf, heats the expanding shell of material causing it to glow. The glow is short-lived, however, lasting for only about 10,000 years.

Planetary nebulae
have nothing to do with planets. Early planet seekers noticed many objects in the sky that resembled the glowing orbs of known gas planets, such as Jupiter, Saturn and Uranus. It wasn’t until much later that scientists discovered the dead stars’ true origin.

Images in visible light of the Helix Nebula show a spectacularly colorful bubble around the central star but no real detail. With Spitzer’s infrared telescope, however, dust not previously seen was found circling the star at a distance of 35 to 150 astronomical units. An astronomical unit is the distance between Earth and the Sun; about 93 million miles. The glow of the dust encircling the dead star surprised astronomers. They believe the dust is most likely churned up by comets smashing into each other at the fringes of this doomed solar system.

The Helix Nebula is found only about 700 light-years from Earth toward the zodiacal constellation Aquarius, the Water Bearer.

Piercing Eye

Credit: NASA and ESA

A dramatic, piercing eye gazes back at us from the sky in this image of NGC 3918 from NASA‘s Hubble Space Telescope.

Explore the colorful layers of gas and dust of this planetary nebula. These bubbles surround a pinpoint of light at the center; the dying remnants of a star that once was much like our Sun. For most of its life, the star converted hydrogen into helium in its core in a process called fusion. Once that hydrogen runs out after billions of years, the star puffs up to become a red giant, engulfing it inner planets. A red giant is nearly the last phase of life for a star like our Sun. The core can start to fuse helium into carbon but this process doesn’t last very long. When that process ends, huge clouds of gas, the outer layers of the star, are puffed out into space as the star convulses. Eventually, all that remains is the white-hot, dead core of the star. Astronomers call this a white dwarf. They are small; about the size of the Earth, and they weigh about as much as half a Sun. In about four billion years, our Sun will enter this stage in its life. The white dwarf is a dead star that will eventually fade into a piece of warm, black ash.

Intense radiation from the tiny remnant causes the nebula to glow. The glow lights up the layers of the nebula showing us strange and irregular shapes. In the case of NGC 3918, it looks like the shells of gas were thrown off in two huge waves. But astronomers studying the nebula believe the bubbles were formed at the same time. The material was thrown away from the star at different speeds. Jets shoot out from the ends of the nebula.

NGC 3918 is found only about 4,900 light-years from Earth toward the constellation Centaurus. The light from this planetary nebula has traveled nearly 5,000 years ago to fall on our eyes here on Earth. Leave a comment below and tell us what you see in this image.

Starship contrail

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

A delicate ribbon of gas floats through this image from NASA‘s Hubble Space Telescope. Is it a contrail left by a starship barreling through the area? Actually, this ribbon of gas is the thin edge of the supernova remnant SN 1006 in our galaxy that exploded more than 1,000 years ago.

What stories can you create about this image? Leave us a note in the comments. We love mail.

Explore the image. SN 1006 is found in our Milky Way Galaxy but it is slightly out of the plane of the galaxy. This means that there are few stars to block or confuse our view of this supernova remnant. We can explore the folds in the gas. We also see many dim, far-off galaxies in the image. The stars in the image are background stars in our galaxy.

Some supernova form when stars five to ten times larger and heavier than our Sun reach the end of their lives. These stars tend to be super-hot and super-big. They burn through their nuclear fuel of hydrogen and helium within 10 million to 20 million years; very young in the life of stars. Once the fuel is used up, the giant stars begin to shrink. This makes the star hotter and the pressure of this increased heat and radiation tears the star apart. Supernovae explode, throwing their innards starward and they can outshine an entire galaxy for a short period of time. What’s interesting is that in the case of SN 1006, something slightly different happened. A white dwarf star was part of a star system with two stars. Astronomers call these binary star systems and we see many of them throughout the galaxy. White dwarf stars are thought to be the final state of stars that don’t have enough mass to become supernovae. The Sun will probably become a white dwarf at the end of its life. White dwarfs have all the weight of the Sun packed into an area the size of the Earth. In the binary star system of SN 1006, the white dwarf captured material from the other star over a long period of time. Astronomers think that white dwarfs can get only so big. When too much mass from the other star is added, POOF! A thermonuclear explosion destroys the dwarf star.

SN 1006 Remnant

SN 1006 supernova remnant

Observers on Earth saw SN 1006. Around May 1, 1006, astronomers in Africa, Europe and the Far East witnessed the first light coming from the new star that glowed in the sky. For weeks, only the Moon was brighter than the supernova in the night sky. It could be seen during they day and did not fade from view for more than two years. The supernova’s name comes from the year it was discovered. In the mid-1960s, radio astronomers detected a circular ring near the recorded position of the supernova. They found the size of the ring was about the size of a full moon as seen from Earth. That meant that in the past 1,000 years, the edge of the supernova’s bubble has been expanding at 20 million miles per hour. Astronomers now know that the bubble created by SN 1006 is about 60 light-years across. Humans didn’t see SN 1006 again until 1976 when astronomers detected the very faint edge of the supernova. The twisting braid of light we see in the image is moving quickly through an area of gas. As the supernova edge slams into the quiet gas, the gas is heated and begins to glow. As the ribbon twists, we can see the edges like a smoke ring rising into the air.

SN 1006 is located about 7,000 light-years from Earth toward the constellation of Lupus, the Wolf. That means that the light had been traveling at nearly six trillion miles per year for 7,000 years before it reached the eyes on Earth in 1006.

Chaotic Butterfly

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Chaos reigns in the center of this butterfly-shaped nebula in the constellation Puppis. NGC 2440 is a plan­e­tary neb­ula and is the remains of a star like our Sun. The complex structure within the center of this nebula suggest to astronomers that the star has ejected material periodically in various directions.

Explore the planetary nebula in this NASA Hubble Space Telescope image. NGC 2440 is also rich in clouds of dust. Travel along the long, dark streaks pointing away from the central star. Ultra­vi­o­let light from the burned-out star, called a white dwarf, causes the gas around the star to glow. Find the white dot in the cen­ter of the neb­ula. This white dwarf is one of the hottest known to astronomers with a temperature of more than 200,000 degrees Centigrade. The cen­tral star cast off its outer lay­ers as it came to the point where it could no longer keep up nuclear fusion in its core. Nuclear fusion is what pow­ers a star, giv­ing out light, heat and other radi­a­tion.

The dying star cre­ated a cocoon of gas and dust around itself. Even­tu­ally our Sun will burn out and cre­ate a neb­ula like this one; but not for another 5 bil­lion years. Some plan­e­tary neb­ula have uni­form rings around the star.

Plan­e­tary neb­ula have noth­ing to do with plan­ets. In the 18th and 19th cen­tury, astronomers came across neb­ula that resem­bled the disks of dis­tant plan­ets. At that time, astronomers didnt know that the neb­ula were the remains of dead or dying stars. Even­tu­ally, astronomers found that the Milky Way is lit­tered with these starry remains.

NGC 2440 lies about 4,000 light-years away toward the con­stel­la­tion Pup­pis. Pup­pis is a con­stel­la­tion in the south­ern sky and is Latin for the poop deck of a ship. The con­stel­la­tion was orig­i­nally part of the larger con­stel­la­tion Argo Navis, named after the ship of the myth­i­cal Jason and the Argonauts.

Starfish

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Six lobes of gas and dust outline the legs of a starfish in this image of planetary nebula He 2-47. The nebula puffed off material at least three times at the end of its life, firing off jets of gas in opposite directions.

Planetary nebula are the last stages of Sun-like star’s life when they cast off their outer layers into space, creating a bubble around the central star. A hot, white dwarf is left behind. The white dwarf floods the newly created bubble of gas and dust with ultraviolet light causing the gas to glow, leaving the nebula with its dramatic colors.

Explore the lobes and interior bubble of He 2-47, seen in this image from NASA’s Hubble Space Telescope. He 2-47 is a young nebula dominated by cool red-colored nitrogen gas. This starfish-shaped nebula is located about 7,000 light-years from Earth toward the southern constellation Carina. This nebula will continue to expand into space but the glow will last only about 10,000 years; a tiny part of a star’s 10 billion year life-span.

While the round shapes of planetary nebula resembled planets as seen through small telescopes of the eighteenth and nineteenth centuries, they really have nothing to do with planets. Astronomers in the early twentieth century realized that planetary nebula lay far outside the solar system as they discovered that the universe was much larger than previously thought.

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