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White Dwarfs & Planetary Nebulas
Animations & Video: White Dwarfs & Planetary Nebulas
Page 12
Click for high-resolution animation
1. Blowing Bubbles
QuicktimeMPEG Astronomers have captured a very special event in space: a so-called 'reborn planetary nebula'. This is a gas bubble inside a previously blown bubble, or nebula, like you can see in this image. Most stars turn into a nebula at the end of their lives, and sometimes, like in this case, they do the same thing twice.

When a star like our Sun has burned all of its fuel, it expands into an enormous red giant of more than ten times its original size. The star then has trouble holding on to its outer layers, which mostly blows off into space. Meanwhile, the leftover core attacks these loose layers with such intense radiation from the inside that it turns them into a planetary nebula - a colorful shining cloud of gas.

In rare cases, the core then performs the same trick: it expands and turns into a nebula. This time, we call it a 'reborn planetary nebula'. In comparison to a star's lifetime, nebulae (this is the plural word for nebula) last a very short while. They dissolve into space after just a few thousand years. This makes nebulae difficult to spot, and reborn nebulae even more so. Yet this time astronomers managed to catch one on camera!
[Runtime: 01:45]
(NASA/CXC/April Jubett)

Related Chandra Images:

Click for high-resolution animation
2. Tour of AM CVn
QuicktimeMPEG In the middle of the twentieth century, an unusual star was spotted in the constellation of Canes Venatici (Latin for "hunting dogs"). Years later, astronomers determined that this object, dubbed AM Canum Venaticorum (or, AM CVn, for short), was, in fact, two stars. These stars revolve around each other every 18 minutes, and are predicted to generate gravitational waves - ripples in space-time predicted by Einstein.

Today, the name AM CVn represents a class of objects where one white dwarf star is pulling matter from a very compact companion star, such as a second white dwarf. (White dwarf stars are dense remains of Sun-like stars that have run out of fuel and collapsed to the size of the Earth.) The pairs of stars in AM CVn systems orbit each other extremely rapidly, whipping around one another in an hour, and in one case as quickly as 5 five minutes. By contrast, the fastest orbiting planet in our Solar System, Mercury, orbits the Sun once every 88 days.

Despite being known for almost 50 years, the question has remained: where do AM CVn systems come from? New X-ray and optical observations have begun to answer that with the discovery of the first known systems of double stars that astronomers think will evolve into AM CVn systems.

Observations with optical telescopes on the ground helped identify two systems, known as J0751 and J1741, that contain two white dwarfs and determined their masses. Scientists used Chandra to help rule out the possibility that J0751 and J1741 contained neutron stars. A neutron star - which would disqualify it from being a possible parent to an AM CVn system - would give off strong X-ray emission due to its magnetic field and rapid rotation. No X-ray emission was seen from either system, thus convincing scientists that these were going to evolve into AM CVn in the future.

As we mentioned before, AM CVn systems are of interest to scientists because they are predicted to be sources of gravitational waves. This is important because even though such waves have yet to be detected, many scientists and engineers are working on instruments that should be able to detect them in the near future. This will open a significant new observational window to the universe.
[Runtime: 02:55]
(NASA/CXC/A. Hobart)

Related Chandra Images:

Click for high-resolution animation
3. Illustrations of an AM CVn system
QuicktimeMPEG This series of artist's illustrations depicts what these systems are like now and what may happen to them in the future. The first still shows the current state of the binary that contains one white dwarf (on the right) with about one-fifth the mass of the Sun and another much heavier and more compact white dwarf about five or more times as massive (unlike sun-like stars, heavier white dwarfs are smaller). As the two white dwarfs orbit around each other, gravitational waves will be given off causing the orbit to become tighter. Eventually the smaller, heavier white dwarf will start pulling matter from the larger, lighter one, as shown in the second still, forming an AM CVn system. This process continues until so much matter accumulates on the more massive white dwarf that a thermonuclear explosion may occur in about 100 million years (final still).
[Runtime: 00:12]
(NASA/CXC/A. Hobart, Illustration: NASA/CXC/M.Weiss)

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Click for high-resolution animation
4. Circus in the Sky
QuicktimeMPEG Before the telescope was invented in the 17th century, people thought that the Earth was the center of the Universe. They thought the Sun, the planets and all the stars revolved around us! It was only when we had the technology to peer deeper into space that we realised that not only does the Earth move around the Sun, but the Sun moves around the center of our galaxy, the Milky Way!

In the last 100 years, telescopes have been advancing at an unbelievable rate. Now we have huge radio telescopes that stretch over 50 kilometers, and we even have telescopes that have been launched into space. With these powerful instruments, we can reveal the secret wonders of the Universe that our ancestors never dreamed of!

Take this picture, for example, it shows a planetary nebula, which is the remains of a star that is blowing itself apart. This one is called the "Clownface Nebula", can you see why? It looks like a clowns head, complete with a crazy hairstyle and a big, shiny nose at the center.

This object was first spotted in 1757, but today we are still discovering new details about it. Shown in purple is gas at a temperature over a million degrees. The red, green and blue pattern shows the ejected outer layers of the exploded star. Much more recently, astronomers realized that a very hot pair of stars may live at the center of this gassy cloud, and they are orbiting each other!
[Runtime: 02:17]
(NASA/CXC/April Jubett)

Related Chandra Images:

Click for high-resolution animation
5. Tour of NGC 2392
QuicktimeMPEG Stars like the Sun can become remarkably photogenic at the end of their lives. A good example is NGC 2392, which is located about 4,200 light years from Earth. NGC 2392, which is nicknamed the "Eskimo Nebula", is what astronomers call a planetary nebula. This name, however, is deceiving because planetary nebulas actually have nothing to do with planets. The term is simply a historic relic since these objects looked like planetary disks to astronomers in earlier times looking through small optical telescopes. Instead, planetary nebulas form when a Sun-like star uses up all of the hydrogen in its core, which our Sun will in about 5 billion years from now. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times its original size. Eventually, the outer layers of the star are swept away by a slow and thick wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a fast wind traveling 6 million kilometers per hour. The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually the central star will collapse to form a white dwarf star. X-ray data from NASA's Chandra X-ray Observatory show the location of million-degree gas near the center of NGC 2392. Data from the Hubble Space Telescope reveal the intricate pattern of the outer layers of the star that have been ejected. Taken together, these data from today's space-based telescopes provide us with spectacular views of planetary nebulas that our scientific ancestors - those that thought these objects were associated with planets -- probably could never have imagined.
[Runtime: 02:17]
(NASA/CXC/J. DePasquale)

Related Chandra Images:

Click for high-resolution animation
6. Tour of A 30
QuicktimeMPEG A planetary nebula is formed in the late stage of the evolution of a sun-like star, after it expands to become a red giant. These images show the planetary nebula A30, located about 5500 light years from Earth, which is going through a special, rarely-seen phase of evolution. The planetary nebula formed, but then the star briefly reverted to being a red giant. The evolution of the planetary nebula then restarted, making it reborn. Here is a close-up view of A30, showing X-ray data from Chandra in purple and optical data from Hubble in orange. A larger view shows optical and X-ray data from Kitt Peak and XMM-Newton, respectively, where the optical data is colored orange, green and blue, and X-ray emission is colored purple.
[Runtime: 01:04]
(NASA/CXC/A. Hobart)

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Click for high-resolution animation
7. Planetary Nebula Survey
QuicktimeMPEG A planetary nebula is a phase of stellar evolution that the sun should experience several billion years from now, when it expands to become a red giant. It will then shed most of its outer layers, leaving behind a hot core that contracts to form a dense white dwarf star. A wind from the hot core will ram into the ejected atmosphere, creating beautiful, shell-like structures seen with optical telescopes. This gallery shows four planetary nebulas from the first systematic survey of such objects in the solar neighborhood made with NASA's Chandra X-ray Observatory. X-ray emission from Chandra is colored purple and optical emission from the Hubble Space Telescope is colored red, green and blue. The diffuse X-ray emission is caused by shock waves as the wind collides with the ejected atmosphere.
[Runtime: 1.00]
(NASA/CXC/A. Hobart)

Related Chandra Images:

Click for high-resolution animation
8. Tour of CH Cyg
QuicktimeMPEG Deep within this optical image lies an intriguing system known as CH Cyg. CH Cyg is a binary star system containing a white dwarf that feeds from the wind of a red giant star. The material from the wind forms a hot accretion disk around the white dwarf before crashing onto the star. CH Cyg is one of only a few hundred so-called symbiotic systems known, and one of the closest to Earth at a distance of only about 800 light years. By combining X-ray data from Chandra, optical data from Hubble, and radio data from the Very Large Array, scientists can study CH Cyg like never before. This image shows material in a jet, moving with a speed of over three million miles per hour, powered by material spinning into the accretion disk around the white dwarf. Systems like CH Cyg are fascinating objects because the components are codependent and influence each other's structure, daily life, and evolution.
[Runtime: 1.03]
(X-ray: NASA/CXC/SAO/M.Karovska et al; Optical: NASA/STScI; Radio: NRAO/VLA]; Wide field [Optical (DSS))

Related Chandra Images:

Click for high-resolution animation
9. Tour of Cepheus B
QuicktimeMPEG A new study from two of NASA's "Great Observatories" provides fresh insight into how some stars are born, along with a beautiful new image of a stellar nursery in our own Milky Way Galaxy. While astronomers have long understood that stars and planets form from the collapse of a cloud of gas, the main causes of this process have remained mysterious. Now, research on an object known as Cepheus B, a cloud of hydrogen about 2400 light years from Earth, helps answer that question. X-rays seen by Chandra show where the young stars in the cloud are, while infrared emission observed by Spitzer reveals whether these stars contain planet-forming disks around them. Taken together, these data reveal that radiation from massive stars is triggering a new generation of stars to be born. This happens more often than previously thought.
[Runtime: 1:18]
(X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.))

Related Chandra Images:

Click for high-resolution animation
10. Chandra and Spitzer Images of Cepheus B
QuicktimeMPEG Astronomers observed an object known as Cepheus B, which is a cloud of molecular hydrogen about 2,400 light years from Earth. X-ray data from Chandra allowed the researchers to pick out the young stars within around Cepheus B. Infrared emission detected by Spitzer revealed whether the young stars had disks around them in which stars may form. By combining the two sets of data, astronomers found that stars in this object are being triggered to form by some external force, such as radiation from a massive star or a shock from a nearby supernova.
[Runtime: 0:08]
(X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.))

Related Chandra Images:

Page 12