This page is a guide to Hubble Space Telescope ("HST") images of planetary nebulae taken by Bruce Balick and his collaborators.

(Click here for a pdf version.)

A montage of Planetary Nebulae observed with the Hubble Space Telescope.
Many of these are by Balick and his collaborators, as described below. Most of the rest
are previously released images found at the Space Telescope Science Institute's WWW site.

If you lived for 100 million years instead of just a century,
then planetary nebulae would be the twinkling ornaments of the Milky Way.

PLANETARY NEBULAE AND THE FUTURE OF THE SOLAR SYSTEM

The following paragraphs link the study of "planetary nebulae" to the future of our own solar system.

OVERVIEW

95% of all stars that we see in our own galaxy, the Milky Way, will ultimately become "planetary nebulae". This includes the Sun.

Much as a butterfly emerges when its chrysalis is ejected, planetary nebulae are formed when a red giant star ejectes its outer layers as clouds of luminescent gas, revealing the dense, hot, and tiny white dwarf star at its core.

The other 5% of stars -- that is, those born with masses more than eight times larger than our Sun -- end their lives as supernovae.

One final note: the name "planetary nebula" is a misnomer. The name arose over a century ago when early astronomers looking through small and poor-quality telescopes saw these objects as compact, round, green-colored objects that reminded them of the view of Uranus.
    However, "planetary nebulae" are not made of planets, and no planets are visible within them. Rather, they are the gaseous and dusty material expelled by a geriatric star just before death. A far better name for these objects would be "ejection nebulae". Think of ejection nebulae as a cloud of smoke which esacpes from a burning log as it collapses and crumbles into embers.

THE LIFE OF A STAR LIKE THE SUN

The Sun generates all of its heat in its core. This heat both warms the Earth and prevents gravity from forcing the Sun to undergo a catastrophic gravitational collapse. The fuel which supplies the heat is hydrogen. Hydrogen nuclei are converted to helium as heat is released.

In five billion years the hydrogen fuel will have been depleted. Gravity will force the spent core, now almost pure helium, to shrink, compress, and become even hotter than at present. The high temperatures will eventually ignite the helium ashes. The result is carbon nuclei and even more heat. The "second wind" of heat release will be furious, increasing the light emitted from the future Sun's surface by a thousand fold. Meanwhile, the same heat will cause the outer layers of the present Sun to expand and form a huge "red giant".

The red giant is so bloated that Mercury and Venus will find themselves orbiting inside of it. Imagine daytime on the Earth when this happens. Sunrises and sunsets will take hours, thanks to the huge apparent diameter of the swelled Sun. At noon the huge bright red Sun will fill half the sky. The view won't be very different than that within a kiln. The oceans will boil and evaporate into space, along with the atmosphere. The intense radiant heat will transform the surface to a thick layer of pottery. In all, a biblical view of hell.

As stellar time goes, the helium won't last long - certainly less than a mere few hundred million years. With its helium transformed into unburnable carbon, the solar core shrinks suddenly (a few thousand years) until just over half the mass of the present Sun is packed into a hot (million degree), dense (a ton per teaspoon) ball the size of the Earth. This amazing stellar remnant is called a white dwarf.

The remnant's fuel reserves are now finally gone. Its shrunken stellar core is now entering retirement. Even so, one large final fling lies ahead for this star.

The story shifts from the dying core to the star's distended outer layers. The core, their underlying foundation, now has all but imploded. The outer layers of the Sun fall inward toward the core. But the base material ignites on the way in, causing the outer surfaces to bounce and vibrate. Eventually the outer 40% of the Sun's mass will be spasmically "coughed" into space, floating outward through the solar system and beyond in a concetric set of spherical bubbles. Seen from far away, these may eventually blend together into a gigantic stellar "halo". As the outer layers are flung outward increasingly deeper and deeper layers of the Sun become exposed as its outermost surface, like peeling an onion.

When the process ends, the former core of the Sun emerges through its exapnding veil of ejected material as a white dwarf. The highly energetic forms of light emitted by the hot white dwarf interact with the electrons attached to the atoms in the gas cloud, resulting in a colorful nebula much like the thousand planetary nebulae that have been catalogued already. The striking symmetries of these objects have led to an array of popular names such as the "Cat's Eye", "Ring", "Eye of Jupiter", "Eskimo", "Saturn", and "Blue Snowball" nebulae.

IMAGINE THE VIEW!

Here on Earth, we'll feel the wind of the ejected gasses sweeping past, slowly at first (a mere 5 miles per second!), and then picking up speed as the spasms continue (eventuially to reach 1000 miles per second!!) The remnant Sun will rise as a dot of intense light, no larger than Venus, more brilliant than 100 present Suns, and an intensely hot blue-white color hotter than any welder's torch. Light from the fiendish blue "pinprick" will braise the Earth and tear apart its surface molecules and atoms. A new but very thin "atmosphere" of free electrons will form as the Earth's surface turns to dust.

Here's what some survivor will observe in the night sky. (After Dec 17 refer to the newly released color images below.) Obviously our own planetary nebula will be viewed from the inside out. In addition to stars, the sky will be aflame with the whispy, colorful shapes of the nebula of ejected solar material. This spectacular show will last a few thousand years as the ejected gasses merge into the interstellar medium from which new generations of stars will form.

Imagine that we lived, not for a hundred years, but for a hundred million. As we viewed our home galaxy, the Milky Way, we would see these "planetary", or ejection nebulae flaring and fading all the time, about one per Earth year, much as the flashes of cameras at a sports stadium at night. At any given instant more than 10,000 nebulae are visible in some stage of their evolution. (Once per century or two a blinding supernova would appear for a week or two, like a powerful firecarcker.)

Planetary nebulae make the Milky Way come alive. From afar the Milky Way would resemble a scintillating galactic Christmas tree. A red flash appears here, and another there, as planetary nebulae form. For a few thousand years each nebula brightens and turns from red to green. Finally, after 10,000 years, the growing nebula will expand and fade into the background of galactic gas, as does air from a popped balloon. Each nebula leaves behind a tiny blue white dwarf. Over the course of billions of years, the "white" dwarves fade to a dull red ember.

THE REVOLUTION STARTED BY IMAGES FROM THE HUBBLE SPACE TELESCOPE

What is the value of the Hubble Space Telescope ("HST") in this research? The answer is simple. Just click here.

The HST has been imaging other planetary nebulae for several years, with equally stunning results. Links to a variety of existing images apepar at the end of this page. All of them were all made using the Wide Field and Planetary Camera version 2 (abbreviated "WFPC2" and pronounced "wif-pic-2"). The WFPC2 provides a view of the objects that has ten times the spatial resolution (details are 100 times finer) than possible from the ground.

THE SCIENTIFIC IMPACT

What's the scientific value of the new images? There are several facets to the answer. Above all is opportunity to compare and confront our models and ideas to are better observations than ever possible before. Since humans are highly visual creatures, new images tend to stimulate new ideas and insights. The images are very new and, as yet, still being understood. We can expect that some old ideas will be demonstrated to be wrong and discarded. Those ideas and models that survive may have to be modified in order to successfully account for many of the details in these images.

The new HST images also allow us to preview our own future by looking at what happens to stars similar to ours as they approach their deaths. A dozen years ago we believed that old, round stars just "huffed and puffed" a few times and threw off a spherical bubble nebula. Images such as those below show that our future is likely to be far more interesting, complex, and handsomely striking than we could have possibly imagined just a few years ago.

We're trying to understand why. How can a round star develop such interesting symmetries in its ejected gas? What will we learn when we understand what the processes of ejection is?

The NASA press conference on 17 December 1997 offered a glimpse to our present thinking. Various experts, including Howard Bond and Mario Livio of the Space Telescope Science Institute (STScI) and me, summarized the state of our knowledge. Here are links to STScI's press background stories:

"The Glorious End of Stellar Life"
"Life on the Edge"
STScI's full press release: Here's the Whole Enchillada

The bottom line is this: Our pre-Hubble ideas were based on ground-based data. They're only as good as the data. The new images show 100 times more detail. When the old ideas are confronted by the new images, changes are inevitable.

The interpretation of the new images and the evaluation of old ideas take time -- sometimes years. The process is well underway. Will the old ideas survive? Or is it time to scrap them and go find a new paradigm to pursue? Stay tuned. We can safely predict that the outcome will change next generation of textbooks.

Already the Hubble images are generating some very creative, as yet speculative ideas. An example, which was described by Mario Livio at the NASA press conference, is that a nearby companion star, or perhaps a large planet, becomes engulfed by the expanding, dying star. The star or planet may just find itself inside the star or close to its edge. The gravitational forces exerted by the companion act like an eggbeater, tossing out the loosely outer layers of the giant star into an equatorial disk. For a dynamic simulation of the process, check out this movie (3.5 Mbytes) prepared by STScI.

For a short and simple description of the research issues, click here.

PRESENTING THE NEW IMAGES

Viewing the images with realistic colors and brightness: If you are viewing the image on a SUN or other high-contrast monitor, display the tiff images using a gamma setting of 2. Macs and other monitors should have no trouble.

Image Orientation: Note that the orientation of the spacecraft, and hence that of the pictures above, is arbitrary. In other words, north is not at the top of these images!

Bipolar Planetary Nebulae: The set of images below are of three nebulae known as "butterfly", "bow-tie", or bipolar nebulae. Each consists of two lobes of fluorescing material conjoined at the central star. Each lobe is expanding outwards, pushed by the pressure of hot interior heated by the extreme winds from the star's surface (up to 1000 miles per second).

Why do these nebula develop into two-lobed structures and not simple round bubbles? This is the driving question behind these pictures. Apparently, a tiny, dense disk surrounds the star. Think of the disk as an equatorial waistband. A search for one such disk is displayed in the second-to-last figure. It appears to be present. As the star's winds ram into the disk, material is deflected to the polar axis. A detailed model for this is described in the final image below. A NASA animation (3.5Mbytes) shows how this might happen if the dying star has a nearby companion object in a nearby orbit.

	M 2-9 "Siamese Squid Nebula" or "Twinjet Nebula"	Click for:    * Figure Caption    * bigger jpeg color picture    * publishable quality image (0.75 Mb)    * NASA Press Release
	Menzel 3 "Ant Nebula"	Click for:    * Figure Caption    * bigger jpeg color picture    * NASA's bigger color picture    * NASA Press Release
	Hubble 5 "Hubble's Double Bubble"	Click for:    * Figure Caption    * bigger jpeg color picture    * publishable quality image(1.0Mb)    * NASA Press Release
	NGC 6537 "The Red Spider Nebula"	Click for:    * Figure Caption    * bigger jpeg color picture    * publishable quality image (1.2Mb)    *    * ESA Press Release
	M 2-9 Central Closeup	Click for:    * bigger picture and accompanying caption
	M 2-9 Comparison to Hydrodynamic Model	Click for:    * bigger picture and accompanying caption

Credits for the images of M2-9, Hubble 5, NGC 6537:

Bruce Balick, University of Washington
Vincent Icke, Leiden University (The Netherlands)
Garrelt Mellema, Stockholm University
NASA

Elliptical and Round Planetary Nebulae The first two nebulae below, NGC6751 and IC418, are elliptical PNe with very striking and unusal morphologies. NGC6752 looks like the puff ball of a dandelion, and gives the impression of an explosion rather than an organized ejection, as for the other nebulae. IC418 is peculiar because its outermost shell almost seems carefully inscribed. NASA added the colors. Generally blue represents highly ionized material, and yellow and red are less ionized gas. NGC 3242, 6826, 7009, and 7662 are planetary nebulae that contain "FLIERs". FLIERs are strange red-colored features that resemble flying sparks at the edge of the expanding nebula. The red FLIERs are known to have higher velocities than the gas in which they are embedded. If so, they should leave a wake, as does a speedboat in still water. We expect to find that the narrow part of the wake points outward, in the direction of the "speedboat's" (FLIERs') motion.

Although we see sturctures that might resemble wakes, they point in precisely the reverse direction from that which was expected! This might mean that the bright red knots of material are falling inward. But this seems highly unlikely for stars that are observed to be ejecting gas in high-speed winds. The bottom line is this: No satisfactory explanation for the FLIERs has yet emerged from these studies.

In these images (red,green,blue) is used for the ([N II], [O III], He II) images, respectively. ([N II], [O III], He II) is a (low,moderate,high)-ionization ion found where the gas is mostly (singly,doubly,triply) ionized.

	NGC 6751 "Dandelion Puff Ball Nebula"	Click for:    * Figure Caption    * NASA big color jpeg    * NASA Press Release
	IC418 "Spirograph Nebula"	Click for:    * Figure Caption    * NASA big color jpeg    * NASA Press Release
	NGC 3242 "Eye of Jupiter Nebula"	Click for:    * Figure Caption    * color picture
	NGC 6826 "Blinking Eye Nebula"	Click for:    * Figure Caption    * color picture
	NGC 7009 "Saturn Nebula"	Click for:    * Figure Caption    * color picture
	NGC 7662 "Blue Snowball Nebula"	Click for:    * Figure Caption    * color picture

Credits for the images of NGC 3242, NGC 6826, NGC 7009, NGC 7662:

Bruce Balick, University of Washington
Jason Alexander, University of Washington
Arsen R. Hajian, U.S. Naval Observatory
Yervant Terzian, Cornell University
Mario Perinotto, University of Florence (Italy)
Patrizio Patriarchi, Arcetri Observatory (Italy)
NASA

The Cat's Eye Nebula:The next four images are various views of the Cat's Eye Nebula, NGC 6543, obtained originally by Harrington and Borkowski in 1994 and reprocessed by Balick, Wilson, and Hajian in 1999. The first image shows a comparison of the HST images with a good ground-based image, whioch illustrates the power of the HST. Like the images above, red shows the location of singly ionized atoms. The green light arises from doubly ionized oxygen. In this image blue is the light from neutral oxygen.

The second image is a mosaic of six frames, all based on Harrington & Borkowski's images retrieved from the HST archives and recalibrated.

Upper left: another three-color mosaic much like the first image, but showing more of the fain structure.

Upper middle and upper right: the original images used for the red and green layers of the color image.

Lower left: The images above were made with just one of the four imaging camers in the WFPC2, called the "PC". or "Planetary Camera". This image contains the PC image and portions of the image from the three "WF", or "Wide-Field" Cameras. The lower left image shows that the Cat's Eye is surrounded by a concentric set of circular rings, at least 9 in number. Each of these is probably a spherical bubble of gas projected onto the sky, so each bubble appears like a circle. More about this in the third image.

Lower middle and right: The original images contain so much information that it is difficult to display a complete image. It help to divide the images by some sort of template, in this case a third image, called Halpha. Many more faint features appear, all of which are real. It is interesting that the two images are negatives of each other in appearance. This is because the singly and doubly ionized images, which comprise all of the gas, lie in complementary volumes of space.

The final image combines the HST observations with a wide-field image obtained from the ground in 1992 using the 4-meter Mayall telescope at Kitt Peak. As if the Cat's Eye isn't spectacular enough, this large image shows that the Cat's Eye and the Bull's Eye pattern that surrounds it are embedded in another "halo" of whiskery tattered, wind-eroded gas.