Category Archives: planetary nebulae

astronomy, planetary nebulae, star death, stellar winds, sun

Questions Astronomers Get

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And An Answer to One of Them

Last week aboard the good ship Corinthian II, I was sitting out on the deck having a little lunch and chatting with some of fellow passengers about fascinating topics in astronomy. It’s always interesting to hear what fascinates people about space and astronomy and I’m always happy to answer questions about those topics.

One of the questions that comes up frequently (and did in the conversation I had that afternoon) is “What will happen to the Sun?” Most of the time, people really ARE interested in the science behind the Sun’s existence and I”m happy to oblige them with the executive summary of end-times astrophysics for our star.

And it IS (or will be) an astrophysical event. Each thing that will happen to the Sun can be figured out by applying the laws of physics, of gravity, gas laws, and other scientific knowledge.  No mysterious death rays or aliens figure into these, because those “actors” don’t usually follow the laws of physics (or of normality, as far as I can tell).  And yeah, there are all these crazy ideas out there floating around about how the Aztecs or Mayans or the Illuminati or the Pleiadians or some other alien race has predicted the Sun will go wonky next year, or that the death beam from the center of the Milky Way will cream us all at a predetermined time. However, nothing that anybody can dream up after a couple of beers (or surfing through weird Web sites) is as interesting as what will really happen to the Sun.

The Necklace Nebula, a recently discovered planetary nebula in the constellation Sagitta. This is a Hubble Space Telescope image. Courtesy NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

So, what WILL happen?  Take a gander at this image here to the left. It’s a planetary nebula — essentially what’s left over after a sun-like star loses most of its mass to space. The star doesn’t blow itself to smithereens — that’s what stars that are many times more massive than the Sun do when THEY die. No, stars like the Sun go to their fates more gently (for stars).  The short story is that it huffs off its outer atmosphere over long periods of time, and then what’s left collapses to become a white dwarf.  So, the Sun — in about 6-7 billion years, could look something like this.

This image actually shows what happens when two stars are involved in a planetary nebula. A pair of stars orbiting very close together are at the heart of this nebula (called PN G054.2-03.4). About 10,000 years ago one of the aging stars ballooned to the point where it enveloped its companion star. This caused the larger star to spin so fast that much of its gaseous envelope expanded into space. Due to centrifugal force, most of the gas escaped along the star’s equator, producing a dense ring. The embedded bright knots are the densest gas clumps in the ring.

The stars are furiously whirling around each other, completing an orbit in a little more than a day. (For comparison, Mercury, the closest planet to the Sun, takes 88 days to orbit the Sun.)

An artist's-eye view of what the Sun and solar system will look like in a few billion years as the Sun ages and dies. Courtesy ESA.

The Sun’s planetary nebula will be a glowing cloud of gas and dust, heated by radiation from the leftover white dwarf.  It will light up the clouds and highlight the clumpiness in the nebula.

What people are really wanting to know when they ask that question about the Sun dying is what will happen to Earth. Sad to say, the prognosis for our  little oasis in space isn’t good at that point. Life will have been crisped in the heat of the expanding outer atmosphere of the Sun–since it will swell up to become a red giant in the process of dying. The oceans will boil away. What ever is left could be a cinder. I say “could” because it’s possible that the Sun’s stellar wind will be very strong, which could cause the orbits of the planets to drift outwards. So, our planet might escape the fiery death part–at least for a while.

How does star death for the Sun happen? Look at what the Sun does. It goes about its daily business of turning hydrogen into helium in its core. It has been doing this for billions of years, like all stars do. The heat and pressure of the burning in this nuclear furnace is enough to keep the outer layers of the Sun from collapsing in. This is what’s happening now–the Sun we enjoy is in equilibrium–meaning the heat and pressures in the core balance the gravitational tendencies of the outer layers to want to fall in to the center.

But, in a few billion years, our star will start to run out of hydrogen in its core and lose the core pressure that holds up the other layers.  At that point, all they will collapse under the pull of gravity, and what’s left of the hydrogen will heat up. Fusion (the hydrogen-to-helium process) will resume. This time, however, the outer layers–particularly the outer atmosphere–will swell up a few hundred times larger and be cooler and redder than the Sun we know today.

At that point, our lovely yellow star will become a red giant. And, in that swelling, it will likely smother the inner planets. If the dying Sun has a strong-enough and mass-loaded stellar wind, that could push the planets out a bit, and that’s where astronomers speculate the Earth could escape being turned into a crispy planetary critter.  It’s hard to tell at this point what would really happen, but the ultimate fate of Earth and the inner planets isn’t going to be like we know it today.

So, that’s the answer to the question, “What will happen when the Sun dies?”  It’s a stellar process that occurs throughout the universe, and we understand more about it by studying the planetary nebulae whose remains chart the future of our own star.

geodesium, planetary nebulae, space imagery, space music, star death, supernova

A Haunting Gallery of Destruction

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The Deaths of Stars

This HST mosaic image of the Crab Nebula shows a six-light-year-wide expanding remnant of a supernova explosion. Courtesy STScI.

Stardeath produces some of the most intricate-looking objects in astronomy. If you have ever gone to the Hubble Space Telescope’s Web site and searched for planetary nebulae, you know what I mean. Giant stars produce giant explosions, like the long-known Crab Nebula.

The Eskimo Nebula (NGC 2392). The intricate "face" is a bubble of material being blown into space by the central star's intense "wind". Courtesy STScI.

This Hubble Space Telescope image shows us what the supernova remnant is made of (hydrogen gas, particles of heavier elements), and also shows us the structure of the nebula and how it’s influenced by the neutron star at the center. That neutron star is what’s left of the original star — a dense object spinning more than 30 times per second.

Stars like the Sun go a bit less violently, huffing off their atmospheres for millions of years before collapsing to make white dwarfs. The radiation from the central star continues to light up the remains of the former star, creating complicated visions of stellar death. The Eskimo Nebula (right), is a fine example of such a sun-like star’s death. The remains are called a planetary nebula, one of those odd misnomers in astronomy that has nothing to do with a planet, but is a nebula. This sunlike star began to die some 10,000 years ago, blowing bubbles of gas out away from itself and flinging its outer atmosphere to space. Our own Sun might look like this some billions of years from now.

Well, I’ve been long fascinated with the images of star death, ever since I wrote my first book (with Jack Brandt), about Hubble Space Telescope science (called Hubble Vision).  A few years ago when I did an update of one of my more-popular planetarium shows, called Hubble Vision 2, I had a great selection of star death images to choose from to tell the story of stellar demise. I wrote about sun-like stars, “Hubble’s images of these stars in their death throes comprise a haunting gallery of destruction.”

As is always the case with my shows, I knew that the soundtrack artist (who also happens to be my husband and co-producer) would find a way to make the scene  memorable with his trademark space music and video choreography. The scene in the show is a solemn, beautiful procession of planetary nebula images that bring home to audiences the majesty of a star’s passing.

Fast-forward a few years to this month, and Mark has now released the music from that show soundtrack in an album called Geodesium Stella Novus (where you can preview and buy the album if you’re interested). And, he created a music video based on that planetary nebula scene that really does bring home the majesty of that haunting gallery of destruction we first introduced in the show. We created a fulldome version of the music video, which you might get to see someday at your local digital planetarium.

But, we’ve also got a “flat-screen” version available on our Youtube channel for people to watch and I’ve embedded it below.  The piece of music is called “Light Echoes”, and it accompanies these gorgeous views of star death, ranging from supernova remnants to planetary nebula, as cosmic art.  It’s not a new concept — the universe as art. But, you have to admit, when you see the way nature has arranged the aftermath of stardeath, it can look evocative, haunting… and artistic!