One of the often-asked questions astronomers get is “What will happen when the Sun dies?” It’s an obvious concern, since whatever happens to the Sun will affect Earth, but it’s not an immediate concern. The death of the Sun isn’t going to happen for another few billion years yet, so we don’t have to worry about facing it grow larger during its red giant stage and then shrink down to become a tiny ghost of its former brilliance. Many, many generations of humans will live and die on our planet before future astronomers will start to detect the first instabilities that indicate the Sun’s upcoming demise.
There are stars like the Sun out there in space that have already gone through the death process, and so astronomers study them to understand what our star will look like when it finally gets down to the serious business of stardeath. One of the objects they have studied quite a bit is called the Helix Nebula.
ESO’s VISTA telescope, at the Paranal Observatory in Chile, has captured a striking new image of the Helix Nebula. This picture, taken in infrared light, reveals strands of cold nebular gas that are invisible in images taken in visible light, as well as bringing to light a rich background of stars and galaxies.
The Helix was created as a Sun-like star reached the final stages of its life. It began to lose its outer layers of gas, which you can see in the image above as they expand into space. What’s left of the star appears as a tiny blue dot at the center of shell of material surrounding it. That ring spreads out over an area about four light-years across (almost the distance between the Sun and the nearest star in the Alpha Centauri system. This infrared view shows the extent of the gas cloud.
The nebula is made up of of dust, ionized material and molecular gas. it’s all being heated up by ultraviolet light streaming out from the central star (which is very hot). Notice the details in the cloud—there are clumpy, comet-shaped objects called cometary knots. They aren’t really comets, but they look similar to comets with their tails blowing out in the solar wind. In this case, the knots are strands of molecular hydrogen being shaped by the flow of high-energy radiation streaming out from the dying star. Even though they look small, each is about the size of our solar system.
This, in a nutshell (or a gas shell) is about how our Sun will look billions of years from now. Perhaps our descendants will watch it all unfold from a planet around neighboring star, and take similar pictures with their orbiting space telescopes.
Want to know more about this image. Check out the European Southern Observatory site for more details and an array of downloadable images.
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.
