Category Archives: sun

The Boiling Sun

Living with a star, our Sun, is something we do every day. Of course, most of us just bask in the sunlight when it’s available. But, for solar physicists, the astronomers who study the Sun, our star presents a great opportunity to delve deeper into what makes it tick. Or, in the case of some recently released images and vids, what makes it look like a boiling Sun.

The Daniel K. Inouye Solar Telescope on the Hawaiian island of Maui is the latest giant telescope to turn its high-resolution instruments to look at our Sun. The video below shows a view of the Sun that we’d never see if we were to travel to it. But, the telescope is sensitive to light beyond the spectrum that we can see (which is a range between 400 and 700 nanometers). This view is of light that radiates at 705 nanometers, so just beyond what we can see.

Why a Boiling Sun?

What’s happening here? Well, we know the Sun is hot at its core, where it’s more than 15 million degrees! That heat travels out from the center and is released at the surface, called the chromosphere. There, we see a turbulent motion in the gases that make up the Sun’s atmosphere. That action is what makes it look like a boiling Sun in the video.

Those cells of superhot gases are a cooling mechanism. They bring the heat up from beneath the solar surface and then release it. It’s the way our star sends heat out to the rest of the solar system. Watch the video for a short bit and it might remind you of boiling fudge, or syrup on the stove. Those also operate under the same principle of heat “release”.

On the Sun, the heat rises up from this region into space through the outer layers of the Sun’s atmosphere. Temperatures there are about 6,000 C (10,800 F). A funny thing happens above the surface—the heat steadily rises until it’s more than a million degrees in the uppermost region called the corona. Solar scientists are busily figuring out why this superheating happens, and they know that solar magnetic fields are somehow involved.

The interesting thing about this video (and the images from DIST) is that these are the sharpest images of the boiling surface of the Sun ever taken. And, they were taken from Earth! Want to know more about this telescope and see additional images? Check out their website here.

The End of Sun-like Stars

Planetary Nebulae

Several times a year I go out and give public talks about astronomy and one of the questions I get a lot is, “What will happen to the Sun?”  Sometimes people have this idea that the Sun will blow up in a huge explosion and overtake Earth. Others worry about something hitting the Sun and causing it to do something.  Actually, things DO hit the Sun— comets do this, for example. But so far, none has made a difference in how the Sun behaves.

This intriguing new picture from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star located about 3300 light-years away in the constellation of Scutum (The Shield). This is the most detailed picture of this object ever taken.
This intriguing new picture from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star located about 3300 light-years away in the constellation of Scutum (The Shield). This is the most detailed picture of this object ever taken.

What DOES make a difference in how the Sun (and other stars) acts are age and mass. Stars with masses ranging from one solar mass to about 8 solar masses have fairly quiet deaths — that is, they don’t blow up in titanic explosions so much as they just “puff out” their outer atmospheres to space and then fade away.

The Sun is the one we care the most about. It is about 4.6 billion years old and it will likely live another four billion years before it starts to age and die. That aging process is of great interest to astronomers and so they study other stars as they die to see how the Sun will do it. The Sun and stars like it (similar in mass and luminosity) shine for billions of years before they hit retirement age and start to swell up.

As they do this, their atmospheres get “huffed off” by a stellar wind similar to our solar wind. It’s almost as if the star is gently sneezing its outer layers to space. This takes a while — and all that material eventually ends up in a cloud of gas and dust that surrounds the cloud. That cloud (with the dying star at the center) is what’s called a “planetary nebula”. The name was bestowed by William Herschel, who thought they looked similar to a distant gas giant planet.  There’s nothing planetary about these things — they’re really stars like the Sun moving through an important step in the aging and death process. 

Planetary nebulae come in many different shapes.  This image comes from the European Southern Observatory’s Very Large Telescope. It’s of a nebula called IC 1295, and since the image is such high resolution, you can actually make out multiple shells of material surrounding the dying star. This implies the atmosphere blew out in episodes as the star’s faltering core emitted sudden bursts of energy.

The gas surrounding the dying star (which is the small blue-white spot in the heart of the nebula next to a reddish spot) is bathed in strong ultraviolet radiation from the aging star, which makes the gas glow. Different chemical elements glow with different colors, and the green color you see here comes from ionized oxygen (that is, oxygen gas heated by radiation from the central star and is now emitting greenish light).

This cloud won’t last forever. In a few tens of thousands of years, the clouds will slowly dissipate. Eventually only the remains of the star will be left behind as a white dwarf.  It will continue to shrink a bit longer, but eventually that will stop and the white dwarf will continue to cool for billions of years. I read somewhere that in the entire history of the universe, not one white dwarf has yet cooled to completion. There hasn’t been time in the 13.8-billion-year age of the cosmos for them do that.

So, that’s the fate of the Sun in general. It won’t blow up as a supernova (because it doesn’t have the mass to do so). It will gently (for a star) sigh its life away. Hopefully by that time, humanity will have found other worlds to live on.