A Dying Star

8 May

Our Sun

No, I’m not posting about Hollywood. I’m talking about an actual star. A star that is (or was) a lot like our Sun.

Astronomers spend a lot of time searching the cosmos for stars that are like our own, in hopes of being able to better understand how ours is working. You see, not all stars are created equal. Some are larger or smaller, some burn hotter or cooler, some will exhaust their fuel supplies over hundreds of millions of years, and others will burn for several billion years.

Without getting too technical, our Sun is on the larger and brighter end of the spectrum, though it is nowhere near as massive as some other stars in our stellar neighbourhood.

It is important to understand though that the Sun is not massive enough to trigger a Supernova explosion when its life ends in 4 or 5 billion years. Only the biggest stars end their lives so dramatically.

Why? Again, without being technical about it, as a massive star dies the outer layers of the star collapse in towards the core. These outer layers tend to be made of lighter elements, and so they essentially ‘bounce’ off the core and explode out into space. That’s what we call a Supernova.

Our Sun doesn’t have enough mass/gravity at it’s core to trigger a Supernova. The outer layers/lighter elements will not be drawn back towards the core as the Sun dies, and so they won’t have the opportunity to bounce/explode. Instead the Sun will slowly expand and cool, and will create a sort of planetary nebula (a cloud of reasonably hot gas and dust). Eventually the dust will clear, and just the core of the sun will remain. A very small, dense object, called a White Dwarf. And of course remember: this process takes millions of years, and won’t start for another ~4 billion years.

That takes us to this image:

A star that was like our own is in the planetary nebula stage of it’s life. Seeing this is exceptionally rare and important, as it helps us to better understand how own star will live its life.

Here is the description of that image from NASA:

Within the Realm of a Dying Star

The NASA/ESA Hubble Space Telescope has been on the forefront of research into the lives of stars like our sun. At the ends of their lives, these stars run out of nuclear fuel in a phase that is called the preplanetary or protoplanetary nebula stage. This Hubble image of the Egg Nebula shows one of the best views to date of this brief, but dramatic, phase in a star’s life.

During the preplanetary nebula phase, the hot remains of an aging star in the center of the nebula heat it up, excite the gas and make it glow over several thousand years. The short lifespan of preplanetary nebulae means there are relatively few of them in existence at any one time. Moreover, they are very dim, requiring powerful telescopes to be seen. This combination of rarity and faintness means they were only discovered comparatively recently. The Egg Nebula, the first to be discovered, was first spotted less than 40 years ago, and many aspects of this class of object remain shrouded in mystery.

At the center of this image, and hidden in a thick cloud of dust, is the nebula’s central star. While scientists can’t see the star directly, four searchlight beams of light coming from it shine out through the nebula. Researchers hypothesize that ring-shaped holes in the thick cocoon of dust, carved by jets coming from the star, let the beams of light emerge through the otherwise opaque cloud. The precise mechanism by which stellar jets produce these holes is not known, but one explanation is that a binary star system, rather than a single star, exists at the center of the nebula.

The onion-like layered structure of the more diffuse cloud surrounding the central cocoon is caused by periodic bursts of material being ejected from the dying star. The bursts typically occur every few hundred years.

This image is produced from exposures in visible and infrared light from Hubble’s Wide Field Camera 3.”

(source: http://www.nasa.gov/multimedia/imagegallery/image_feature_2235.html)

Science is awesome.


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