Van rode naar witte dwerg

[Robbe]

<img src="http://upload.userbase.be/upload/tn_mira_bowshock.jpg" align="left"> In the constellation of Cetus, the whale, is what appears to be a run of the mill red star. At a distance of about 400 light years, the fact that you can see it with your unaided eye at all means it’s an intrinsically luminous star: at that distance the Sun would be completely invisible.

The star is a red giant, a star that was once much like the Sun but is now terminally ill. Stars make energy in their core through the fusion of light elements into heavier ones; the Sun is currently fusing hydrogen into helium. Eventually it will run out of hydrogen, and will begin to fuse helium into carbon and oxygen. In 7 billion years or so the helium in the core will run out as well. The carbon and oxygen ash from the process will form a ball about the size of the Earth. It will contract and get incredibly hot. Helium outside the core, previously unavailable for fusion (like having a spare can of gasoline in the trunk of your car) will start to fuse in a thin shell surrounding the core. This will dump vast amounts of heat into the outer part of the Sun, which will respond like any gas will when heated: it will expand and cool.

The Sun will become a red giant. But thin shell helium fusion is unstable, and so a red giant can expand and contract, sometimes almost in a spasm, ejecting material off its surface, and briefly becoming very luminous before settling down again. This will happen three or four times for the Sun, and it will totally eject its outer layers, exposing the hot core to space*. When this is all done, the Sun will be a white dwarf, and will slowly cool for the next few hundred billion years.

The image at the top shows a star that is undergoing this process right now. Called Mira — "wonderful" — it’s slightly more massive than the Sun, and far older. It has only a short time left — maybe only hundreds of thousands of years, maybe less — before its paroxysms slough off that last bit of outer layer, and it becomes a white dwarf. These spasms change its luminosity, and we see this as a brightening and dimming of the star; it’s sometimes too faint to see with the unaided eye, and other times can brighten considerably.

Mira has long been studied by astronomers to give us insight on what will happen when the Sun dies. Observations have revealed the star isn’t round: that makes sense, since it is ejecting huge amounts of material in expanding clouds. It has a small companion, a more normal star that appears to be collecting some of the ejected material and forming it into a disk around itself.

Mira is definitely wonderful, in the sense of evoking wonder. And now we have found out it’s even more amazing than we thought. Most stars near the Sun orbit the center of the Galaxy at roughly the same speed, but some are faster than others. Mira, it so happens, is plowing through this local region of space at about 130 kilometers per second (about 80 miles per second). There is gas and dust out there, a thin haze floating among the stars. As Mira screams through this fog, the gas it is ejecting as it convulses is blown backwards, leaving a long tail behind it — imagine running down the street with a smoke bomb in your hand and you’ll get the idea.

Meer bij de bron : BadAstronomy.com (vertaling via babelfish)

[Draco888]

Ik vind zulke zaken steeds en interessant en prachtig.
Wou dat er wat grotere resolutie foto's waren van dit en andere kosmologische fenomenen, want hier is duidelijk life = art.

[Robbe]

Heb wat rondgeneusd ..
White Dwarf Star Spiral, Image of the day gallery, visible earth en deze "frisse ster" (grotere versie).

[Blue-Sky]

Hier 'n link van Jan 15, 2007 (klik het image links boven)

Dank zij 'n beetje speurwerk mooie images om kalender uit te printen.
(best niet de hoogste resolutie, wegens het volume)

http://www.userbase.be/forum/viewtopic. ... 133#141133