Pulsating Red Giants Hide Inside Deceptive Shells

[zavvy]

<b>Pulsating Red Giants Hide Inside Deceptive Shells</b><br /><br />LINK<br /><br />An optical illusion has caused astronomers to overestimate the size of a class of giant stars by a factor of two, according to new observations. The revised size measurements are likely to clear up some mysteries about the strange objects, while deepening others.<br /><br />Pulsating red giants – called Mira variable stars – have long fascinated astronomers. They brighten and dim by a thousand times or more over periods of 100 to 1000 days. Mira stars are of particular interest as they began life about the same size as the Sun.<br /><br />However, by the time they become pulsating red giants – between 5 billion and 10 billion years of age – their diameter has grown hundreds of times greater. In another 5 billion years, the Sun will go through a similarly bloated phase.<br /><br />But gauging the sizes of even such large stars is difficult, as they still look like points of light through telescopes. And Mira stars appear to be different sizes depending on which wavelength of light is used to observe them, looking larger in visible light, for example, and smaller at near-infrared wavelengths.<br /><br /><br />Vapour shells <br /><br /><br />Previous observations have also revealed the relatively cool stars to be shrouded in extended cocoons of water, carbon monoxide, and other molecules.<br /><br />Now, an international team of astronomers has studied six nearby Mira stars using an array of linked infrared telescopes in Mount Hopkins, Arizona. They say that Mira stars are half the size they were thought to be because their vapour shells make them look deceptively large.<br /><br />Though titanium oxide - a molecule found in the white pigment of sunscreens - makes the shells look opaque in visible light, the shells were transparent to the Infrared-Optical Telescope Array (IOTA) used by the team.<br /><br />They peered through

 

[kelle]

It was an article about this on space.com recently too, kind of interesting. But where does all the water come from??

 

[Maddad]

Water is composed of hydrogen and oxygen. There is plenty of hydrogen. Both stars and interstellar gas is about 75% hydrogen. The question is where does the oxygen come from. It's manufactured in star cores after they go off main sequence, but before they burn out. When helium fuses, the resulting ash is oxygen. This collects in the core and in atmospheric shells about a Red Giant star, one that is past main sequence. This star will return up to about 50% of it's material to the interstellar medium as a planetary nebula. Additionally, a more massive star will detonate as a supernova after it runs out of fuel. In the process it makes all the heavier natural elements. It should make at least some oxygen, and much of this material is also returned to the interstellar medium. The result is that oxygen seeds the gas clouds between the stars along with the hydrogen that was already there.<br /><br />The amounts of water produced as hydrogen and oxygen combine in space is staggering. The Orion Nebula makes enough water to replinish all the Earth's oceans ever twenty minutes.

 

[Maddad]

Note: Oxygen is not a direct ash of helium fusion. There is an intermediate step in which carbon ash from the helium fuses into neon and oxygen.

 

[kelle]

<font color="yellow">Note: Oxygen is not a direct ash of helium fusion. There is an intermediate step in which carbon ash from the helium fuses into neon and oxygen.</font><br /><br />Doesn't the helium first fuse into beryllium, which then fuses into carbon and oxygen?<br /><br /><font color="yellow">The amounts of water produced as hydrogen and oxygen combine in space is staggering. The Orion Nebula makes enough water to replinish all the Earth's oceans ever twenty minutes.</font><br /><br />Wow...

 

[Maddad]

kelle<br />I'd have to look it up to be sure, and I'm short on time today. If I see this tomorrow I'll find a good web page describing the processes. Maybe one of the others here can do the leg work for us. It's always good to get fresh input so it's not all coming from one or a very few people.