I am intrigued by this article on the Orion nebula.
How dense are these gases? What area of space is occupied by them? What is the distance across the gas cloud?
http://adsabs.harvard.edu/full/1955ApJ...122..235O
Tl;dr: density so low that it makes the inside of a light bulb seem breathable in comparison.
The pressure of the gas in a light bulb is about 0.7 atmospheres, so it practically IS breathable pressure. The best vacuum achieved on Earth is about 10^-15 atm. I can’t find a number specifically about the Orion nebula, but gas pressure in nebulae typically ranges from about 10^-19 atm to 10^-17 atm (100 to 10,000 particles per cc), so nebula gas is a far better vacuum than anything achieved by humans.
Thanks. Through what distance does the gas occur to be visible to the telescope?
I can’t figure out what you mean by that question.
If the gas is so thinly dispersed, why can the telescope see it? Is it looking through a cloud of gas that is very large? Is it miles across and deep, or is it light years?
It may be diffuse, but you’re looking at a cloud light-years thick.
The size of the Orion nebula is measured in light-years – roughly about 24 ly across. It can be seen because of various physical effects, some of them photon-emitting electron transitions to lower energy levels in hydrogen and other gases, others due to radiation from the stars within it.
On that last point, one may wonder why an enormous cloud of gas doesn’t collapse due to its own gravitational attraction. I believe the answer is that this thing is so incredibly huge, and non-homogenous, that the gas is indeed collapsing, but it’s doing so in isolated clumps, thus forming stars, many of them extremely massive. The Orion nebula has been called a “star nursery”. Within it have been observed not only young stars and protostars, but stars surrounded by protoplanetary disks, such as the one that formed our solar system.
This brings up an interesting question of scale. If the gas of our sun was spread out as thinly as a nebula, how big would it be?
I’m on my phone atm but if no one crunches the numbers before I get a chance to it should just be some cross multiplication
You can get a good idea from the following two numbers: the nebula is about 24 ly across, and its total mass is about 2000 times that of the sun.
Thanks, wolfpup.
OR how big would the nebula be at standard pressure.
Roughly a cubic lightyear.
Note that the Orion Nebula and other HII regions[*] are not currently collapsing to form stars. They’ve already done that and the stars they formed are now emitting UV light which causes the remaining gas to glow. The nebulae that collapse are dark and cold (usually less than 10 Kelvins). The clouds are inefficient at collapsing so there’s lots of gas left over. That gas is then ionized by the UV light of the brighter stars, so it glows. But that UV light is also heating up the gas, so it won’t collapse any further.
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[*] HII (pronounced H-2; those are capital I’s, not lowercase L) is astronomy talk for ionized hydrogen.