Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_dslr_mirrorlesss.thumb.jpg.5b348d6a5e7f27bdcb79e9356b7fc03b.jpg

Manok101

One thing I've always wondered..

Recommended Posts

My thing is understanding nebulae and the one thing I've never been able to comprehend is how a massive cloud of gas condenses into a star or anything for that matter... it doesnt seem like there should be enough mass in any gas. Or is it much much denser than gasses here on earth?

Share this post


Link to post
Share on other sites

The nebulae are much less dense than gas clouds on Earth. In fact they are so tenuous that they are less dense than all but relatively recent laboratory vacuums. In most of the books I have read the density is given as less than a lab vacuum but a couple of Manchester University physicsts I know said that this is no longer true. However, M42 is not very dense!

So why do they condense? My understanding is that most of the time they don't. They are, though, very cold so their atoms are not moviing around fast enough to repel each other if they are given a nudge bringing them together. Such nudges come from events like supernova explosions sending out shockwaves or passing massive bodies attracting gas atoms towards them. Once a slightly overdense patch has formed the process is irreversible and denser patches become denser, collapsing towards their own newly formed centre of gravity. Any motion they contain (angular momentum) is conserved and, as they shrink, this 'winds up' ever faster. Soon (in astronomical terms!) you have a spinning ball of gas heating up as it becomes smaller and denser until nuclear reactions are triggered in its core. Then the outflowing radiation begins to blast a cavity in the nebula in which the star or cluster of stars were born. On the deep sky imaging board at the moment are some excellent images of the Rosette Nebula, a fine example of the above in progress.

Olly

Edited by ollypenrice

Share this post


Link to post
Share on other sites

Great description Olly - I've allways pondered this myself and feel I understand it a lot better now. Good question Manok ;)

Share this post


Link to post
Share on other sites

Thanks Olly, when it's well explained like that, we can get our

heads around it.

But can you do the same for Quantum mechanics please ;)

Cheers, Ed.

Share this post


Link to post
Share on other sites
Thanks Olly, when it's well explained like that, we can get our

heads around it.

But can you do the same for Quantum mechanics please ;)

Cheers, Ed.

On his deathbed Heisenberg (or it might have been Schroedinger??) was asked if he had any questions for God. He said, Yes, quantum mechanics and turbulent flow. I think I might get an answer on quantum mechanics...'

A lot of my friends here are paraglider pilots and I often think of this. They are relying on flows described by equations that a great physicist considered beyond the reach of God! This cannot really be a good idea...

Olly

Edited by ollypenrice

Share this post


Link to post
Share on other sites

This begs another question could there not be miniature stars? So small we don't have the capability to detect?

Share this post


Link to post
Share on other sites

i could and most probably am wrong (no degree in astrophysics) but i belive that a star has to reach a certain size (critical mass?) before the nuclear reaction starts to take place. so i think they would have to get upto a certain minimum size before it turns into a star and not just a stupidly big gas giant.

but as i say i'm no physist so all of what i just said is probably wrong, and at the best only partly right.

Share this post


Link to post
Share on other sites
i could and most probably am wrong (no degree in astrophysics) but i belive that a star has to reach a certain size (critical mass?) before the nuclear reaction starts to take place. so i think they would have to get upto a certain minimum size before it turns into a star and not just a stupidly big gas giant.

but as i say i'm no physist so all of what i just said is probably wrong, and at the best only partly right.

No, you are spot on.

Share this post


Link to post
Share on other sites

Another cause of compression of gas clouds is 'bow shock' - when one large object like a galaxy collides with another. The Tarantula Nebula is a good example of a gas cloud collapsing spectacularly because the Large Magellanic Cloud is crashing through the tenuous gas around the Milky Way.

Of course, at the beginning of the universe, gas clouds did collapse all by themselves without the help of supernovae. The collapses must have been spectacular, forming the globular clusters we admire today (and of course all the galaxies and supermassive black holes!).

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.