Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 31/01/2008 00:02:31

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: neilep on 31/01/2008 00:02:31

Dear Galaxy Gladiators,

D'ya like my Galaxy ?


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Nice !!...it's being delivered next Tuesday !.. it even comes with it's own waste-disposal unit....a Super Massive Black Hole right in the middle of it !

Did you know (preaching to all here)...that surprisingly/astonishingly/amazingly in the last few years it has been discovered that massive and super massive black holes exist wham-bam in the middle of all galaxies (please correct me if I am wrong Ian)....even our own !!

Now then....it seems that it's kinda strange that the mass of these black holes equates to half a percent of the galaxy that surrounds it !!

Why's that then ?...how does such a correlation exist ?

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: Saganist on 31/01/2008 06:40:25

Hi nielep,

Because they've only had time to gobble up 1/2% of their galaxies' matter?

Are you saying that this percentage is shared by all galaxies or spiral galaxies?


Cheers.

Saganist

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: DoctorBeaver on 31/01/2008 08:02:31

I was watching a program the other night about SMBH and it was stated on that about a correlation between the mass of the BH and the size of the galaxy; but I don't remember them giving a ratio. It's possible I missed it as I was writing some code for Beaverland at the time.

Just a thought - if BHs preceded galaxy formation and the other matter in the universe was fairly evenly spread out, then the mass of the BH would determine the range of its gravitational attraction, so a bigger BH would attract more matter. That matter would coalesce into the stars of the galaxy and, hence, a more massive BH would cause a larger galaxy to form.

I don't know enough about galaxy evolution to know whether that's a feasible explanation.

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: neilep on 01/02/2008 02:25:08

Quote from: Saganist on 31/01/2008 06:40:25

Hi nielep,

Because they've only had time to gobble up 1/2% of their galaxies' matter?

Are you saying that this percentage is shared by all galaxies or spiral galaxies?


Cheers.

Saganist

Hi Saganist.

Thank You for your reply.

It seems (from what I can recall) that this percentage is shared by all galaxies !...As the Doc is referring to above it kind of goes like this.

Lots of swirly gassy stuff swirling around being busy swirly stuff !..the central portion of the swirly stuff becomes so dense that it creates a Black hole..and a big old muva of one too! (our one in the middle of the Milky Way having two million times more mass than our own Sun)...anyway...after Super massive Black Hole is born it goes on a feeding frenzy and by doing so actually starts to throw stuff our farther away..this eventually leads to the cessation of the feeding frenzy...Stars then form and then you have a galaxy !..VOILA !!....boiling an egg is more complicated !! [;)]....but I am still not sure why (and as I said I need corroboration here)....the big black hole always seems to equate to 1/2percent the mass of the entire galaxy !!

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: DoctorBeaver on 01/02/2008 07:51:15

Quote from: neilep on 01/02/2008 02:25:08

...but I am still not sure why (and as I said I need corroboration here)....the big black hole always seems to equate to 1/2percent the mass of the entire galaxy !!

If, as I speculated, the matter was fairly evenly distributed, then it could be that, whatever the mass of the BH, 1/2% is the amount of that matter that is close enough to be gobbled up.

As I said, the more massive the BH, the larger its gravitational field. Therefore it can not only gobble up more matter, but matter further away will be influenced by its gravitational field and form into its galaxy. So, the bigger the BH, the bigger the galaxy that forms, and the 1/2% becomes a larger amount even though the percentage remains the same.

QED  [^]

Title: But why 1/2 percent ? (relationship between black holes and galaxies)
Post by: neilep on 01/02/2008 14:03:28

Quote from: DoctorBeaver on 01/02/2008 07:51:15

Quote from: neilep on 01/02/2008 02:25:08

...but I am still not sure why (and as I said I need corroboration here)....the big black hole always seems to equate to 1/2percent the mass of the entire galaxy !!

If, as I speculated, the matter was fairly evenly distributed, then it could be that, whatever the mass of the BH, 1/2% is the amount of that matter that is close enough to be gobbled up.

As I said, the more massive the BH, the larger its gravitational field. Therefore it can not only gobble up more matter, but matter further away will be influenced by its gravitational field and form into its galaxy. So, the bigger the BH, the bigger the galaxy that forms, and the 1/2% becomes a larger amount even though the percentage remains the same.

QED  [^]

All Hail !!

Yes, yes you have indeed afforded us the benefit of your postural speculations. For this I applaud and display to you such reverence that you deserve. [ Invalid Attachment ]  [;D]

I imagine SMBD's are even more daunting !! (Super Massive Beaver Dams)