| | Today I learned something new I had never heard of before in all my following of astronomical discoveries. At the Universe Today blog, where I check all and read most posts, there was a general interest item entitled "What Is The Biggest Thing in The Universe?". Normally I don't bother with items of this type as they usually just rehash well-known facts in a novice-friendly format. |
Today, something made me have a look. As is common with astrophysics, the answer was "it depends...." on what you define as a thing: "Consider the regions around supermassive black holes. Within our own galaxy, things are pretty quiet, but around actively feeding black holes, there can be disks of material with such temperature and density that they act like the core of a star, fusing hydrogen into helium. Which, purely based on high volumetric density of pure awesome, I’m going to call a thing. An accretion disk around a quasar could be light days across, extending well past the orbit of Pluto and killing us all, if you dumped it in our Solar System."
That is pretty big, however what struck me was the statement "...around actively feeding black holes, there can be disks of material with such temperature and density that they act like the core of a star, fusing hydrogen into helium."
That is pretty big, however what struck me was the statement "...around actively feeding black holes, there can be disks of material with such temperature and density that they act like the core of a star, fusing hydrogen into helium."
Now, supermassive black holes I already thought were pretty awesome "things" in themselves. They contain as much matter as from hundreds of thousands to a BILLION suns, and the sun is already awesomely big at close to 2 x 10^30 kg (That's 2 THOUSAND BILLION BILLION BILLION kg!).
These objects are believed to exist at the centre of most galaxies, where their high gravity attracts dust, gas, and even whole stars into a rotating region of matter falling into them. This flattened region is known as an accretion disc.
This I knew, and I think it is known to many of the general public as well. What is new to me is that the density and temperature of the disc itself can be such that it is like a smeared-out star-stuff region, and could play a star-ring role in metal formation in the universe. (Excuse my pun!)
In case you are not familiar with Metallicity : -
First, astronomers call all elements heavier than hydrogen "metals".
Second, it is believed the original Big Bang would have produced almost entirely hydrogen, and "... all of the elements that are heavier than lithium and beryllium were created much later, by stellar nucleosynthesis in evolving and exploding stars." (Wikipedia, note that accretion discs are not mentioned.)
The whole concept of nucleosynthesis around black holes intrigued me, but a little digging has revealed that the concept is not new.
I found: -
1987 "Nucleosynthesis inside thick accretion disks around black holes. I - thermodynamic conditions and preliminary analysis"
2000 "Nucleosynthesis in accretion flows around black holes" This mentions metal formation: - " ...could be contributing to the metallicities of the galaxies."
2010 "Nucleosynthesis from Black Hole Accretion Disks" Ref. the summary: - "Black hole accretion disks make a lot of nickel, and likely some other rare elements"
I don't claim to have the mathematical skills to follow the above papers, but anyone can gather enough from the text to see what they cover.
I hope I have given some insight into this subject,
which I found both novel and intriguing.
These objects are believed to exist at the centre of most galaxies, where their high gravity attracts dust, gas, and even whole stars into a rotating region of matter falling into them. This flattened region is known as an accretion disc.
This I knew, and I think it is known to many of the general public as well. What is new to me is that the density and temperature of the disc itself can be such that it is like a smeared-out star-stuff region, and could play a star-ring role in metal formation in the universe. (Excuse my pun!)
In case you are not familiar with Metallicity : -
First, astronomers call all elements heavier than hydrogen "metals".
Second, it is believed the original Big Bang would have produced almost entirely hydrogen, and "... all of the elements that are heavier than lithium and beryllium were created much later, by stellar nucleosynthesis in evolving and exploding stars." (Wikipedia, note that accretion discs are not mentioned.)
The whole concept of nucleosynthesis around black holes intrigued me, but a little digging has revealed that the concept is not new.
I found: -
1987 "Nucleosynthesis inside thick accretion disks around black holes. I - thermodynamic conditions and preliminary analysis"
2000 "Nucleosynthesis in accretion flows around black holes" This mentions metal formation: - " ...could be contributing to the metallicities of the galaxies."
2010 "Nucleosynthesis from Black Hole Accretion Disks" Ref. the summary: - "Black hole accretion disks make a lot of nickel, and likely some other rare elements"
I don't claim to have the mathematical skills to follow the above papers, but anyone can gather enough from the text to see what they cover.
I hope I have given some insight into this subject,
which I found both novel and intriguing.
| | Woodstock by Joni Mitchell I came upon a child of God He was walking along the road And I asked him where are you going And this he told me I'm going on down to Yasgur's farm * I'm going to join in a rock 'n' roll band I'm going to camp out on the land I'm going to try an' get my soul free We are stardust We are golden And we've got to get ourselves Back to the garden Then can I walk beside you I have come here to lose the smog And I feel to be a cog in something turning Well maybe it is just the time of year Or maybe it's the time of man I don't know who I am But you know life is for learning We are stardust We are golden And we've got to get ourselves Back to the garden By the time we got to Woodstock We were half a million strong And everywhere there was song and celebration And I dreamed I saw the bombers Riding shotgun in the sky And they were turning into butterflies Above our nation We are stardust Billion year old carbon We are golden Caught in the devil's bargain And we've got to get ourselves back to the garden |
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