by Ann » Thu May 18, 2017 11:39 pm
douglas wrote:
I really "need" to understand how central black holes can cause such uniform extent of illumination.
Elliptical galaxies can form in different ways, and it is true that black holes can be involved. Typically, however, when black holes inhibit star formation, they have jets that inject enormous energy into their interstellar medium (make that, their gas and dust), and this gas and dust becomes far too hot to be able to form any new stars. In order to form new stars, pockets of gas must cool, shrink in size and become ever more concentrated. Hot, turbulent gas generally can't form any new stars.
These nuclear jets form as matter is fed into a supermassive black hole in the center of the galaxy. Since the physical size of the black hole is small, even for supermassive black holes, it can't swallow huge amounts of matter in one go. Instead, inspiralling matter forms an accretion disk around the black hole, which generates enormous amounts of heat and light. Also magnetic lines get trapped and "wound up" in the accretion disk, eventually leading to a jet shooting out from the black hole at the same time as the black hole is ingesting matter. See
this video for a simulation of what is happening.
A huge jet can affect not only the galaxy where the jet was formed, but it can actually affect nearby galaxies too, stirring up their gas and dust too and making those galaxies, too, unsuitable for star formation.
When no new stars are formed, the existing stars age. Hot, massive, blue stars die first, then intermediate stars like Sirius and Vega die, then the "high-end mass of low-mass stars" like the Sun die. It takes about 10-12 billion years. But the tremendous amounts of small red dwarf stars don't die for trillions of years. Not a single small red dwarf that has ever formed in the universe has died of old age.
As the bright blue stars die, and the intermediate stars die, and the Sun-like stars die, only red dwarf stars (and some evolved red giants) remain, orbiting the center of the galaxy like a swarm of bees. (Well, it seems certain that practically all elliptical galaxies still have some Sun-like stars in them, because Sun-like stars live for 10-12 billion years, and the universe is only about 14 billion years old. Not all Sun-like stars have had time to die in elliptical galaxies.)
As interactions with other galaxies have stirred up and destroyed the dust lane of the galaxy, no visible structure remains, only the bee-swarm of mostly old red stars buzzing around the center of the galaxy, with its supermassive black hole.
Watch this youtube video to see a simulation of what will happen when the Milky Way and the Andromeda galaxy collide and give rise to an elliptical galaxy.
Click to play embedded YouTube video.
Ann
[quote]douglas wrote:
I really "need" to understand how central black holes can cause such uniform extent of illumination.[/quote]
[float=left][img2]https://apod.nasa.gov/apod/image/0007/m87jet_hst_big.jpg[/img2][/float]Elliptical galaxies can form in different ways, and it is true that black holes can be involved. Typically, however, when black holes inhibit star formation, they have jets that inject enormous energy into their interstellar medium (make that, their gas and dust), and this gas and dust becomes far too hot to be able to form any new stars. In order to form new stars, pockets of gas must cool, shrink in size and become ever more concentrated. Hot, turbulent gas generally can't form any new stars.
These nuclear jets form as matter is fed into a supermassive black hole in the center of the galaxy. Since the physical size of the black hole is small, even for supermassive black holes, it can't swallow huge amounts of matter in one go. Instead, inspiralling matter forms an accretion disk around the black hole, which generates enormous amounts of heat and light. Also magnetic lines get trapped and "wound up" in the accretion disk, eventually leading to a jet shooting out from the black hole at the same time as the black hole is ingesting matter. See [url=https://www.youtube.com/watch?v=71_1_otAhwA]this video[/url] for a simulation of what is happening.
A huge jet can affect not only the galaxy where the jet was formed, but it can actually affect nearby galaxies too, stirring up their gas and dust too and making those galaxies, too, unsuitable for star formation.
When no new stars are formed, the existing stars age. Hot, massive, blue stars die first, then intermediate stars like Sirius and Vega die, then the "high-end mass of low-mass stars" like the Sun die. It takes about 10-12 billion years. But the tremendous amounts of small red dwarf stars don't die for trillions of years. Not a single small red dwarf that has ever formed in the universe has died of old age.
As the bright blue stars die, and the intermediate stars die, and the Sun-like stars die, only red dwarf stars (and some evolved red giants) remain, orbiting the center of the galaxy like a swarm of bees. (Well, it seems certain that practically all elliptical galaxies still have some Sun-like stars in them, because Sun-like stars live for 10-12 billion years, and the universe is only about 14 billion years old. Not all Sun-like stars have had time to die in elliptical galaxies.)
As interactions with other galaxies have stirred up and destroyed the dust lane of the galaxy, no visible structure remains, only the bee-swarm of mostly old red stars buzzing around the center of the galaxy, with its supermassive black hole.
Watch this youtube video to see a simulation of what will happen when the Milky Way and the Andromeda galaxy collide and give rise to an elliptical galaxy.
[youtube]https://www.youtube.com/watch?v=Jsqh-kNMxoM[/youtube]
Ann