Black holes suffer a bad rap. Indicted by the press as gravity monsters, labeled highly secretive by astronomers, and long considered in theoretical circles as mere endpoints of cosmic evolution, these unseen objects are depicted as mysterious drains of destruction and death.
So it may seem odd to reconsider them as indispensable forces of creation.
Yet this is the bright new picture of black holes and their role in the evolution of the universe. Interviews with more than a half dozen experts presently involved in rewriting the slippery history of these elusive objects reveals black holes as galactic sculptors.
In this revised view, which still contains some highly debated facts, fuzzy paragraphs and sketchy initial chapters, black holes are shown to be fundamental forces in the development and ultimate shapes of galaxies and the distribution of stars in them. The new history also shows that a black hole is almost surely a product of the galaxy in which it resides. Neither, it seems, does much without the other.
The emerging theory has a nifty, Darwinist buzzword: co-evolution.
As a thought exercise, co-evolution has been around for less than a decade, or as much as 30 years, depending on who you ask. Many theorists never took it seriously, and no one had much evidence to support it. Only in the past six years or so has it gained steam. And only during the past three years have observations provided rock-solid support and turned co-evolution into the mainstream idea among the cognoscenti in both black hole development and galaxy formation.
"The emerging picture of co-evolving black holes and galaxies has turned our view of black holes on its head," says Meg Urry, an astronomer and professor of physics at Yale University. "Previously, black holes were seen as the endpoints of evolution, the final resting state of most or all of the matter in the universe. Now we believe black holes also play a critical role in the birth of galaxies."
The idea is particularly pertinent to explaining how massive galaxies developed in the first billion years of the universe. And it is so new that just last week theorists got what may be the first direct evidence that galaxies actually did form around the earliest black holes.
Chicken-and-egg question
Like archeologists, astronomers spend most of their careers looking back. They like to gather photons that have been traveling across time and space since well before Earth was born, some 4.5 billion years ago. Rogier Windhorst, an Arizona State University astronomer, has peered just about as deep into the past as anyone, to an era when the universe was roughly 5 percent of its present age.
Black Holes & Co-evolution: A Primer
A merger may have triggered the output of energy in this galaxy, Centaurus A.
The puzzleVery compact but bright objects called quasars, which can outshine a thousand normal galaxies, were abundant when the universe was less than 10 percent of its present age. Quasars are powered by black holes weighing more than a billion suns. How did they get so big so fast?
The front-running theoryCo-evolution holds that galaxies and supermassive black holes evolve together, each counting on the other for its ultimate heft. If true, and once fully understood, the new theory should help solve the growth puzzle.
The evidence
Early quasars appear to be surrounded by large galaxies loaded with tons of gas, which fuels star formation and feeds the black holes, a report last week suggested.
Black hole mass increases with galactic bulge mass.Near the quasars in time are other, normal galaxies that have likely just passed through a quasar phase, as seen in images released earlier this month.
Central bulges of stars in many galaxies, such as our Milky Way, are directly related to the masses of the black holes buried inside, as detailed in June of 2000. A galaxy's dimensions seem tied to its black hole's dietary habits.
Most black hole mass seems to come from direct consumption (called accretion) of gas, indicating that a black hole needs a surrounding galaxy to grow.
Dark matter is studied in part by examining hot gas clouds like this one.
The dark horseA halo of mysterious dark matter is thought to infuse the space surrounding each of the bulge-packing galaxies. The invisible gravity generator would play a crucial role in galaxy and black hole construction.
The also-ransIf co-evolution reigns, as most researchers believe, then two older (but not-dead-yet) theories are wrong: that a galaxy forms first and directs the development of a black hole; or that a black hole is generated first, providing the seed around which a galaxy can coalesce. It is also possible that different types of galaxies form by different means, and that co-evolution will only be found to describe one path to galactic adulthood.
-- Robert Roy Britt
Visit SPACE.com each Tuesday for another science feature. Archives
Earlier this month, Windhorst and a colleague, Haojing Yan, released a Hubble Space Telescope image showing the most distant "normal" galaxies ever observed.
Though stretched and distorted by the technique used to spot them (an intervening galaxy cluster was used as a "gravitational lens"), the newfound galaxies, Windhorst's team assures us, resemble our own Milky Way. They are seen as they existed more than 13 billion years ago, within 1 billion years of the Big Bang.
Practically side-by-side in time, discovered in separate observations made as part of the Sloan Digital Sky Survey, are compact but bright objects known as quasars. These galaxies-to-be shine brilliantly because, researchers believe, each has a gargantuan black hole at its core, whose mass is equal to a billion suns or more, all packed into a region perhaps smaller than our solar system.
The resulting gravity pulls in nearby gas. The material is accelerated to nearly the speed of light, superheated, and swallowed. The process is not entirely efficient, and there is a byproduct: An enormous amount of energy -- radio waves, X-rays and regular light -- hyper-illuminates the whole scene.
Quasars also seem to be surrounded by halos of dark matter, a cryptic and unseen component of all galaxies. Co-existing around and amongst all this, researchers are coming to realize, is a collapsing region of stars and gas as big or larger than our galaxy.
It was no coincidence that the announcements of the two findings -- distant quasars and normal galaxies --were made together at a meeting of the American Astronomical Society (AAS) Jan. 9. Co-evolution was on the minds of the discoverers.
Among co-evolution's significant impacts is its ability to render mostly moot a longstanding chicken-and-egg question in astronomy: Which came first, the galaxy or the black hole?
"How about both?" Windhorst asks. "You could actually have the galaxy form simultaneously around a growing black hole."
Urry, who was not involved in either finding but was asked to analyze them, explained it this way: "We believe that galaxies and quasars are very intimately connected, that in fact quasars are a phase of galaxy evolution. In our current picture, as every galaxy forms and collapses, it has a brief quasar phase."
So when a quasar goes dormant, what's left are the things we associate with a normal galaxy -- stars and gas swirling around a central and hidden pit of matter.
Quasars are cagey characters, however. (The term is short for quasi-stellar radio source; astronomers first mistook the objects for stars within our galaxy in the early 1960s.) When one is firing, its brightness can exceed a thousand normal galaxies. The quasar outshines its entire host galaxy so significantly that scientists have not been able to see what's really causing all the commotion. That veil is lifting as you read this, however, as telescopic vision extends ever backward in time and data is fed into powerful new computer models.
So it may seem odd to reconsider them as indispensable forces of creation.
Yet this is the bright new picture of black holes and their role in the evolution of the universe. Interviews with more than a half dozen experts presently involved in rewriting the slippery history of these elusive objects reveals black holes as galactic sculptors.
In this revised view, which still contains some highly debated facts, fuzzy paragraphs and sketchy initial chapters, black holes are shown to be fundamental forces in the development and ultimate shapes of galaxies and the distribution of stars in them. The new history also shows that a black hole is almost surely a product of the galaxy in which it resides. Neither, it seems, does much without the other.
The emerging theory has a nifty, Darwinist buzzword: co-evolution.
As a thought exercise, co-evolution has been around for less than a decade, or as much as 30 years, depending on who you ask. Many theorists never took it seriously, and no one had much evidence to support it. Only in the past six years or so has it gained steam. And only during the past three years have observations provided rock-solid support and turned co-evolution into the mainstream idea among the cognoscenti in both black hole development and galaxy formation.
"The emerging picture of co-evolving black holes and galaxies has turned our view of black holes on its head," says Meg Urry, an astronomer and professor of physics at Yale University. "Previously, black holes were seen as the endpoints of evolution, the final resting state of most or all of the matter in the universe. Now we believe black holes also play a critical role in the birth of galaxies."
The idea is particularly pertinent to explaining how massive galaxies developed in the first billion years of the universe. And it is so new that just last week theorists got what may be the first direct evidence that galaxies actually did form around the earliest black holes.
Chicken-and-egg question
Like archeologists, astronomers spend most of their careers looking back. They like to gather photons that have been traveling across time and space since well before Earth was born, some 4.5 billion years ago. Rogier Windhorst, an Arizona State University astronomer, has peered just about as deep into the past as anyone, to an era when the universe was roughly 5 percent of its present age.
Black Holes & Co-evolution: A Primer
A merger may have triggered the output of energy in this galaxy, Centaurus A.
The puzzleVery compact but bright objects called quasars, which can outshine a thousand normal galaxies, were abundant when the universe was less than 10 percent of its present age. Quasars are powered by black holes weighing more than a billion suns. How did they get so big so fast?
The front-running theoryCo-evolution holds that galaxies and supermassive black holes evolve together, each counting on the other for its ultimate heft. If true, and once fully understood, the new theory should help solve the growth puzzle.
The evidence
Early quasars appear to be surrounded by large galaxies loaded with tons of gas, which fuels star formation and feeds the black holes, a report last week suggested.
Black hole mass increases with galactic bulge mass.Near the quasars in time are other, normal galaxies that have likely just passed through a quasar phase, as seen in images released earlier this month.
Central bulges of stars in many galaxies, such as our Milky Way, are directly related to the masses of the black holes buried inside, as detailed in June of 2000. A galaxy's dimensions seem tied to its black hole's dietary habits.
Most black hole mass seems to come from direct consumption (called accretion) of gas, indicating that a black hole needs a surrounding galaxy to grow.
Dark matter is studied in part by examining hot gas clouds like this one.
The dark horseA halo of mysterious dark matter is thought to infuse the space surrounding each of the bulge-packing galaxies. The invisible gravity generator would play a crucial role in galaxy and black hole construction.
The also-ransIf co-evolution reigns, as most researchers believe, then two older (but not-dead-yet) theories are wrong: that a galaxy forms first and directs the development of a black hole; or that a black hole is generated first, providing the seed around which a galaxy can coalesce. It is also possible that different types of galaxies form by different means, and that co-evolution will only be found to describe one path to galactic adulthood.
-- Robert Roy Britt
Visit SPACE.com each Tuesday for another science feature. Archives
Earlier this month, Windhorst and a colleague, Haojing Yan, released a Hubble Space Telescope image showing the most distant "normal" galaxies ever observed.
Though stretched and distorted by the technique used to spot them (an intervening galaxy cluster was used as a "gravitational lens"), the newfound galaxies, Windhorst's team assures us, resemble our own Milky Way. They are seen as they existed more than 13 billion years ago, within 1 billion years of the Big Bang.
Practically side-by-side in time, discovered in separate observations made as part of the Sloan Digital Sky Survey, are compact but bright objects known as quasars. These galaxies-to-be shine brilliantly because, researchers believe, each has a gargantuan black hole at its core, whose mass is equal to a billion suns or more, all packed into a region perhaps smaller than our solar system.
The resulting gravity pulls in nearby gas. The material is accelerated to nearly the speed of light, superheated, and swallowed. The process is not entirely efficient, and there is a byproduct: An enormous amount of energy -- radio waves, X-rays and regular light -- hyper-illuminates the whole scene.
Quasars also seem to be surrounded by halos of dark matter, a cryptic and unseen component of all galaxies. Co-existing around and amongst all this, researchers are coming to realize, is a collapsing region of stars and gas as big or larger than our galaxy.
It was no coincidence that the announcements of the two findings -- distant quasars and normal galaxies --were made together at a meeting of the American Astronomical Society (AAS) Jan. 9. Co-evolution was on the minds of the discoverers.
Among co-evolution's significant impacts is its ability to render mostly moot a longstanding chicken-and-egg question in astronomy: Which came first, the galaxy or the black hole?
"How about both?" Windhorst asks. "You could actually have the galaxy form simultaneously around a growing black hole."
Urry, who was not involved in either finding but was asked to analyze them, explained it this way: "We believe that galaxies and quasars are very intimately connected, that in fact quasars are a phase of galaxy evolution. In our current picture, as every galaxy forms and collapses, it has a brief quasar phase."
So when a quasar goes dormant, what's left are the things we associate with a normal galaxy -- stars and gas swirling around a central and hidden pit of matter.
Quasars are cagey characters, however. (The term is short for quasi-stellar radio source; astronomers first mistook the objects for stars within our galaxy in the early 1960s.) When one is firing, its brightness can exceed a thousand normal galaxies. The quasar outshines its entire host galaxy so significantly that scientists have not been able to see what's really causing all the commotion. That veil is lifting as you read this, however, as telescopic vision extends ever backward in time and data is fed into powerful new computer models.
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