by Ann » Mon Mar 02, 2015 12:29 am
I disagree with you, Chris. First of all I've never heard the expression "dormant galaxy". I made a quick search, but nothing turned up on the first page except dormant black holes in galaxies.
It is a known fact that star formation in the universe is on the decline.
http://www.space.com/18370-universe-sta ... cline.html wrote:
The rate of star formation in the universe has dropped to just 3 percent of its long-ago peak, and there's no end in sight to the decline, a new study finds.
A team of astronomers has determined that the rate of star birth peaked around 11 billion years ago, just 2.7 billion years after the Big Bang that created the universe. It has been dropping ever since, and the rate now stands at just just one-thirtieth its historic high, researchers said.
"You might say that the universe has been suffering from a long, serious 'crisis:' cosmic GDP output is now only 3 percent of what it used to be at the peak in star production," study lead author David Sobral, of the University of Leiden in the Netherlands, said in a statement.
Not only is the overall cosmic star formation rate on the decline, but astronomers have also found a likely culprit in the quenching of star formation in galaxies, namely their central black holes:
https://public.nrao.edu/news/pressrelea ... black-hole wrote:
High-energy jets powered by supermassive black holes can blast away a galaxy’s star-forming fuel, resulting in so-called "red and dead" galaxies: those brimming with ancient red stars yet containing little or no hydrogen gas to create new ones.
Now astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that black holes don’t have to be nearly so powerful to shut down star formation. By observing the dust and gas at the center of NGC 1266, a nearby lenticular galaxy with a relatively modest central black hole, the astronomers have detected a “perfect storm” of turbulence that is squelching star formation in a region that would otherwise be an ideal star factory.
This turbulence is stirred up by jets from the galaxy’s central black hole slamming into an incredibly dense envelope of gas. This dense region, which may be the result of a recent merger with another smaller galaxy, blocks nearly 98 percent of material propelled by the jets from escaping the galactic center.
“Like an unstoppable force meeting an immovable object, the particles in these jets meet so much resistance when they hit the surrounding dense gas that they are almost completely stopped in their tracks,” said Katherine Alatalo, an astronomer with the California Institute of Technology in Pasadena and lead author on a paper published in the Astrophysical Journal. This energetic collision produces powerful turbulence in the surrounding gas, disrupting the first critical stage of star formation. “So what we see is the most intense suppression of star formation ever observed,” noted Alatalo.
Because of the cosmic decline in star formation, mergers in the present universe don't always produce star formation.
I have searched, quite unsuccessfully, for articles about the low rate of star formation in galactic clusters. But even if I haven't found any articles about it,
color pictures of almost all massive galaxy clusters show that the members of these clusters are almost all yellow ellipticals and lenticular galaxies. And if jets from supermassive black holes can disrupt and quench star formation in individual galaxies, it makes good sense that powerful jets can disturb and disrupt star formation in the crowded environment of massive clusters of galaxies.
Given this kind of star formation decline, I don't think we can just assume that vigorous star formation is quite likely to switch on again in large yellow galaxies with supermassive black holes, or in most yellow galaxies in massive clusters.
Ann
I disagree with you, Chris. First of all I've never heard the expression "dormant galaxy". I made a quick search, but nothing turned up on the first page except dormant black holes in galaxies.
It is a known fact that star formation in the universe is on the decline.
[quote]http://www.space.com/18370-universe-star-formation-rate-decline.html wrote:
The rate of star formation in the universe has dropped to just 3 percent of its long-ago peak, and there's no end in sight to the decline, a new study finds.
A team of astronomers has determined that the rate of star birth peaked around 11 billion years ago, just 2.7 billion years after the Big Bang that created the universe. It has been dropping ever since, and the rate now stands at just just one-thirtieth its historic high, researchers said.
"You might say that the universe has been suffering from a long, serious 'crisis:' cosmic GDP output is now only 3 percent of what it used to be at the peak in star production," study lead author David Sobral, of the University of Leiden in the Netherlands, said in a statement.[/quote]
Not only is the overall cosmic star formation rate on the decline, but astronomers have also found a likely culprit in the quenching of star formation in galaxies, namely their central black holes:
[quote]https://public.nrao.edu/news/pressreleases/item/614-perfect-storm-suffocating-star-formation-around-a-supermassive-black-hole wrote:
High-energy jets powered by supermassive black holes can blast away a galaxy’s star-forming fuel, resulting in so-called "red and dead" galaxies: those brimming with ancient red stars yet containing little or no hydrogen gas to create new ones.
Now astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that black holes don’t have to be nearly so powerful to shut down star formation. By observing the dust and gas at the center of NGC 1266, a nearby lenticular galaxy with a relatively modest central black hole, the astronomers have detected a “perfect storm” of turbulence that is squelching star formation in a region that would otherwise be an ideal star factory.
This turbulence is stirred up by jets from the galaxy’s central black hole slamming into an incredibly dense envelope of gas. This dense region, which may be the result of a recent merger with another smaller galaxy, blocks nearly 98 percent of material propelled by the jets from escaping the galactic center.
“Like an unstoppable force meeting an immovable object, the particles in these jets meet so much resistance when they hit the surrounding dense gas that they are almost completely stopped in their tracks,” said Katherine Alatalo, an astronomer with the California Institute of Technology in Pasadena and lead author on a paper published in the Astrophysical Journal. This energetic collision produces powerful turbulence in the surrounding gas, disrupting the first critical stage of star formation. “So what we see is the most intense suppression of star formation ever observed,” noted Alatalo.[/quote]
Because of the cosmic decline in star formation, mergers in the present universe don't always produce star formation.
[quote][url=http://arxiv.org/abs/1411.2595v1]S Kaviraj, J Devriendt, Y Dubois, A Slyz, C Welker, C Pichon, S Peirani, DL Borgne[/url] wrote:
While almost all major mergers at z>3 are 'blue' (i.e. have significant associated star formation), the proportion of 'red' mergers increases rapidly at z<2, with most merging systems at z~1.5 producing remnants that are red in rest-frame UV-optical colours.[/quote]
I have searched, quite unsuccessfully, for articles about the low rate of star formation in galactic clusters. But even if I haven't found any articles about it, [url=http://www.astronomynotes.com/galaxy/abell1689-gravlens.jpg]color pictures[/url] of almost all massive galaxy clusters show that the members of these clusters are almost all yellow ellipticals and lenticular galaxies. And if jets from supermassive black holes can disrupt and quench star formation in individual galaxies, it makes good sense that powerful jets can disturb and disrupt star formation in the crowded environment of massive clusters of galaxies.
Given this kind of star formation decline, I don't think we can just assume that vigorous star formation is quite likely to switch on again in large yellow galaxies with supermassive black holes, or in most yellow galaxies in massive clusters.
Ann