Working in collaboration with Andrea Ferrara of the University of Florence in Italy, we have found that when the abundance of metals in star-forming clouds rises above one thousandth of the metal abundance in the sun, the metals rapidly cool the gas to the temperature of the cosmic background radiation. (This temperature declines as the universe expands, falling to 19 kelvins a billion years after the big bang and to 2.7 kelvins today.) This efficient cooling allows the formation of stars with smaller masses and may also considerably boost the overall rate at which stars are born. In fact, it is possible that the pace of star formation did not accelerate until after the first metals had been produced. In this case, the second-generation stars might have been the ones primarily responsible for lighting up the universe and bringing about the cosmic renaissance.
At the start of this active period of star birth, the cosmic background temperature would have been higher than the temperature in present-day molecular clouds (10 kelvins). Until the temperature dropped to that level—which happened about two billion years after the big bang—the process of star formation may still have favored massive stars. As a result, large numbers of such stars may have formed during the early stages of galaxy building by successive mergers of protogalaxies. A similar phenomenon may occur in the modern universe when two galaxies collide and trigger a starburst—a sudden increase in the rate of star formation. Such events are now fairly rare, but some evidence suggests that they may produce relatively large numbers of massive stars.
Puzzling Evidence This hypothesis about early star formation might help explain some puzzling features of the present universe. One unsolved problem is that galaxies contain fewer metal-poor stars than would be expected if metals were produced at a rate proportional to the star formation rate. This discrepancy might be resolved if early star formation had produced relatively more massive stars; on dying, these stars would have dispersed large amounts of metals, which would have then been incorporated into most of the low-mass stars that we now see.
Another puzzling feature is the high metal abundance of the hot x-ray-emitting intergalactic gas in clusters of galaxies. This observation could be accounted for most easily if there had been an early period of rapid formation of massive stars and a correspondingly high supernova rate that chemically enriched the intergalactic gas. The case for a high supernova rate at early times also dovetails with the recent evidence suggesting that most of the ordinary matter and metals in the universe lies in the diffuse intergalactic medium rather than in galaxies. To produce such a distribution of matter, galaxy formation must have been a spectacular process, involving intense bursts of massive star formation and barrages of supernovae that expelled most of the gas and metals out of the galaxies.
Stars that are more than 250 times more massive than the sun do not explode at the end of their lives; instead they collapse into similarly massive black holes. Several of the computer simulations mentioned above predict that some of the first stars would have had masses this great. Because the first stars formed in the densest parts of the universe, any black holes resulting from their collapse would have become incorporated, via successive mergers, into systems of larger and larger size. It is possible that some of these black holes became concentrated in the inner part of large galaxies and seeded the growth of the supermassive black holes—millions of times more massive than the sun—that are now found in galactic nuclei.
Furthermore, astronomers believe that the energy source for quasars is the gas whirling into the black holes at the centers of large galaxies. If smaller black holes had formed at the centers of some of the first protogalaxies, the accretion of matter into the holes might have generated “mini quasars.” Because these objects could have appeared soon after the first stars, they might have provided an additional source of light and ionizing radiation at early times.
Thus, a coherent picture of the universe’s early history is emerging, although certain parts remain speculative. The formation of the first stars and protogalaxies began a process of cosmic evolution. Much evidence suggests that the period of most intense star formation, galaxy building and quasar activity occurred a few billion years after the big bang and that all these phenomena have continued at declining rates as the universe has aged. Most of the cosmic structure building has now shifted to larger scales as galaxies assemble into clusters.
In the coming years, researchers hope to learn more about the early stages of the story, when structures started developing on the smallest scales. Because the first stars were most likely very massive and bright, instruments such as the Next Generation Space Telescope—the planned successor to the Hubble Space Telescope—might detect some of these ancient bodies. Then astronomers may be able to observe directly how a dark, featureless universe formed the brilliant panoply of objects that now give us light and life.
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Add Commentubiquitous bright blue 1-12 pixel sources on darker 3D fractal web in five 2007.09.06 IR and visible light HUDF images, Nor Pirzkal, Sangeeta Malhotra, James E Rhoads, Chun Xu, -- might be clusters of earliest hypernovae in recent cosmological simulations: Rich Murray 2008.08.17
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Sunday, August 17, 2008
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The 5 closeups are about 2.2x2.2 arc-seconds wide and high, about 70x70 pixels.
The HUDF is 315x315 arc-seconds, with N at top and E at left.
Each side has 10,500x10,500 pixels at 0.03 arc-second per pixel.
Click on All Sizes and select Original to view the highest resolution image of 3022x2496 pixels, which can be also be conveniently seen directly at their Zoomable image:
www.spacetelescope.org/images/html/zoomable/heic0714a.html
Notable in the deep background of the five closeups are ubiquitous bright blue sources, presumably extremely hot ultraviolet before redshifting, 1 to a dozen or so pixels, as single or short lines of spots, and a few irregular tiny blobs, probably, as predicted in many recent simulations, the earliest massive, short-lived hypernovae, GRBs with jets at various angles to our line of sight, expanding bubbles, earliest molecular and dust clouds with light echoes and bursts of star formation, and first small dwarf galaxies, always associated with a subtle darker 3D random fractal mesh of filaments of H and He atomic gases.
As a scientific layman, I am grateful for specific cogent, civil feedback, based on the details readily visible in images in the public domain.
www.spacetelescope.org/images/html/heic0714a.html
Hubble and Spitzer Uncover Smallest Galaxy Building Blocks
notable bright blue tiny sources on darker 3D fractal web in HUDF VLT ESO 28 images from 506 galaxies, z about 6 , RJ Bouwens, GD Illingworth,
JP Blakeslee, M Franx 2008.02.04 draft 36 page: Rich Murray 2008.08.17
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Sunday, August 17, 2008
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bright blue 1-4 pixel sources on darker 3D fractal web in IR and visible light
HUDF images -- might be the clusters of earliest hypernovae in the Naoki Yoshida and Lars Hernquist simulation: Rich Murray 2008.07.31
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Thursday, July 31, 2008
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Rich Murray, MA Room For All rmforall@comcast.net
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Thankyou! Excellent in content and writing style. Fascinating even to this layman.
Reply | Report Abuse | Link to thisKlaus Jaritz
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Please read my web-site www.kosmonom.dk and you will know Peder's law and you may print as much of the articles as you like with mentioning of the origin
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