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more animation images.
Computer simulations suggest that many, if not
all, of the universe's first generation of stars
(Population III) were brighter, hotter, and more
massive than even today's luminous blue variable
stars, such as Eta Carinae and the Pistol Star, that
were born with as much as 200 Solar-masses.
In a letter published in Nature on April 28, 2011, a team of scientists reported finding evidence that the first stars were probably not only high in mass but also fast-spinning stars, some five times faster than today's massive stars or 250 times the Sun's current rotational speed. They analyzed eight ancient stars in NGC 6522, a 12-billion-year-old globular cluster of our Milky Way Galaxy, and found unusual abundances of elements on their surfaces, including Europium, Barium, and Lanthanum (with respect to Iron). While such unusual elemental ratios are thought to be created through nucleosynthesis in low-mass stars (via the slow-neutron-capture "s-process"), recent theory indicated that metal-poor but fast-rotating, massive stars may be able to increase s-process yields of such elements by up to four orders of magnitude. The team reported that their re-analysis of earlier spectra collected by another team also found that Yittrium and Strontium were also "overabundant" with respect to Iron with "a large scatter similar to that observed in extremely metal-poor stars," although the abundances of Carbon isotopes were not enhanced. Their hypothesis is that the eight stars were formed from gas and dust already polluted by supernovae from an earlier generation of metal-poor but fast-rotating, massive stars, "which might point to a common property of the first stellar generations and even of the ‘first stars,’" as recent simulations of the early universe tended to form massive stars with spin speeds near the breaking point (Chiappini et al, 2011; and David Shiga, New Scientist, April 27, 2011).
The Cosmos after the Big Bang
Analysis of background
indicates that the cosmos
inflated rapidly in the
first trillionth of a second
after the Big Bang about
13.7 billion ago, before
the birth of the first stars
(latest WMAP results).
According to conventional cosmological theory, all space, time, and energy began with the Big Bang, now estimated to have occurred around 13.8 billion years ago (ESA news release). In a new twist to standard theoretical models, however, many astrophysicists now believe that the universe may have suddenly inflated from a tiny point after this incredible explosion to create dark energy (74 percent) and dark matter (22 percent), as well as a small amount (four percent) of ordinary matter in the form of electrons and quarks in a superhot plasma (more on the proportion of matter in the "Cinderella Universe" model from SDSS). Within the first second after the Big Bang, the plasma may have cooled enough for quarks to combine and form protons (the most common atomic nuclei of hydrogen) and neutrons. After about three minutes, a small portion of the neutrons avoided decay by bonding with protons (to produce deuterons, the atomic nuclei of the deuterium form of hydrogen) which undergoes rapid reactions to form helium and a trace of lithium (see a list of links to more discussion on Big Bang Nucleosynthesis). For a few hundred thousand years afterwards, however, the universe remained extremely hot at around a billion degrees and so ordinary matter remained ionized, as a plasma of positively charged ions and unbound, negatively charged electrons.
The cosmos appears to be
comprised of very little
ordinary matter made of
atoms (around four percent),
that form the stars, planets,
and clouds of gas and dust
(latest WMAP results).
Three to four hundred thousand years may have passed before continuing cosmological expansion and cooling enabled atomic nuclei to hold onto electrons and create neutral hydrogen and helium gas (along with a trace of lithium at around a redshift of z ~ 1,000). Measurements of the modern universe suggest that, by mass, about three-fourths of the ordinary matter formed from the Big Bang became hydrogen while virtually all of the rest became helium; by number, around nine-tenths of all atoms may still be hydrogen, while roughly nine percent has become helium. After this initial cooling, the early universe became dark.
Larger microwave image.
Big-Bang-era photons redshifted to
microwaves suggest that the early
universe was very smooth, although
slight energy fluctuations enabled
gravity to create concentrations of
dark and ordinary matter (more at
WMAP and APOD).
Although cosmic microwave background radiation from around 380,000 years after the Big Bang suggest that the early universe was remarkably smooth, very small-scale density fluctuations (possibly related to small variations in early cosmological inflation predicted by quantum mechanics) may have led to uneven concentrations in the primordial distribution of matter in the universe, of which around nine-tenths may be comprised of dark matter. While particles of ordinary matter readily interact with one another and, if electrically charged, with electromagnetic radiation, dark matter is comprised of particles that do not react with such radiation, although dark matter interacts gravitationally just like ordinary matter (Christopher J. Conselice, 2007). In theory, gravitational attraction should have caused these dark matter density variations to condense into a network of filaments and sheets over time. Unlike ordinary matter, however, the dark matter hypothesized by theorists either cannot or mostly did not collapse into dense objects like stars, brown dwarfs, and stellar remnants (white dwarfs, neutron stars, and black holes).
© Tom Abel,
(Used with permission)
Larger simulation image.
According to one computer simulation, some dark
matter concentrations began to condense into a
network of filaments and sheets that attracted
hydrogen and helium gas through gravitational
attraction at around 100 million years (z=24)
after the Big Bang (more discussion and images;
see also: Abel et al, 2000).
Although dark matter is thought to be relatively segregated from ordinary baryonic matter in outer galactic halos and intergalactic space today, the two may have been mixed initially. As the dark matter condensed into a denser filamentary network, ordinary matter made of hydrogen and helium gas also was gravitationally attracted by these relative concentrations of dark matter, creating Lyman-alpha "forest" clouds of gas. At the nodes of the dark matter filaments, these gas clouds collapsed under gravitation towards of the cores of denser clumps of 100,000 to one million Solar-masses that may have measured around 30 to 100 light-years across and still consisted mostly of dark matter.
© Tom Abel,
(Used with permission)
Larger simulation image.
Hydrogen and helium gas, that was attracted into
large dark matter clumps of around one million
Solar-masses, may have been able to fall into
their cores and, unlike the dark matter, to begin
further collapse into stars as soon as 155 million
years after the Big Bang (more discussion and
images; see also: Abel et al, 2000).
As the gas clouds contracted, compression would have heated the gas to temperatures above 1,000° Kelvin (727° C or 1,340° F). Some hydrogen atoms would have paired up within the dense, hot gas to create molecular hydrogen, which would then help to cool the densest parts of the gas cloud by emitting infrared radiation after collision with atomic hydrogen. Eventually, the temperature in the densest regions of such clouds would drop to around 200 to 300° Kelvin (-73 to 27° C or -100 to 80° F), reducing the gas pressure and allowing the cloud to continue contracting into gravitationally bound clumps (Larson and Bromm, Scientific American, December 2001, in pdf).
© Tom Abel,
(Used with permission)
Larger simulation image,
about 1,000 light-years wide.
After around 150 million years, a proto-galactic
clump of around a million Solar-masses of mostly
dark matter surrounds a collapsing core of ordinary
matter, made of mostly hydrogen and helium gas
(more discussion and images; see also: Abel et al,
Cooling by molecular hydrogen could have allowed ordinary matter at the larger nodes of the dark matter filament network to collapse into flattened, rotating clumps -- possibly shaped like disks that resembled miniature spiral galaxies. Thus, ordinary matter would have separated from the surrounding dark matter, which does not emit radiation and lose energy and so remained scattered outside these flattened disks like today's galactic halos. Inside the disks of ordinary matter, however, the densest gas clumps would continue to contract, and eventually some would undergo a runaway collapse to form the first stars.
© Tom Abel,
(Used with permission)
Larger simulation image.
Proto-star forming out of a relatively cooler
core of 200 Solar-masses within a proto-galactic
clump of about one million Solar-masses (more
discussion and images; see also: Abel et al,
The first star-forming clumps, however, were almost 30 times warmer than the molecular gas clouds that form stars today near Sol. They may have reached 500 to 800° Kelvin (227 to 527° C or 440 to 980° F) at the highest densities attained because they lacked dust grains and molecules with heavier elements that work much more efficiently to cool such clouds (Richard B. Larson, 1999). Hence, the minimum "Jeans mass" that a relatively warm, primordial clump of gas needed to collapse under its gravity is hypothesized to be almost a thousand times what it is today (Larson and Bromm, Scientific American, December 2001, in pdf; and Tim Folger, Discover, December 2002).
Simulation: Tom Abel, Greg Bryan/Oxford,
Mike Norman/UCSD (Used with permission)
Larger simulation image (a light-month wide).
A recent simulation suggests that "clean
cocoons" could have condensed into stars
with more than 30 Solar-masses (more at
Astronomy Picture of the Day).
The results of various simulations by several teams of astronomers suggest that these nearly "metal-free" clumps were able to resist fragmentation into smaller clumps. Hence, the first stars (often called Population III stars) may have been very massive, hot, and bright, with 100 to 1,000 Solar-masses (more discussion on Jeans mass and metal-free stars and Bromm et al, 2002, in pdf). At least one simulation suggests that only one massive star star may have formed for each proto-galactic clump because of resistance to renewed fragmentation of the star-forming cloud and intense radiation once the star is formed (Abel et al, 2002).
Weinberg, Lars Hernquist,
(Used with permission)
Larger simulation image of Lyman-alpha
forest clouds at z=5.
Gravitational attraction created clouds of neutral
hydrogen gas around relative concentrations of dark
matter in the early universe, which was coalescing
into a network of filaments and sheets (more
discussion on smoothed particle hydrodynamics
simulations, or see: Katz et al, 1996).
Various computer simulations suggest that the first stars could have appeared between 100 and 250 million years after the Big Bang, when the universe had expanded to at least 1/30 of its present size. In 2003, astronomers announced that analyses of NASA's recent WMAP satellite images of the cosmic microwave background indicate that this primordial light was ionized by the first generation of stars, which may have come and gone within only 200 million years after the Big Bang (more discussion), but further analysis of data led astronomers to conclude by March 2006 that ionization may not have occurred as much as 400 million years after the Big Bang latest WMAP results). When this first generation of massive stars lighted up, the so-called "Cosmic Dark Age" ended. Even then, these stars were surrounded by a "fog" of light-absorbing neutral hydrogen (Barkana and Loeb, 2001). The first stars, however, began emitting intense ultraviolet radiation -- perhaps as much as a million times that of Sol -- that "re-ionized" neutral hydrogen atoms by energizing electrons away from their proton nuclei (Larson and Bromm, Scientific American, December 2001, in pdf). Gradually, the first stars created ever-wider bubbles of clearer space. Since these stars were short lived, it probably took another generation of stars and a few hundred million years for that hydrogen fog to dissipate, as strong absorption of ultraviolet light from quasars dating to 860 to 900 million or so years after the Big Bang suggest that the last patches of neutral hydrogen were being ionized at that time (for more discussion, see early quasar SDSS J1030+0524).
Weinberg, Lars Hernquist,
Jordi Miralda-Escudé (Used with permission)
Larger simulation image of Lyman-alpha
forest clouds at z=2.
The Lyman-alpha clouds of neutral hydrogen
gas continued to evolve over time to produce
quasars at the cores of early galaxies (more
from SDSC and Katz et al, 1996).
Many, if not most or all, of the first stars exploded as supernovae within three to four million years. They may have dispersed the heavier elements that they created widely, even into intergalactic space to contaminate other collapsing proto-galactic clumps. Some may have created black holes that clumped into even more massive holes (Mandau and Rees, 2001), to form the first quasars and small proto-galaxies, which coalesced over time into the larger galaxies of today. In 2003, astronomers announced that iron from supernovae of the first stars (possibly from Type Ia supernovae involving white dwarfs) indicate that "massive chemically enriched galaxies formed" within one billion years after the Big Bang, and so the first stars may have preceded the birth of supermassive black holes (more from Astronomy Picture of the Day, ESA, and Freudling et al, 2003). (For an example of a quasar that may have formed very early from the first stellar black holes, see SDSS J1030+0524.)
and Seth Cohen, Arizona State
University, STScI, NASA
Larger image of three of 30 early
proto-galaxies detected in 2002.
The first stars led to the creation
of proto-galaxies, of which there
may have been at least 400 million
by around 13 billion years ago (if
the universe is now about 14 billion
years old -- more).
On March 16, 2006, scientists announced new evidence for the theory that the cosmos inflated from subatomic to astronomical size in a tiny fraction of a second after its birth in the Big Bang. Analysis of three years of data uncovered a weak polarization pattern (or "signal") in the Big Bangs microwave "afterglow" -- using NASA's Wilkinson Microwave Anisotropy Probe (WMAP). As a result, the scientists were able to map not only the brightness but also the polarization of cosmic microwaves, which reveals how much the waves have been modified by bouncing off ionized gas. After subtracting the polarization effect from the temperature map, the scientists found that inflation theory fits the results by predicting that larger clumps in the background are brighter than smaller clumps (press release; latest WMAP results; and Astronomy Picture of the Day).
The polarization signal, where the
white lines indicate the direction of
polarization) allows for a test of
inflation theory as part of the
Big Bang (press release).
Earlier WMAP data also suggested that the birth of the first stars could have started ionizing gas within only 200 million years after the Big Bang. Such a time period seemed too short for gas to gather into clumps that condense into stars. The new data, however, indicates that ionization may not have happened for 400 million years, which leaves plenty of time for the first stars to form. WMAP researchers now seek evidence of strong gravitational waves, which would leave their own distinctive imprint on the polarization pattern of the microwave background and would help physicists begin to learn why inflation happened.
JPL, CalTech, NASA
The first stars may have
lighted up the cosmos
within 200 to 400 million
years after the Big Bang,
and then clustered together
into what later became
On January 7, 2009, astronomers (including Chris Carilli, Dominik Riechers, Fabian Walter, Frank Bertoldi, Karl Menten, Pierre Cox, and Roberto Neri) presented findings at the 213th American Astronomical Society meeting which support the hypothesis that supermassive black holes formed before galaxies in the early universe (NRAO press release). Previous studies of galaxies and their central black holes uncovered a relationship between the masses of the black holes and of the central bulges of stars and gas in the galaxies, where their ratio is nearly the same over a wide range of galactic sizes and ages so that central black holes from a few million to many billions of times the mass of our Sun have about one one-thousandth of the mass of the surrounding galactic bulge. This commonly found ratio indicated that a central black hole and its surrounding bulge affect each others' growth in an interactive way, at least in the nearby universe. However, by measuring the masses of black holes and central bulges in several galaxies observed in the first billion years after the Big Bang, the astronomers found that the constant ratio seen billion of years later in the nearby universe does not appear to hold in the early universe, as the black holes measured in those young galaxies appear to be much more massive compared to their central bulges than those seen in the nearby universe, which suggests that the black holes started growing first.
In the early universe,
holes appear to have
formed before the
first galaxies (more).
According to a theory being promoted by some astronomers gained modelling support in 2008, the first stars formed around 200 million years after the Big Bang in the cores of the densest dark matter clumps, where gravity would have pulled in the ordinary matter of hydrogen and helium gases needed for them to form, could have absorbed microscopic primordial black holes that could have been created by the Big Bang. A team of astronomers (including Cosimo Bambi and Katherine Freese) modelled what would happen if the dark matter was composed of black holes around the mass of the dwarf planet Ceres, since previous observations have ruled out larger masses as dark matter candidates and much lighter masses would have quickly evaporated through quantum effects. Stars that formed then could haved contained around a million black holes each mixed in with ordinary gaseous matter, and their great density would have quickly made the black holes fall into a star's core and merge with each other so that the resulting larger black hole would consume the star within a million years. Once a black hole had grown to between 10 and 1000 Solar-masses, such black holes could grow even more quickly by sucking in surrounding gas and eventually turning into the supermassive black holes found at the centers of galaxies with billions of Solar-masses. In the modern universe, however, most stars now form outside of galactic cores where primordial black holes should be much rarer and so most new stars are now unlikely to encounter primordial black holes. However, some astronomers (such as Mitchell Begelman) believe that the big central black holes of galaxies are more likely to be the descendants of million-Solar-mass black holes formed by the collapse of gas clouds since a supermassive hole would faster from a larger "seed" (David Shiga, New Scientist, December 19, 2008).
First Stars / Population III
On July 31, 2008, a team of astronomers (led by Naoki Yoshida) announced that new simulation results which indicate that the first stars formed within 300 million years after the Big Bang. First, "seed" proto-stars formed from the collapsing core of gas clouds that go through a stage as a flattened disc, with two trailing spiral arms of gas. Despite having only only 0.1 Solar-mass, the proto-stars quickly "bulked up" on surrounding gases into behemoths of at least 100 Solar-masses within 10,000 years. After a million years as a very bright star, some of these massive stars may have become supernovae -- depending on their mass (CfA press release; and Stephen Battersby, New Scientist, July 31, 2008).
David A. Aguilar,
The first stars may have
begun as "seed" proto-stars
with only 0.1 Solar-mass
that quickly "bulked up"
on surrounding gases into
behemoths with around
100 Solar-masses (more).
On December 3, 2007, a team of theoretical physicists (including Katherine Freese, Douglas Spolyar, and Paolo Gondolo) released the results of a paper which suggests that the first proto-stars could have been powered by the annihilation of opposite forms of dark matter (Weakly Interacting Massive Particles or WIMPs, such as neutralinos). In theory, each dark matter particle should have its own anti-particle. When such particle pairs meet, they would annihilate each other, whereby one-third of the resulting energy is produced as neutrinos which escape, one-third becomes gamma-ray photons, and the last third becomes electrons and positrons.
University of Utah
Larger infrared illustration.
The first "dark" proto-stars
may have been powered by
dark-matter annihilation (more).
Glowing at infrared wavelengths, these "dark stars" could have formed about 100 and 200 million years after the Big Bang at the center of million-Solar-mass haloes. In order for these proto-stars of dark and ordinary matter to condense into the first stars, however, ordinary matter had to be able cool off enough to collapse into denser objects. Competing with the process of cooling in the first proto-stars was their inability to collapse down small enough to get fusion going because they were still giving off energy that kept them inflated. Some 400 to 200,000 times wider than the Sun, these dark stars can possibly be prevented from transitioning from the dark-matter annihilation phase into the ordinary-matter fusion phase because dark-matter "annihilation products [can get] stuck" and allow dark-matter heating to stay trapped inside the star. Only after all the dark matter was annihilated could the star can collapse enough for hydrogen fusion to take over inside the star. Hence, it's possible that some dark proto-stars may still be around (more from University of Utah press release; New Scientist; BBC News; physorg.com; and Spolyar et al, 2007).
If the first stars were very massive, astronomers may never find any stars of "zero metallicity" in the local universe due to their short lifetimes. Some computer simulations indicate that, as long as these very massive stars were larger than 260 Solar-masses or smaller than 140 Solar-masses, the supernovae generated by such stars should have created black holes without significant mass ejection and so these stars would not haved contributed significantly to the metal enrichment of the surrounding medium. (Given the abundance of gas at the core of these early proto-galaxies, however, the black hole remnants of such massive stars may have formed microquasars such as XTE J1550-564.)
Larger true-color composite image.
Many Population III stars were
probably more massive than
even the Pistol Star, which may
have already ejected half of its
initial 200 Solar-masses since
its birth as much as three
million years ago.
Early stars born in the range of 140 to 260 Solar-masses may have ended their short lives quite differently, however. In theory, a supernova implosion from such an "intermediate" massive star would create a giant thermonuclear explosion that leaves no remnant by ejecting all the heavy elements previously synthesized to contribute to the metal-enrichment of the intergalactic medium (more discussion; and Heger and Woosley, 2002). Subsequently, the presence of these metals should have changed the cooling properties of the gas and reduced the size of the subsequent generations of Population II and I stars born -- such as HE 0107-5240 and Sol, respectively -- when the metallicity of interstellar gas reached a little as 1/1000th of the abundance of Sol's (Bromm et al, 2001).
The first stars lit up a 100-to-250-
million-year-long "Dark Age" with
spectacular intensity, leading to
the rapid creation of heavy
elements and black holes that
coalsced to form bright quasars
and proto-galaxies (more).
The discovery of HE 0107-5240 in the Milky Way's halo demonstrated that stars that are less massive than Sol can form from very metal-poor gas. This finding was unexpected, as most current theoretical calculations indicate that it should have been very difficult to form low-mass stars shortly after the Big Bang because heavier elements are needed to efficiently cool gas clouds as they contract into stars (see discussion on the expected mass of Population III stars from Bernard Carr, 1994 versus Richard B. Larson, 1999). However, the existence of HE 0107-5240 suggests that there must be other ways of achieving the necessary cooling. Moreover, the star's discovery suggests to some astronomers that even relatively low-mass Population III stars could have formed and survived until today, still shining faintly below easy detectability as main sequence dwarf stars in distant reaches of the galactic halo.
First announced on November 2, 2005, and expanded upon on December 18, 2006, a team of astronomers (including Alexander Kashlinsky, Richard G. Arendt, John Mather, and S. Harvey Moseley) using NASA's Spitzer Space Telescope described the detection of near-infrared light that may radiated from the the very first stars and/or from hot gas falling into the first black holes more than 13 billion years ago (Spitzer 2006 and 2005 news releases; Kashlinsky et al, 2006; Mike Peplow, Nature, 2005; and Kashlinsky et al, 2005). Based at NASA's Goddard Space Flight Center, the team captured a diffuse glow of infrared light (at 3.6, 4.5, 5.8, and 8 micron wavelengths) six-months apart in Constellation Draco and four other regions of the sky after the removal of light attributed to stars, galaxies, and artifacts of telescopic observation. The resulting near-infrared image shows a field of merging blobs of light that may have beem radiated by extremely massive Population III stars and/or superheated gas near black hole horizons within 200 to 400 million years after the Big Bang. Such a strong signal was detected that the first stars are deduced to be very massive stars, much bigger than those seen today. They may have been hundreds of times as massive as Sol, burning out in just a few million years but emitting vast amounts of ultraviolet radiation which was stretched out as the Universe expanded, leaving an infrared signature. Other astronomers (such as Rodger Thompson and Asantha Cooray), however, used Hubble observations at the shorter, near-infrared wavelength of 1.6 microns and found all of the infrared light at 1.6 microns could be accounted for dim galaxies seen by Hubble, which had formed just 6 billion years ago – not 13.6 billion years ago as posited by Kashlinsky's team (Maggie McKee, New Scientist, December 19, 2006).
SSC, JPL, CalTech, NASA
Larger near-infrared image.
What may be the glow
from the first stars (and/or
hot gas falling into black
holes) may have detected
in Constellation Draco by
removing light from stars,
galaxies, and telescopic
artifacts from an area of
50 by 100 million light-
Computer simulations had previously indicated that the first stars would be clustered, due to quantum fluctuations in the early Universe after the Big Bang. If eventually confirmed (contrary to Hubble observations at 1.6 microns), the blotchy infrared signature found suggests that the light did come from stars that were clustered. This clustering was found at four different wavelengths, in different parts of the sky, and at different times of the year. The apparent finding of clustering helps to rule out interference from more local sources of infrared light and agrees with astronomers' best estimates of how the first stars formed.
Elisabeth (Roen) Kelly,
Astronomers may have
detected a radio signal
created by the death
of the first stars
as they imploded into
black holes (more).
On January 7, 2009, astronomers (including Alan Kogut, Michael Seiffert, Dale Fixsen, Phil Lubin, and Jack Singal) discussed four new papers at a press conference during the 213th American Astronomical Society meeting which hypothesize that radio signals may have been detected from the death of the first stars in the early universe as they became black holes (NASA/GSFC news release; UC Santa Barbara press release; Rachel Courtland, New Scientist, January 8, 2009; and Dennis Overbye, New York Times, January 8, 2009). The finding is derived from data collected with NASA's Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE)2 project, which used a helium-filled balloon, large enough to envelope a football field. The balloon floated for four hours at an altitude of 21 miles (or 37 kilometers) above Texas in July 2006 and mapped a doughnut-shaped region that covered some seven percent of the sky. It detected slight deviations in the spectrum of the cosmic microwave background -- the first radiation emitted after the Big Bang -- that represented six times more energy than expected. After ruling out known radio sources in the Milky Way and other galaxies, the astronomers propose that the signal was generated as the cores of the first stars collapsed into black holes and spewed out jets of charged particles that produced the detected radio emission.
The signals were detected
in a NASA ARCADE survey
of a dough-nut shaped area
that covered seven percent
of the sky in July 2006 (more).
In a January 2006 presentation at the 209th annual meeting of the American Astronomical Society, physicist Robert Nemiroff suggested that a previously unknown type of energy may have dominated the early universe (MTU new release provided to Astronomy Magazine; and Robert J. Nemiroff, 2006). Called "ultralight energy," it is consistent with Einstein's General Theory of Relativity and can be considered as the opposite of "dark energy" in a sense. While a stable dark energy, such as the cosmological constant, grows more important in the universe over time with cosmological expansion since it does not dilute as fast as normal matter, stable ultralight energy dilutes with time so fast that matter eventually dominates it. Today, limits imposed by theory on the abundance of some forms of ultralight energy suggests that ultralight composes less than one hundred billionth of the energy density of normal matter today. Even early in the universe, the atomic nuclei of elements formed in a way that is understood without the dominating presence of ultralight energy, although it might have been dominant previously. Indeed, ultralight is the most gravitationally attractive energy species yet hypothesized, while dark energy and domain walls are both gravitationally repulsive. Radiation, on the other hand, is more gravitationally attractive than matter, and ultralight energy should be even more gravitationally attractive than radiation. (More from Professor Nemiroff's Powerpoint presentation.)
In the hot, dense, young universe right after the Big Bang, cosmologists believe that neutrinos should have been created in high-energy particle collisions. About two seconds after the big bang, this universe of colliding particles should have cooled down enough that most particles would not have have had sufficent energy to interact strongly with neutrinos. Hence, neutrinos should then have "de-coupled" from other matter and radiation. In theory, such "cosmic" neutrinos should still be zipping around today, creating a soup of slippery particles that has chilled to a temperature of only 1.9° Celsius above absolute zero today. In March 2008, scientists working with data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) released new evidence supporting the presence of such "chilled" cosmic neutrinos. Travelling at nearly the speed of light, these cosmic neutrinos should have discouraged matter from forming tight clumps, and so smoothed out the texture of the universe slightly.
Evidence for chilled "cosmic
neutrinos" that decoupled from
other matter and radiation two
seconds after the Big Bang
has accummulated (more).
Since it was launched in 2001, the WMAP spacecraft has been collecting data that provides increasing detail over time of the cosmic microwave background radiation, which carries a detailed imprint of the state of the universe some 380,000 years after the Big Bang that details the pattern of density fluctuations in space during the early universe. Travelling at nearly light speed, the creation of cosmic neutrinos would have discouraged matter from forming tight clumps and so slightly smoothed out the texture of the universe. Accumulating WMAP data now clearly show such a smoothing effect and indicate that those fast-flowing cosmic neutrinos formed about 10 percent of all matter in the 380,000-year-old universe (Stephen Battersby, New Scientist, March 5, 2008; Hinshaw et al, 2008; Helen Muir, New Scientist, June 16, 2005; and Trotta and Melchiorri, 2005).
For more information, illustrations, and animations on the formation of the first stars, see astronomer Tom Abel's web site on the First Stars and the web site on First Luminous Sources/Stars of the Osservatorio Astrofisico di Arcetri's Cosmology Group. References and contact addresses for some astronomers involved in research on early stellar formation are also available at firststars.org.
Well-illustrated articles on the formation of the first stars are available from the December 2001 issue of Scientific American by astronomers Richard Larson and Volker Bromm (in pdf) and the December 2002 issue of Discover by Tim Folger. The National Center for Supercomputing Applications of the University of Illinois at Urbana-Champaign also has an on-line article on modelling "A First Glimpse of First Stars."
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