Debates surrounding the basic formation of the universe

Cosmologists can basically be divided into two groups: those who study fundamental laws, such as the initial conditions or the content of the early universe and those who specialize in more difficult problems. like the evolution of galaxies filled with gas and hot stars then cool, forming rays, creating black holes and sometimes exploding.

The computer simulation model of the accumulation of matter constitutes huge structures, starting the formation of galaxies.Partial illustration of the universe is 100 million light-years across.The yellow spots follow the flow and the group of matter returns as it moves towards the red zone, the densest region, and moves away from the black, thinnest region.(Photo: K. Dolag and the WDS team, ESO)

Martin Rees of Cambridge University, he called the two groups of scientists 'players' and 'mud wrestlers' . The cosmology is ' a basic science just like molecular physics. The first few million years of the universe have been described in several parameters, but the cosmic environment of the galaxies and constellations is now very chaotic and complex. '

Currently "players" have established basic parameters - such as the relative amount of invisible dark matter, both more mysterious dark energy and ordinary matter - many cosmologists are turning to the second school. Recent works on shape, color, weight of galaxies have set a new focus for the essence of cosmic formation.

According to Dekel, Jewish University, Jerusalem, 'now that we have the cosmic parameters, this is really the time to understand how galaxies form . ' To do that, 'we have to follow the gases,' not dark matter because the new gases form stars. 'This is the area that needs research'. The physics industry studies the interactions between gases, the aerospace physics industry, which is much more complicated than dark matter research. Gas molecules react with a lot of force while dark matter is easier to simulate: it reacts primarily to gravity. Dekel himself is now turning to aerosol physics.

The process cools

From around the 1980s until the 1990s, Dekel spent most of his time trying to estimate the concentration of matter in the universe by mapping the speed at which galaxies and matter moved through limits. vast invisible of dark matter. Although no one knows what constitutes dark matter, it accounts for nearly 85% of the mass of the universe. And simply because it has so much, the dark matter block provides gravity material that pulls ordinary gas electrons, protons, molecules, and the like together to form stars and galaxies. Therefore, the operation of dark matter is considered a reliable diagram for the galaxy's formation path.

Each galaxy lies in a halo of cold dark matter, including external molecules that move more slowly than the speed of light (this relatively slow velocity causes this dark matter to be called 'cold' ). This halo starts small but continuously connects to each other to grow larger, indicating that all structures in the universe evolved in the same way, from small to large. This growing dark mass of matter forms the backbone of a cosmic network, with galaxies or super galaxies distributed along the most concentrated lines, such as painting on dark oil paintings. According to Piero Madau of the University of California, Santa Cruz, at the largest scale in the universe, dark matter constitutes a surprising galactic structure - the place and the way the galaxy gathers.

But in 2003, Dekel and other scientists became interested in an inexplicable discovery of galaxies based on only dark matter. Astronomers have known since the 20s that the universe today consists of two main galaxies groups - young, disk-shaped helices like the Milky Way, and older ball-shaped ellipses. The elliptical shapes have a red stain - a sign that they are long-standing and end the star formation process long ago - while the spiral lines have blue streaks, a sign of recent star formation .

A few years ago, scientists discovered that in the universe today, these two groups are much different in volume. Analysis from the Sloan Digital Sky Study, a project that records about 1 million recent galaxies in the northern sky, revealed that the 'red and death' estrus is almost always out of range. The galaxy is on a mass scale, while the spiral is forming stars below that mass. Somehow, the birth of stars is prevented systematically and seriously in large galaxies but is free in smaller galaxies than spirals.

Hot and cold: Describe the gas inside a dark matter halo when the galaxy is only 1.6 billion years old (left photo).Gas is sucked into the interior heated by a collision (outer circle).Only a few narrow channels can penetrate this hot layer to form a galaxy disk at the center and form stars.The bigger the halo, the more likely it is to block star formation because of the heating above.Images become different when the gas inside a dark halo is large enough to contain a cluster of galaxies (right picture) (Photo: A. Kravtsov, et al)

This puzzle became more complicated in 2005 when Sandy Faber of the University of California, Santa Cruz and colleagues reported that they had discovered similar galaxies when the universe was only 7 billion years old, equal to half of the current life. Faber's group used a spectrometer designed for Keck Observatory atop Mauna Kea, Hawaii, to calculate the masses of distant galaxies, part of a study of galactic composition at 7 billion years old. She presented the results of this study, called Deep-2, at the January meeting of the American Astronomical Community in Austin, Texas.

At first glance, this dichotomy seems to contrast with cold dark matter theory. The advantage of the giant 'red and death' galaxies in the early universe implies that the initial halo is very massive but then divided into smaller parts, a direction that is opposite to the direction of the object dark matter.

Dekel and colleagues, including Yuval Birnboim, now at the Harvard-Smithsonian Center for Astrophysics in Cambridge, gave the explanation that might be consistent with the theory of cold dark matter, but it requires a combination of gas physics. universe with dark matter. The gas sucked into a dark matter halo will often enter the center, where it will cool and thicken enough to form stars. But as the universe ages, the dark matter halo becomes larger and larger, some become billions of billions of times more massive than the Sun.

When a halo reaches the required value, the galactic separation phase begins. Calculations and simulations of Birnboim and Dekel show that the gases absorbed in the concentration concentrate on a fairly cool static gas which is located in the center of the halo. This impact creates a long-lasting tremor and heating cold air causes it to create a pressure. The pressure builds up on the gases that are sucked in and pushes this material into the periphery of the halo, where it exists as an exile in Siberia in the galaxy, unable to bind and form stars. As long as the matter at the center of the halo maintains its outer pressure, the new gas is blocked and the galaxy cannot form. Over a period of time, the giant galaxy growing in the center of the halo, once a cradle for stars, became red and died.

Smaller halo - creating smaller galaxies - cannot withstand such long lasting shocks. Gas continues to pour freely into the central area and produces new generations of stars. Simulations from other groups, including the group of Dusan Keres - Harvard-Smithsonian Astrophysics Center, Darren Croton - University of California, Berkeley, Richard Bower - Durham University, England and Andrea Cattaneo - Potsdam University, Germany , have produced similar results. 'The idea is that big central galaxies are stopped before the universe is 7 billion years old because they are in giant halo while smaller galaxies are stopped later, if ever happened, when the halo is Their mother reaches the required mass. '

The role of black holes

Dekel further emphasized the mystery of how the central gas of a giant halo could maintain the outward pressure to keep new air in the outer halo for up to 10 billion years in cosmic history. . He calculated that the pressure could last only about one tenth of that time. Another source has kept star formation from returning. Further research into the field of aerosol physics, he and other researchers aim to an unusual role that black holes can play a role in preventing star formation in giant galaxies. Researchers now believe that every giant galaxy contains a large mass black hole in the center and these weightless spirits influence beyond its near environment.

Young and old: The spiral-shaped galaxy NGC 300 (left photo), located 7 million light-years from Earth, is full of newborn stars.In contrast, an adult galaxy of elliptic shape NGC 1313 (right), 62 million light-years from Earth, looks quieter.(Photo: NASA JPL / Caltech, Las Campñas; NASA JPL / Caltech, CTIO)

Wrapping millions to billions of suns in a system not bigger than our solar system, black holes are not only sucking matter. The energy from the gas and stars spiraling into the hole also created material streams that ravaged back a million light-years from the center. In this way, a black hole can play a role in regulating or even quenching star formation.

Furthermore, scientists found that black holes at the center of the galaxy grow in proportion to the mass of stars in that galaxy. The black hole seems to be always equal to 1/500 of the star's mass. This rule means that the most massive galaxies will contain the heaviest black holes - most likely the culprits that make the flow of matter strong enough to prevent star formation.

According to Tim Heckman, John Hopkins University, Baltimore 'What's surprising is that the correlation seems very tight' between the mass of the central black hole and the surrounding galaxy. 'I do not think more than 10 years ago, we will find an astronomer out of a total of 1000 people who think black holes have a fundamental role in galaxy formation. We still don't know whether the black hole determines the formation of a galaxy or otherwise. '
Dekel and Birnboim, along with Jerry Ostriker - Princeton University, recently began to underestimate the idea that black holes need not be the cause of galactic division. According to their calculations, the heat generated from the gas drawn into the center of the giant dark matter halo may be enough to block the cold star gas from forming.

Early stage

A new project examines the farthest timeline so far to find out the difference between different types of galaxies.
Using distant standards as signal lights, a group of scientists led by Art Wolfe, University of California, San Diego, said their search may have returned to the era when galaxies The giant is still forming stars before these "giants" are killed. During his five-year project, Wolfe and his colleagues, including Jason Prochaska - University of California, Santa Cruz, used spectroscopy at Keck Observatory to study star formation at 143 thick gas clouds. dense, each of them gets through a stream of radiation from another quasar. Astronomers generally agree that these clouds, known as wet Lyman-alpha systems, are likely to form before galaxies today. They reveal what galaxies look like when the universe is only 2 billion years old.

Different gas concentrations are related to the evolution of the structure in the universe and of galaxy formation.Gas concentration (gradual brightness) is displayed along with the temperature (gradually changing from green to red).Yellow circles denote a black hole (larger mass is represented by a larger diameter).Left photo simulates the universe about 450 million years after the Big Bang.The early universe still showed a fairly synchronous structure.At the age of 6 billion (right), the universe has more black holes and has a more fibrous structure.(Photo: T. Di Matteo, et al)

To assess the rate of star formation in clouds, the team aimed at the presence of carbon atoms separated from a single electron. Newly formed stars stimulate these carbon ions. The more carbon this is, the greater the rate of star formation. The team used the spectrum of another ion, silicon separated from an electron, to understand the mass of dark matter halo containing dense clouds.

To the astonishment of scientists, this work shows that the birth of stars is most pronounced in the clouds within the heaviest dark matter halo. According to the Astrophysical Journal research team, the clouds are probably the ancestors of most giant galaxies today,

This scenario contrasts with the current galaxy, which according to Wolfe, 'giant galaxies, if any, only form stars at low levels. But that was just the model Dekel-Birboim predicted. Going back in time, massive massive galaxies are still forming stars at high speed. ' Furthermore, observing distant galaxies from many researchers, such as Chuck Steidel - California Institute of Technology, Pasadena, also showed that star formation took place at high speeds in giant galaxies.

According to Wolfe 'We go back far enough to see the star formation phase of the mass system.' He also notes that later, the birth of a new star is blocked in these massive masses, a victim of excessively heated gas and perhaps a "monster" intervention. black.

At the present time, Dekel said he still hasn't completely given up his passion for understanding the fundamental characteristics of the universe. The evolution of galaxies is a chaotic but interesting background to test his ideas.'I see myself as a' player 'darting into a pile of mud. The interesting thing is there. '