• Observational Cosmology Stephen Serjeant Pdf Merger
• Observational Cosmology
• Observational Cosmology Stephen Serjeant Pdf Merger

Astronomers have shown for the first time that even the smallest galaxies in the Universe have complex structures that indicate a complex history. Using the Subaru Telescope, a team of astronomers from the National Astronomical Observatory of Japan, the Institute of Physics in Lithuania, the University of Durham, Paris Observatory, Kyoto University, Gunma Astronomical Observatory, and the University of Tokyo have discovered an extended halo of stars with a sharp cutoff in the dwarf irregular galaxy Leo A, a member of the Local Group of galaxies that includes the Milky Way. The discovery challenges current scenarios of galaxy formation by showing that instead of being the preservers of pristine building blocks that combined to form larger galaxies, dwarf irregular galaxies have their own history of build-up.Understanding galaxy formation and evolution on time scales comparable to the age of the Universe is one of astronomy’s greatest challenges. In the scenarios of standard cosmology (Note 1), galaxies are built up via hierarchical merging: small primordial density fluctuations in the smooth distribution of matter in the early Universe grow and combine to form larger structures like the Milky Way.

The most numerous type of galaxies in the universe — dwarf irregular galaxies (Note 2) — are supposed to preserve their properties unchanged over billions of years and represent pristine primeval building blocks. This is one reason why astronomers have recently been studying dwarf irregular galaxies with great interest.The team led by Professors Nobuo Arimoto (National Astronomical Observatory of Japan) and Vladas Vansevicius (Institute of Physics, Lithuania) has studied Leo A — an isolated and extremely gas rich dwarf irregular galaxy with only 0.01% of the mass of the Milky Way and a low fraction chemical elements produced by earlier generations of stars. These characteristics suggest that this galaxy has been evolving without significant interaction with other galaxies. This galaxy has been believed to have quite a simple structure, in contrast to large disk galaxies like the Milky Way. However, this view needs to be changed due to deep imaging of the outer regions of this galaxy with the Subaru Telescope.Prior to these observations, Leo A was already known to have a large angular size (7′ x 5′; Note 3) and Subaru Telescope equipped with its Prime Focus Camera (Suprime-Cam) was an ideal instrument to study the stars at the galaxy’s outer limits (Fig. A single exposure with Suprime-Cam covers a field of view of 34′ x 27′ (pixel size 0”.2 x 0”.2) with high sensitivity.

The team acquired optical images of the dwarf irregular galaxy Leo A with three broad band filters in November 2001. In order to trace the entire extent of the old stars in Leo A, the team employed red giant branch (RGB) stars which are evolved low-mass stars with very high luminosity and are expected to represent well the extended structures of galaxies.

They investigated inside an ellipse of semi-major axis a = 12′ which fully covers the galaxy, and detected 1394 RGB stars distributed symmetrically and smoothly within this field.Fig. 2 shows the radial profile of the surface number density of the red giant stars. The team found significantly larger disk structure (with a semi-major axis of 5.5′) than previously known (3.5′).

Moreover, the deep observations permitted the discovery of a new stellar component in dwarf irregular galaxies, which the team calls a?halo? (5.5′-7.5′), which has a less steep slope in the number density of RGB stars.

The halo component ends at 8′ from the center of the galaxy with a sharp cutoff in the RGB star distribution. The existence of such a halo structure in dwarf irregular galaxies had been unconfirmed before these observations.The size of Leo A revealed by these new observations is twice as large as its previously accepted size, suggesting that even in the nearby universe we see galaxies only as?tips of icebergs” that are actually a few times more extended.The newly discovered halo with a sharp stellar cutoff and the disk of the dwarf irregular galaxy Leo A closely resembles the structure as well as stellar and gaseous content found in large full-fledged disk galaxies like the Milky Way. The complicated structure of large massive galaxies has been believed to be a result of the merging of less massive galaxies like dwarf irregular ones. However, this study clearly reveals that the dwarf irregular galaxy Leo A already has disk and halo components, and suggests complex build-up histories for even very low mass galaxies like Leo A, which are supposed to form directly from the primordial density fluctuations in the early universe (Note 1), and challenges contemporary understanding of galaxy evolution. Professors N.

Arimoto and V. Vansevicius believe Leo A is a?Rosetta stone? (Note 4) for understanding the process of galaxy formation and evolution.The scientific paper on this research has been accepted for publication in the August 20, 2004, Astrophysical Journal Letters (Volume 611, Number 2, L93).Original Source. A gamma-ray burst detected by ESA’s Integral gamma-ray observatory on 3 December 2003 has been thoroughly studied for months by an armada of space and ground-based observatories.

Astronomers have now concluded that this event, called GRB 031203, is the closest cosmic gamma-ray burst on record, but also the faintest. This also suggests that an entire population of sub-energetic gamma-ray bursts has so far gone unnoticedCosmic gamma-ray bursts (GRBs) are flashes of gamma rays that can last from less than a second to a few minutes and occur at random positions in the sky. A large fraction of them is thought to result when a black hole is created from a dying star in a distant galaxy. Astronomers believe that a hot disc surrounding the black hole, made of gas and matter falling onto it, somehow emits an energetic beam parallel to the axis of rotation.According to the simplest picture, all GRBs should emit similar amounts of gamma-ray energy. The fraction of it detected at Earth should then depend on the ‘width’ (opening angle) and orientation of the beam as well as on the distance.

The energy received should be larger when the beam is narrow or points towards us and smaller when the beam is broad or points away from us. New data collected with ESA’s high energy observatories, Integral and XMM-Newton, now show that this picture is not so clear-cut and that the amount of energy emitted by GRBs can vary significantly. “The idea that all GRBs spit out the same amount of gamma rays, or that they are ‘standard candles’ as we call them, is simply ruled out by the new data,” said Dr Sergey Sazonov, from the Space Research Institute of the Russian Academy of Sciences, Moscow (Russia) and the Max-Planck Institute for Astrophysics, Garching near Munich (Germany).Sazonov and an international team of researchers studied the GRB detected by Integral on 3 December 2003 and given the code-name of GRB 031203. Within a record 18 seconds of the burst, the Integral Burst Alert System had pinpointed the approximate position of GRB 031203 in the sky and sent the information to a network of observatories around the world. A few hours later one of them, ESA’s XMM-Newton, determined a much more precise position for GRB 031203 and detected a rapidly fading X-ray source, which was subsequently seen by radio and optical telescopes on the ground.This wealth of data allowed astronomers to determine that GRB 031203 went off in a galaxy less than 1300 million light years away, making it the closest GRB ever observed. Even so, the way in which GRB 031203 dimmed with time and the distribution of its energy were not different from those of distant GRBs. Then, scientists started to realise that the concept of the ‘standard candle’ may not hold.

“Being so close should make GRB 031203 appear very bright, but the amount of gamma-rays measured by Integral is about one thousand times less than what we would normally expect from a GRB,” Sazonov said.A burst of gamma rays observed in 1998 in a closer galaxy appeared even fainter, about one hundred times less bright than GRB 031203. Astronomers, however, could not conclusively tell whether that was a genuine GRB because the bulk of its energy was emitted mostly as X-rays instead of gamma-rays. The work of Sazonov’s team on GRB 031203 now suggests that intrinsically fainter GRBs can indeed exist.A team of US astronomers, coordinated by Alicia Soderberg from the California Institute of Technology, Pasadena (USA), studied the ‘afterglow’ of GRB 031203 and gave further support to this conclusion.

The afterglow, emitted when a GRB’s blastwave shocks the diffuse medium around it, can last weeks or months and progressively fades away. Using NASA’s Chandra X-ray Observatory, Soderberg and her team saw that the X-ray brightness of the afterglow was about one thousand times fainter than that of typical distant GRBs. The team’s observations with the Very Large Array telescope of the National Radio Astronomy Observatory in Socorro (USA) also revealed a source dimmer than usual.Sazonov and Soderberg explain that their teams looked carefully for signs that GRB 031203 could be tilted in such a way that most of its energy would escape Integral’s detection. However, as Sazonov said, “the fact that most of the energy that we see is emitted in the gamma-ray domain, rather than in the X-rays, means that we are seeing the beam nearly on axis.” It is, therefore, unlikely that much of its energy output can go unnoticed.This discovery suggests the existence of a new population of GRBs much closer but also dimmer than the majority of those known so far, which are very energetic but distant.

Objects of this type may also be very numerous and thus produce more frequent bursts.The bulk of this population has so far escaped our attention because it lies at the limit of detection with past and present instruments. Integral, however, may be just sensitive enough to reveal a few more of them in the years to come.

These could be just the tip of the iceberg and future gamma-ray observatories, such as the planned NASA’s Swift mission, should be able to extend this search to a much larger volume of the Universe and find many more sub-energetic GRBs.Original Source. On the evidence to date, our solar system could be fundamentally different from the majority of planetary systems around stars because it formed in a different way. If that is the case, Earth-like planets will be very rare. Today, August 2nd 2004, particle physicists from the UK and around the world working on the BABAR experiment at the Stanford Linear Accelerator Center (SLAC) in the USA, announced exciting new results demonstrating a dramatic difference in the behaviour of matter and antimatter. Their discovery may help to explain why the Universe we live in is dominated by matter, rather than containing equal parts matter and anti-matter.SLAC’s PEP-II accelerator collides electrons and their antimatter counterparts, positrons, to produce an abundance of exotic heavy particle and anti-particle pairs known as B and anti-B mesons. These rare forms of matter and antimatter are short-lived, decaying in turn to other lighter subatomic particles, such as kaons and pions, which can be seen in the BABAR experiment.“If there were no difference between matter and antimatter, both the B meson and the anti-B meson would exhibit exactly the same pattern of decays.

However, our new measurement shows an example of a large difference in decay rates instead.” said Marcello Giorgi, of SLAC, Pisa University and INFN, Spokesman of BABAR.By sifting through the decays of more than 200 million pairs of B and anti-B mesons, experimenters have discovered striking matter-antimatter asymmetry. “We found 910 examples of the B meson decaying to a kaon and a pion, but only 696 examples for the anti-B”, explained Giorgi. “The new measurement is very much a result of the outstanding performance of SLAC’s PEP-II accelerator and the efficiency of the BABAR detector. The accelerator is now operating at 3 times its design performance and BABAR is able to record about 98% of collisions.”While BABAR and other experiments have observed matter-antimatter asymmetries before, this is the first time that a difference has been found by simple counting of the number of decays of B and anti-B mesons to the same final state. This effect is known as direct CP violation and is found to be 13%; a similar effect occurs for decays of Kaons and antiKaons but only at the level of 4 parts in a million!“This is a strong, convincing signal of direct CP violation in B decays, a type of matter-antimatter asymmetry which was expected to exist but has not been observed before. With this discovery the full pattern of matter-antimatter asymmetries is coming together into a coherent picture.

I am very excited and pleased as one of my postgraduate students, Carlos Chavez who is currently at SLAC, was directly involved.” said Christos Touramanis of the University of Liverpool.Dan Bowerman, a member of the BABAR team from Imperial College adds “When the universe began with the big bang, matter and antimatter were created in equal amounts. However, all observations indicate that we live in a universe made only of matter. So we have to ask, what happened to the antimatter? The work at BABAR is bringing us closer to answering this question.”Subtle differences between the behaviour of matter and antimatter must be responsible for the matter-antimatter imbalance that developed in our universe. But our current knowledge of these differences is incomplete and insufficient to account for the observed matter domination. CP violation is one of the three conditions outlined by Russian physicist Andrei Sakharov to account for the observed imbalance of matter and antimatter in the universe.Professor Ian Halliday, Chief Executive of the Particle Physics and Astronomy Research Council which funds UK participation in BABAR said: “We still don’t understand fully how the matter dominated Universe we live in has evolved. However this new result, and recent related measurements in BABAR and other experiments around the world, have greatly advanced our understanding in this area.

There is still much to discover and learn on this fundamental issue.”Original Source: PPARC News Release. Astronomers studying data from the National Science Foundation’s Very Long Baseline Array (VLBA) and other telescopes have concluded that a binary pair of stars forming an energetic microquasar was blasted out of the cluster in which it was born by a supernova explosion some 1.7 million years ago.

This is the first time that a fast-moving stellar pair has been tracked back to a specific star cluster.The scientists analyzed numerous observations of a microquasar called LSI +61 303, and concluded that it is moving away from a star cluster named IC 1805 at nearly 17 miles per second.A microquasar is a pair of stars, one of which is either a dense neutron star or a black hole, in which material sucked from a “normal” star forms a rapidly-rotating disk around the denser object. The disk becomes so hot it emits X-rays, and also spits out “jets” of subatomic particles at nearly the speed of light.“In this case, both the microquasar and the star cluster are about 7,500 light-years from Earth and the characteristics of the ‘normal’ star in the microquasar match those of the other stars in the cluster, so we feel confident that the microquasar was shot out from a birthplace in this cluster,” said Felix Mirabel, an astrophysicist at the Institute for Astronomy and Space Physics of Argentina and French Atomic Energy Commission.

Observational Cosmology Stephen Serjeant Pdf Merger

Mirabel worked with Irapuan Rodrigues, of the Federal University of Rio Grande do Sul, Brazil, and Qingzhong Liu of the Purple Mountain Observatory in Nanjing, China. The astronomers reported their results in the August 1 issue of the scientific journal Astronomy & Astrophysics.Many neutron stars have been found to be moving rapidly through the sky, leading scientists to conclude that the supernova explosions that produced them were asymmetric, giving a “kick” to the star. LSI +61 303’s motion has carried it about 130 light-years from the cluster IC 1805. The cluster is in the constellation Cassiopeia.LSI +61 303 contains, the astronomers say, either a black hole or a neutron star with twice the mass of the Sun, orbiting a normal star 14 times more massive than the Sun every 26.5 days.

The supernova explosion that produced the black hole or neutron star blew away about twice the mass of the Sun.The black hole or neutron star originally was much more massive than its companion. The scientists still are unsure about how massive it was. Some evidence, they say, indicates that it was formed only four or five million years ago and exploded a million or so years ago. While rovers and orbiting spacecraft scour Mars searching for clues to its past, researchers have uncovered another piece of the red planet in the most inhospitable place on Earth — Antarctica.The new specimen was found by a field party from the U.S.

Antarctic Search for Meteorites program (ANSMET) on Dec. 15, 2003, on an ice field in the Miller Range of the Transantarctic Mountains, roughly 750 km (466 miles) from the South Pole. Using observations of 3,000 quasars discovered by the Sloan Digital Sky Survey (SDSS), scientists have made the most precise measurement to date of the cosmic clustering of diffuse hydrogen gas. These quasars–100 times more than have been used in such analyses in the past–are at distances of eight to ten billion light years, making them among the most distant objects known.Filaments of gas between the quasars and the Earth absorb light in the quasar’s spectra, allowing researchers to map the gas distribution and to measure how clumpy the gas is on scales of one million light years. The degree of clumping of this gas, in turn, can answer fundamental questions such as whether neutrinos have mass and what the nature of dark energy is, hypothesized to be driving the accelerated expansion of the universe.“Scientists have long studied the clustering of galaxies to learn about cosmology,” explained Uros Seljak of Princeton University, one of the SDSS researchers. “However, the physics of galaxy formation and clustering is very complicated. A major breakthrough in pinpointing some of the most primordial and violently star forming galaxies in the Universe has been made by a joint collaboration of UK and US astronomers using the Spitzer Space Telescope to resolve primordial galaxies initially detected by the James Clerk Maxwell telescope JCMT.

UK astronomers from the University of Kent, The Royal Observatory Edinburgh and the University of Oxford teamed up with American cosmologists to finally identify these elusive galaxies. The work will be published in the Astrophysical Journal Supplement Spitzer Special Issue in September 2004.Back in 1995, the UK’s SCUBA camera (Sub-millimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope in Hawaii, which detects light with wavelengths just under a millimetre, began finding fuzzy traces of very distant, primordial galaxies. Some of these are either too distant or too dusty to be seen even by the Hubble Space Telescope. But SCUBA’s images on their own, and those of other similar cameras, are not fine enough: within the fuzzy SCUBA detections are sometimes many galaxies. So astronomers have spent enormous effort following up these SCUBA galaxies on other telescopes, particularly radio telescopes, to answer the question: which one is the primordial galaxy, and which ones are in the foreground? But even with the most sensitive radio telescope images ever made, only around half the SCUBA galaxies can be pinpointed unambiguously. Even worse, the radio telescopes miss all of the most distant and most primordial of SCUBA’s galaxies.UK and US astronomers teamed up to combine Spitzer’s sharp images with SCUBA’s ability to find primordial galaxies.

The team were stunned to find all the SCUBA galaxies in Spitzers field of view detected in only ten minutes with Spitzer. These breakthrough observations, described as a watershed by the team, finally give astronomers a way of unambiguously pinpointing even the most distant of SCUBA’s galaxies. This could only be done by combining SCUBA with the Spitzer Space Telescope: SCUBA shows there is a primordial, violent starburst somewhere in the vicinity, which is then pinpointed by Spitzer.At the same time, Spitzer solved another mystery about SCUBA galaxies. When Galileo first trained a telescope at the Milky Way, he was astonished to find the fuzzy light resolved into many individual stars.

This is, in essence, what the team of astronomers have done with the diffuse extragalactic background light seen from all directions at a wavelength of about half a millimetre. By comparing the distinct Spitzer galaxies with the SCUBA data, the team discovered that they had identified the sources of this cosmic background for the first time.

This background is caused by an important population of galaxies: most of the stars in the early Universe are created in these galaxies, and star formation is where everything comes from – including the material that makes planets like our own. Finding where this star formation happens tells us, in a sense, where we came from. Identifying most of these galaxies is a second coup for the joint UK/US team.Dr.

Stephen Serjeant (University of Kent, UK) said, Our Spitzer Space Telescope images picked our galaxies out astonishingly quickly, in only ten minutes, when the community has been pouring effort into detecting them. This really is pioneering work and a great triumph for the Spitzer Space Telescope and the UKs SCUBA camera.

To cap it all, at the same time weve found the galaxies that dominate the star formation in the early Universe. The Earth and everything on it is made from the dust created in stars like those people, trees, beef burgers, the lot.Dr. Rob Ivison (Royal Observatory Edinburgh, UK) said, In 10 minutes, the Spitzer Space Telescope has managed to pinpoint the galaxies we have been chasing for 7 years. We can finally begin to sort the babies and teenagers of the galaxy world from the adults and senior citizens.Dr. Herv Dole (University of Arizona USA and IAS, Orsay, France) said, These Spitzer observations were designed as the first joint survey using the MIPS and IRAC instruments on Spitzer, to assess the instrument sensitivities.

Observational Cosmology

As a matter of fact, it’s a great technological, operational and scientific success, overwhelming our wildest expectations. This demonstrates the amazing capabilities of Spitzer for studying galaxy evolution at high redshifts; no doubt that deeper and larger ongoing surveys will give even more exciting results!Dr. Steve Willner (Harvard-Smithsonian Center for Astrophysics, USA) said, We expected to detect one or a few of these galaxies, but I was stunned that we detected all of the ones we looked at. The new data finally tell us what these galaxies are all about.

We’ve known all along that they had to be far away and rapidly turning all their gas into stars, but now we know their true distances and ages.Original Source: PPARC News Release. Astronomers using ESA?s X-ray observatory XMM-Newton have detected a small, bright?hot spot? On the surface of the neutron star called Geminga, 500 light-years away. The hot spot is the size of a football field and is caused by the same mechanism producing Geminga?s X-ray tails. This discovery identifies the missing link between the X-ray and gamma-ray emission from Geminga.Neutron stars are the smallest kind of stars known. They are the super-dense remnants of massive stars that died in cataclysmic explosions called supernovae. They have been thrown through space like cannonballs and set spinning at a furious rate, with magnetic fields hundreds of billions of times stronger than Earth?s.In the case of Geminga, this cannonball contains one and a half times the mass of the Sun, squeezed into a sphere just 20 kilometres across and spinning four times every second.A cloud bustling with electrically charged particles surrounds Geminga.

These particles are shepherded by its magnetic and electric fields. ESA?s XMM-Newton observatory had already discovered that some of these particles are ejected into space, forming tails that stream behind the neutron star as it hurtles along.Scientists did not know whether Geminga?s tails are formed by electrons or by their twin particles with an opposite electrical charge, called positrons. Nevertheless, they expected that, if for instance electrons are kicked into space, then the positrons should be funnelled down towards the neutron star itself, like in an?own goal? Where these particles strike the surface of the star, they ought to create a hot spot, a region considerably hotter than the surroundings.An international team of astronomers, lead by Patrizia Caraveo, IASF-CNR, Italy, has now reported the detection of such a hot spot on Geminga using ESA?s XMM-Newton observatory.With a temperature of about two million degrees, this hot spot is considerably hotter than the one half million degrees of the surrounding surface.

Observational Cosmology Stephen Serjeant Pdf Merger

In this week's questions show, I explain why we can see meteor showers every year, why we're not 3D printing telescopes in space, why there aren't any plans to launch telescopes with SpaceX Starship. And a lengthy answer to one of the most common James Webb questions we get: can it be refueled?