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Posts Tagged ‘dark matter’

Scientists At Keck Discover The Fluffiest Galaxies


Credit: P. van Dokkum, R. Abraham, J. Brodie

Credit: P. van Dokkum, R. Abraham, J. Brodie

An international team of researchers led by Pieter van Dokkum at Yale University have used the W. M. Keck Observatory to confirm the existence of the most diffuse class of galaxies known in the universe. These “fluffiest galaxies” are nearly as wide as our own Milky Way galaxy – about 60,000 light years – yet harbor only one percent as many stars. The findings were recently published in the Astrophysical Journal Letters.

“If the Milky Way is a sea of stars, then these newly discovered galaxies are like wisps of clouds”, said van Dokkum. “We are beginning to form some ideas about how they were born and it’s remarkable they have survived at all. They are found in a dense, violent region of space filled with dark matter and galaxies whizzing around, so we think they must be cloaked in their own invisible dark matter ‘shields’ that are protecting them from this intergalactic assault.”

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Dark Matter Half What We Thought, Say Scientists

October 9, 2014 Leave a comment

A new measurement of dark matter in the Milky Way has revealed there is half as much of the mysterious substance as previously thought.

Australian astronomers used a method developed almost 100 years ago to discover that the weight of dark matter in our own galaxy is 800 000 000 000 (or 8 x 1011) times the mass of the Sun.

They probed the edge of the Milky Way, looking closely, for the first time, at the fringes of the galaxy about 5 million trillion kilometres from Earth.

Astrophysicist Dr Prajwal Kafle, from The University of Western Australia node of the International Centre for Radio Astronomy Research, said we have known for a while that most of the Universe is hidden.

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Interactive Dark Matter Could Explain Milky Way’s Missing Satellite Galaxies

September 11, 2014 Leave a comment

Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.

This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.

Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.

Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.

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Mapping Dark Matter, 4.5 Billion light Years Away


Credit: ESA/Hubble, NASA, HST Frontier Fields

Credit: ESA/Hubble, NASA, HST Frontier Fields

Using the NASA/ESA Hubble Space Telescope, an international team of astronomers have mapped the mass within a galaxy cluster more precisely than ever before. Created using observations from Hubble’s Frontier Fields observing programme, the map shows the amount and distribution of mass within MCS J0416.1–2403, a massive galaxy cluster found to be 160 trillion times the mass of the Sun.

The detail in this ‘mass map’ was made possible thanks to the unprecedented depth of data provided by new Hubble observations, and the cosmic phenomenon known as strong gravitational lensing. The team, led by Dr Mathilde Jauzac of Durham University in the UK and the Astrophysics & Cosmology Research Unit in South Africa, publish their results in the journal Monthly Notices of the Royal Astronomical Society.

Measuring the amount and distribution of mass within distant objects in the Universe can be very difficult. A trick often used by astronomers is to explore the contents of large clusters of galaxies by studying the gravitational effects they have on the light from very distant objects beyond them. This is one of the main goals of Hubble’s Frontier Fields, an ambitious observing programme scanning six different galaxy clusters — including MCS J0416.1–2403.

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Mysterious X-Ray Signal Intrigues Astronomers


Credit: X-ray: NASA/CXC/SAO/E.Bulbul, et al.

Credit: X-ray: NASA/CXC/SAO/E.Bulbul, et al.

A mysterious X-ray signal has been found in a detailed study of galaxy clusters using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. One intriguing possibility is that the X-rays are produced by the decay of sterile neutrinos, a type of particle that has been proposed as a candidate for dark matter.

While holding exciting potential, these results must be confirmed with additional data to rule out other explanations and determine whether it is plausible that dark matter has been observed.

Astronomers think dark matter constitutes 85% of the matter in the Universe, but does not emit or absorb light like “normal” matter such as protons, neutrons and electrons that make up the familiar elements observed in planets, stars, and galaxies. Because of this, scientists must use indirect methods to search for clues about dark matter.

The latest results from Chandra and XMM-Newton consist of an unidentified X-ray emission line, that is, a spike of intensity at a very specific wavelength of X-ray light. Astronomers detected this emission line in the Perseus galaxy cluster using both Chandra and XMM-Newton. They also found the line in a combined study of 73 other galaxy clusters with XMM-Newton.

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Radiation From Early Universe Found Key To Answer Major Questions In Physics


Astrophysicists at UC San Diego have measured the minute gravitational distortions in polarized radiation from the early universe and discovered that these ancient microwaves can provide an important cosmological test of Einstein’s theory of general relativity. These measurements have the potential to narrow down the estimates for the mass of ghostly subatomic particles known as neutrinos.

The radiation could even provide physicists with clues to another outstanding problem about our universe: how the invisible “dark matter” and “dark energy,” which has been undetectable through modern telescopes, may be distributed throughout the universe.

The scientists are publishing details of their achievement in the June issue of the journal Physical Review Letters, the most prestigious journal in physics, which highlighted their paper as an “editor’s suggestion” because of its importance and significance to the discipline.

The UC San Diego scientists measured variations in the polarization of microwaves emanating from the Cosmic Microwave Background—or CMB—of the early universe. Like polarized light (which vibrates in one direction and is produced by the scattering of visible light off the surface of the ocean, for example), the polarized “B-mode” microwaves the scientists discovered were produced when CMB radiation from the early universe scattered off electrons 380,000 years after the Big Bang, when the cosmos cooled enough to allow protons and electrons to combine into atoms.

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NASA’s Hubble Extends Stellar Tape Measure 10 Times Farther Into Space


Using NASA’s Hubble Space Telescope, astronomers now can precisely measure the distance of stars up to 10,000 light-years away — 10 times farther than previously possible.

Astronomers have developed yet another novel way to use the 24-year-old space telescope by employing a technique called spatial scanning, which dramatically improves Hubble’s accuracy for making angular measurements. The technique, when applied to the age-old method for gauging distances called astronomical parallax, extends Hubble’s tape measure 10 times farther into space.

“This new capability is expected to yield new insight into the nature of dark energy, a mysterious component of space that is pushing the universe apart at an ever-faster rate,” said Noble laureate Adam Riess of the Space Telescope Science Institute (STScI) in Baltimore, Md.

Parallax, a trigonometric technique, is the most reliable method for making astronomical distance measurements, and a practice long employed by land surveyors here on Earth. The diameter of Earth’s orbit is the base of a triangle and the star is the apex where the triangle’s sides meet. The lengths of the sides are calculated by accurately measuring the three angles of the resulting triangle.

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Fermi Data Tantalize With New Clues To Dark Matter


Image Credit: T. Linden, Univ. of Chicago

Image Credit: T. Linden, Univ. of Chicago

A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe. Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory (Fermilab), the Harvard-Smithsonian Center for Astrophysics (CfA), the Massachusetts Institute of Technology (MIT) and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

The galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It’s also where astronomers expect to find the galaxy’s highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

No one knows the true nature of dark matter, but WIMPs, or Weakly Interacting Massive Particles, represent a leading class of candidates. Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide. Both of these pathways end with the production of gamma rays — the most energetic form of light — at energies within the detection range of Fermi’s Large Area Telescope (LAT).

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Gamma-Rays Tighten Window On Dark Matter Theories

February 28, 2014 Leave a comment

Observed data fitting the dark matter component, after subtracting all other components toward the Galactic Center.

Observed data fitting the dark matter component, after subtracting all other components toward the Galactic Center.

UC Irvine astrophysicists report that gamma-ray photons observed from the center of the Milky Way Galaxy are consistent with the intriguing possibility of dark matter annihilation, according to research submitted to the journal Physical Review D.

Kevork Abazajian, Nicolas Canac, Shunsaku Horiuchi and Manoj Kaplinghat analyzed data from NASA’s space-borne Fermi Gamma-ray Space Telescope and found that only a narrow range of dark matter models can produce an excess of gamma rays coming from the Milky Way. These gamma rays could be produced as particles of dark matter annihilate one another.

“The data provides a better-than 10 percent precise determination of the dark matter’s particle mass with the best estimates we have of what else is going on in the Galactic Center,” says Abazajian.

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Active Supermassive Black Holes Revealed In Merging Galaxies

January 29, 2014 Leave a comment

Artist's rendition. Credit: NAOJ

Artist’s rendition. Credit: NAOJ

A team of astronomers has conducted infrared observations of luminous, gas-rich, merging galaxies with the Subaru Telescope to study active, mass-accreting supermassive black holes (SMBHs). They found that at least one SMBH almost always becomes active and luminous by accreting a large amount of material (Figure 1). However, only a small fraction of the observed merging galaxies show multiple, active SMBHs. These results suggest that local physical conditions near SMBHs rather than general properties of galaxies primarily determine the activation of SMBHs.

In this Universe, dark matter has a much higher mass than luminous matter, and it dominates the formation of galaxies and their large-scale structures. The widely accepted, cold-dark-matter based galaxy formation scenario posits that collisions and mergers of small gas-rich galaxies result in the formation of massive galaxies seen in the current Universe. Recent observations show that SMBHs with more than one-million solar masses ubiquitously exist in the center of galaxies. The merger of gas-rich galaxies with SMBHs in their centers not only causes active star formation but also stimulates mass accretion onto the existing SMBHs. When material accretes onto a supermassive black hole (SMBH), the accretion disk surrounding the black hole becomes very hot from the release of gravitational energy, and it becomes very luminous.

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