Their detailed maps show the ‘local’ cosmos out to a distance of 600 million light years, identifying all the major superclusters of galaxies and voids. They also provide important clues regarding the distribution of the mysterious ‘dark matter’ and ‘dark energy’ which are thought to account for up to 96% of the apparent mass of the Universe.
The reconstructed density fields in the supergalactic coordinates (SGX, SGY). In this coordinate system, the equator is aligned with the Virgo Cluster, Great Attractor and Perseus-Pisces superclusters. The main overdensities are Hydra-Centaurus (centre-left), Perseus-Pisces (centre-right), Shapley Concentration (upper left), Coma (upper-middle).
Within this vast volume, the most massive galaxy supercluster is 400 million light years away. It was named after its identifier, the American astronomer Harlow Shapley. The Shapley supercluster is so big that it takes light at least 20 million years to travel from its one end to the other. However, Shapley is not the only massive supercluster in our vicinity.
The Great Attractor supercluster, which is three times closer than Shapley, plays a bigger role in the motion of our Galaxy. According to the team, our Milky Way galaxy, its sister galaxy Andromeda and other neighbouring galaxies are moving towards the Great Attractor at an amazing speed of about a million miles per hour. The researchers also established that the Great Attractor is indeed an isolated supercluster and is not part of Shapley.
The new maps are based on the observation that, as the Universe expands, the colours of galaxies change as their emitted light waves are stretched or “redshifted”. By measuring the extent of this redshift, astronomers are able to calculate approximate distances to galaxies.
The new survey, known as the 2MASS Redshift Survey (2MRS), has combined two dimensional positions and colours from the Two Micron All Sky Survey (2MASS), with redshifts of 25,000 galaxies over most of the sky. These redshifts were either measured specifically for the 2MRS or they were obtained from an even deeper survey of the southern sky, the 6dF Galaxy Redshift Survey (6dFGS).
The great advantage of 2MASS is that it detects light in the near-infrared, at wavelengths slightly longer than the visible light. The near-infrared waves are one of the few types of radiation that can penetrate gases and dust and that can be detected on the Earth’s surface. Although the 2MRS does not probe as deeply into space as other recent narrow-angle surveys, it covers the entire sky.
Galaxy redshift surveys are only able to detect luminous matter. This luminous matter accounts for no more than a small fraction of the total matter in the Universe. The remainder is composed of a mysterious substance called ‘dark matter’ and an even more elusive component named ‘dark energy’.
“We need to map the distribution of dark matter rather than luminous matter in order to understand large-scale motions in our Universe,” explained Dr. Pirin Erdogdu (Nottingham University), lead author of the paper. “Fortunately, on large scales, dark matter is distributed almost the same way as luminous matter, so we can use one to help unravel the other.”
Her collaborator, Dr. Thomas Jarrett from Caltech, added, “The other advantage of observing in the near-infrared wavelength is the fact that it traces directly the luminous matter, and thus the dark matter, as well.”
“Our nearly two decade effort has produced the absolute best ever map of the nearby Universe,” said Prof. John Huchra of Harvard University. “With this we hope to elucidate the nature and disposition of dark matter and understand much, much more about our cosmological model and about galaxies themselves.”
In order to map the dark matter probed by the survey, the team used a novel technique borrowed from image processing. The method was partly developed by Prof. Ofer Lahav, a co-author of the paper and head of the astrophysics group at University College London. The technique utilizes the relationship between galaxy velocities and the total distribution of mass.
“It is like reconstructing the true street map of London just from a satellite image of London taken at night. The street lights, like the luminous galaxies, act as beacons of the underlying roads,” said Prof. Lahav.
"This extraordinarily detailed map of the Milky Way’s cosmic neighbourhood provides a benchmark against which theories for the formation of structure in the Universe can be tested,” commented Prof. Matthew Colless, director of the Anglo-Australian Observatory and leader of the 6dF Galaxy Survey.
“In the near future, the predicted motions derived from this map will be confronted with direct measurements of galaxies’ velocities obtained by the 6dF Galaxy Survey, providing a new and stringent test of cosmological models.”
Dr. Pirin Erdogdu | alfa
Neutron star merger directly observed for the first time
17.10.2017 | University of Maryland
Breaking: the first light from two neutron stars merging
17.10.2017 | American Association for the Advancement of Science
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
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