ESA Herschel: key to discovery of spectacular gravitational lens

An irregular ring of radiation can be seen around the distant galaxy in the center of this 2.2-micron CCD photograph, made with the 10-meter Keck telescope on Hawaii. 

The lensing galaxy is associated with radio source 3C 220.3. 

The radiation of the ring originates from an extremely distant galaxy-in-formation and is a result of the gravitational-lens effect. 

Just below the lensing galaxy a neighboring galaxy can be seen, which also contributes to the lensing effects. 

Credit: ESA and the W. M. Keck Observatory.

An international team of astronomers including Dutch astronomers Peter Barthel and Léon Koopmans (University of Groningen) reports the discovery of a unique case of a cosmic gravitational lens.

Using several telescopes on the ground and in space, the scientists show that a distant radio galaxy, acting as a cosmic lens, distorts and magnifies the radiation of an even more distant mysterious dark object, thereby making that object visible.

Owing to the lens magnification, the faint background object becomes visible as a ring-like structure around the lensing foreground radio galaxy, seen well on an image made with one of the two 10-meter Keck telescopes on Hawaii.

Led by Martin Haas of Bochum University, Germany, the research started as rather simple observations with the Herschel Space Telescope of a sample of distant radio galaxies.

It rapidly grew into a project where crucial supplementary observations demonstrated the unique character of this cosmic lens.

While formally the Herschel Space Observatory did not discover this gravitational lens, it was the breakthrough Herschel performance that allowed the astronomers to measure the far-infrared emission of 3C 220.3, which in turn made them suspicious about its origin.

The original target, the very massive radio galaxy, emitted simply too much far-infrared radiation. Additional observations, with optical and radio telescopes, subsequently demonstrated unambiguously the cosmic lens effect of the radio galaxy making the dark background object visible in the far-infrared.

Astronomers have known of the cosmic gravitational lens phenomenon since 1979, although the light bending of distant stars by the Sun was already observed in 1919.

Calculations by Einstein in 1912 already predicted the existence of such cosmic lenses.

Gravitational lenses allow astronomers to investigate the properties of both the very distant lens and the even more distant object, a galaxy in the process of formation.

Modeling of the geometry of the lensing situation for instance demonstrated that the lensing galaxy which hosts the radio source contains an unexpectedly low fraction of mysterious dark matter compared with that predicted for large radio galaxies.

More information: 3C 220.3: A Radiogalaxy Lensing a Submillimeter Galaxy" by an international group of 20* astronomers led by Martin Haas (Ruhr University, Bochum, Germany) is accepted for publication in The Astrophysical Journal. Preprint: arxiv.org/abs/1406.2872

Fermi observatory: First gamma-ray study of a gravitational lens

In the heart of an active galaxy, matter falling toward a supermassive black hole creates jets of particles traveling near the speed of light. 

For active galaxies classified as blazars, one of these jets beams almost directly toward Earth. 

Credit: NASA /Goddard Space Flight Center Conceptual Image Lab

An international team of astronomers, using NASA's Fermi observatory, has made the first-ever gamma-ray measurements of a gravitational lens, a kind of natural telescope formed when a rare cosmic alignment allows the gravity of a massive object to bend and amplify light from a more distant source.

This accomplishment opens new avenues for research, including a novel way to probe emission regions near supermassive black holes.

It may even be possible to find other gravitational lenses with data from the Fermi Gamma-ray Space Telescope.

Teddy Cheung

"We began thinking about the possibility of making this observation a couple of years after Fermi launched, and all of the pieces finally came together in late 2012," said Teddy Cheung, lead scientist for the finding and an astrophysicist at the Naval Research Laboratory in Washington.

In September 2012, Fermi's Large Area Telescope (LAT) detected a series of bright gamma-ray flares from a source known as B0218+357, located 4.35 billion light-years from Earth in the direction of a constellation called Triangulum.

These powerful flares, in a known gravitational lens system, provided the key to making the lens measurement.

Astronomers classify B0218+357 as a blazar—a type of active galaxy noted for its intense emissions and unpredictable behavior.

At the blazar's heart is a supersized black hole with a mass millions to billions of times that of the sun.

As matter spirals toward the black hole, some of it blasts outward as jets of particles traveling near the speed of light in opposite directions.

The extreme brightness and variability of blazars result from a chance orientation that brings one jet almost directly in line with Earth.

Astronomers effectively look down the barrel of the jet, which greatly enhances its apparent emission.

Long before light from B0218+357 reaches us, it passes directly through a face-on spiral galaxy—one very much like our own—about 4 billion light-years away.

The galaxy's gravity bends the light into different paths, so astronomers see the background blazar as dual images.

With just a third of an arcsecond (less than 0.0001 degree) between them, the B0218+357 images hold the record for the smallest separation of any lensed system known.

While radio and optical telescopes can resolve and monitor the individual blazar images, Fermi's LAT cannot. Instead, the Fermi team exploited a "delayed playback" effect.

More Information: Fermi Gravitational Study

Gravitational Lensing: Missing dark matter located

The two images illustrate the effect of gravitational lensing. A massive galaxy at the center of the right panel causes the images of the background galaxies (white spots) to be enlarged and brightened.(Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS)

Researchers at IPMU and Nagoya University used large-scale computer simulations and recent observational data of gravitational lensing to reveal how dark matter is distributed around galaxies.

Galaxies have no definite "edges", the new research concludes. Instead galaxies have long outskirts of dark matter that extend to their nearby galaxies; the inter-galactic space is not empty but filled with dark matter.

It is well known that there is a large amount of unseen matter called "dark matter" in the universe. It constitutes about 22 percent of the present-day universe while ordinary matter constitutes only 4.5 percent. An important question still remains - Where is most of the dark matter in the universe ?

Einstein's theory of general relativity predicts that a light ray passing through near a massive object such as a galaxy is bent by the effect called "gravitational lensing". For example, the effect causes the image of a distant galaxy to be deformed and brightened by an intervening galaxy.

However the effect itself is very small and so cannot be easily detected for a single galaxy. Only recently, images of millions of galaxies from Sloan Digital Sky Survey (SDSS) made it possible to derive an averaged mass distribution around the galaxies.

Earlier in 2010, an international research group led by Brice Menard then at University Toronto and Masataka Fukugita at IPMU used twenty four millions galaxy images from SDSS and successfully detected gravitational lensing effect caused by dark matter around the galaxies.

From the result, they determined the projected matter density distribution over a distance of a hundred million light years from the center of the galaxies.

Masataka Fukugita and Naoki Yoshida at IPMU, together with Shogo Masaki at Nagoya University, used very large computer simulations of cosmic structure formation to unfold various contributions to the projected matter distribution. They showed that galaxies have extended outskirts of dark matter, well beyond the region where stars exist.

The dark matter distribution is well organized but extended to intergalactic space, whereas luminous components such as stars are bounded within a finite region.

More interestingly, the estimated total amount of dark matter in the outskirts of the galaxies explains the gap between the global cosmic mass density and that derived from galaxy number counting weighted by their masses.

A long standing mystery on where the missing dark matter is now solved by the research. There is no empty space in the universe. The inter-galactic space is filled with dark matter.

NASA Gravity Lens: Bending the Light

This image of galaxy cluster MACS J1206.2-0847 (or MACS 1206 for short) is part of a broad survey with NASA's Hubble Space Telescope.

The distorted shapes in the cluster are distant galaxies from which the light is bent by the gravitational pull of an invisible material called dark matter within the cluster of galaxies.

This cluster is an early target in a survey that will allow astronomers to construct the most detailed dark matter maps of more galaxy clusters than ever before.

These maps are being used to test previous, but surprising, results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.

The multi-wavelength survey, called the Cluster Lensing And Supernova survey with Hubble (CLASH), probes, with unparalleled precision, the distribution of dark matter in 25 massive clusters of galaxies. So far, the CLASH team has completed observations of six of the 25 clusters.

Dark matter makes up the bulk of the universe's mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps space like a fun-house mirror so that the light from distant objects is distorted.

Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter's gravitational effects because they are the most massive structures in the universe. Because of their heft, the clusters act like giant cosmic lenses, magnifying, distorting and bending any light that passes through them — an effect known as gravitational lensing.

MACS 1206 lies 4.5 billion light-years from Earth. Hubble's keen vision helped CLASH astronomers uncover 47 multiple images of 12 newly identified faraway galaxies. Finding so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey is optimized to find them. The new observations build on earlier work by Hubble and ground-based telescopes.

The era when the first clusters formed is not precisely known, but is estimated to be at least 9 billion years ago and possibly as far back as 12 billion years ago. If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues to the early stages in the origin of structure in the universe.

Image Credit: NASA, ESA, M. Postman (STScI), and the CLASH Team

Distant Star Factory

Arp 220 is a nearby example of a merged starburst galaxy similar to SMM J2135-0102. Located 250 million light-years from Earth, Arp 220 is the aftermath of a collision between two spiral galaxies. The collision, which began about 700 million years ago, has sparked a crackling burst of star formation, resulting in about 200 huge star clusters in a packed, dusty region about 5,000 light-years across (about 5 percent of the Milky Way's diameter). The star clusters are the bluish-white bright knots visible in the Hubble image. Credit: NASA, ESA, the Hubble Heritage-ESA/Hubble Collaboration, and A. Evans (UVa/NRAO/Stony Brook)

Astronomers have combined a natural gravitational lens and a sophisticated telescope array to get the sharpest view ever of "star factories" in a galaxy over 10 billion light-years from Earth. They found that the distant galaxy, known as SMM J2135-0102, is making new stars 250 times faster than our Galaxy, the Milky Way.

They also pinpointed four discrete star-forming regions within the galaxy, each over 100 times brighter than locations (like the Orion Nebula) where stars form in our Galaxy. This is the first time that astronomers have been able to study properties of individual star-forming regions within a galaxy so far from Earth.

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