Video

Gravitational Lensing

In a long line of intellectual triumphs, Einstein’s theory of general relativity was his greatest and most imaginative.  It tells us that what we experience as gravity can be most accurately described as the bending of space itself.  This idea leads to consequences, including gravitational lensing, which is caused by light traveling in this curved space.  This is works in a way analogous to a lens (and hence the name).  In this video, Fermilab’s Dr. Don Lincoln explains a little general relativity, a little gravitational lensing, and tells us how this phenomenon allows us to map out the matter of the entire universe, including the otherwise-invisible dark matter.

Detection of the Gravitational Lens Magnifying a Type Ia Supernova

supernovaAn exceptionally bright supernova that baffled scientists has been explained.

It is so luminous because a galaxy sitting in front amplifies its light – making it appear 100 billion times more dazzling than our Sun.

This cosmic magnifying glass lay hidden between Earth and the supernova – and has now been detected with a telescope in Hawaii.

The discovery, reported in the journal Science, settles an important controversy in the field of astronomy…
Read more at http://www.bbc.com/news/science-environment-27118405

Most distant gravitational lens helps weigh galaxies

… but deepens a galactic mystery

The most distant gravitational lens yet discoveredAn international team of astronomers has found the most distant gravitational lens yet — a galaxy that, as predicted by Albert Einstein’s general theory of relativity, deflects and intensifies the light of an even more distant object. The discovery provides a rare opportunity to directly measure the mass of a distant galaxy. But it also poses a mystery: lenses of this kind should be exceedingly rare. Given this and other recent finds, astronomers either have been phenomenally lucky — or, more likely, they have underestimated substantially the number of small, very young galaxies in the early Universe.

Light is affected by gravity, and light passing a distant galaxy will be deflected as a result. Since the first find in 1979, numerous such gravitational lenses have been discovered. In addition to providing tests of Einstein’s theory of general relativity, gravitational lenses have proved to be valuable tools. Notably, one can determine the mass of the matter that is bending the light — including the mass of the still-enigmatic dark matter, which does not emit or absorb light and can only be detected via its gravitational effects. The lens also magnifies the background light source, acting as a “natural telescope” that allows astronomers a more detailed look at distant galaxies than is normally possible.

Gravitational lenses consist of two objects: one is further away and supplies the light, and the other, the lensing mass or gravitational lens, which sits between us and the distant light source, and whose gravity deflects the light. When the observer, the lens, and the distant light source are precisely aligned, the observer sees an Einstein ring: a perfect circle of light that is the projected and greatly magnified image of the distant light source.

Now, astronomers have found the most distant gravitational lens yet. Lead author Arjen van der Wel (Max Planck Institute for Astronomy, Heidelberg, Germany) explains: “The discovery was completely by chance. I had been reviewing observations from an earlier project when I noticed a galaxy that was decidedly odd. It looked like an extremely young galaxy, but it seemed to be at a much larger distance than expected. It shouldn’t even have been part of our observing programme!”

Van der Wel wanted to find out more and started to study images taken with the Hubble Space Telescope as part of the CANDELS and COSMOS surveys. In these pictures the mystery object looked like an old galaxy, a plausible target for the original observing programme, but with some irregular features which, he suspected, meant that he was looking at a gravitational lens. Combining the available images and removing the haze of the lensing galaxy’s collection of stars, the result was very clear: an almost perfect Einstein ring, indicating a gravitational lens with very precise alignment of the lens and the background light source [1].

The lensing mass is so distant that the light, after deflection, has travelled 9.4 billion years to reach us [2]. Not only is this a new record, the object also serves an important purpose: the amount of distortion caused by the lensing galaxy allows a direct measurement of its mass. This provides an independent test for astronomers’ usual methods of estimating distant galaxy masses — which rely on extrapolation from their nearby cousins. Fortunately for astronomers, their usual methods pass the test.

But the discovery also poses a puzzle. Gravitational lenses are the result of a chance alignment. In this case, the alignment is very precise. To make matters worse, the magnified object is a starbursting dwarf galaxy: a comparatively light galaxy (it has only about 100 million solar masses in the form of stars [3]), but extremely young (about 10-40 million years old) and producing new stars at an enormous rate. The chances that such a peculiar galaxy would be gravitationally lensed is very small. Yet this is the second starbursting dwarf galaxy that has been found to be lensed. Either astronomers have been phenomenally lucky, or starbursting dwarf galaxies are much more common than previously thought, forcing astronomers to re-think their models of galaxy evolution.

Van der Wel concludes: “This has been a weird and interesting discovery. It was a completely serendipitous find, but it has the potential to start a new chapter in our description of galaxy evolution in the early Universe.”

Notes

[1] The two objects are aligned to better than 0.01 arcseconds — equivalent to a one millimetre separation at a distance of 20 kilometres.

[2] This time corresponds to a redshift z = 1.53. This can be compared with the total age of the Universe of 13.8 billion years. The previous record holder was found thirty years ago, and it took less than 8 billion years for its light to reach us (a redshift of about 1.0).

[3] For comparison, the Milky Way is a large spiral galaxy with at least one thousand times greater mass in the form of stars than this dwarf galaxy.

Read more at http://www.spacetelescope.org/news/heic1319/

Quasars Acting as Gravitational Lenses

Image Credit: NASA, ESA, and F. Courbin (EPFL, Switzerland)

Astronomers using NASA’s Hubble Space Telescope have found several examples of galaxies containing quasars, which act as gravitational lenses, amplifying and distorting images of galaxies aligned behind them.

Quasars are among the brightest objects in the universe, far outshining the total starlight of their host galaxies. Quasars are powered by supermassive black holes.
To find these rare cases of galaxy-quasar combinations acting as lenses, a team of astronomers led by Frederic Courbin at the Ecole Polytechnique Federale de Lausanne (EPFL, Switzerland) selected 23,000 quasar spectra in the Sloan Digital Sky Survey (SDSS). They looked for the spectral imprint of galaxies at much greater distances that happened to align with foreground galaxies. Once candidates were identified, Hubble’s sharp view was used to look for gravitational arcs and rings (which are indicated by the arrows in these three Hubble photos) that would be produced by gravitational lensing.

Quasar host galaxies are hard or even impossible to see because the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. However, gravitational lensing candidates are invaluable for estimating the mass of a quasar’s host galaxy because the amount of distortion in the lens can be used to estimate a galaxy’s mass.

The next step for the team is to build a catalog of “quasar-lenses” that will allow them to determine masses for a statistically significant number of quasar host galaxies and to compare them with galaxies without quasars. With the numerous wide-field surveys that will start in the near future or that are already started, hundreds of thousands of quasars will be accessible for looking for lensing effects…..
Read more: nasa.gov

A Horseshoe Einstein Ring from Hubble

 Explanation: What’s large and blue and can wrap itself around an entire galaxy? A gravitational lens mirage. Pictured above, the gravity of a luminous red galaxy (LRG) has gravitationally distorted the light from a much more distant blue galaxy.
More typically, such light bending results in two discernible images of the distant galaxy, but here the lens alignment is so precise that the background galaxy is distorted into a horseshoe — a nearly complete ring.
Since such a lensing effect was generally predicted in some detail by Albert Einstein over 70 years ago, rings like this are now known as Einstein Rings. Although LRG 3-757 was discovered in 2007 in data from the Sloan Digital Sky Survey (SDSS), the image shown above is a follow-up observation taken with the Hubble Space Telescope’s Wide Field Camera 3. Strong gravitational lenses like LRG 3-757 are more than oddities — their multiple properties allow astronomers to determine the mass and dark matter content of the foreground galaxy lenses….

Read more: apod.nasa.gov

Gravitational Lensing as a Mechanism For Effective Cloaking

Benjamin K. Tippett
In light of the surge in popularity of electromagnetic cloaking devices, we consider whether it is possible to use general relativity to cloak a volume of spacetime through gravitational lensing. A metric for such a spacetime geometry is presented, and its geometric and physical implications are explained.

The procedure for designing an electromagnetic cloaking device

In general relativity, there is a tradition of engineering spacetime geometries with exotic attributes previously seen only in science fiction. Tipler [11] and Morris [7] have introduced time machines; and Alcubierre [2] introduced a warp drive. In science fiction, one popular conceit is the idea of a cloaking device: a mechanism through which a spaceship could be made undetectable. The revelation that curved spaces can be matched to the electromagnetic properties of a medium has sparked a recent interest in optical cloaking [1, 3–6, 8, 10]. We seek to construct a spacetime geometry which cloaks an interior region from null geodesics….
Read more: http://arxiv.org/PS_cache/arxiv/pdf/1108/1108.3793v1.pdf