Composite image of the gravitational lens SDP.81 showing the distorted ALMA image of the more distant galaxy (red arcs) and the Hubble optical image of the nearby lensing galaxy (blue center object).
Composite image of the gravitational lens SDP.81 showing the distorted ALMA image of the more distant galaxy (red arcs) and the Hubble optical image of the nearby lensing galaxy (blue center object). By analyzing the distortions in the ring, astronomers have determined that a dark dwarf galaxy (data indicated by white dot near left lower arc segment) is lurking nearly 4 billion light-years away.
Y. Hezaveh, Stanford Univ.; ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble Space Telescope
The Warped Beauty of Gravitational Lenses: Photos
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In November 1915, Albert Einstein published his famous theory of general relativity, a theory that began a revolution in physics and transformed our view on the entire universe. A key component of general relativity is that a massive object like a planet, star, galaxy or cluster of galaxies can have a dramatic warping effect on the "fabric" of the universe -- known as "spacetime." As light travels in straight lines through spacetime, should a mass cause an otherwise "flat" spacetime to curve, the path of light also becomes curved. Therefore, by this theoretical reasoning, we should be able to see the warped light of distant galaxies as that light travels past other galaxies on its way to being observed at Earth. And sure enough, there are countless examples in the cosmos of this warped light caused by a mechanism known as "gravitational lensing" -- like artifacts etched in ancient light, stunning arcs, misshapen orbs and even near-perfect circles have been observed in star fields. These artifacts are the lensed light from distant galaxies and these observations have been used to superboost some of our most powerful telescopes. Hubble at 25: Space Telescope's Top Science Discoveries In this dramatic observation by the Hubble Space Telescope and NASA's Chandra X-ray Observatory , a cartoon "Cheshire Cat" seems to be looking back at us. In fact, this is a collection of galaxies over 4 billion light-years away in the constellation Ursa Major -- some of the galaxies' light has become warped and deformed on its way through the universe to our telescopes, creating what looks like a Cheshire Cat smile.
X-ray: NASA/CXC/UA/J.Irwin et al; Optical: NASA/STScI
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provides a good description as to how gravitational lensing works. Light from a distant galaxy travels through spacetime as it curves around a cluster of galaxies in the foreground. Interestingly, the mass of the foreground cluster has a similar effect on this distant light as a glass lens would have if placed in front of a candle flame. Should the positioning be just right, the gravitational lens can amplify the distant light, creating a natural lens in space, magnifying the light from distant galaxies that would have otherwise remained too faint to be seen. It is this effect of gravitational lenses that is being leveraged by Hubble astronomers who have embarked on a project called " Frontier Fields " that is on the lookout for cosmic lenses to superboost Hubble's observing power. Hubble at 25: What's Next for the Space Telescope?
ESA
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Of course, the alignment isn't always perfect between Earth, gravitational lens and distant galaxy. Also, the foreground object creating the lens is usually not regularly shaped. These factors cause most lensed galaxies to appear as broken arcs. Multiple instances of the same galaxy can also be projected as the distant starlight becomes warped and fragmented. In this Hubble observation of the galaxy cluster Abell 370 , many galaxies are present, but several prominent arcs of galactic light can be seen. Often, for well-defined examples, these arcs can be reconstructed to reveal what that galaxy looks like without being warped.
NASA, ESA, the Hubble SM4 ERO Team, and ST-ECF
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This is another massive galaxy cluster called Abell 2218 filled with some stunning examples of gravitationally-lensed galaxies. These arcs are thought to be light from galaxies located 5 to 10 times further away from Earth than the galactic cluster. The cluster is credited with amplifying the weak light from galaxies that existed over 13 billion years ago, less than a billion years after the Big Bang. These arcs truly are artifacts from the beginning of time. ANALYSIS: Hunting Black Holes Through a Gravitational Lens
Andrew Fruchter (STScI) et al., WFPC2, HST, NASA
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Should the alignment be just right, and the lensing object be less complex than a cluster of galaxies, it's possible to see near-perfect circles of light or "horseshoe" shaped lenses where the light of a distant galaxy has been almost perfectly warped 360 degrees around the lensing object. The passage of an isolated massive black hole, for example, in front of a distant galaxy could create such a dramatic scene. ANALYSIS: Monstrous Star-Forming Regions Seen in Ancient Galaxy
ESA/Hubble & NASA
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As shown in this striking Atacama Large Millimeter/submillimeter Array (ALMA) observation , the light of a distant galaxy has formed a complete circle aptly known as an "Einstein Ring." The light originated from an ancient "starburst" galaxy called SDP.81 and is the finest example of an Einstein Ring found to date. MORE: ALMA Captures Ancient Galaxy's Near-Perfect Einstein Ring
ALMA/ESO
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Occasionally multiple images of the same object can be seen around gravitational lenses. In this spectacular example, an ancient supernova in a distant galaxy has been magnified by the masses of galaxies contained within the MACS J1149.6+2223 cluster, located 5 billion light-years away. The supernova, located another 4 billion light-years behind the cluster, has been multiplied 4 times as the light from the same supernova took different paths around the lens. As this was a transient event, the different supernova images were detected at different times by Hubble. Such a configuration of lensed images is known as an "Einstein Cross." NEWS: Hubble's Successor Will See Universe's First Light
NASA, ESA, AND S. RODNEY (JHU) AND THE FRONTIERSN TEAM; T. TREU (UCLA), P. KELLY (UC BERKELEY), AND THE GLASS TEAM; J. LOTZ (STSCI) AND THE FRONTIER FIELDS TEAM; M. POSTMAN (STSCI) AND THE CLASH TEAM; AND Z. LEVAY (STSCI)
There are few things that get us more excited than the mysteries of dark matter and the warping of spacetime, but when you have both wrapped into a stunning image of an Einstein ring, you know you’re onto something special.
In 2014, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile observed a striking cosmic quirkduring its Long Baseline Campaign. It saw a distant galaxy, warped beyond recognition, by the gravitational field of a massive galaxy in the foreground. This “Einstein ring” is so-called after Einstein’s theory of general relativity, which predicts spacetime can become bent by the presence of a powerful gravitational field.
In this case, the foreground galaxy had drifted in front of the more distant galaxy located some 12 billion light-years away, causing the distant galaxy’s light to be redirected around the warped spacetime. The result was a near-perfect circle of galactic light received by ALMA as one of the more extreme examples of gravitational lensing. Gravitational lensing is common in observations of the deep cosmos, where massive galaxies and galactic clusters bend spacetime like a malleable rubber sheet, often creating a “funhouse” mirror-like effect, distorting the observed shapes of distant galaxies whose light has taken a helter-skelter path through the confused spacetime landscape.
But sometimes, as this example proved, the alignment can be so perfect that the distant galaxy’s light can be warped around the symmetrical foreground galaxy, creating a ring that resembles a candle flame passing behind a magnifying glass. Gravitational lenses are the universe’s natural magnifying lenses and they are being used by the Hubble Space Telescope, for example, to superboost its observational power as part of the Frontier Fields project.
Though it looks like a pristine ring, this particular observation of the “SDP.81″ gravitational lens holds some tiny distortions in the shape of its ring and astronomers have used these distortions to reveal the presence of an invisible dwarf galaxy situated right next to the more massive lensing galaxy. And this tiny cluster of stars is packed with dark matter.
“We can find these invisible objects in the same way that you can see rain droplets on a window,” said Yashar Hezaveh at Stanford University, Calif., in a statement. “You know they are there because they distort the image of the background objects.” Raindrops will subtly refract light, distorting the light passing through a window; in much the same way, the invisible dwarf galaxy’s gravitational field is creating a minute distortion in the Einstein ring, revealing its presence in a tiny spacetime warp.
Finding this distortion and realizing it was due to the presence of an unseen galaxy was no easy task and required a huge computational effort, requiring, in part, time on one of the world’s most powerful supercomputers, the National Science Foundation’s Blue Waters.
Because of its close proximity to the larger galaxy, its estimated mass and lack of optical data, Hezaveh’s team thinks they’ve found a very dim dwarf galaxy that is dominated by dark matter.
It is predicted that large galaxies should have a large population of satellite dwarf galaxies, but astronomical surveys can only seem to detect a few examples. Our galaxy is known to have around 40 such satellites, but models predict that there should be thousands of them.
“This discrepancy between observed satellites and predicted abundances has been a major problem in cosmology for nearly two decades, even called a ‘crisis’ by some researchers,” said team member Neal Dalal, of the University of Illinois. “If these dwarf objects are dominated by dark matter, this could explain the discrepancy while offering new insights into the true nature of dark matter.”
Now it is hoped that many more gravitational lenses can be studied to look for the distortions caused by other dark matter-dominated dwarfs to hopefully explain why there’s such a strange discrepancy in observations when compared to theory. If we can do this, then perhaps we can better refine dark matter models and move a step closer to understanding why dark matter constitutes 85 percent of all the mass in the universe.
Source: NRAO