Gravitational lensing is an effect on light from a background source that arises because of this of the curvature of spacetime, the three dimensions of space and time united right into a single entity, brought on by mass.
The effect is most observable when light from a brilliant background source, like a star, a quasar, or a complete galaxy, passes a really massive object like one other galaxy or a cluster of galaxies, described as a lensing object or simply a gravitational lens.
This will have several results; it may possibly make an object shift its apparent position within the sky over Earth, or it may possibly cause a single object to look at multiple points within the sky, occasionally giving rise to spectacular formations like rings and crosses constituted of the identical object.
Greater than this, gravitational lensing can actually cause the sunshine from a background object to be amplified. That implies that astronomers can use the gravitational lensing arising from galactic clusters as natural cosmic magnifying glasses.
This has made it a very important tool for the investigation of the universe when it was in its infancy, making light from the earliest galaxies that might often be too faint to see observable by instruments just like the James Webb Space Telescope and the Hubble Space Telescope, NASA says.
How does gravitational lensing work?
In 1915 Albert Einstein revolutionized how we expect of gravity by introducing general relativity, a theory that can be sometimes referred to as the geometric theory of gravity. It’s from this theory that gravitational lensing was born.
Einstein’s idea was that gravity arises from the proven fact that mass causes the very fabric of spacetime to curve, and the greater the mass, the greater this curvature is. Consider this as being analogous to balls of accelerating mass being placed on a stretched rubber sheet, with a bowling ball causing a greater “dent” than, say, a tennis ball.
In fact, this curvature has an effect on other matter passing over it. So, as an example, the curvature of spacetime brought on by the sun keeps Earth in orbit, while the curvature Earth itself causes keeps the moon in orbit [R. J. A Lambourne., 2010, pg 166].
American theoretical physicist John Wheeler succinctly described the effect of general relativity as such: “Matter tells space-time the best way to curve, and space-time tells matter the best way to move.”
But, the curvature of spacetime doesn’t just affect matter; it affects light too, meaning that light at all times travels in straight lines, aside from when it doesn’t. If this sounds contradictory, consider a straight line drawn on a sheet of paper. If that paper is then curved, the road itself hasn’t deviated from its path, but yet it remains to be not straight. The trail photons of sunshine follow as they travel through space known as a geodesic, and it may possibly be curved like a line drawn on paper [R. J. A Lambourne., 2010, pg 133].
The bending of sunshine because it passes a curved region of spacetime created by an enormous object gives rise to gravitational lensing [R. J. A Lambourne., 2010, pg 223].
Until general relativity, within the physics of Issac Newton, space and time had been considered the unchanging stages upon which the events of the universe played out, though Newton had also predicted the bending of sunshine but to a much lesser extent than Einstein.
Changing spacetime right into a dynamic and changing aspect of the universe was controversial and meant general relativity would require an excellent deal of evidence before it could be accepted by the physics community of the twentieth century. Fortunately, gravitational lensing provided precisely the form of predictable and observable effect that could possibly be used to deliver this evidence.
How gravitational lensing proved Einstein right
General relativity suggests that as an upshot of gravitational lensing, the curvature of sunshine from a background source because it passes a gravitational lens causes the item it originates from appear in a special location within the sky than it could normally.
Astronomer Arthur Stanley Eddington believed that this shift in apparent position was key to providing verification of general relativity. He thought that he could use a solar eclipse and the darkening of the sun to look at the apparent position shift of well-studied stars brought on by the mass of the sun.
Eddington took advantage of the 1919 eclipse to check this concept, traveling to Sobral in northern Brazil to look at the eclipse while a second team journeyed to the island of Príncipe off the coast of West Africa to make similar observations.
Through the 1919 eclipse, the sun sat in front of the Hyades, a cluster of brilliant stars within the constellation of Taurus. The sunshine-bending effect could be at its most extreme closest to the disk of the sun, and fortunately, many stars of the Hyades could be visible near the disk of the sun through the eclipse.
Despite many technical issues experienced through the double expedition, Eddington and the second team led by astronomer Andrew Claude de la Cherois Crommelin observed a deflection of sunshine from these stars because of this of the sun coming between them and Earth that was consistent with the predictions of general relativity. The change in apparent position was twice that which was predicted by Newton’s theory of gravity.
Though the findings haven’t been without controversy, many similar eclipse experiments performed after this have further confirmed gravitational lensing and the curvature of space by massive objects and have revealed more about this incredible phenomenon arising from gravity.
Kinds of gravitational lensing
There are three major forms of gravitational lensing, in accordance with the University of California, Berkeley, strong lensing, weak lensing, and microlensing.
Strong gravitational lensing
Because the name suggests, strong lensing is essentially the most extreme of those and occurs when the gravitational lens is especially massive, and the background source that’s being lensed is near it. Because of this the sunshine from this source can take multiple paths past the gravitational lens, depending on how close its path carries it. Because of this, strongly lensed light from a single object can arrive at an observer at different times.
If the background object that’s being lensed varies with time, then its multiple images may also vary. Not only can this be used to trace the event of explosive events like supernovas, the explosive deaths of massive stars, but it may possibly even be used to measure how rapidly the universe is expanding, a rate referred to as the Hubble constant, University of California, Berkeley explains.
Results of strong gravitational lensing
The primary time that multiple images were seen from a single object was in 1979 when astronomers saw the double image of a quasar, which has come to be known, somewhat inaccurately, because the “Twin Quasar.”
Initially believing these to be two separate quasars, designated Q0957+561 A and B, astronomers studied their radio and visual light spectra, discovering they’re similar. A team of scientists led by Dennis Walsh concluded that these twin quasars are, in actual fact, the identical object, the sunshine from which has taken different paths around a faint but detectable galaxy between the quasar and Earth, with that galaxy acting as a gravitational lens [R. J. A Lambourne., 2010, pg 223].
Since 1979, astronomers have discovered that stang gravitational lensing can create some extraordinary manifestations.
In keeping with ESA, the outcomes of strong gravitational lensing are different depending on the form of the item that’s doing the lensing. The best forms of gravitational lensing occur when there’s a single object warping spacetime and bending light.
If a gravitational lens is spherical, then it creates what’s referred to as an Einstein ring by which a single object is repeated in a circular arrangement. If the gravitational lens object is elongated, like some galaxies, as an example, that the background object is replicated in a cross-like arrangement, known as an Einstein cross.
ESA adds that more complex gravitational lensing happens when the lensing object is an irregular shape or an arrangement of massive objects, resembling a galactic cluster. In these cases, the effect on background sources is warping their appearance, smearing them across a picture, and making them appear as arcs and even stretched out like taffy.
This striking effect is especially outstanding within the arcs and swirls that represent lensed galaxies seen in the primary image delivered to the general public from the James Webb Space Telescope (JWST), the deep field image of galaxy cluster SMACS 0723 revealed by U.S. President Joe Biden on July 11, 2022.
These smears created by galactic clusters acting as gravitational lenses will be studied to evaluate the distribution of mass inside those clusters. This is especially useful to astronomers studying the distribution of dark matter around galaxies.
Though dark matter doesn’t interact with electromagnetic radiation and thus doesn’t emit, absorb, or reflect light, it does have mass, meaning it warps spacetime and interacts gravitationally, identical to “abnormal matter” that makes up the visible components of galaxies.
Meaning by the quantity of gravitational lensing brought on by a galaxy or a cluster of galaxies after which comparing this to the lensing that might have arisen from just the visible matter in that gathering, like stars and hot gas, astronomers can determine how much invisible dark matter is present and the way it’s distributed.
Weak and micro gravitational lensing
Weak lensing occurs when the gravitational lensing is not extreme enough to provide rise to multiple instances of the identical object in the identical view of the universe or to create visually striking smeared galaxies. Weak lensing still causes some distortion, but this will’t be seen on individual galaxies, so the one option to really see the effect of weak lensing is by lots of galaxies and averaging the effect across them.
Strong and weak gravitational lensing come from incredibly massive objects like galaxies or galactic clusters, but rather more diminutive objects can even warp spacetime and divert the trail of sunshine. Gravitational microlensing [R. J. A Lambourne., 2010, pg 225] occurs when a lensing object has a mass much like that of the sun or as large as several times that of our star.
While the distortion created by gravitational microlensing could also be too subtle to detect, it does create a brightening of objects. This implies gravitational microlensing will be utilized by monitoring changes within the brightness of well-studied stars. The brightening of a distant star for a period of days or perhaps weeks can indicate that a dense and dark unseen object has passed in front of those stars, causing them to be temporarily lensed.
Microlensing has turn into a viable option to detect black holes, which don’t emit any light from beyond the light-trapping surface that acts as their boundary, referred to as the event horizon, and thus cannot be seen unless they’re creating turbulent and violent conditions in gas and dirt around them causing it to glow. It’s because as they still possess mass, black holes still warp space and thus still give rise to a small amount of gravitational lensing.
How the JWST and Hubble space telescope use gravitational lensing to look back in time
As the sunshine from distant and thus early galaxies travels to Earth, it loses energy and thus becomes fainter. Meaning early galaxies are so faint they aren’t visible to even essentially the most powerful equipment created by humanity. That’s unless they get a helping handing from a magnifying glass the scale of a complete galactic cluster.
The magnification of sunshine brought on by gravitational lensing has been used to great effect by the Hubble Space Telescope, which has employed it to review the structure of early galaxies. From its position over Earth, freed from the blurring effects of our planet’s atmosphere, Hubble, which has been studying the universe since 1990, can see gravitationally lensed early galaxies that ground-based telescopes would miss.
This has helped the ground-breaking telescope to review the structure of galaxies that would not be seen without the usage of gravitational lensing, even by Hubble’s latest, more powerful partner, the James Webb Space Telescope (JWST) in accordance with NASA.
The JWST has followed the lead of Hubble, using gravitational lensing to great effect and producing images with galaxies warped and smeared around a galactic cluster lens in such a way it could make abstract painter Salvador Dali proud.
In only its first 12 months of operation since coming online in mid-2022, the JWST has built upon the work of Hubble using gravitational lensing to see 4 of essentially the most distant and, thus, earliest galaxies known thus far. These galaxies, JADES-GS-z10–0, JADES-GS-z11–0, JADES-GS-z12–0, and JADES-GS-z13–0, existed when the 13.8 billion-year-old universe was just around 350 million years old.
Gravitational lensing FAQs answered by an authority
We asked Victor Chan, a Ph.D. student within the University of Toronto’s David A. Dunlap Department of Astronomy & Astrophysics, some steadily asked questions on gravitational lensing.
Victor Chan is a Ph.D. student within the University of Toronto’s David A. Dunlap Department of Astronomy & Astrophysics. He focuses on cosmology, cosmic microwave background, data modeling and evaluation.
What’s gravitational lensing and what causes it?
Gravitational lensing is when light is deflected by objects with very strong gravity. We normally think of sunshine traveling in straight lines. For instance, you may see the hearth on a candle because its light travels straight to your eyes. Sometimes the trail that a lightweight ray takes will be deflected, and we generally seek advice from this as lensing. We see this occur in on a regular basis life when light travels from one medium into one other medium with different density. That is how glasses work. Gravitational lensing also refers back to the bending of a lightweight path, but this time it’s as a consequence of gravity! Similar to how gravity can affect the trail of normal objects, light rays will be deflected by objects with very large mass.
When does gravitational lensing occur?
Three things are required! First, we require an observer. This is often someone, or a telescope, on Earth. Next, we’d like a lens. Again, a really large mass is required to significantly change the trail of sunshine, so this is often a galaxy or a galaxy cluster. Finally, we’d like a source of sunshine that might be lensed. The geometry of gravitational lensing generally requires the source to be behind the lens from the angle of the observer. This specific configuration implies that it’s relatively rare for us to look at gravitationally lensed objects.
How can astronomers use gravitational lensing?
It takes A LOT of mass to significantly deflect light away from its original path. It often requires the mass of a galaxy or perhaps a cluster of galaxies. This is the reason gravitational lensing is often only observed at cosmic scales. Similar to a magnifying glass, lensed light will be magnified or de-magnified. If the sunshine coming towards us from a distant source is lensed by an enormous galaxy situated in between, then we will make the most of magnified (and due to this fact brighter) images to review them in additional detail. We can even learn concerning the mass of the lens itself by studying how strongly it lenses the sunshine around it.
Why is it useful in seeing early galaxies?
Light speed is a finite quantity, so it takes time for light to travel cosmic distances. The “lookback time” of early galaxies tells us that those we will see are situated very distant. This makes them difficult to look at due to their apparent size and brightness, and gravitationally lensed images of those faraway galaxies (specifically the magnified versions) will be higher observed and studied since they’re brighter than their un-lensed counterparts. I like to think about it as if we’re putting those faraway galaxies under a microscope (after all, that is not what is definitely happening, but the concept is comparable).
How is gravitational lensing related to dark matter?
Dark matter is anything that interacts gravitationally (identical to regular matter) but does circuitously emit or absorb light. Astronomers understand it exists because we see the results of gravity at cosmic scales, they usually observe stronger gravitational effects than visible matter can account for. The identical thing applies to gravitational lensing. The extent to which images are magnified by gravitational lenses is way stronger than the visible matter within the lenses can account for. If we compare the mass of the gas and stars we see in a galaxy to the mass we infer from gravitational lensing, we are inclined to notice that there’s lots of mass that we don’t see. We will then infer how much dark matter should be present within the lens to ensure that us to look at such a level of lensing.
Are there several types of gravitational lensing
Yes! There are several sorts of gravitational lensing, but they will be described by the identical phenomenon of sunshine paths being deflected by gravity. Sometimes astronomers differentiate between and lensing, which refers to how much the trail of sunshine has been deflected (the angle between the unique and deflected paths). Images will be magnified or demagnified, as I described earlier, but they will also be warped, which astronomers seek advice from as lensing). Astronomers also sometimes distinguish between the of sunshine that’s being observed. Galaxy lensing is often observed with optical light. We can even observe gravitational lensing with microwave light leftover from the Big Bang!
How do you utilize gravitational lensing in your research?
I study the results of gravitational lensing on the cosmic background radiation (also called the cosmic microwave background or CMB) from the Big Bang. That is residual light leftover from when the Big Bang, and we will observe it from virtually every direction. In some sense, it’s the right source of sunshine to be gravitationally lensed because this light involves us from behind the entire cosmic structures and galaxies that formed after the Big Bang. The issue is that we do not know the way the unique CMB looked since we will only observe the lensed version. My research focuses on benefiting from our knowledge of how gravitational lensing works to disentangle the data concerning the Universe’s massive structures within the observed CMB.
Additional resources
General relativity explains that the curving of spacetime by mass gives rise to other stunning and infrequently shocking phenomena apart from gravitational lensing. One example is “frame dragging,” by which a rotation object of great mass literally drags space and time around with it. In 2015 an astronomer from the University of California, Berkeley, discovered a distant supernova being lensed 4 times by an enormous galaxy creating an explosive Einstein cross.
Bibliography
Gravitational Lensing, ESA, [Acessed 05/20/23], [https://esahubble.org/wordbank/gravitational-lensing/#:~:text=Gravitational%20lensing%20occurs%20when%20a,accordingly%20called%20a%20gravitational%20lens.]
Gravitational lensing, Hubblesite NASA, [Acessed 05/20/23], [https://hubblesite.org/contents/articles/gravitational-lensing]
Spyglasses into the Universe: gravitational lenses, ESA, [Acessed 05/20/23], [https://esahubble.org/science/gravitational_lensing/]
Several types of gravitational lenses, ESA, [Acessed 05/20/23], [https://esahubble.org/images/heic0404b/]
R. J. A., Lambourne., Relativity, Gravitation and Cosmology, Cambridge University Press, [2010], ISBN 978 0 521 13138 4
Gravitational lensing, University of California, Berkeley, [Acessed 05/20/23], [https://w.astro.berkeley.edu/~jcohn/lens.html]
Discoveries – Highlights | Shining a Light on Dark Matter, Hubble Space Telescope, NASA, [Acessed 05/20/23], [https://www.nasa.gov/content/discoveries-highlights-shining-a-light-on-dark-matter]
G. Gilmore., G. Tausch-Pebody., The 1919 eclipse results that verified general relativity and their later detractors: a story re-told, Royal Society Journal of the History of Science, [2021] https://royalsocietypublishing.org/doi/10.1098/rsnr.2020.0040]
