Over 9 billion years ago, a distant star exploded. Thanks to Einstein, we’ve seen it multiple times on replay.
All across the Universe, matter and energy curve the fabric of space, with dramatic consequences.
An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, such as a foreground galaxy cluster. The ‘fabric of space’ analogy is just an analogy, and isn’t physically meaningful, but the curved light paths are verified by observation. (NASA/ESA)
Masses are most concentrated in quasars, large individual galaxies, and enormous galaxy clusters.
HE0435–1223, located in the centre of this wide-field image, is among the five best lensed quasars discovered to date. The foreground galaxy creates four almost evenly distributed images of the distant quasar around it. (ESA/HUBBLE, NASA, SUYU ET AL.)
With enough mass, sufficiently distorted space causes light to travel along multiple paths, arriving at the same destination.
Six examples of the strong gravitational lenses the Hubble Space Telescope discovered and imaged. The arcs and ring-like structures are capable of probing both dark matter and General Relativity, by reconstructing the mass magnitude and distribution and comparing it with the background light observed. (NASA, ESA, C. FAURE (ZENTRUM FÜR ASTRONOMIE, UNIVERSITY OF HEIDELBERG) AND J.P. KNEIB (LABORATOIRE D’ASTROPHYSIQUE DE MARSEILLE))
These masses behave as gravitational lenses, creating multiple stretched, magnified images of background stars and galaxies.
The galaxy imaged here by Hubble, UZC J224030.2+032131, doesn’t have five separate components to it, but is merely the central, diffuse light source. The four lights surrounding it is due to the bending and stretching of space due to gravitational lensing, and produces the ‘Einstein Cross’ shown here. This image is likely the sharpest Einstein Cross ever discovered. (ESA/HUBBLE AND NASA)
When the lens and a background source align in a particular fashion, quadruple images will result.
A zoomed-in view of the gravitationally lensed supernova iPTF16geu. The insets shows a view of the foreground lensing galaxy and on the far right the resolve multiple images of the lensed supernova as observed with the Hubble Space Telescope and the Keck Telescope/NIRC2 instrument. (SDSS; ESA/HUBBLE & NASA; KECK OBSERVATORY; JOEL JOHANSSON)
With slightly different light-travel paths, the brightness and arrival time of each image is unique.
When an observatory views a strong source of mass, like a quasar, galaxy, or galaxy cluster, it can often find multiple images of the lensed, magnified, distorted background sources due to the bending of space by the foreground mass. (ALMA (ESO/NRAO/NAOJ), L. CALÇADA (ESO), Y. HEZAVEH ET AL.; JOEL JOHANSSON)
In November 2014, a quadruply-lensed supernova was observed, showcasing exactly this type of alignment.
In November of 2014, a serendipitously-aligned background galaxy with a foreground galaxy within a galaxy cluster was found. The background galaxy experienced a supernova more than 9 billion years ago, and the light from all four images arrived almost all at once. (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))
Although a single galaxy caused the quadruple image, that galaxy was part of a huge galaxy cluster, exhibiting its own strong lensing effects.
Color-composite image of the galaxy cluster MACSJ1149.6+2223, with critical curves for sources at the z = 1.49 redshift of the host galaxy overlaid. From the original discovery paper published in Science in 2015. The quadruple image of the supernova was just one of three locations where the same galaxy was identified. (P.L. KELLY ET AL., SCIENCE (2015): VOL. 347, ISSUE 6226, PP. 1123–1126)
Elsewhere in the cluster, two additional images of the same galaxy also appear.
A distant, background galaxy is lensed so severely by the intervening, galaxy-filled cluster, that three independent images of the background galaxy, with significantly different light-travel times, can all be seen. (NASA & ESA)
According to Einstein’s General Relativity, one image should have shown a supernova in 1995, the other should appear in late 2015 or early 2016.
This image illustrates a gravitational lensing effect, and the multiple paths that light can take to arrive at the same destination. Given the great cosmic distances and enormous masses at play, arrival times can differ by as little as hours or as much as decades between images. (NASA, ESA, AND JOHAN RICHARD (CALTECH, USA); ACKNOWLEDGEMENTS: DAVIDE DE MARTIN & JAMES LONG (ESA/HUBBLE))
On December 11, 2015, that predicted supernova appeared and was quickly discovered.
The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circle indicates the predicted position of the newest appearance of the supernova. To the lower right the Einstein cross event from late 2014 is visible. The image on the top right shows observations by Hubble from October 2015, taken at the beginning of the observation programme to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the Refsdal Supernova on 11 December 2015, as predicted by several different models. (NASA & ESA AND P. KELLY (UNIVERSITY OF CALIFORNIA, BERKELEY))
The combination of this gravitational lens, dark matter, and General Relativity confirms our modern picture of the Universe.
A galaxy cluster can have its mass reconstructed from the gravitational lensing data available. Most of the mass is found not inside the individual galaxies, shown as peaks here, but from the intergalactic medium within the cluster, where dark matter appears to reside. The time-delay observations of the Refsdal supernova cannot be explained without dark matter in this galaxy cluster. (A. E. EVRARD. NATURE 394, 122–123 (09 JULY 1998))
Mostly Mute Monday tells the astronomical story of an object, phenomenon or event in images, visuals, and no more than 200 words. Talk less; smile more. Ethan Siegel is the author of
Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.