The above image, captured by NASA’s Hubble telescope in April 2018, almost resembles the deep sea in microcosm – a vast, black canvas peppered with plankton-like spirals and ellipses. In fact, the picture shows a small segment of the universe in macrocosm: a sprawl of light-emitting galaxies, each one home to billions of suns and exoplanets. Indeed, the vastness of space is incomprehensible, but what captures the attention of NASA scientists is the curious halo encircling part of the picture.
The galaxies snapped by Hubble form a galaxy cluster with the not-so-snappy name of SDSS J0146-0929. Galaxy clusters consist of multiple galaxies, often thousands of them, held together by gravity. They form part of the superstructure of the universe and are the largest gravitationally influenced objects known to science.
Galaxy clusters also have the greatest density of any known gravitationally bound objects in the universe. However, they are not the largest part of the universal superstructure. Galaxy clusters form groups called superclusters, but gravity does not bound them. The Milky Way, for example, is part of the Virgo galaxy cluster which falls within the Laniakea Supercluster, which is slowly dispersing into its surroundings.
The strange circle visible at the center of the image represents a physical phenomenon rarely observed by science. The halo, though broken and incomplete, has a glowing circumference and a bubble-like appearance. In fact, the phenomenon, captured by NASA optics in 2018, is the result of a massive and mysterious warp in spacetime.
Of course, with more than two trillion galaxies in the observable universe, mystery is par for the course in matters astronomical. According to current calculations, the observable universe is an expanding sphere with physical signals that can be traced to an inception moment popularly known as the Big Bang. In fact, it consists of all matter in outer space that can be detected using telescopes and probes.
By contrast, the unobservable universe consists of those areas invisible to us, such as very distant places where light has yet to arrive from. Furthermore, according to Hubble’s Law, light from sufficiently remote places will never reach earth because the expansion of the universe is occurring faster than the speed of light. Therefore, parts of the universe are dark and undetectable to us.
Nonetheless, the technological developments of the late 20th and early 21st century have enabled humanity to observe previously hidden phenomena. And these have often been deep in space or at the edge of the known universe. In fact, astronomy is presently experiencing a golden age. And our scientific study of space is sure to supply new discoveries – and new mysteries – well into the future.
Meanwhile, recent astronomical achievements include the discovery of Proxima Centauri b. This nearby, rocky exoplanet is slightly larger than the Earth and has a surface temperature capable of supporting liquid water. Elsewhere, other research is concerned with the mechanics of black holes, including a decades-long study of the supermassive black hole at the center of our home galaxy, the Milky Way.
Indeed, where metaphysical philosophers once debated how many angels could dance on the head of a pin, astrophysicists are now searching for alien life. Others are investigating the possible implications of so-called mega-stars – enormous suns, many times bigger than our own. Others yet are testing the hypothesis that our universe is not the first, or indeed the only universe in existence.
Meanwhile, the National Aeronautics and Space Administration (NASA) has led the world in space exploration since its establishment in 1958. It is a U.S. federal agency with a civilian character and its research is used for peaceful ends. It is one of just six government space agencies around the world with launch capabilities.
Indeed, NASA has long been a pioneer in the design and launch of piloted spacecraft. In fact, starting with Project Mercury, a one-person capsule, NASA has flown over 200 crewed missions to space. Their two most famous vehicles, both of which have now retired, are Apollo, which landed on the moon, and the space shuttle, the world’s first reusable spacecraft.
In recent years, NASA has focused on the development of space-based technologies for research purposes. For example, its Earth Observing System includes several orbiting satellites that monitor the physical systems of the Earth. Its Heliophysics Research Program studies the Sun and its effect on the solar system. And its New Horizons program is one of several that uses probes and robots to explore nearby planets, moons and meteors.
Finally, NASA’s Great Observatories program is concerned with astrophysics. It consists of four space-based telescopes launched from 1990 to 2003. Each one measures a different electromagnetic range such as gamma rays, ultraviolet or infrared light. They include the Compton Gamma Ray Observatory (CGRO), the Chandra X-ray Observatory (CXO), the Spitzer Space Telescope (SST) and the Hubble Space Telescope (HST).
Named after the celebrated American astronomer Edwin Hubble, the HST entered space in 1990. Considered one of the biggest and most adaptable space telescopes in the world, it has been providing NASA with images of deep space for nearly three decades. In fact, the HST is now a well-established and critically important instrument for astronomical research.
HST images of distant nebula, planets and other remote cosmic events have also helped to popularize astronomy. Sublime photos of the Carina and Eagle nebulas feature pillar-like formations of dust and gas, a phenomenon produced by incipient stars. They demonstrate that the physical processes of the universe can have a spectacular and mystical aesthetic.
Meanwhile, the concept of a space telescope dates to the 1920s. However, the conception and planning for Hubble began in the 1970s. Various delays and technical challenges meant its launch began seven years later than originally intended. But due to a problem with its main mirror, it did not capture images properly until a servicing mission corrected its optics in 1993.
Orbiting the Earth outside its atmosphere, Hubble has an unobstructed view of outer space. Its mirror measures 7.9 feet across and its camera captures images in the near infrared, ultraviolet and visible ranges. It also has considerably less background light than any telescope based on the ground. Meanwhile, the Space Telescope Science Institute (STScl) handles the selection and processing of Hubble data and the Goddard Space Flight Center manages its flight.
The HST has facilitated a range of research projects over the years, many of them concerned with the most ancient parts of the observable universe. For example, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was one of the largest projects in the history of Hubble. Its aim was to expand our knowledge of the early Universe, around one billion years after the Big Bang.
In fact, the HST has given scientists a newer, more accurate estimated age of the universe. Moreover, its observation of remote supernovae provided proof that the expansion of the universe appears to be accelerating not decelerating, perhaps due to the influence of dark energy. Three members of the groups responsible for the discovery, the Supernova Cosmology Project and the High-z Supernova Search Team, received Nobel Prizes for their work.
HST has also proven particularly adept at locating black holes. For example, scientists in the 1960s hypothesized that some galaxies would have black holes at their centers. Today, HST data indicates that all galaxies probably have black holes at their centers. Furthermore, the mass of a black hole appears to be related to the properties of its galaxy.
In 1994 Hubble photographed the moment when Comet Shoemaker-Levy 9 slammed into Jupiter. Comet collisions with the planet are rare events and happen once every few hundred years. Fortunately, NASA was able to complete its servicing of Hubble in time. Its images of Jupiter were the sharpest since a NASA probe, Voyager 2, completed a flyby in 1979.
HST has also peered into the most remote regions of our Solar System to chart dwarf planets such as Eris. And in 2012 it identified a fifth moon orbiting Pluto. Then three years later, scientists used the HST to study the aurorae on Ganymede, one of Jupiter’s moons. And their data indicated that a vast ocean, perhaps 60 miles deep, lay beneath its surface.
Meanwhile, in 2018 scientists noticed a strange halo of light in galaxy cluster SDSS J0146-0929. Surrounding approximately 20 individual galaxies, the halo appears to have an almost numinous quality. In the space around it, scores of swirls and spirals – each one an individual galaxy – attest to the enormous scale of the image.
For its part, the halo is not an error or an optical illusion. In fact, there is a very simple and rational explanation for it. Known as an Einstein ring, the halo is an example of so-called “gravitational lensing.” This consists of the bending of light by an object with a very large mass, such as a black hole or a galaxy.
The effect is named after Albert Einstein, who predicted gravitational lensing in 1912, approximately four years prior to the publication of his groundbreaking theory of general relativity. Also known as “halo effect,” the phenomenon was first referenced by an academic article in 1924. However, it was not until the late 20th century that an Einstein ring was physically documented.
An Einstein ring is created when three independent elements – source, lens and observer – perfectly align. The source refers to a light source, which can be a single star or an entire galaxy. The light travels in a straight line until it reaches the lens, which causes it to bend.
Meanwhile, the lens is a massive object which distorts spacetime. Technically, another star could act as a lens – indeed, Einstein’s calculations hypothesized exactly that scenario – but this has yet to be observed. Rings produced by galaxies or black holes are much easier to detect, partly because they are larger than those created by individual stars.
The light, after bending at the lens plane, travels towards the observer – in this case, the eye of the HST. The alignment of source, lens and observer is a type of “syzygy.” Derived from an ancient Greek word meaning “yoked together”, a syzygy is simply the alignment of three or more cosmic bodies, such as during an eclipse.
Meanwhile, NASA described the phenomenon in an April 2018 press release. It said, “With the charming name of SDSS J0146-0929, this is a galaxy cluster – a monstrous collection of hundreds of galaxies all shackled together in the unyielding grip of gravity.” It continued, “The mass of this galaxy cluster is large enough to severely distort the space-time around it, creating the odd, looping curves that almost encircle the center of the cluster.”
“In this image,” continued the press release, “the light from a background galaxy is diverted and distorted around the massive intervening cluster and forced to travel along many different light paths toward Earth, making it seem as though the galaxy is in several places at once.”
Presently, scientists have identified hundreds of gravitational lenses, but no more than a dozen Einstein rings. And although there is no accepted definition of what constitutes an Einstein ring – for example, in terms of completeness – a perfectly symmetrical ring has yet to found. Typically, asymmetries in the lens or a misalignment between source, lens and observer cause the circle to distort.
Hewitt et al identified the first ever partial Einstein ring in 1988 using the Very Large Array – a radio astronomy observatory based in New Mexico. Observing a radio source known as MG1131+0456, they detected a quasar distorted into a near-perfect ring by a nearby galaxy. The lens also produced dual images, possibly due to misalignment.
Meanwhile, double rings are particularly rich sources of information concerning dark matter and dark energy. Indeed, 50 double rings might provide enough data to extrapolate the dark matter content of the universe more precisely. However, double are rings rare – the chances of finding one are approximately one in 10,000.
Nonetheless, in 2008 Tommaso Treu of the University of California and Raphael Gavazzi of the STScl announced the discovery of the first ever double Einstein ring. A trio of perfectly aligned galaxies create the rings and they are located approximately 11, six and three billion light years from Earth.
The first complete Einstein ring, B1938+666 was discovered by King et al in 1998. The source was a dark dwarf satellite and the gravitational lens – which was first documented using the Multi-Element Radio Linked Interferometer Network (MERLIN), an array of radio telescopes based in England – consisted of a very old elliptical galaxy. In fact, the source was so distant that it would have been invisible to us without the lens.
Indeed, one of the main astronomical uses of gravitational lenses is magnification. Gravitational lenses bring objects into view that would normally be invisible to our current level of technology. As such, they can supply data on very remote regions of outer space and extend our knowledge of how the universe works.
For example, in 2015 scientists used an Einstein ring to observe a very ancient galaxy that formed in the relative dawn of the universe, just 2.4 billion years after the Big Bang. And by documenting those regions of the galaxy where stars form, the researchers gleaned fresh insights into the early formation of the universe.
Meanwhile, in 2016 experts discovered an Einstein ring in a dwarf galaxy known as the Sculptor. Scientists believe the ring will provide new information about dark matter. Approximately 80 percent of the universe is thought to consist of dark matter and dark energy. However, since both phenomena are not directly observable, we currently know very little about them.
If you would like to search for your own Einstein ring, the HST is available for public use to persons of all nationalities. Proposals are considered on a yearly basis and include “snapshot observations” of 45 minutes or less. However, competition is fierce – approximately 80 percent of public proposals are rejected.
Meanwhile, work on a successor to the HST is well underway. Scheduled for launch in 2021, the James Webb Space Telescope (JWST) will have an enhanced resolution and optical sensitivity capable of peering further than ever into the early universe. It is sure to yield surprising astronomical discoveries.