It’s a dangerous universe out there, for a budding young space-faring species.
Killer comets, planet sterilizing gamma ray bursts, and death rocks from above are all potential hazards that an adolescent civilization has to watch out for.
This week offers two close shaves, as newly discovered Near Earth Asteroids (NEAs) 2014 WC201 and 2014 WX202 pass by the Earth-Moon system.
The passage of 2014 WC201 is coming right up tonight, as the 27-metre space rock passes about 570,000 kilometres from the Earth. That’s 1.4 times farther than the distance from the Earth to the Moon.
And the good news is, the Virtual Telescope Project will be bringing the passage of 2014 WC201 live tonight starting at 23:00 Universal Time/6:00 PM EST.
Shining at an absolute magnitude of +26, 2014 WC201 will be visible as a +13 apparent magnitude “star” at closest approach at 4:51 UT (December 2nd)/11:51 PM EST (December 1st) moving through the constellation Ursa Major. This puts it within range of a large backyard telescope, though the 80% illuminated waxing gibbous Moon will definitely be a mitigating factor for observation.
The JPL Horizons ephemerides generator is an excellent place to start for crafting accurate coordinates for the asteroid for your location.
A capture of NEO 2003 DZ15 from 2015. Credit: The Virtual Telescope Project.
At an estimated 27 metres/81 feet in size, 2014 WC201 will no doubt draw “house-sized” or “building-sized” comparisons in the press. Larger than an F-15 jet fighter, asteroids such as WC201 cry out for some fresh new descriptive comparisons. Perhaps, as we near a “Star Wars year” in 2015, we could refer to 2014 WC201 as X-wing sized?
Another Apollo NEO also makes a close pass by the Earth this week, as 6-metre 2014 WX202 passes 400,000 kilometres (about the same average distance as the Earth to the Moon) from us at 19:56 UT/2:56 PM EST on December 7th. Though closer than WC201, WX202 is much smaller and won’t be a good target for backyard scopes. Gianluca Masi over at the Virtual Telescope Project also notes that WX202 will also be a difficult target due to the nearly Full Moon later this week.
The orbital path of NEO asteroid 2014 WX202. Credit: NASA/JPL
The last Full Moon of 2014 occurs on December 6th at 6:26 AM EST/11:26 Universal Time.
2014 WX202 has also generated some interest in the minor planet community due to its low velocity approach relative to the Earth. This, coupled with its Earth-like orbit, is suggestive of something that may have escaped the Earth-Moon system. Could WX202 be returning space junk or lunar ejecta? It’s happened before, as old Apollo hardware and boosters from China’s Chang’e missions have been initially identified as Near Earth Asteroids.
The Earth also occasionally hosts a temporary “quasi-moon,” as last occurred in 2006 with the capture of RH120. 2014 WX202 makes a series of more distant passes in the 2030s, and perhaps it will make the short list of near Earth asteroids for humans to explore in the coming decades.
And speaking of which, humanity is making two steps in this direction this week, with two high profile space launches.
First up is the launch of JAXA’s Hayabusa 2 from the Tanegashima Space Center on December 3rd at 4:22 UT/11:22 PM EST. The follow up to the Hayabusa asteroid sample return mission, Hayabusa 2 will rendezvous with asteroid 1999 JU3 in 2018 and return samples to Earth in late 2020. The vidcast for the launch of Hayabusa 2 goes live at 3:00 UT/10:00 PM EST on Tuesday, December 2nd.
And the next mission paving the way towards first boot prints on an asteroid is the launch of a Delta 4 Heavy rocket with EFT-1 from Cape Canaveral this Thursday morning on December 4th near sunrise at 7:05 AM EST/12:05 UT. EFT-1 is uncrewed, and will test key technologies including reentry on its two orbit flight. Expect to see crewed missions of Orion to begin around 2020, with a mission to an Earth crossing asteroid sometime in the decade after that.
NASA gotchu: An artist’s rendition of a future asteroid capture. Credit: NASA.
And there are some decent prospects to catch sight of EFT-1 on its first pass prior to its orbit raising burn over the Atlantic. Assuming EFT-1 lifts off at the beginning of its launch window, western Australia may see a good dusk pass 55 minutes after liftoff, and the southwestern U.S. may see a visible pass at dawn about 95 minutes after EFT-1 leaves the pad.
The footprint of EFT-1 on its first North American pass. Credit: Orbitron.
We’ll be tracking these prospects as the mission evolves on launch day via Twitter, and NASA TV will carry the launch live starting at 4:30 AM EST/9:30 UT.
The Orion capsule will come in hot on reentry at a blistering 32,000 kilometres per hour over four hours after liftoff in a reentry reminiscent of the early Apollo era.
Of course, if an asteroid the size of WC201 was on a collision course with the Earth it could spell a very bad day, at least in local terms. For comparison, the 2013 Chelyabinsk meteor was estimated to be 18 metres in size, and the 1908 Tunguska impactor was estimated to be 60 metres across. And about 50,000 years ago, a 50 metre in diameter space rock came blazing in over the ponderosa pine trees near what would one day be the city of Flagstaff, Arizona to create the 1,200 metre diameter Barringer Meteor Crater you can visit today.
A fragment of the Barringer meteorite on display at the Lowell Observatory. Photo by author.
All the more reason to study hazardous space rocks and the technology needed to reach one in the event that we one day need to move one out of the way!
The Rosetta stone, now displayed at the British Museum in London, was used by Jean-Francois Champollion to decipher Egyptian heiroglyphics, Credit: Hans Hillewaert, British Museum
On television and in the movies, it’s so easy. Aliens almost always speak English (at least in America they do). If it’s explained at all, we are typically told that they learned it by intercepting communications with our astronauts, or tapping into our television broadcasts. A universal translator device instantly abolishes communication difficulties. Hollywood aliens are, of course, human beings in costumes (these days augmented by computer graphics). They are equipped, as are we all, with a human brain, a human larynx, and human vocal cords; all singular products of the distinctive evolutionary history of our species.
Real extraterrestrials, if they exist, will be the product of a different evolutionary history, played out on another world.
They will know no human language, and be unfamiliar with the typical activities of human beings. Here on Earth no archeologist has ever deciphered an ancient script without knowing the language it corresponds to, even though such scripts deal with recognizable human activities. How could we ever devise a message that aliens could understand? Could we ever understand a message they sent to us? Communicating with alien minds may be one of the most daunting challenges the human intellect has ever faced.
In mid-November, the SETI Institute in Mountain View, California sponsored an academic conference on the problem interstellar communication ‘Communicating across the Cosmos’. The conference drew 17 speakers from a variety of disciplines, including linguistics, anthropology, archeology, mathematics, cognitive science, radio astronomy, and art. In this final installment, we will search for clues to a solution to the daunting problem of making ourselves understood to an extraterrestrial civilization.
Conference presenter and archeologist Paul Wason believes that the history of archeology provides an important lesson for how we might devise a message that can be deciphered by extraterrestrials. In the early 19th century the French archeologist Jean-Francois Champollion solved one of the great riddles of his field by deciphering Egyptian hieroglyphics. The critical clue was provided by an artifact discovered in 1799 in an Egyptian town that Europeans called Rosetta. It became known as the Rosetta stone.
The stone contained the same inscription in three different scripts. One of them was Egyptian hieroglyphics, and another was Greek, which Champollion knew how to read. Champollion used the Greek to decipher the hieroglyphics. Could we use the same strategy to create a cosmic Rosetta stone? Like Wason, Carl Sagan also grasped the importance of the Rosetta stone, and discussed it extensively in his 1980’s book and television series Cosmos. To create a cosmic Rosetta stone, we would need a language to stand in the role of Greek. It would need to be known both to us, and to the aliens. Could there possibly be such a thing?
Many mathematicians and physical scientists involved in SETI believe that mathematical and physical concepts could play the needed role. According to mathematician and conference speaker Carl DeVito, the natural numbers (0, 1, 2, 3 …) are useful to humans in dealing with the cyclical processes that are a everywhere in nature, and probably arise universally in the minds of intelligent beings. Astronomers have strong evidence that the laws of physics and chemistry worked out in laboratories here on Earth hold everywhere in the universe. That being the case, they hope that humans and aliens share a common understanding of basic concepts in these fields. If this is so, then such concepts might play the same role that Greek did for Champollion. SETI pioneers Carl Sagan and Frank Drake, along with their collaborators, employed a rudimentary version of this strategy when they constructed the message encoded on the phonographic record launched into space in 1977 aboard the Voyager 1 and 2 spacecraft. These spacecraft hurtled into interstellar space following the completion of their missions to explore the outer solar system.
An image encoded on the phonographic record carried aboard Voyager 1 and 2, intended to communicate how humans symbolize basic mathematical concepts. The left side depicts how humans, in western culture, represent the natural numbers using binary code and Arabic numerals. The vertical lines indicate binary ‘1’, and the horizontal lines binary ‘0’. On the right, additional numerals are given, and the use of scientific notation, and the operations of addition, multiplication, and division are depicted. Credit: Frank DrakeAn image encoded on the Voyager record intended to communicate standards of time, mass, and length to an extraterrestrial viewer, using basic concepts in physics encoded symbolically. In the upper right corner, each circle symbolizes a hydrogen atom. The diagram as a whole symbolizes a transition of the spin state of the electron. This transition involves the emission of a microwave radio wave of wavelength 21 centimeters, which is symbolized on the right side of the diagram. Radio emissions produced by this transition occurring in clouds of hydrogen gas in interstellar space are well known to radio astronomers. The wavelength is used as the standard of length (1 L). The time that this transition takes to occur is used as the unit of time (1t) and the mass of a hydrogen atom (1 M) is used as the standard of mass. Various units of measurement used by humans are then defined in terms of these standards. The units are then used throughout the pictorial portion of the message to indicate masses, lengths and times. Credit: Frank Drake
Sagan, Drake, and their collaborators first used symbols in an attempt to communicate how humans represent the natural numbers using binary and base ten numerals. They used another set of symbols to depict some properties of the hydrogen atom, which they used to establish standards of distance and time. The distance and time standards were used repeatedly throughout the digital image portion of the message to specify the sizes and time scales depicted. The Voyager record included a greeting from then President Carter encoded as English text. Sagan, Drake, and their collaborators didn’t even attempt the monumental, and perhaps impossible, task of explaining President Carter’s text statement using their Rosetta stone.
Much like Wason and Sagan, computer scientist and conference presenter Kim Binsted, felt that the solution to interstellar communication lies in constructing a pidgin, a simplified version of a language developed to communicate between groups that share no language in common. She was doubtful though, that a cosmic Rosetta stone based on physics and math would let humans and aliens communicate about anything other than physics and math. It might never, for example, provide a way to convey the President’s good wishes. The hieroglyphics of the Rosetta stone were decipherable, in part, because they described the familiar human activities of an Egyptian pharaoh. Humans are clueless about what sorts of activities aliens typically engage in, and aliens are equally clueless about us. It’s hard to see how a Rosetta stone based on physics could bridge this sort of gap.
Philosophers Nicholas Rescher and Andre Kukla, neither of whom presented at the conference, have raised a more fundamental objection. They question whether extraterrestrials would use the same concepts to understand the physical and chemical world that we do. The concepts that modern western science uses to understand the physical world surely reflect the structure of that world. But they also reflect the history of our culture and the structure of our minds. Since aliens would differ from humans on both counts, it’s at least possible that their physical, and even their mathematical concepts might be different from ours. If that’s so, then physics can’t play the role that Greek did for Champollion. Every path forward is full of unknowns and difficulties, and Kim Binsted doubts a solution is possible.
There is a glimmering of hope for another kind of Rosetta stone based on another sort of “Greek”. Given the central role that visual images played in the Voyager message, it’s surprising that image based communication strategies didn’t receive greater emphasis at the conference. It’s true that here on Earth; animals have evolved a wide variety of non-visual ways to sense their surroundings. Some fishes can sense their environments by generating and detecting electric fields in the water. Many fish can use fields of water flow around their bodies to detect nearby objects. Bats, along with dolphins and whales, have evolved a sonar system, emitting sounds and analyzing their returning echoes. Scorpions can sense ground vibrations, elephants can hear sounds below the range of human hearing, and dogs have a remarkably acute sense of smell, to name just a few examples. Still, almost every Earthly animal has eyes of some sort.
Earthly evolution has invented vision several times, in different animal lineages. Vision is especially important for larger animals that live on land. This is because larger bodies can make larger eyes and larger eyes can give sharper vision and better light gathering abilities. Land environments are typically better lit than aquatic ones. Birds and mammals are the Earthly animals with the biggest and most sophisticated brains, and they also have the most acute vision.
Are alien environments likely to be well lit? Exoplanet hunters have focused their efforts on finding planets like the Earth, rocky terrestrial planets at the right distance from their star for temperatures to be in the range where water is a liquid. They have shown us that such worlds are fairly commonplace in the cosmos. The daytime surfaces of these exoplanets are likely to be flooded with visible light, just as is Earth. This light may be necessary for life on such a world, because most life on Earth depends on the energy of sunlight as trapped by green plants. For large, land dwelling animals in this kind of environment, vision provides more information, at a distance, than any other sense can. Since it evolved numerous times on Earth, it’s likely to do so elsewhere as well. With a lens at the front and a sheet of light sensing cells at the back, the eye of a squid is remarkably similar to our own. Squids are part of a group of animals called molluscs, which also includes slugs, snails, and shellfish. Molluscs are very distantly related to the vertebrates (animals with backbones, a group which includes humans). The most recent common ancestor of molluscs and vertebrates was a simple worm-like creature that lived more than 600 million years ago. The two groups have followed an independent course of evolution ever since. The fact that molluscs evolved complex brains and bodies along a different evolutionary path than vertebrates makes them a good model for understanding some of the ways in which extraterrestrials, with an entirely separate evolutionary history, might be different from or similar to us. One group of molluscs, the cephalopods, a group which includes squids, octopuses, and cuttlefish, have evolved the largest and most complex brains of any invertebrates. Despite their separate evolutionary origin, the eyes of cephalopods are remarkably similar to vertebrate eyes, a phenomenon known as convergent evolution. Evolution solved similar problems in similar ways. Perhaps, even on another planet, evolution solves similar problems in similar ways. If aliens, like cephalopods, have some visual similarities to us, then visual images may be useful in interstellar messages. Credit: Carl Chun Die Cephaloden
The human visual system gathers information about a three dimensional world of objects and surfaces, partly by using motion cues. We have the ability to represent that world in two dimensions, using images. Kim Binsted worried that an alien visual system might not be capable of making sense of pictures made by humans. This worry was a potent one for the stick figures and line drawings that played such a prominent role in the pioneering interstellar messages of the 70’s. Those kinds of depictions use abstract visual conventions that an alien viewer might find impossible to figure out. Today, though, we needn’t worry about stick figures, because the information revolution gives us the ability to send high definition video. Still, we can’t be sure what an alien visual system would make of imagery encoded with the human visual system in mind.
Video imagery may provide a promising complement or alternative to the abstractions of physics and chemistry as the “Greek” for a cosmic Rosetta stone. If the aliens live on a planet like Earth, with liquid water on its surface, then we will share a mutual familiarity with water’s many manifestations. Just like us, aliens will have seen rain and snow, oceans, rivers, lakes, ponds, clouds, fog, and rainbows. If they have a sense of hearing, over a range of sound frequencies at least somewhat similar to ours, they will have heard waves crashing on beaches, rain hitting the ground, gurgling brooks, and the splash of a pebble dropped into a pond. When the senses work together to confirm one another, the certainty of perceptual recognition is even greater.
An audio-video movie depicting the mutually familiar phenomena of water could be just the bridge we need to cross the gulf of mutual incomprehension. This splashy, gurgling “Greek” could be the key to helping the aliens understand our audio-visual and still images, and ultimately, our symbols. As with the Voyager record, a simpler symbol system would first be needed to communicate to the aliens about how to view and listen to the presentation. That might be a big stumbling block. In the case of Voyager, a stylus head for playing the record was included on the spacecraft, which made it simpler to explain how to play it. A Rosetta stone that led the extraterrestrials to an understanding of our images could provide a means of communication extending well beyond the topics of physics, chemistry, and math. Several conference participants felt that imagery might help to convey things about human altruism, cooperation, morality, and aesthetic sensibilities.
The main message of the ‘Communicating across the Cosmos’ conference is a recognition of just how hard the problem of making ourselves understood to aliens will be. Kim Binsted ended her talk on a faint note of optimism. Even if all else fails, she supposed, there is something we can still communicate to the aliens. She showed a slide of her home doorbell. When it rings, she said, it conveys the message that someone is there, and where they are. It shows intent to communicate, and a benign willingness to reveal one’s presence. Even if it can’t be interpreted, an interstellar message conveys the information that a doorbell conveys. That message, the message that someone is there, would still be of monumental importance. Even an interstellar message that can’t be deciphered still tells us what a doorbell tells us: that someone is there. Credit: Jim Kuhn
Communicating across the Cosmos: How can we make ourselves understood by other civilizations in the galaxy (2014), SETI Institute Conference Website.
F. Cain (2013) How Could We Find Aliens? The Search for Extraterrestrial Intelligence (SETI), Universe Today.
F. Cain (2013) Where Are All The Aliens? The Fermi Paradox, Universe Today.
A. Kukla (2010) Extraterrestrials: A Philosophical Perspective, Rowman and Littlefield Publishers Inc. Plymouth, UK.
M. F. Land and D-E. Nilsson (2002), Animal Eyes, Oxford University Press.
N. Rescher (1985) Extraterrestrial Science, in Extraterrestrials: Science and Alien Intelligence, Edited by E. Regis, Cambridge University Press, Cambridge, UK.
C. Sagan, F. D. Drake, A. Druyan, T. Ferris, J. Lomberg, L. S. Sagan, (1978) Murmurs of Earth: The Voyager Interstellar Record. Random House, New York.
C. Sagan (1980) Cosmos, Random House, New York.
J. J. Vitti (2013) Cephalopod cognition in an evolutionary context: Implications for ethology, Biosemiotics, 6:393-401.
Orion (at right), Sirius (bottom) and the pale wintertime Milky Way (center) are well-placed for viewing around 11 o'clock local time in late November. Credit: Bob King
Several nights ago the chill of interstellar space refrigerated the countryside as temperatures fell well below zero. That didn’t discourage the likes of Orion and his seasonal friends Gemini, Perseus and Auriga. They only seemed to grow brighter as the air grew sharper.
Wending between these familiar constellations like a river steaming in the cold was the Milky Way. The name has always been slightly confusing as it refers to both the milky band of starlight and the galaxy itself. Every single star you see at night belongs to our galaxy, a 100,000 light-year-wide flattened disk scintillating with over 400 billion suns.
Face-on (left) and edge-on views of the Milky Way. Our solar system lies in the flat plane of a barred spiral galaxy called the Milky Way. Looking through the plane, the stars pile up to form the Milky Way band. In summer, we face toward the richer, denser core; in winter we look out toward the edge. Credit: NASA with annotations by the author
Earth, Sun and planets huddle together within the mid-plane of the disk, so that when we look straight into it, the density of stars piles up over thousands of light years to form a thick band across the sky. Since most of the stars are very distant and therefore faint, they can’t be seen individually with the naked eye. They blend together to give the Milky Way a milky or hazy look.
During a snowfall, we can see individual flakes nearby but more distant ones increase in number and blend to make a uniform haze similar to what happens when we look across the flat disk of the Milky Way. Credit: Bob King
In a snowstorm, we easily distinguish individual snowflakes falling in front of our face, but looking into the distance, the flakes blend together to create a white, foggy haze. Replace the snowflakes with stars and you have the Milky Way – with a caveat. If we lived in the center of our galaxy, the sky would be milky with stars in all directions just like that snowstorm, but since the Sun occupies the flat plane, they only appear thick when our line of sight is aimed along the galaxy’s equator. Look above and below the disk and the stars quickly thin out as our gaze pierces through the galaxy’s plane and into intergalactic space.
In this view, the ground – Earth – has been removed from the picture and we can see all around us in space. Now we can see that the Milky Way band describes a full circle in the sky. The blue circle represents the galactic equator. The view shows the sky around midnight in early December. The Sun, at lower right, lies in the same direction as the galaxy’s center this month. Source: Stellarium
If you could float in space some distance from the brilliant ball of Earth, you’d see that the Milky Way band passes above, around and below you like a giant hula-hoop. Back on the ground, we can only see about two-thirds of the band over the course of a year. The other third is below the horizon and visible only from the opposite hemisphere, providing yet another good reason to make that trip to Tahiti or Ayers Rock in Australia.
Few know the winter version of the Milky Way that stands above the southeastern horizon around 10:30-11 p.m. local time on moonless nights in early December. No surprise, given it hardly compares to the brightness of the summertime version. This has much to do with where the Sun is located inside the galaxy, some 30,000 light years away from the center or more than halfway to the edge.
Opposite the galaxy’s center lies the anticenter, located near El Nath in the northern horn of Taurus above the constellation Orion. Source: Stellarium
On late fall and winter nights, our planet faces the galaxy’s outer suburbs and countryside where the stars thin out until giving way to relatively starless intergalactic space. Indeed, the anticenter of the Milky Way lies not far from the star El Nath (Beta Tauri) where Taurus meets Auriga. While the hazy band of the Milky Way is still visible through Auriga and Taurus, it’s thin and anemic compared to summer’s billowy star clouds.
The summertime Milky Way from Scorpius to Cygnus is broader and brighter than the winter version because we face toward the galactic center at nightfall. Credit: Stephen Bockhold
At nightfall in July and August, we face toward the galaxy’s center where 30,000 light years worth of stars, star clouds and nebulae stack up to fatten the Milky Way into a bright, chunky arch on summer evenings compared to winter’s thin gruel.
The slanting winter Milky Way touches many of the familiar, bright constellations of December. This map shows the sky facing southeast around 11 o’clock local time in early December or 9 p.m. in late December. Source: Stellarium
The winter Milky Way starts east of brilliant Sirius and grazes the east side of Orion before ascending into Gemini and Auriga and arching over into the western sky to Cassiopeia’s “W”. Binoculars and telescopes resolve it into individual stars and star clusters and help us appreciate what a truly beautiful and rich place our galactic home is.
Few sights that impress us with the scope and scale of where we live than seeing the Milky Way under a dark sky during the silence of a winter night. Picture Earth and yourself as members of that glowing carpet of stars, and when you can’t take the cold anymore, enjoy the delicious pleasure of stepping inside to unwrap and warm up. You’ve been on a long journey.
This artist's conception illustrates a supermassive black hole (central black dot) at the core of a young, star-rich galaxy. Now astronomers have found a rogue SMBH travelling through space. Image credit: NASA/JPL-Caltech
Scientists have long suspected that supermassive black holes (SMBH) reside at the center of every large galaxy in our universe. These can be billions of times more massive than our sun, and are so powerful that activity at their boundaries can ripple throughout their host galaxies.
In the case of the Milky Way galaxy, this SMBH is believed to correspond with the location of a complex radio source known as Sagittarius A*. Like all black holes, no one has even been able to confirm that they exist, simply because no one has ever been able to observe one.
But thanks to researchers working out of MIT’s Haystack Observatory, that may be about to change. Using a new telescope array known as the “Event Horizon Telescope” (EHT), the MIT team hopes to produce this “image of the century” very soon.Initially predicted by Einstein, scientists have been forced to study black holes by observing their apparent effect on space and matter in their vicinity. These include stellar bodies that have periodically disappeared into dark regions, never to be heard from again.
As Sheperd Doeleman, assistant director of the Haystack Observatory at Massachusetts Institute of Technology (MIT), said of black holes: “It’s an exit door from our universe. You walk through that door, you’re not coming back.”
Image of the M87, a giant elliptical galaxy that is believed to have a SMBH at its center. Credit: NASA/CXC/KIPAC/NSF/NRAO/AUI
As the most extreme object predict by Einstein’s theory of gravity, supermassive black holes are the places in space where, according to Doeleman, “gravity completely goes haywire and crushes an enormous mass into an incredibly close space.”
To create the EHT array, the scientists linked together radio dishes in Hawaii, Arizona, and California. The combined power of the EHT means that it can see details 2,000 times finer than what’s visible to the Hubble Space Telescope.
These radio dishes were then trained on M87, a galaxy some 50 million light years from the Milky Way in the Virgo Cluster, and Sagittarius A* to study the event horizons at their cores.
Other instruments have been able to observe and measure the effects of a black hole on stars, planets, and light. But so far, no one has ever actually seen the Milky Way’s Supermassive black hole.
According to David Rabanus, instruments manager for ALMA: “There is no telescope available which can resolve such a small radius,” he said. “It’s a very high-mass black hole, but that mass is concentrated in a very, very small region.”
Doeleman’s research focuses on studying super massive black holes with sufficient resolution to directly observe the event horizon. To do this his group assembles global networks of telescopes that observe at mm wavelengths to create an Earth-size virtual telescope using the technique of Very Long Baseline Interferometry (VLBI).
Image of Sagittarius A*, the complex radio source at the center of the Milky Way, and believed to be a SMBH. Credit: NASA/Chandra
“We target SgrA*, the 4 million solar mass black hole at the center of the Milky Way, and M87, a giant elliptical galaxy,” says Doeleman. “Both of these objects present to us the largest apparent event horizons in the Universe, and both can be resolved by (sub)mm VLBI arrays.” he added. “We call this project The Event Horizon Telescope (EHT).”
Ultimately, the EHT project is a world-wide collaboration that combines the resolving power of numerous antennas from a global network of radio telescopes to capture the first image ever of the most exotic object in our Universe – the event horizon of a black hole.
“In essence, we are making a virtual telescope with a mirror that is as big as the Earth,” said Doeleman who is the principal investigator of the Event Horizon Telescope. “Each radio telescope we use can be thought of as a small silvered portion of a large mirror. With enough such silvered spots, one can start to make an image.”
“The Event Horizon Telescope is the first to resolve spatial scales comparable to the size of the event horizon of a black hole,” said University of California, Berkeley astronomer Jason Dexter. “I don’t think it’s crazy to think we might get an image in the next five years.”
First postulated by Albert Einstein’s Theory of General Relativity, the existence of black holes has since been supported by decades’ worth of observations, measurements, and experiments. But never has it been possible to directly observe and image one of these maelstroms, whose sheer gravitational power twists and mangle the very fabric of space and time.
Finally being able to observe one will not only be a major scientific breakthrough, but could very well provide the most impressive imagery ever captured.
Image of the spiral galaxy NGC 4151, aka. "Sauron's Eye". Credit: X-ray: NASA/CXC/CfA/J.Wang et al.; Optical: Isaac Newton Group of Telescopes, La Palma/Jacobus Kapteyn Telescope; Radio: NSF/NRAO/VLA.
Determining the distance of galaxies from our Solar System is a tricky business. Knowing just how far other galaxies are in relation to our own is not only key to understanding the size of the universe, but its age as well. In the past, this process relied on finding stars in other galaxies whose absolute light output was measurable. By gauging the brightness of these stars, scientists have been able to survey certain galaxies that lie 300 million light years from us.
However, a new and more accurate method has been developed, thanks to a team of scientists led by Dr. Sebastian Hoenig from the University of Southampton. Similar to what land surveyors use here on Earth, they measured the physical and angular (or apparent) size of a standard ruler in the galaxy to calibrate distance measurements.
It happens to all lovers of astronomy sooner or later.
I once had a friend who was excited about an upcoming conjunction of Saturn and Venus. They were passing closer than the apparent diameter of the Full Moon in the dawn sky, and you could fit ‘em both in the same telescopic field of view. I invited said friend to stop by at 5 AM the next morning to check this out. I was excited to see this conjunction as well, but not for the same reasons.
Said friend was into astrology, and I’m sure that the conjunction held a deep significance in their world view. Sure, I could have easily told them that ‘astrology is bunk,’ and the skies care not for our terrestrial woes… or I could carefully help guide this ‘at risk friend’ towards the true wonders of the cosmos if they were willing to listen.
We bring this up because this weekend, the Sun enters the constellation Ophiuchus, one of 13 modern constellations that it can appear in from our Earthly vantage point.
If you’re born from November 30th to December 18th, you could consider yourself an “Ophiuchian,” or being born under the sign of Ophiuchus the Serpent Bearer. But I’ll leave it up to you to decide what they might be like.
Seen at the Albany Park Zoo: Herpetology, or a modern day “serpent bearer?” Photo by author.
You might remember how the “controversy” of the 13th sign made its news rounds a few years back. Hey, it was cool to at least see an obscure and hard to pronounce constellation trending on Twitter. Of course, this wasn’t news to space enthusiasts, and to modern astronomers, a ‘house’ is merely where you live, and a ‘sign’ is what you follow to get there.
The modern 88 constellations we use were formalized by the International Astronomical Union in 1922. Like political boundaries, they’re imaginary constructs we use to organize reality. Star patterns slowly change with time due to our solar system’s motion — and that of neighboring stars —about the galactic center.
Astrologers will, of course, counter that their craft follows a tropical scheme versus a sidereal cosmology. In the tropical system, ecliptic longitude 0 starts from the equinoctial point marking the beginning of spring in the northern hemisphere, and the zodiac is demarcated by 12 ‘houses’ 30 degrees on a side.
This neatly ignores the reality of our friend, the precession of the equinoxes. The Earth’s poles do a slow wobble like a top, taking about 26,000 years to make one turn. This means that in the sidereal scheme of things, our vantage point of the Sun’s position along the zodiac against the background stars if reference to our Gregorian calendar is slowly changing: live out a 72 year lifespan, and the constellations along the zodiac with respect to the Sun will have shifted about one degree due to precession.
Our changing pole star. Credit: Starry Night Education Software.
Likewise, the direction of the North and South Pole is changing as well. Though Polaris makes a good pole star now, it’ll become increasingly less so as our north rotational pole begins to pull away from it after 2100 A.D. To the ancient Egyptians, Thuban (Alpha Draconis) was the pole star.
Precession over time. Credit: Tfr000 under Wikimedia Creative Commons 3.0 license.
Astrology and astronomy also have an intimate and hoary history, as many astronomers up until the time of Kepler financed their astronomical studies by casting royal horoscopes. And we still use terms such as appulse, conjunction and occultation, which have roots in astrology.
But the science of astronomy has matured beyond considering whether Mercury in retrograde has any connection with earthly woes. Perhaps you feel that you’re unlucky in love and have a vast untapped potential… sure, me too. We all do, and that just speaks to the universal state of the human condition. Astrology was an early attempt by humanity to find a coherent narrative, a place in the cosmos.
But the rise of the Ophiuchians isn’t nigh. Astrology relented to astronomy because of the latter’s true predictive power. “Look here, in the sky,” said mathematician Urbain Le Verrier, “and you’ll spy a new planet tugging on Uranus,” and blam, Neptune was discovered. If the planets had any true influence on us, why didn’t astrologers manage to predict the same?
Combating woo such as astrology is never simple. In the internet era, we often find tribes of the like-minded folks polarized around electronic camp fires. For example, writing ‘astrology is woo’ for an esteemed audience of science-minded readers such as Universe Today will no doubt find a largely agreeable reception. We have on occasion, however, written the same for a general audience to a much more hostile reception. Often, it’s just a matter of being that lone but patient voice of rationalism in the woods that ultimately sinks in.
Zodiacal artwork seen at the Yerkes observatory. Photo by author.
So, what’s the harm? Folks can believe whatever they want, and astrology’s no different, right? Well, the harm comes when people base life decisions on astrology. The harm comes when world leaders make critical decisions after consulting astrologers. Remember, Nancy and President Ronald Reagan conferred with astrologers for world affairs. It’s an irony of the modern age that, while writing a take down on astrology, there will likely be ads promoting astrology running right next to this very page. And while professional astronomers spend years in grad school, you can get a “PhD in Astrology” of dubious value online for a pittance. And nearly every general news site has a astrology page. Think of the space missions that could be launched if we threw as much money at exploration as we do at astrology as a society. Or perhaps astronomers should revert back to the dark side and resume casting horoscopes once again?
But to quote Spiderman, “with great power comes great responsibility,” and we promise to only use our astronomical powers for good.
What astronomers want you to know is that we’re not separate from the universe above us, and that the cosmos does indeed influence our everyday lives. And we’re not talking about finding your car keys or selling your house. We’re thinking big. The Sun energizes and drives the drama of life on Earth. The atoms that make you the unique individual that you are were forged in the hearts of stars. The ice that chills our drink may well have been delivered here via comet. And speaking of which, a comet headed our way could spell a very bad day for the Earth.
Don’t leave home without one… a travelling “pocket planetarium” circa 16th century seen at the Tampa Bay History Center. Photo by author.
All of these are real things that astronomy tells us about our place in the cosmos, whether you’re an Ophiuchian or a Capricorn. To paraphrase Shakespeare, the heavens may (seem to) blaze forth for the death of princes, but the fault lies not in the heavens, but ourselves. Don’t forget that, as James Randi says, “you’re a member of a proud species,” one loves to look skyward, and ultimately knows when to discard fantasy for reality.
Artist's concept of a NASA airship that would fly at a suborbital altitudes for hours at a time. Credit: Mike Hughes (Eagre Interactive)/Keck Institute for Space Studies
Dreams of space are often tied to jet engines or solar sails or taking a ride on a rocketship. But it’s often quite efficient to do research from Earth, especially from the high reaches of the atmosphere where there are few molecules to get in the way of observations.
NASA wants to do more of this kind of astronomy with an airship — but at an extreme height of 65,000 feet (20 kilometers) for 20 hours. No powered-airship mission has managed to last past eight hours at this height because of the winds in that zone, but NASA is hoping that potential creators would be up to the challenge.
This isn’t a guaranteed mission yet. NASA has a solicitation out right now to gauge interest from the community, and to figure out if it is technically feasible. This program would be a follow-on to ideas such as SOFIA, a flying stratospheric telescope that the agency plans to defund in future budgets.
Their goal is to fly an airship with a 44-pound (20-kilogram) payload at this altitude for 20 hours. If a company is feeling especially able, it can even try for a more difficult goal: a 440-pound (200-kilogram) payload for 200 hours.
NASA’s Stratospheric Observatory for Infrared Astronomy 747SP aircraft flies over Southern California’s high desert during a test flight in 2010. Credit: NASA/Jim Ross
“We are seeking to take astronomy and Earth science to new heights by enabling a long-duration, suborbital platform for these kinds of research,” stated lead researcher Jason Rhodes, an astrophysicist at NASA’s Jet Propulsion Laboratory in California.
And why not just use a balloon? It comes down to communications, NASA says: “Unlike a balloon, which travels with air currents, airships can stay in one spot,” the agency states. “The stationary nature of airships allows them to have better downlink capabilities, because there is always a line-of-sight communication.”
A new research paper reveals more details of the effect gamma ray bursts (GRB) have had on the development of complex life throughout the cosmos. Illustration depicts a beam from a GRB as might have been directed toward early life on Earth during the Cambrian or Ordovician periods, ~500 million years ago. (Illustration Credit: T. Reyes)
If too close to an environment harboring complex life, a gamma ray burst could spell doom for that life. But could GRBs be the reason we haven’t yet found evidence of other civilizations in the cosmos? To help answer the big question of “where is everybody?” physicists from Spain and Israel have narrowed the time period and the regions of space in which complex life could persist with a low risk of extinction by a GRB.
GRBs are some of the most cataclysmic events in the Universe. Astrophysicists are astounded by their intensity, some of which can outshine the whole Universe for brief moments. So far, they have remained incredible far-off events. But in a new paper, physicists have weighed how GRBs could limit where and when life could persist and evolve, potentially into intelligent life.
In their paper, “On the role of GRBs on life extinctions in the Universe”, published in the journal Science, Dr. Piran from Hebrew University and Dr. Jimenez from University of Barcelona consider first what is known about gamma ray bursts. The metallicity of stars and galaxies as a whole are directly related to the frequency of GRBs. Metallicity is the abundance of elements beyond hydrogen and helium in the content of stars or whole galaxies. More metals reduce the frequency of GRBs. Galaxies that have a low metal content are prone to a higher frequency of GRBs. The researchers, referencing their previous work, state that observational data has shown that GRBs are not generally related to a galaxy’s star formation rate; forming stars, including massive ones is not the most significant factor for increased frequency of GRBs.
As fate would have it, we live in a high metal content galaxy – the Milky Way. Piran and Jimenez show that the frequency of GRBs in the Milky Way is lower based on the latest data available. That is the good news. More significant is the placement of a solar system within the Milky Way or any galaxy.
The brightest gamma-ray burst ever seen in X-rays temporarily blinded Swift’s X-ray Telescope on 21 June 2010. This image merges the X-rays (red to yellow) with the same view from Swift’s Ultraviolet/Optical Telescope, which showed nothing extraordinary. Credit: NASA/Swift/Stefan Immler
The paper states that there is a 50% chance of a lethal GRB’s having occurred near Earth within the last 500 million years. If a stellar system is within 13,000 light years (4 kilo-parsecs) of the galactic center, the odds rise to 95%. Effectively, this makes the densest regions of all galaxies too prone to GRBs to permit complex life to persist.
The Earth lies at 8.3 kilo-parsecs (27,000 light years) from the galactic center and the astrophysicists’ work also concludes that the chances of a lethal GRB in a 500 million year span does not drop below 50% until beyond 10 kilo-parsecs (32,000 light years). So Earth’s odds have not been most favorable, but obviously adequate. Star systems further out from the center are safer places for life to progress and evolve. Only the outlying low star density regions of large galaxies keep life out of harm’s way of gamma ray bursts.
The paper continues by describing their assessment of the effect of GRBs throughout the Universe. They state that only approximately 10% of galaxies have environments conducive to life when GRB events are a concern. Based on previous work and new data, galaxies (their stars) had to reach a metallicity content of 30% of the Sun’s, and the galaxies needed to be at least 4 kilo-parsecs (13,000 light years) in diameter to lower the risk of lethal GRBs. Simple life could survive repeated GRBs. Evolving to higher life forms would be repeatedly set back by mass extinctions.
Piran’s and Jimenez’s work also reveals a relation to a cosmological constant. Further back in time, metallicity within stars was lower. Only after generations of star formation – billions of years – have heavier elements built up within galaxies. They conclude that complex life such as on Earth – from jelly fish to humans – could not have developed in the early Universe before Z > 0.5, a cosmological red-shift equal to ~5 billion years ago or longer ago. Analysis also shows that there is a 95% chance that Earth experienced a lethal GRB within the last 5 billion years.
The question of what effect a nearby GRB could have on life has been raised for decades. In 1974, Dr. Malvin Ruderman of Columbia University considered the consequences of a nearby supernova on the ozone layer of the Earth and on terrestrial life. His and subsequent work has determined that cosmic rays would lead to the depletion of the ozone layer, a doubling of the solar ultraviolet radiation reaching the surface, cooling of the Earth’s climate, and an increase in NOx and rainout that effects biological systems. Not a pretty picture. The loss of the ozone layer would lead to a domino effect of atmospheric changes and radiation exposure leading to the collapse of ecosystems. A GRB is considered the most likely cause of the mass extinction at the end of the Ordovician period, 450 million years ago; there remains considerable debate on the causes of this and several other mass extinction events in Earth’s history.
The paper focuses on what are deemed long GRBs – lGRBs – lasting several seconds in contrast to short GRBs which last only a second or less. Long GRBs are believed to be due to the collapse of massive stars such as seen in supernovas, while sGRBs are from the collision of neutron stars or black holes. There remains uncertainty as to the causes, but the longer GRBs release far greater amounts of energy and are most dangerous to ecosystems harboring complex life.
The paper narrows the time and space available for complex life to develop within our Universe. Over the age of the Universe, approximately 14 billion years, only the last 5 billion years have been conducive to the creation of complex life. Furthermore, only 10% of the galaxies within the last 5 billion years provided such environments. And within only larger galaxies, only the outlying areas provided the safe distances needed to evade lethal exposure to a gamma ray burst.
This work reveals how well our Solar System fits within the ideal conditions for permitting complex life to develop. We stand at a fairly good distance from the Milky Way’s galactic center. The age of our Solar System, at approximately 4.6 billion years, lies within the 5 billion year safe zone in time. However, for many other stellar systems, despite how many are now considered to exist throughout the Universe – 100s of billions in the Milky Way, trillions throughout the Universe – simple is probably a way of life due to GRBs. This work indicates that complex life, including intelligent life, is likely less common when just taking the effect of gamma ray bursts into consideration.
The cover of the phonograph record on the Voyager 1 and 2 spacecraft, which contains an interstellar message encoded on a phonographic record. The encoded instructions attempt to explain to extraterrestrials how to play the record. Credit: NASA JPL
If extraterrestrial civilizations exist, the nearest is probably at least hundreds or thousands of light years away. Still, the greatest gulf that we will have to bridge to communicate with extraterrestrials is not such distances, but the gulf between human and alien minds.
In mid-November, the SETI Institute in Mountain View, California sponsored an academic conference on interstellar communication, “Communicating across the Cosmos“. The conference drew 17 speakers from a variety of disciplines, including linguistics, anthropology, archeology, mathematics, cognitive science, radio astronomy, and art. In this installment we will explore some of the formidable difficulties that humans and extraterrestrials might face in constructing mutually comprehensible interstellar messages.
Optical PAyload for Lasercomm Science (OPALS) Flight System, the first laser communication from space. Credit: NASA/JPL-Caltech.
If we knew where they were, and we wanted to, the information revolution has given us the capability to send an extraterrestrial civilization a truly vast amount of information. According to SETI Institute radio astronomer Seth Shostak, with broadband microwave radio we could transmit the Library of Congress, or the contents of the World Wide Web in 3 days; with broadband optical (a laser beam for space transmission) we could transmit this same amount of information in 20 minutes. This transmission would, of course, take decades or centuries to cross the light years and reach its destination. These truly remarkable capabilities give us the ability to send almost any message we want to the extraterrestrials. But transmitting capabilities aren’t the hard part of the problem. If the aliens can’t interpret it, the entire content of the World Wide Web is just a mountain of gibberish.
Many conference participants felt that the problems involved in devising a message that could be understood by a non-human mind were extremely formidable, and quite possibly insurmountable.
Having its own separate origin, extraterrestrial life could be different from Earthly life all the way down to its biochemical foundations. The vast diversity of life on Earth gives us little reason to think that aliens will look like us. Given the different conditions of another planet, and the contingencies of a different history, evolution will have produced a different set of results. For interstellar messaging to be possible at all, these results must include an alien creature capable of language, culture, and tool-making. But if these abilities are founded on a different biology and different perceptual systems, they might differ from their human counterparts in ways that we would find hard to even imagine. Looking to our own possible future development, we can’t even be sure that extraterrestrials will be biological creatures. They might be intelligent machines.
According to cognitive scientist Dominique Lestel, who presented at the conference, understanding extraterrestrials poses an unprecedented set of problems. We face all of the problems that ethologists (scientists who study animal behavior) face when they study perception and signaling in other animal species. These are compounded with all of the problems that ethnologists face when they study other human cultures. Lestel worries that humans might not be smart enough to do it. He wasn’t alone in that opinion.
Explanation of the symbols on the cover of the Voyager record. Credit: NASA JPL
Linguist and conference presenter Sheri-Wells Jensen said that humans have created more than 7,000 different spoken and signed languages. No one knows whether all human languages sprung from a single instance of the invention of language or whether several human groups invented language independently. Given the ease with which children learn a language, many linguists think that our brain has a specialized language “module” underlying the “universal” grammar of human languages. These special features of the human brain might pose a formidable barrier to learning the language of a creature with a different brain produced by a different evolutionary history. An alien language might make demands on our short term memory or other cognitive abilities that humans would find impossible to meet.
When human beings talk to one another, they rely on a system of mutually understood conventions. Often gestures and body language are essential to conveying meaning. Conference presenter Klara Anna Capova, a cultural anthropologist, noted that interstellar messaging poses unique problems because the conventions to be followed in the message can’t be mutually arranged. We must formulate them ourselves, without knowing anything about the recipients. The intended recipients are distant in both time and space. The finite speed of light ensures that query and response will be separated by decades or centuries. With so little to go on, the message will inevitably reflect our cultural biases and motives. In 1962, the Soviet Union transmitted a message towards the planet Venus. It was in Morse code, and consisted of the Cyrillic characters “Lenin”, “CCCP” (USSR), and “MIR” (the Russian word for “peace”). But the posited Venusians couldn’t possibly have known the conventions of Morse code, the Cyrillic alphabet, human names, countries, or possible relationships between them, no matter how intimately familiar these things would have seemed to the Soviets. Whether they are meant to build national prestige, sell a product, or cause humans to think deeply about their place in the universe, interstellar messages play to a human audience.
Given the long timescales involved in interstellar messaging, many conference participants noted the parallels with archeology. Archeologists have learned quite a lot about past human cultures by studying the artifacts and symbols they have left for us. Still, archeological methodologies have their limits. According to conference presenter and archeologist Paul Wason, these limits have much to teach us about interstellar messaging. Certain meanings are accessible to archeological analysis and others aren’t, because we lack the contextual knowledge needed to interpret them. Neolithic cave paintings speak to modern investigators about the skill and abilities of the painters. But, because we don’t have the needed contextual knowledge, they don’t tell us what the paintings meant to their creators.
To interpret symbols used in the past, we need to know the conventions that related the symbols to the things they symbolized. Linguistic symbols pose special problems. To understand them, we need to know two different sets of conventions. First, we need to know the conventions that relate the script to the words of the spoken language. Second, we need to know how the words of the spoken language relate to the things and situations it refers to. It is a sobering thought for would-be exolinguists that no one has ever succeeded in deciphering an ancient script without knowing the language it was written in.
What does all this tell us about our fledgling attempts to devise messages for aliens? The phonograph record carried on the Voyager 1 and 2 spacecraft includes a moving message from then President Carter, encoded as English text. It reads in part: “We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”
Human archeologists have never deciphered linear A, the writing system of the ancient Minoan civilization, due to its apparent lack of association with any known language. Unfortunately, since extraterrestrials likewise lack contextual knowledge of any human language, it is almost certain that they could never discern the meaning of President Carter’s text. The team that developed the Voyager message, which included astronomers and SETI pioneers Carl Sagan and Frank Drake, were well aware of the problem. Carter was, most likely, made aware. Interstellar messages play to a human audience.
An inscription written around the inner surface of a cup in Linear A, a script used by the Minoan civilization that has never been deciphered. Credit: Sir Arthur Evans, Scripta Minoa: The Written Documents of Minoan Crete
Is it possible for us to do better? Some off-beat ideas were proposed. Both astronomer Seth Shostak and designer Marek Kultys thought we might consider sending the sequence of the human genome. This idea was quickly shot down by a comment from the audience. Why send them a key, they said, if the aliens don’t have a lock. The metaphor is apt. DNA can only do its job as a constituent part of a living cell. Reading and implementing the genetic code involves numerous highly specialized enzymes and other cellular parts. Even if alien biochemistry and cell structure are generally similar to their Earthly counterparts, there are many features of Earthly biochemistry that appear to be quirky products of the history of life on Earth. The probability that they would repeat themselves precisely on another world are, for all practical purposes, nil. Without the context of an Earthly cell, the sequence of the human genome would be meaningless gibberish.
In the twenty first century, our ability to transmit and process information has become astounding, but we still don’t know how information conveys meaning. Is there even a glimmering of a hope that we can reach beyond the limitations of our humanity to convey meaning to an alien mind? In the final installment of this report, we’ll consider some possibilities.
C. Sagan, F. D. Drake, A. Druyan, T. Ferris, J. Lomberg, L. S. Sagan, (1978) Murmurs of Earth: The Voyager Interstellar Record. Random House, New York.
The four dots around the bright source, an elliptical galaxy, are multiple images of the new supernova taken with the Hubble Space Telescope between November 10-20, 2014. In the bottom image, the galaxy has been digitally removed to show only the supernova. The line segments are diffraction spikes from a nearby star. Credit: P.L. Kelly et. all
How about four supernovae for the price of one? Using the Hubble Space Telescope, Dr. Patrick Kelly of the University of California-Berkeley along with the GLASS (Grism Lens Amplified Survey from Space) and Hubble Frontier Fields teams, discovered a remote supernova lensed into four copies of itself by the powerful gravity of a foreground galaxy cluster. Dubbed SN Refsdal, the object was discovered in the rich galaxy cluster MACS J1149.6+2223 five billion light years from Earth in the constellation Leo. It’s the first multiply-lensed supernova every discovered and one of nature’s most exotic mirages.
The lensed supernova was discovered far behind the rich galaxy cluster MACS J1149.6+2223. The cluster is one of the most massive known and gained notoriety in 2012 when astronomers harnessed its powerful lensing ability to uncover the most distant galaxy known at the time. Credit: NASA/ESA/M. Postman STScI/CLASH team
Gravitational lensing grew out of Einstein’s Theory of Relativitywherein he predicted massive objects would bend and warp the fabric of spacetime. The more massive the object, the more severe the bending. We can picture this by imagining a child standing on a trampoline, her weight pressing a dimple into the fabric. Replace the child with a 200-pound adult and the surface of the trampoline sags even more.
Massive objects like the Sun and even the planets warp the fabric of space. Here a planet orbits the Sun but doesn’t fall in because of its sideways orbital motion.
Similarly, the massive Sun creates a deep, but invisible dimple in the fabric of spacetime. The planets feel this ‘curvature of space’ and literally roll toward the Sun. Only their sideways motion or angular momentum keeps them from falling straight into the solar inferno.
Curved space created by massive objects also bends light rays. Einstein predicted that light from a star passing near the Sun or other massive object would follow this invisible curved spacescape and be deflected from an otherwise straight path. In effect, the object acts as a lens, bending and refocusing the light from the distant source into either a brighter image or multiple and distorted images. Also known as the deflection of starlight, nowadays we call it gravitational lensing.
This illustration shows how gravitational lensing works. The gravity of a large galaxy cluster is so strong, it bends, brightens and distorts the light of distant galaxies behind it. The scale has been greatly exaggerated; in reality, the distant galaxy is much further away and much smaller. Credit: NASA, ESA, L. Calcada
Simulation of distorted spacetime around a massive galaxy cluster over time
Turns out there are lots of these gravitational lenses out there in the form of massive clusters of galaxies. They contain regular matter as well as vast quantities of the still-mysterious dark matter that makes up 96% of the material stuff in the universe. Rich galaxy clusters act like telescopes – their enormous mass and powerful gravity magnify and intensify the light of galaxies billions of light years beyond, making visible what would otherwise never be seen.
This cropped image shows the central slice of the MACS J1149 galaxy cluster. A massive elliptical galaxy lenses the light of SN Refsdal into four separate images. It also distorts the purplish spiral galaxy that’s host to the supernova. Credit: NASA/ESA/M. Postman STScI/CLASH team
Let’s return to SN Refsdal, named for Sjur Refsdal, a Norwegian astrophysicist who did early work in the field of gravitational lensing. A massive elliptical galaxy in the MACS J1149 cluster “lenses” the 9.4 billion light year distant supernova and its host spiral galaxy from background obscurity into the limelight. The elliptical’s powerful gravity’s having done a fine job of distorting spacetime to bring the supernova into view also distorts the shape of the host galaxy and splits the supernova into four separate, similarly bright images. To create such neat symmetry, SN Refsdal must be precisely aligned behind the galaxy’s center.
What looks like a galaxy with five nuclei really has just one (at center) surrounded by a mirage of four images of a distant quasar. The galaxy lies 400 million light years away; the quasar about 8 billion. Credit: NASA/ESA/Hubble
The scenario here bears a striking resemblance to Einstein’s Cross, a gravitationally lensed quasar, where the light of a remote quasar has been broken into four images arranged about the foreground lensing galaxy. The quasar images flicker or change in brightness over time as they’re microlensed by the passage of individual stars within the galaxy. Each star acts as a smaller lens within the main lens.
Color-composite image of the lensing elliptical galaxy and distorted background host spiral (top). The green circles, S1-4, show the locations of the supernova images, while another quadruply imaged segment of the spiral arm is marked in red. The bottom panels show two additional lensed images of the spiral host galaxy visible in the galaxy cluster field. Talk about a funhouse mirror! Credit: P.L. Kelly/GLASS/Hubble Frontier Fields
Detailed color images taken by the GLASS and Hubble Frontier Fields groups show the supernova’s host galaxy is also multiply-imaged by the galaxy cluster’s gravity. According to their recent paper, Kelly and team are still working to obtain spectra of the supernova to determine if it resulted from the uncontrolled burning and explosion of a white dwarf star (Type Ia) or the cataclysmic collapse and rebound of a supergiant star that ran out of fuel (Type II).
The time light takes to travel to the Earth from each of the lensed images is different because each follows a slightly different path around the center of the lensing galaxy. Some paths are shorter, some longer. By timing the brightness variations between the individual images the team hopes to provide constraints not only on the distribution of bright matter vs. dark matter in the lensing galaxy and in the cluster but use that information to determine the expansion rate of the universe.
