Category: Innovation

Just as many staid adults were once rebellious teenagers in interesting clothing, many marine fish species enter life as flamboyant larvae that bear little resemblance to their mature forms. The juvenile scalloped ribbonfish pictured here, for example, eventually loses its flowing fin rays and grows into a teardrop-shaped adult that can reach over a meter long.

Or take the ribbon sawtail fish, which begins life with charmingly dopey eye stalks a quarter of the length of its body, and later becomes a svelte-eyed monster with an underbite full of snaggled needle teeth. Still others have guts that dangle like a second tail or offer dazzling color displays that they shed with time.

The differences between larvae and adults can be so significant that, through the 19th and 20th centuries, many larvae were misclassified as separate species or genera from the adults they would become. Scientists believe that these body changes have to do with diverging evolutionary pressures on larvae and adults.

The food-rich zone near the ocean’s surface is, after all, a very dangerous place to be tiny. The scalloped ribbonfish’s resemblance to a jellyfish with a nasty sting may be an effective deterrent to potential predators. And the ribbon sawtail fish’s eyestalks may do double duty by both easing its own efforts to find prey, and allowing it to search the water with minimal body movement that could attract creatures hoping to gulp it down.

Larval marine fish and invertebrates across the globe also participate en masse in defensive vertical migration. During the day, they descend to deeper water to avoid predators that hunt by eyesight. But by night, under cover of darkness, they rise to the surface to feed. The U.S. Navy first discovered this phenomenon in the ocean during World War II, when pings from sonar revealed a deep layer of interference that disappeared at night, like some kind of phantom web.

The ocean’s surface is a very dangerous place to be tiny.

But some knowledge of larvae’s morphological adaptations is more current. The cone-shaped trawl nets that scientists have long used to collect zooplankton, including larval fish, can mangle and break off the creatures’ ostentatious parts. And the fixatives used to preserve specimens drain their color. Recently though, the emerging practice of blackwater photography has brought these animals into clearer focus. Blackwater divers enter the water in the dead of night with bright lights and macro lenses. The resulting images of tiny creatures going about their lives in full color reveal much more about their bodies and behaviors than do their bleached, partial corpses.

Hitchhiking, for example, is ubiquitous. Magnus Lundgren, the Swedish underwater photographer who captured this scalloped ribbonfish, has also photographed nautiluses riding atop jellyfish and fish swimming among their tentacles, as well as fish and octopuses traveling inside or atop floating tunicates. What these creatures accomplish by sticking together isn’t clear. But perhaps with enough teamwork of their own, scientists and blackwater divers will illuminate answers as spectacular as the creatures themselves.

Magnus Lundgren is a decades-long, Swedish-born professional photographer who has been taking images for as long as he can remember. He is widely regarded as one of the world’s leading underwater photographers and is honored to work in the field of conservation photography. For him, conservation is the ultimate motivation. 

This story originally appeared in bioGraphic, an independent magazine about nature and regeneration powered by the California Academy of Sciences.

• Sarah Gilman

  Posted on December 29, 2023

  Sarah Gilman is a writer, illustrator, and editor who covers the environment, science, and place from rural Washington state. She’s also a contributing editor at Hakai Magazine. Her work has appeared in The Atlantic, Audubon, Smithsonian, High Country News, National Geographic, and others.

Twenty years ago, Andrea Tiengo was a junior scientist watching data stream in from a distant space telescope. He was keeping tabs on routine waves of cosmic X-rays washing over the orbiting, bus-size contraption, relayed to his computer on Earth. 

One December afternoon, a peculiar X-ray signal came in. “I saw something like fog, or something blurry, around the point source,” Tiengo says. This one looked different, but it looked so different from any other X-ray observation he had seen that he thought it could be a problem with the hardware. It was getting late in the day, and Tiengo decided to go home and wait to address the problem in the morning. That, he says, “was a big mistake.” 

By the next day, the glow was no longer visible to the telescope—and other researchers, instead of him, had made a big discovery. That fog-like signal was the first rings of X-ray “light” from a brilliant gamma-ray burst reflecting off nearby dust. It was an X-ray echo of the blast, an observation no one had ever detected before. 

The echoed light arrives minutes to millenia later than the original burst.

Since that missed opportunity, Tiengo, now an astrophysicist at the Scuola Universitaria Superiore IUSS in Pavia, Italy, has spent the past two decades searching for the echoes of other cosmic blasts and interpreting them. Those reflections, it turns out, are gifts akin to a time machine, a way to watch a replay of the bursting, flaring sources. And from that replay, astronomers can decipher details of the original explosion they couldn’t otherwise uncover.

A bit like how bats and other animals use sound bouncing off objects and back to them to understand their surroundings, astronomers can use pings of light energy—not all of which is in the visible range—bouncing off material in the universe. Some types of light, like radio waves, just pass through material instead of scattering off it. But other types, including X-rays and visible light from a star’s explosion—or any changing cosmic light source like a brightening star or a burping black hole—bounce off intervening dust on its way to our eyes and telescopes. 

That echoed light ends up taking a longer path to Earth, arriving minutes to millenia later than the original burst’s signal. The length of the delay depends on how much the light roamed and bounced on its way to Earth. And from these second-hand signals, astronomers can begin to reconstruct the stellar blast, rewind the events that led to it, and map the material that lay between it and us. 

Although the study of these distant echoes has risen to the fore over the past 20 years, its history extends much further back.

In February 1901, astronomers saw a brilliant “new star,” or nova, in the sky. This star, Nova Persei, had brightened temporarily after an explosion at its surface. This several-day flash of visible light radiated away from the star and bounced around nearby clouds. Later that same year, observers spied a fog around the star—light echoes. 

These sorts of events create ideal sources of light echoes for study. And our sky hosts heaps of them. Or has, over the centuries. 

In November 1572, it looked like a bright new star had suddenly appeared in the sky. Seen by many and visible to the naked eye, it was described most extensively by Danish astronomer Tycho Brahe—and subsequently dubbed Tycho’s supernova. Some time in the next century, light from another supernova, Cassiopeia A arrived on Earth. The original light flashes from the catastrophic explosions of these once-stars have long-since dissipated, but their echoes are now washing over us. They are the radiating landscapes on which Johns Hopkins University astronomer Armin Rest trains his focus. Through them, he says, “We basically can go back in time.”

Within these echoes, he has found, lie patterns of imprinted information: missing spectral colors that correspond to specific molecules and elements. This is the same pattern as what the original source released, and so seeing an echo later means astronomers can step back and reconstruct the details of the original event. And because oftentimes, they don’t see just one echo but instead see multiple echoes over time, they can watch how the stellar explosion evolved. 

With echoes working as sort-of portals to the distant past, Rest and his colleagues have been able to watch a supernova’s blast and paint a picture of how it exploded. We haven’t been able to watch a star explode in real-time, and computer models still struggle to get the details right. So replaying the blast with the delayed echoes lets astronomers peek into the crucial moments.

Even fresh echoes have much to teach us. On Oct. 9, 2022, the brightest gamma-ray burst ever detected showered Earth with its rays. While its original X-ray light blinded most telescopes—making immediate headlines across the globe—the brilliant light energy bounced off nearby dust clouds and gave Tiengo and colleagues echoing rings of that X-ray emission a couple days later. Over the next month, the XMM-Newton satellite he works with captured 20 rings, all surrounding the site of the original blast. 

“Each ring,” says Tiengo, “is the vehicle of the same emission” and carries the burst’s imprint. By studying the spectral imprint in these rings, the astronomers reconstructed the details of the original flash: They could see into the past and watch a burst that couldn’t have been observed any other way. From those 20 rings, Tiengo says, they see a hint of something surprising in the explosion, which released more X-rays but with lower energies than expected. Tantalizing clues they and other scientists will continue puzzling over in the quest to better understand how massive stars live—and die. 

We see the light from our black hole’s last snack as echoes, hundreds of years later.

Other groups of astronomers are using light echoes to study some of the most mysterious cosmic monsters in the universe. Shuo Zhang of Michigan State University is piecing together the history of outbursts from the supermassive black hole at the center of our galaxy. This behemoth, Sagittarius A*, or Sgr A* for short, today is quiet compared with the tumultuous beasts at the centers of other galaxies. But light reflections off blobs of material at our galaxy’s core imply Sgr A* had a more active and louder past. 

Zhang has combined some 20 years of X-ray images from giant clouds of molecular gas, blobs that, she says, “are the perfect recorder to any past outbursts in the galactic center.” Such an outburst follows the black hole snacking on a gas stream, an unlucky star, or some other material that came too close to Sgr A*’s strong gravity. Before being ingested, the snack stretches and swirls around the black hole, spiraling at its outskirts. Those tumultuous movements spew heat and X-rays, which hit the molecules in the nearby giant gas clouds. The light gives some of its energy to the gas in the clouds, making them light up. But some of the X-rays aren’t absorbed and instead bounce off particles in the cloud, like sunlight bouncing off the rippling surface of a lake. That bouncing light’s detour gives it a longer and delayed path to our telescopes. And so, today’s telescopes see the delayed light released during our black hole’s last swirling snack as echoes, hundreds of years later. 

The echoes Zhang and her colleagues have tracked over the years, in addition to other X-ray data from different teams, show our galaxy’s central black hole was more active about 200 years ago. The scientists will keep watching as those echoes from the gas clouds continue to evolve over the next several years. They’re looking for the echoes to quiet, which will tell them how long the black hole flared.  

Much of the spotting of these echoes is still done the old-fashioned way, by humans pouring over surveys, squinting for the faint fog or rings that large cosmic events leave behind. 

But that will change over the next several years. “We are soon ushering in this era of time domain surveys,” says MIT astrophysicist Erin Kara, describing the new approach that will quickly map the sky and reveal minute changes. Kara, who uses light echoes to study the innermost portions of a black hole’s environment, notes that this will be key in finding more radiating echoes in the universe. 

Upcoming projects, like the Vera C. Rubin Observatory—scheduled to begin operations in January 2025—and its Legacy Survey of Space and Time will collect scattered light across huge swaths of the sky at once and return to the same view frequently. Complex computer programs will subtract images to look for changes—like brightness variations that could lead to light reflections and foggy light arcs that move from one image to another, indications of echoes. Other future endeavors, such as the China-Europe Einstein Probe, will use a perch above our planet and new technology inspired by lobster eyes to capture an even wider area of the cosmos. With these and others, scientists will step back in time and untangle how these spectacular cosmic events unfolded. 

This work takes a broad view. “It’s always better to have more photons than less,” says Tiengo, especially when you’re searching for the faint whispers of flareups from across space—and time.

Lead image: NASA/CXC/U. Wisconsin/S. Heinz

• Liz Kruesi

  Posted on December 29, 2023

  Liz Kruesi writes about the stories of the universe from her home base in Colorado, a mile closer to the stars.

application: A particular use or function of something.

atmosphere: The envelope of gases surrounding Earth, another planet or a moon.

atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

behavior: The way something, often a person or other organism, acts towards others, or conducts itself.

carbon: A chemical element that is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules. (in climate studies) The term carbon sometimes will be used almost interchangeably with carbon dioxide to connote the potential impacts that some action, product, policy or process may have on long-term atmospheric warming.

carbon capture: (climate science) A term for processes that directly remove carbon dioxide gas from air or water through some chemical means so that it can be stored and then either disposed or reused as a raw material.

carbon footprint: A popular term for measuring the global warming potential of various products or processes. Their carbon footprint translates to the amount of some greenhouse gas — usually carbon dioxide — that something releases per unit of time or per quantity of product.

caustic: An adjective for alkaline materials that can chemically burn or corrode tissue. A common example is lye (potassium hydroxide). Some people also use caustic to describe strong acids that also burn and corrode. To be accurate, however, caustic term should be applied only to alkaline chemicals.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H₂O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

climate: The weather conditions that typically exist in one area, in general, or over a long period.

climate change: Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H₂O.

corrosive: An adjective for something that can weaken, erode or damage materials (usually metal or rock) gradually as a result of chemical reactions.

crystal: (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The crystalline components of a rock are usually too small to be seen with the unaided eye.

develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.

dissolve: To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

diversity: A broad spectrum of similar items, ideas or people. In a social context, it may refer to a diversity of experiences and cultural backgrounds. (in biology) A range of different life forms.

electrical conductivity: The ability of some substance (such as water or metals) to transport an electrical charge or current.

electricity: A flow of charge, usually from the movement of negatively charged particles, called electrons.

electron: A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

element: A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

engineering: The field of research that uses math and science to solve practical problems. Someone who works in this field is known as an engineer.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

fluoride: A chemical, such as sodium fluoride, that contains the element fluorine. In small doses, fluorides can help prevent tooth decay.

fluorine: An element first discovered in 1886 by Henri Moissan. It takes its name from the Latin word meaning “to flow.” Very reactive, chemically, this element had little commercial use until World War II, when it was used to help make a nuclear-reactor fuel. Later, it was used as ingredients (fluorocarbons) in refrigerants and aerosol propellants. Most recently, it has found widespread use to make nonstick coatings for frying pans, plumbers’ tape, and waterproof clothing.

football field: The field on which athletes play American football. Owing to its size and familiarity, many people use this field as a measure of how big something is. A regulation field (including its end zones) runs 360 feet (almost 110 meters) long and 160 feet (almost 49 meters) wide.

formic acid: A strong-smelling, colorless irritant that occurs naturally in the venom of some ants. The venom can kill many types of insects.

fossil fuel: Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed within the Earth over millions of years from the decayed remains of bacteria, plants or animals.

materials scientist: A researcher who studies how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.

mechanical: Having to do with the devices that move, including tools, engines and other machines (even, potentially, living machines); or something caused by the physical movement of another thing.

membrane: A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.

metal: Something that conducts electricity well, tends to be shiny (reflective) and is malleable (meaning it can be reshaped with heat and not too much force or pressure).

microscope: An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

mineral: Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

molten: A word describing something that is melted, such as the liquid rock that makes up lava.

MXenes: A class of super-thin, layered synthetic nanomaterials that are planar in structure (like sheets of paper). They are made from alternating layers of of atoms. One layer is made of linked atoms of some transition metal (which is referred to as M). The next layer will be linked atoms of another element that’s referred to as X (which is typically carbon, nitrogen or bromine). Being so thin, these materials have an enormously high surface area, relative to their mass. Many also are chemically reactive.

nanometer: A billionth of a meter. It’s such a small unit that researchers use it as a yardstick for measuring wavelengths of light or distances within molecules. For perspective, an average human hair is about 60,000 nanometers wide.

nitrogen: A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth’s atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn. It comes in two stable forms. Both have 14 protons in the nucleus. But one has 14 neutrons in that nucleus; the other has 15. For that difference, they are known, respectively, as nitrogen-14 and nitrogen-15 (or ¹⁴N and ¹⁵N).

oxygen: A gas that makes up about 21 percent of Earth’s atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

physicist: A scientist who studies the nature and properties of matter and energy.

pollutant: A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

potent: An adjective for something (like a germ, poison, drug or acid) that is very strong or powerful.

salt: A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.

Sandia National Laboratories: A series of research facilities run by the U.S. Department of Energy’s National Nuclear Security Administration. It was created in 1945 as the so-called “Z Division” of nearby Los Alamos Laboratory to design, build and test nuclear weapons. Over time, its mission expanded to the study of a broad range of science and technology issues, mostly related to energy production (including wind and solar to nuclear power). Most of Sandia’s roughly 10,000 employees work in Albuquerque, N.M, or at a second major facility in Livermore, Calif.

society: An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.

sodium hydroxide: A chemical that is used in the production of paper and soap. It is used to make solutions more basic (alkaline).

surface area: The area of some material’s surface. In general, smaller materials and ones with rougher or more convoluted surfaces have a greater exterior surface area — per unit mass — than larger items or ones with smoother exteriors. That becomes important when chemical, biological or physical processes occur on a surface.

transition metal: Also known as transition elements. These metals are found in the center of the periodic table. In comparison to other elements, their properties tend to be more unpredictable. This unpredictability is due to their valence electrons being located in an electron shell section known as the d block. Mercury is one example.

unique: Something that is unlike anything else; the only one of its kind.