Science
Jets from powerful black holes can point astronomers toward where − and where not − to look for life in the universe
David Garofalo, Kennesaw State University
One of the most powerful objects in the universe is a radio quasar – a spinning black hole spraying out highly energetic particles. Come too close to one, and you’d get sucked in by its gravitational pull, or burn up from the intense heat surrounding it. But ironically, studying black holes and their jets can give researchers insight into where potentially habitable worlds might be in the universe.
As an astrophysicist, I’ve spent two decades modeling how black holes spin, how that creates jets, and how they affect the environment of space around them.
What are black holes?
Black holes are massive, astrophysical objects that use gravity to pull surrounding objects into them. Active black holes have a pancake-shaped structure around them called an accretion disk, which contains hot, electrically charged gas.
The plasma that makes up the accretion disk comes from farther out in the galaxy. When two galaxies collide and merge, gas is funneled into the central region of that merger. Some of that gas ends up getting close to the newly merged black hole and forms the accretion disk.
There is one supermassive black hole at the heart of every massive galaxy.
Black holes and their disks can rotate, and when they do, they drag space and time with them – a concept that’s mind-boggling and very hard to grasp conceptually. But black holes are important to study because they produce enormous amounts of energy that can influence galaxies.
How energetic a black hole is depends on different factors, such as the mass of the black hole, whether it rotates rapidly, and whether lots of material falls onto it. Mergers fuel the most energetic black holes, but not all black holes are fed by gas from a merger. In spiral galaxies, for example, less gas tends to fall into the center, and the central black hole tends to have less energy.
One of the ways they generate energy is through what scientists call “jets” of highly energetic particles. A black hole can pull in magnetic fields and energetic particles surrounding it, and then as the black hole rotates, the magnetic fields twist into a jet that sprays out highly energetic particles.
Magnetic fields twist around the black hole as it rotates to store energy – kind of like when you pull and twist a rubber band. When you release the rubber band, it snaps forward. Similarly, the magnetic fields release their energy by producing these jets.
These jets can speed up or suppress the formation of stars in a galaxy, depending on how the energy is released into the black hole’s host galaxy.
Rotating black holes
Some black holes, however, rotate in a different direction than the accretion disk around them. This phenomenon is called counterrotation, and some studies my colleagues and I have conducted suggest that it’s a key feature governing the behavior of one of the most powerful kinds of objects in the universe: the radio quasar.
Radio quasars are the subclass of black holes that produce the most powerful energy and jets.
You can imagine the black hole as a rotating sphere, and the accretion disk as a disk with a hole in the center. The black hole sits in that center hole and rotates one way, while the accretion disk rotates the other way.
This counterrotation forces the black hole to spin down and eventually up again in the other direction, called corotation. Imagine a basketball that spins one way, but you keep tapping it to rotate in the other. The tapping will spin the basketball down. If you continue to tap in the opposite direction, it will eventually spin up and rotate in the other direction. The accretion disk does the same thing.
Since the jets tap into the black hole’s rotational energy, they are powerful only when the black hole is spinning rapidly. The change from counterrotation to corotation takes at least 100 million years. Many initially counterrotating black holes take billions of years to become rapidly spinning corotating black holes.
So, these black holes would produce powerful jets both early and later in their lifetimes, with an interlude in the middle where the jets are either weak or nonexistent.
When the black hole spins in counterrotation with respect to its accretion disk, that motion produces strong jets that push molecules in the surrounding gas close together, which leads to the formation of stars.
But later, in corotation, the jet tilts. This tilt makes it so that the jet impinges directly on the gas, heating it up and inhibiting star formation. In addition to that, the jet also sprays X-rays across the galaxy. Cosmic X-rays are bad for life because they can harm organic tissue.
For life to thrive, it most likely needs a planet with a habitable ecosystem, and clouds of hot gas saturated with X-rays don’t contain such planets. So, astronomers can instead look for galaxies without a tilted jet coming from its black hole. This idea is key to understanding where intelligence could potentially have emerged and matured in the universe.
Black holes as a guide
By early 2022, I had built a black hole model to use as a guide. It could point out environments with the right kind of black holes to produce the greatest number of planets without spraying them with X-rays. Life in such environments could emerge to its full potential. https://www.youtube.com/embed/b7mTVX9IE0s?wmode=transparent&start=0 Looking at black holes and their role in star formation could help scientists predict when and where life was most likely to form.
Where are such conditions present? The answer is low-density environments where galaxies had merged about 11 billion years ago.
These environments had black holes whose powerful jets enhanced the rate of star formation, but they never experienced a bout of tilted jets in corotation. In short, my model suggested that theoretically, the most advanced extraterrestrial civilization would have likely emerged on the cosmic scene far away and billions of years ago.
David Garofalo, Professor of Physics, Kennesaw State University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The science section of our news blog STM Daily News provides readers with captivating and up-to-date information on the latest scientific discoveries, breakthroughs, and innovations across various fields. We offer engaging and accessible content, ensuring that readers with different levels of scientific knowledge can stay informed. Whether it’s exploring advancements in medicine, astronomy, technology, or environmental sciences, our science section strives to shed light on the intriguing world of scientific exploration and its profound impact on our daily lives. From thought-provoking articles to informative interviews with experts in the field, STM Daily News Science offers a harmonious blend of factual reporting, analysis, and exploration, making it a go-to source for science enthusiasts and curious minds alike. https://stmdailynews.com/category/science/
STM Blog
From Hand Signals to Smart Crosswalks: The Evolution of the Modern Pedestrian Signal
Discover the history of the modern pedestrian signal, from Garrett A. Morgan’s groundbreaking traffic signal to today’s smart, accessible crosswalks.
Every day, millions of people rely on pedestrian signals to cross busy street safely. A glowing white walking figure, an orange-red hand, and a countdown timer have become familiar sights around the world. While these signals may seem like simple pieces of infrastructure, they are the result of more than a century of innovation, engineering, and public safety improvements.
The modern pedestrian signal did not appear overnight. Instead, it evolved through the contributions of inventors, engineers, city planners, and transportation officials who continually refined traffic control systems as cities grew and automobiles became more common.
The Early Days of Traffic Control
Before electric traffic signals, intersections were controlled by police officers, railway-style semaphores, or even hand signals. As horse-drawn wagons gave way to automobiles in the early 1900s, traffic congestion and accidents increased dramatically, creating an urgent need for better traffic management.
One of the earliest electric traffic lights was installed in Cleveland, Ohio, in 1914. It used red and green lights and was manually operated. While it improved vehicle movement, pedestrians still had to judge for themselves when it was safe to cross.
Garrett A. Morgan’s Breakthrough
One of the most important milestones came in 1923 when inventor and entrepreneur Garrett Augustus Morgan received U.S. Patent No. 1,475,024 for an improved traffic signal.
Morgan’s design introduced a third position in addition to “Stop” and “Go.” This intermediate phase temporarily stopped traffic in every direction before allowing vehicles to proceed. The brief pause reduced confusion at intersections and provided additional time for pedestrians to cross safely.
Morgan reportedly developed his design after witnessing a serious traffic accident. His invention demonstrated how thoughtful engineering could improve public safety while making increasingly busy streets more efficient.
Although Morgan did not invent the illuminated “WALK” and “DON’T WALK” pedestrian signal used today, his three-position signal became a foundational step in the evolution of modern traffic control.
The Birth of Dedicated Pedestrian Signals
As cities expanded after World War II, pedestrian safety became an even greater concern. More people were walking in increasingly crowded downtown districts, and separating pedestrian movements from vehicle traffic became a priority.
During the early 1950s, several American cities began experimenting with dedicated pedestrian signals. New York City became one of the first major municipalities to install illuminated “WALK” and “DON’T WALK” signs at busy intersections.
These early systems gave pedestrians their own designated crossing phase, reducing conflicts with turning vehicles and improving safety at some of the nation’s busiest intersections.
Standardization Across America
By the 1960s and 1970s, traffic engineers recognized the importance of creating consistent traffic control devices nationwide.
The Manual on Uniform Traffic Control Devices (MUTCD) established national standards for traffic signs, pavement markings, and pedestrian signals. Standardized designs helped ensure that pedestrians could understand crossing signals regardless of where they traveled in the United States.
Eventually, words gave way to internationally recognized symbols—a walking person to indicate it was safe to cross and an upraised hand to indicate pedestrians should wait. These symbols transcended language barriers and improved accessibility for visitors and non-English speakers.
The Countdown Era
One of the most significant modern improvements arrived with pedestrian countdown timers.
Rather than simply flashing a warning, countdown displays show exactly how many seconds remain before the crossing phase ends. Research has shown that countdown timers help pedestrians make better crossing decisions and improve compliance with traffic signals.
Today, countdown timers have become standard equipment at intersections across much of the United States.
Accessibility Takes Center Stage
Modern pedestrian signals are designed to serve everyone.
Accessible Pedestrian Signals (APS) now provide audible tones, spoken messages, vibrating push buttons, and locator sounds that assist pedestrians who are blind or have low vision. These features allow more people to navigate intersections independently and safely.
The continued development of accessible technology reflects a broader commitment to making transportation systems inclusive for all users.
The Future of Pedestrian Safety
Pedestrian signals continue to evolve.
Many cities now use smart traffic systems that detect pedestrians waiting to cross, automatically adjust signal timing based on traffic conditions, and prioritize people walking during busy periods.
Researchers are exploring artificial intelligence, connected vehicle technology, and sensor-based systems capable of communicating directly with autonomous vehicles. Future pedestrian crossings may adapt in real time to weather conditions, crowd sizes, emergency vehicles, and even the needs of older adults or individuals with disabilities.
A Legacy Built by Many Innovators
The pedestrian signal we know today is the product of more than a century of collaboration and innovation.
Early traffic engineers created the first electric traffic lights. Garrett A. Morgan improved intersection safety with his groundbreaking three-position traffic signal. Transportation agencies standardized traffic control devices, while engineers continued refining pedestrian technology through countdown timers, accessible features, and intelligent traffic systems.
Every safe crossing today reflects the work of countless inventors, planners, researchers, and public officials dedicated to protecting lives.
As cities continue to grow and transportation technology advances, the humble pedestrian signal remains one of the most effective—and often overlooked—public safety innovations ever developed.
At STM Daily News, we celebrate the inventors, engineers, and visionaries whose everyday innovations quietly improve life for millions of people. Sometimes the most important inventions aren’t the ones that grab headlines—they’re the ones we depend on every single day without giving them a second thought.
Related Reading
- Federal Highway Administration – Manual on Uniform Traffic Control Devices (MUTCD)
- National Museum of African American History and Culture – Garrett Augustus Morgan
- United States Patent and Trademark Office
- Federal Highway Administration – Accessible Pedestrian Signals
- National Highway Traffic Safety Administration (NHTSA)
🧠 Discover the remarkable innovators, inventors, and trailblazers who helped shape our world but rarely receive the recognition they deserve. Share your thoughts in the comments and subscribe to the STM Daily News newsletter to catch every new Forgotten Genius Friday feature and more inspiring stories delivered to your inbox.
The Earth
Cement has a climate problem — here’s how geopolymers with add‑ins like cork could help fix it
Portland cement drives ~8% of global emissions. Learn how low-carbon geopolymers—enhanced with add-ins like cork—could cut concrete’s footprint.
Alcina Johnson Sudagar, Washington University in St. Louis
Concrete is all around you – in the foundation of your home, the bridges you drive over, the sidewalks and buildings of cities. It is often described as the second-most used material by volume on Earth after water.
But the way concrete is made today also makes it a major contributor to climate change.
Portland cement, the key component of concrete, is responsible for about 8% of global greenhouse gas emissions. That’s because it’s made by heating limestone to high temperatures, a process that burns a large amount of fossil fuels for energy and releases carbon dioxide from the limestone in the process.
The good news is that there are alternatives, and they are gaining attention.
Portland cement: A greenhouse gas problem
Cementlike substances have been used in construction for thousands of years. Architects have found evidence of their use in the pyramids of Egypt and the buildings and aqueducts of the Roman Empire.
The Portland cement commonly used in construction today was patented in 1824 by Joseph Aspdin, a British bricklayer.
Modern cement preparation starts with crushing the excavated raw materials limestone and clay and then heating them in a kiln at around 2,650 degrees Fahrenheit (about 1,450 degrees Celsius) to form clinker, a hard, rocklike residue. The clinker is then cooled and ground with gypsum into a fine powder, which is called cement.
About 40% of the carbon dioxide emissions from cement production come from burning fossil fuels to generate the high heat needed to run the kiln. The rest come as the heat converts limestone (calcium carbonate) to lime (calcium oxide), releasing carbon dioxide.
In all, between half a ton and 1 ton of greenhouse gas is released per ton of Portland cement. Cement is a binding agent that, mixed with water, holds aggregate together to create concrete. It makes up about 10% to 15% of the concrete mix by weight.
Alternative technologies can lower emissions
As populations, cities and the need for new infrastructure expand, the use of cement is growing, making it important to find alternatives with lower environmental costs.
Some techniques for reducing carbon dioxide emissions include substituting some of the clinker – the hard residue typically made from limestone – with supplementary materials such as clay, or fly ash and slag from industries. Other methods reduce the amount of cement by mixing in waste sawdust or recycled materials like plastics.
The long-term solution for reducing cement’s emissions, however, is to replace traditional cement completely with alternatives. One option is geopolymers made from earthen clay and industrial wastes.
Geopolymers: A more climate-friendly solution
Geopolymers can be made by mixing claylike materials that are rich in aluminum and silicon minerals with a chemical activator through a process called geopolymerization. The activator transforms the silicon and aluminum into a structure that will look like cement. All of this can happen at room temperature.
The major difference between cement and geopolymer is that cement is mainly made of calcium, whereas geopolymers are made of silicon and aluminum with some possible calcium in their structure.
These geopolymers have been found to possess high strength and durability, including resilience in freeze-thaw cycles and resistance to heat and fire, which are important requirements in construction. Studies have found that some geopolymers can provide comparable if not better strength than traditional cement and, because they don’t require heat the way clinker does, they can be produced with significantly lower greenhouse gas emissions.
Geopolymers can also be produced from a variety of raw materials rich in aluminum and silicon, including earthen clays, fly ash, blast furnace slag, rice husk ash, iron ore wastes and recycled construction brick waste. Geopolymer technology can be adapted depending on the clay or industrial waste locally available in a region. https://www.youtube.com/embed/NOj3p6m9M7Q?wmode=transparent&start=0 A brief history of cement and geopolymers. Geopolymer International.
An added advantage of geopolymers is that changes to the mixture can produce a range of features.
For example, I and my co-researchers at the University of Aveiro in Portugal added a small amount of cork industry waste – the leftovers from creating bottle corks – to clay-based geopolymer and found it could improve the strength of the material by up to twofold. The cork particles filled the spaces in the geopolymer structure, making it denser, which increased the strength.
Similarly, additives such as sisal fibers from the agave plant, recycled plastic and steel fibers can change geopolymer properties. The additives do not participate in the geopolymerization process but act as fillers in the structure.
The structure of geopolymers can also be designed to act as adsorbents, attracting toxic metals in wastewater and capturing and storing radioactive wastes. Specifically, incorporating materials like zeolite that are natural adsorbents in the geopolymer structure can make them useful for such applications as well.
Where geopolymers are used now
Geopolymers have been used in many types of construction, including roads, coatings, 3D printing, coastal environmental protection, the steel and chemical industries, sewer rehabilitation and building radiation shielding and rocket launchpad and bunker infrastructure.
One of the earliest examples of a modern geopolymer concrete project was the Brisbane West Wellcamp airport in Australia.
It was built in 2014 with 70,000 metric tons of geopolymer concrete, which was estimated to have reduced the project’s carbon dioxide emissions by as much as 80%.
The geopolymer market is currently estimated to be between US$7 billion and $10 billion, with the largest growth in the Asia-Pacific region.
Analysts have estimated that the market could grow at a rate of 10% to 20% per year and reach about $62 billion by 2033.
In several countries, greenhouse gas regulations and green-building certifications are expected to support the continued growth of geopolymers in the construction industry.
Expanding the use of cement alternatives
The advantage of using industrial wastes in geopolymers is a double-edged sword, however. The composition of industrial wastes varies, so it can be difficult to standardize the processing methods. The geopolymer components need to be mixed in particular ratios to achieve desired properties.
Producing the activator for the geopolymer, typically done in chemical facilities, can raise the cost and contribute to the carbon footprint. And the long-term data about these materials’ stability is only now being developed given their newness. Also, these geopolymers can take longer to set than cement, though the setting time can be sped up by using raw materials that react quickly.
Developing cheaper, naturally available activators like agricultural waste rice husk with sustainable supply chains could help lower the costs and environmental impact. Also, printing the recipe on the raw material packaging could help simplify the job of determining the mixing ratio so geopolymers can be more widely used with confidence.
Even though geopolymer technology has some drawbacks, these low-carbon alternatives have great potential for reducing emissions from the construction sector.
Alcina Johnson Sudagar, Research Scientist in Chemistry, Washington University in St. Louis
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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Science
Sonic booms from meteors can release the energy of hundreds of tons of TNT – here’s how they work
Shawn Laatsch, University of Maine
Sonic booms from meteors can release the energy of hundreds of tons of TNT – here’s how they work
As humans, we live out our lives on a planet that is constantly sweeping through a cosmic ocean littered with ancient debris from the formation of the solar system. For the most part, our world glides silently through space, shielded by Earth’s thin atmosphere.
Occasionally, however, the rest of the universe reminds us of its presence with stunning, visceral clarity.
Residents along the Massachusetts–New Hampshire border were startled by a sudden sonic boom on the afternoon of May 30, 2026. A large number of people up and down the Eastern Seaboard witnessed it.
After NASA analyzed imagery from weather satellites, they identified the culprit as a small meteor measuring roughly 3 to 5 feet (1 to 2 meters) across. It was screaming through space at an astonishing 42,000 miles per hour (68,000 kilometers per hour) when it plunged into Earth’s upper atmosphere.
Friction between the meteor and the increasingly dense air quickly turned the kinetic energy of the rock shooting through the sky into blistering heat. At an altitude of roughly 40 miles (60 kilometers), the immense heat and pressure overcame the structural integrity of the meteor, causing it to fragment in a brilliant flash.
The breakup released a staggering burst of energy equivalent to 300 tons of TNT. When an object travels through the air at speeds faster than sound, which is 761 mph (1,225 kph), it creates a shock wave creating a thunderous clap, or sonic boom. While the majority of the rock vaporized, the remaining fragments rained down harmlessly into the waters of Cape Cod Bay.
In the past, such an event might have passed as an unverified sighting in the daytime sky. Today, however, our planet is wired with an accidental network of planetary defense sensors: dashboard cameras, security systems and digital doorbells.
Because meteor entries like this one last only a few fleeting seconds, they were easily missed in the past. Now, our collective digital eyes capture these spontaneous cosmic intrusions almost instantly, bringing the universe directly into our daily news feeds. While dramatic, these events are more common than most people imagine.
As someone who has worked as a planetarium director and astronomy educator for over four decades, I often get emails, social media messages and phone calls about such objects and sightings. While hearing a sonic boom can be a bit unsettling or even shocking, it reminds us we live in an active universe and may want to occasionally look up instead of down at our devices.
A meteoric spring
The Cape Cod fireball was the latest sighting in an active season of meteoritic arrivals. Just months earlier, the solar system seemed to be sending a parade of rocky objects down to Earth.
From March 8-11, observers in Northern Europe witnessed large, slow-moving fireballs in their skies. Enthusiasts and scientists successfully recovered several fragments. Lab analysis of these specimens revealed their place in a fascinating lineage – scientists determined that they had originated from Vesta, a massive, pristine asteroid orbiting between Mars and Jupiter.
On March 17, a 7-ton asteroid measuring roughly 6 feet across entered the atmosphere directly over Lake Erie. Traveling at 45,000 mph (72,400 kph), it generated a brilliant daytime flash and a powerful sonic boom, unloading an energy equivalent to 250 tons of TNT. NASA scientists published data about its trajectory, allowing meteorite hunters to recover pristine fragments in Valley City, just a short drive from Cleveland, Ohio.
Only four days later, on March 21, another cosmic fragment blazed across the skies of Texas. This object was about 3 feet wide, and it traveled at 35,000 mph (56,300 kph), releasing the energy of roughly 26 tons of TNT.
Outside of Houston, homeowner Sherri James was startled by a sudden crash, only to discover a 6-inch (15-cm) hole in her roof and a small piece of the solar system resting on her floor.
Thank goodness for Earth’s atmospheric shield
The benchmark for modern atmospheric impacts is the Chelyabinsk meteor, which exploded over Russia on Feb. 15, 2013.
That object was significantly larger than any of the meteors researchers have observed in 2026, measuring 60 feet (18 m) across and weighing roughly 10,000 tons. When it shattered 18 miles (29 km) above the ground, it produced an airburst with an explosive force 30 times greater than the Hiroshima atomic bomb.
The resulting shock wave shattered glass across hundreds of square miles, injuring nearly 1,500 people and registering as a seismic event between 2.7 and 3.7 on the Richter scale. The incident was a stark reminder that while Earth’s atmosphere is an incredibly effective shield, absorbing the lion’s share of cosmic impacts, a large enough kinetic punch can still reach the surface below.
Despite the dramatic stories around these meteor impacts, history shows that the cosmic lottery rarely targets humans directly. In all of recorded history, there is only one universally confirmed case of a person being directly struck by a space rock.
In 1954, an 8.5-pound (3.8 kg) meteorite crashed through the roof of a house in Sylacauga, Alabama, ricocheted off a heavy wooden radio and struck a sleeping woman named Ann Hodges. Though it left a severe bruise on her hip, the radio absorbed the brunt of the impact. Had it not been for the radio, there is a chance she could have been seriously injured or killed by this object.
Living with the cosmos
So, are you in any imminent danger from meteors? The mathematics of the cosmos provide profound reassurance. The statistical odds of being struck by a meteorite are vanishingly small. You stand a better chance of winning a multimillion-dollar lottery jackpot 10 times in a row than ever being hit by a meteorite.
The vast majority of the tons of space debris that bombard Earth daily arrive as harmless dust grains, burning up as elegant meteors or shooting stars. But when the larger pieces do break through and land on our planet, they offer a rare, tangible connection to the beginning of the solar system.
If you ever happen to witness one of these magnificent fireballs ripping open the sky, consider reporting your observation to the American Meteor Society. The organization keeps track of sightings and falls from around the globe. Recovered fragments provide a way for scientists to gain valuable information about the origin of our solar system, and of our home planet.
Shawn Laatsch, Director of the Versant Power Astronomy Center, University of Maine
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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