If event horizons are real, then a star falling into a central black hole would simply be devoured, leaving no trace of the encounter behind.

If you collect more and more matter in a small enough volume of space, it gets harder and harder to escape from its gravitational pull. Gather enough mass there, and you'll find that the speed you'd need to reach in order to escape is greater than the speed of light! From within that region, escape is impossible, and you have a black hole. From farther out, where the escape velocity is lower than the speed of light, matter and radiation can make it out. The border of these two regions is known as the event horizon, and is one of the most important predictions of General Relativity that's never been tested. Until now, that is, where the signs that matter completely disappears when it crosses over cannot be ignored.

At the center of our galaxy, we find the largest black hole within more than a million light years. By observing the orbits of the stars in its vicinity, we can determine that there's an object with:

  • the mass of around 4 million Suns,
  • that occasionally flares in certain wavelengths (X-ray and radio) of light,
  • that emits no visible/infrared light,
  • and that is consistent with a black hole.

But we've never determined whether it truly has an event horizon or not. Sure, General Relativity has been successful every time we've been able to test it out, but every new challenge is a new opportunity to learn something new about the Universe.

Although there are gas outflows and radio/x-ray signals from matter that isn't absorbed by a black hole, nothing should be able to leave/exit once crossing the event horizon.

Top, optical, Hubble Space Telescope / NASA / Wikisky; lower left, radio, NRAO / Very Large Array (VLA); lower right, X-ray, NASA / Chandra X-ray telescope

Although there are gas outflows and radio/x-ray signals from matter that isn't absorbed by a black hole, nothing should be able to leave/exit once crossing the event horizon.

There are always alternatives to consider, and there are a whole class of modifications to gravity we can make that make it possible for event horizons to not exist at all. In these scenarios, instead of an event horizon surrounding a singularity, a giant mass like this would have a hard surface that objects could smash themselves against. If this were the case, you'd be able to tell the difference in one of two ways. The first (and most obvious) way would be with direct imaging: if you achieved sufficiently good resolution, a telescope would be able to see the event horizon for itself... or to find no horizon at all, if one of the alternatives to General Relativity were true. The Event Horizon Telescope, whose first results are due out later this year, should be able to see whether an event horizon really exists.

Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole's accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results.

GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799

Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole's accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results.

But there's a second way that doesn't rely on direct imaging, and can find the answer anyway. Supermassive black holes occur not only at our own galaxy's center, but at the central cores of most large galaxies throughout the Universe. Our Milky Way's black hole, at four million solar masses, may actually be on the low end: many galaxies have black holes that extend up into the billions or even tens of billions of solar masses. The bigger a black hole is, the larger the cross-sectional area of its event horizon is predicted to be, meaning that it has a much larger chance for a passing object to impact it.

An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, may describe the black hole at the center of our galaxy in many regards. But nothing from within the event horizon could ever get out.

Mark A. Garlick

An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, may describe the black hole at the center of our galaxy in many regards. But nothing from within the event horizon could ever get out.

The largest known black holes have diameters about ten times the size of Pluto's orbit, meaning that if we view very large numbers of them for long enough, we should witness a star running into one of them eventually. The Pan-STARRS telescope, having just completed a huge set of deep observations for 3.5 years — covering some 3/4ths of the entire sky repeatedly — was able to look for transient events, or temporary brightenings and dimmings. If event horizons are real, swallowed stars wouldn't create a transient signal, but star colliding with a hard surface would create a significant burst of light.

If a hard surface, rather than an event horizon, exists around a supermassive object, a collision should result in a luminous burst that telescopes like Pan-STARRS should easily perceive.

Mark A. Garlick / CfA

If a hard surface, rather than an event horizon, exists around a supermassive object, a collision should result in a luminous burst that telescopes like Pan-STARRS should easily perceive.

According to Wenbin Lu, a scientist who studied these observations to test the hard-surface theory,

Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them, if the hard-surface theory is true.

Given all the black holes with masses greater than 100 million solar masses, there should have been a definitive signature if there's a hard surface outside of the black hole's event horizon. Yet no signature at all was seen.

After the collision of a star with a hard-surface around a supermassive object, a large, temporary increase in luminosity would result, yet no such changes have been seen around any of the supermassive black holes within the view of Pan-STARRS.

Mark A. Garlick/CfA

After the collision of a star with a hard-surface around a supermassive object, a large, temporary increase in luminosity would result, yet no such changes have been seen around any of the supermassive black holes within the view of Pan-STARRS.

Ramesh Narayan, a coauthor on the new study, was happy to articulate what it all meant,

Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we’ve expected for decades. General Relativity has passed another critical test.

Of course, it's not really possible to prove that the event horizon is real, but this work allows some impressive constraints to be placed.

Theoretical calculations predict an event horizon to all black holes, obscuring the central region in accordance with General Relativity. This is a prediction that has never been tested observationally, until now.

Ute Kraus, Physics education group Kraus, Universität Hildesheim; Axel Mellinger (background)

Theoretical calculations predict an event horizon to all black holes, obscuring the central region in accordance with General Relativity. This is a prediction that has never been tested observationally, until now.

If there is a hard surface, it must be within 0.01% the radius of the expected event horizon, given the lack of transient signals observed. A heat signature in the optical/infrared would be expected, which is exactly what Pan-STARRS would be sensitive to. Yet nothing was observed. In the future, the Large Synoptic Survey Telescope (LSST), which will have more than 20 times the light-gathering power of Pan-STARRS, will be able to constraint the event horizon to a ridiculously small size. But the LSST won't begin doing science until 2021, if things remain on schedule.

A view of the different telescopes contributing to the Event Horizon Telescope's imaging capabilities from one of Earth's hemispheres. Data was taken in April that should enable the detection (or non-detection) of an event horizon around Sagittarius A* within the next year.

APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin

A view of the different telescopes contributing to the Event Horizon Telescope's imaging capabilities from one of Earth's hemispheres. Data was taken in April that should enable the detection (or non-detection) of an event horizon around Sagittarius A* within the next year.

By that point, the data from the Event Horizon Telescope will already be in. If the event horizon is actually, physically real, we won't need indirect proof like this; we'll already have a picture. In the meantime, we should celebrate the new evidence we have, and recognize what it means: when something falls into a black hole, there is no bounce-back, shattering, or ejecta from within. Once you slip past the event horizon, you're destined to fall all the way into the central singularity. As far as black holes go, there really is a point of no return.

Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang! Check out his first book, Beyond The Galaxy, and look for his second, Treknology, this October!

Source: This article was published forbes.com By Ethan Siegel

Categorized in Science & Tech

The Extremely Large Telescope is five times larger than the top observing instruments in use today

Construction has begun on the world's first "super telescope", which could prove to be a vital tool in the search for alien life.

The telescope, appropriately named Extremely Large Telescope (ELT), will be the world's largest optical telescope - some five times larger than the top observing instruments in use today.

Its main mirror alone will measure 39 metres across, and it will be housed in an enormous rotating dome 85 metres in diameter - comparable in area to a football pitch.

This artist's rendering shows a night view of the Extremely Large Telescope in operation on Cerro Armazones in northern Chile. The telescope is shown using lasers to create artificial stars high in the atmosphere. (Photo: ESO/L. Calada)

Located on a 3,000 metre-high mountain in the middle of the Atacama desert in Chile, it is due to begin operating in 2024.

Among other capabilities, it will probe Earth-like exoplanets for signs of life, study the nature of dark energy and dark matter, and observe the Universe's early stages to explore our origins.

It will also raise new questions we cannot conceive of today, as well as improving life here on Earth through new technology and engineering breakthroughs, scientists claim.

The President of Chile, Michelle Bachelet, arrives at the first stone ceremony for the ELT (Photo: ESO/Juan Pablo Astorga)

    A ceremony to mark the beginning of the construction process was held at the Paranal Observatory in northern Chile. The ceremony was attended by Chilean President Michelle Bachelet.

    "Wee are building more than a telescope here: it is one of the greatest expressions of scientific and technological capabilities and of the extraordinary potential of international cooperation," said Bachelet.

    As well as the laying of the "first stone", the ceremony included the sealing of a time capsule, containing photographs of scientists and engineers who have worked on the project, and a copy of a book describing the future scientific goals of the telescope.

    This infographic provides a basic breakdown of the ELT's structure, focusing particularly on the first-generation of instruments. (Photo: ESO)

    The ELT is being funded by the European Southern Observatory, an organisation consisting of European and southern hemisphere nations.

    The dry atmosphere of the Atacama provides as near perfect observing conditions as it is possible to find on Earth, with some 70% of the world's astronomical infrastructure slated to be located in the region by the 2020s.

    Construction costs were not available but the ESO has said previously that the ELT would cost around €1 billion (£871 million) at 2012 prices.

    The ELT is due to begin operating in 2024 (Photo: ESO/L. Calada)

      "The ELT will produce discoveries that we simply cannot imagine today, and it will surely inspire numerous people around the world to think about science, technology and our place in the Universe," said Tim de Zeeuw, director general of ESO.

      "This will bring great benefit to the ESO Member States, to Chile, and to the rest of the world."

      Source: This article was mirror.co.uk By JORGE VEGASOPHIE CURTIS

      Categorized in Science & Tech

      NASA is in hot pursuit of a supermassive black hole that is hurtling through its galaxy.

      NASA finds astonishing supermassive black hole HURTLING through galaxy

      The huge phenomenon which has a mass of approximately 160 million times that of our sun and is being propelled at an astonishing speed.

      Boffins at NASA believe that it could have been formed when two smaller black holes collided and merged. 

      However, the experts believe that the gravitational waves generated by the clash could be stronger in one direction, causing the supermassive black hole, which are usually stationary and consume everything that crosses their path due to their immense gravitational pull, to be shot across the universe.

      NASA said in a statement: “The strength of the kick depends on the rate and direction of spin of the two smaller black holes before they merge.

      supermassive black hole
      After all of this searching, a good candidate for a recoiling black hole was discovered.”

      “Therefore, information about these important but elusive properties can be obtained by studying the speed of recoiling black holes.”

      Scientists found the recoiling supermassive black hole candidate, which is in a galaxy 3.9 billion light years from Earth, by “sifting through X-ray and optical data for thousands of galaxies”.



      black hole merge
      NASA believes two black holes merged

      They used observations from the Sloan Digital Sky Survey (SDSS) to look for X-ray emissions and correlated their findings with images from the Hubble Space Telescope to see if the supermassive blackhole is moving.

      NASA said: “After all of this searching, a good candidate for a recoiling black hole was discovered.”

      It added: “The host galaxy of the possible recoiling black hole also shows some evidence of disturbance in its outer regions, which is an indication that a merger between two galaxies occurred in the relatively recent past. 

      “Since supermassive black hole mergers are thought to occur when their host galaxies merge, this information supports the idea of a recoiling black hole in the system.”

      Source: This article was published express.co.uk By SEAN MARTIN

      Categorized in Science & Tech

      The Search For Technosignatures

      For those familiar with indie space game Stellaris, one of the key moments before encountering ancient intelligent life is finding traces of technology. While the game is a work of science fiction, the concept isn’t  outlandish to those behind the real life search for extraterrestrial life (SETI). According to astronomer Jason Wright, discovering traces of advanced technology, termed technosignatures, from alien civilizations is just as important as looking for biosignatures. He outlines his theory in new paper published online, and while he doesn’t claim there’s existing, direct evidence of aliens, he does wonder if we’re just not looking hard enough – or for the right signs.

      Contrary to what some have said, Wright’s paper isn’t saying that there’s already evidence pointing to an alien civilization that existed in the solar system before us. Instead, he merely asked whether we’ve exhausted all possible angles in our search for extraterrestrials.

      “There is zero evidence for any prior indigenous technological civilizations,” Wright told Gizmodo. “My paper asks, have we completely foreclosed the possibility, or is there a chance that there could be some evidence we overlooked? [And] if we have overlooked something and we find it in the future, what are the chances it could have come from a prior indigenous technological species versus an interstellar one?”

      Currently, the hunt for aliens is focused on finding even the smallest signs of life, or mechanisms that could support life (most notably, the presence of water). These are all good, of course, but Wright suggests that we might also start looking for technosignatures from ancient alien civilizations.

      “A ‘technosignature’ is evidence of technology,” he said, which potential could have been left behind by some long-gone alien civilization. In his paper, he explained his point further: “We might conjecture that settlements or bases on [rocky moons or asteroids] would have been built beneath the surface for a variety of reasons, and so still be discoverable today.”

      What Are We Really Searching For?

      The discovery of a new planet — or even better, a new system in some near or distant galaxy — is always good news for alien hunters. Most recently, the TRAPPIST system presented some possibilities — albeit ones quickly dashed by the intensity of solar flares its planets experience. Another possible candidate is a huge, Earth-like planet dubbed super-Earth LHS 1140b. Inside our own solar system, the planetary satellites of Jupiter and Saturn — particularly Europa and Enceladus — tickle the imagination because of the presence of water. And where there is water, the chance of life is higher.

      However, despite the odds seemingly in our favor, we really haven’t found any such example of alien life out there — yet. Fermi Paradox, yes? But, could it be that we’ve been looking at the wrong things? Or are we simply not looking hard enough?

      Wright just wants us to explore all possible options: “While all geological records of prior indigenous [extraterrestrial] technological species might be long destroyed, if the species were spacefaring there may be technological artifacts to be found throughout the Solar system.”

      Source: This article was published futurism.com By Dom Galeon and Abby Norman

      Categorized in Science & Tech

      Here’s an artist’s rendering of a large asteroid breaking up as it begins to plow through Earth’s atmosphere. If it lands it could do a lot of damage, but how much would depend on its size and collision site.ATPACK223/ISTOCKPHOTO

      Every now and then a really big rock from space comes careening through Earth’s atmosphere. Depending on its size, angle of approach and where it lands, few people may notice — or millions could face a risk of imminent death.

      Concern about these occasional, but potentially catastrophic, events keeps some astronomers scanning the skies. Using all types of technologies, they’re scouting for a killer asteroid, one that could snuff out life in a brief but dramatic cataclysm. They’re also looking for ways to potentially deter an incoming biggie from an earthboard path.

      But if a big space rock were to make it to Earth’s surface, what could people expect? That’s a question planetary scientists have been asking themselves — and their computers. And some of their latest answers might surprise you. 

      For instance, it’s not likely a tsunami will take you out. Nor an earthquake. Few would need to even worry about being vaporized by the friction-heated space rock. No, gusting winds and shock waves set off by falling and exploding space rocks would claim the most lives. That’s one of the conclusions of a new computer model.

      Explainer: What are Asteroids? 

      It investigated the likely outcomes of more than a million possible asteroid impacts. In one extreme case, a space rock 200 meters (660 feet) wide whizzes 20 kilometers (12 miles) per second into London, England. This smashup would kill more than 8.7 million people, computers estimate. And nearly three-quarters of those expected to die in that doomsday scenario would lose their lives to winds and shock waves.

      Clemens Rumpf and his colleagues reported this online March 27 in Meteoritics & Planetary Science. Rumpf is a planetary scientist in England at the University of Southampton.

      In a second report, Rumpf’s group looked at 1.2 million potential smashups. Here, the asteroids could be up to 400 meters (1,300 feet) across. Again, winds and shock waves were the big killers. They’d account for about six in every 10 deaths across the spectrum of asteroid sizes, the computer simulations showed.

      Many previous studies had suggested tsunamis would be the top killer. But in these analyses, those killer waves claimed only around one in every five of the lives lost.

      Explainer: What is a tsunami?

      Even asteroids that explode before reaching Earth’s surface can generate high-speed wind gusts, shock waves of pressure in the atmosphere and intense heat. Space rocks big enough to survive the descent pose  far greater risks. They can spawn earthquakes, tsunamis, flying debris — and, of course, gaping craters.

      “These asteroids aren’t an everyday concern,” Rumpf observes. Yet clearly, he notes, the risks they pose “can be severe.” His team describes just how severe they could be in a paper posted online April 19 in Geophysical Research Letters.

      Previous studies typically considered individually each possible effect of an asteroid impact. Rumpf’s group instead looked at them collectively. Quantifying the estimated hazard posed by each effect, says Steve Chesley, might one day help some leaders make one of the hardest calls imaginable — work to deflect an asteroid or just let it hit. Chesley is a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. (NASA stands for National Aeronautics and Space Administration.) Chesley was not involved with either of the new studies.

      Story continues below image.

      asteroid Earth
      Computer simulations reveal that most of the deaths caused by an earthbound asteroid (illustrated) would come from gusting winds and shock waves.

      Land hits would pose the biggest risks

      The 1.2 million simulated asteroid impacts each fell into one of 50,000 scenarios. They varied in location, speed and angle of strike. Each scenario was run for 24 different asteroids. Their diameters ranged from 15 to 400 meters (50 to 1,300 feet). About 71 percent of the Earth is covered by water, so the simulations let asteroids descend over water in nearly 36,000 of the scenarios (about 72 percent).

      The researchers began with a map of human populations. Then they added in data on the likely energy that a falling asteroid would unleash at a given site. Existing casualty data from studies of extreme weather and nuclear blasts helped the scientists calculate death rates at different distances from a space rock’s point of impact. All that was then combined into the computer model to gauge how deadly each modeled impact would likely be.

      Explainer: What is a computer model?

      The most deadly one would have killed around 117 million people. Many asteroid hits, however, would pose no threat, the simulations found. More than half of asteroids smaller than 60 meters (200 feet) across caused zero deaths. And no asteroids smaller than 18 meters (60 feet) across led to deaths. Rocks smaller than 56 meters (180 feet) wide didn’t even make it to Earth’s surface before exploding in the atmosphere. Those explosions could still be deadly, though. They would generate intense heat that could burn skin, the team found. They also would set off high-speed winds that would hurl debris and trigger pressure waves that could rupture internal organs.

      Where asteroids fell into the ocean, tsunamis became the dominant killer. The giant waves accounted for between seven and eight of every 10 deaths from these asteroid splashdowns. Still, the casualties from water impacts were only a fraction as high as those due to asteroids that smashed into land. (That’s because asteroid-generated tsunamis are relatively small and quickly lose steam as they plow through the ocean, the computer model showed.)

      Heat, wind and shock waves topped the impacts from land smashups, especially if they hit near large population centers.

      Bottom line: For all asteroids big enough to hit Earth’s surface, heat, wind and shock waves caused the most casualties overall. Other land-based effects, such as earthquakes and blast debris, resulted in fewer than 2 percent of total deaths, the computer projected.

      Story continues below image.

      Chelyabinsk meteor
      Large asteroid impacts are rare. Here, a 20-meter- (66-foot-) wide meteor left behind a smoky trail across the sky above Chelyabinsk, Russia, in 2013. Space rocks that big only strike Earth about once every 100 years.
      Alex Alishevskikh/Wikimedia Commons (CC-BY-SA 2.0)

      Protecting Earth

      While asteroids have the potential to kill, deadly impacts are rare, Rumpf says. Most space rocks that bombard Earth are tiny. They burn up in the atmosphere, causing little harm.

      Consider the rock that lit up the sky in 2013 and shattered windows around the Russian city of Chelyabinsk. Such 20-meter- (66-foot-) wide meteors strike Earth only about once a century. Far bigger impacts are capable of wiping out species. An asteroid at least 10 kilometers (6 miles) wide that smashed into Earth 66 million years ago has been blamed for wiping out the dinosaurs. Such mega-events are especially rare, however. They may occur only once every 100 million years or so.

      Today, astronomers scan the skies with automated telescopes scouting for those potential killer space rocks. So far, they’ve cataloged 27 percent of those 140 meters (450 feet) or larger whizzing through our solar system.

      asteroid deflector
      If a killer asteroid were detected, heading for Earth, NASA has plans for developing a spacecraft to slam into the space rock, deflecting it to a path that would miss us. Such a system is, however, at least some 20 years away. Once it is available, it might require a warning time of a year or two to target and redirect small asteroids.

      Other scientists are analyzing how they might divert or catch an earthbound asteroid. Proposals include whacking the asteroid like a billiard ball with a high-speed spacecraft. Or perhaps part of the asteroid’s surface might be fried with a nearby nuclear blast. The vaporized material should propel the asteroid away like a jet engine.

      Understanding the potential threats — and options available to deal with them — could offer guidance on how people should react to a warning that an asteroid was heading Earth’s way. It might help people decide whether it’s better to evacuate or shelter in place — or even mobilize space troops to try and divert the asteroid.

      “If the asteroid’s in a size range where the damage will be from shock waves or wind, you can easily shelter in place,” Chesley says. He says this should work for even a large population. But if the heat generated as it falls, impacts or explodes “becomes a bigger threat,” he says “and you run the risk of fires — then that changes the response of emergency planners.”

      Making such tough calls will require more information about what the asteroids are made of, says Lindley Johnson. He serves as the “planetary defense” officer for NASA in Washington, D.C. Those properties in part determine an asteroid’s potential for bringing devastation. Rumpf’s team couldn’t consider how those characteristics might vary, Johnson says. But several asteroid-bound missions are planned to provide some answers to such questions.

      For now, making decisions based on the average deaths presented in the new study could be misleading, warns Gareth Collins. He’s a planetary scientist at Imperial College London. A 60-meter- (200-foot-) wide incoming space rock, for instance, would cause an average of 6,300 deaths in the simulations. But just a handful of high-fatality events inflated that average. These included one scenario that resulted in more than 12 million casualties. In fact, most space rocks of that size struck away from population centers in the simulations. And they killed no one. “You have to put it in perspective,” he advises. 

      Death from the skies 

      A new project simulated 1.2 million asteroid strikes on Earth. That let scientists estimate how many deaths could result from each effect of a falling space rock. (Averages for three of the classes of asteroids that were evaluated are shown in the interactive below. People who could have died from two or more effects are included in multiple columns.) 

      Click the graphic to explore the asteroid simulation data. 
      Screenshot 2

      Power Words

      (for more about Power Words, click here)

      angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

      asteroid     A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

      atmosphere     The envelope of gases surrounding Earth or another planet.

      cataclysm     An enormous, violent, natural event. A meteor hitting Earth and wiping out most living species would qualify as a cataclysmic event.

      climate     The weather conditions prevailing 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 the clearing of forests.

      colleague     Someone who works with another; a co-worker or team member.

      computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

      crater     A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.

      data     Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. 

      death rates     The share of people in a particular, defined group that die per year. Those rates can change if the group is affected by disease or other deadly conditions (such as accidents, natural disasters, extreme heat or war and other sources of violence).

      debris     Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

      deter     An event, action or material that keeps something from happening. For instance, a visible pothole in the road will deter a driver from steering his car over it.

      diameter     The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.

      dinosaur     A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago. 

      extinction     The permanent loss of a species, family or larger group of organisms.

      friction     The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.

      mechanism     The steps or process by which something happens or “works.” 

      meteor     A lump of rock or metal from space that hits the atmosphere of Earth. In space it is known as a meteoroid. When you see it in the sky it is a meteor. And when it hits the ground it is called a meteorite.

      National Aeronautics and Space Administration     (or NASA) Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.

      numerical     Having to do with numbers.

      online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

      organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

      planetary science     The science of planets other than Earth.

      population     (in biology) A group of individuals from the same species that lives in the same area.

      pressure     Force applied uniformly over a surface, measured as force per unit of area.

      propulsion     The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.

      range     The full extent or distribution of something. 

      risk     The chance or mathematical likelihood that some bad thing might happen.

      scenario     An imagined situation of how events or conditions might play out.

      shock waves     Tiny regions in a gas or fluid where properties of the host material change dramatically owing to the passage of some object (which could be a plane in air or merely bubbles in water). Across a shock wave, a region’s pressure, temperature and density spike briefly, and almost instantaneously.

      simulation     (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might vary over time or in response to different anticipated situations.

      solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

      telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

      tsunami     One or many long, high sea waves caused by an earthquake, submarine landslide or other disturbance.

      wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

      weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

      Source : This article was published sciencenewsforstudents.org By THOMAS SUMNER

      Categorized in Science & Tech

      As far as we know the universe is not infinite, there's actually a place where it ends. While astronomers have never actually seen the edge of the universe, they know it's out there. Theoretical physicist and director of the Institute for Advanced Study at Princeton, Robbert Dijkgraaf explains how scientists know there's an edge of the universe.

      Following is a transcript of the video: 

      It’s a fascinating question, “How far can you see in the universe?”

      And the point is that if you look at very distant objects, it takes a lot of time for the light to travel all the way to us. And since the universe was kind of created 13.8 billion years ago, there's a finite distance that we can see.

      We can almost see the edge of the visible universe. In fact, the earliest thing that we can see is the first light that was created just after the Big Bang.

      Well, just 380,000 years after the Big Bang. At that point the universe was kind of transparent enough for light to escape.

      So using our satellites we can pick up a signal that was emitted at this very brief moment after the Big Bang.

      While in the meantime the universe has expanded and so that first light has kind of cooled down and it's now a microwave signal.

      In fact what you can do, if you take an old-fashioned television set and you just unplug the cable, there will be static noise on your screen. Roughly 1% of that static noise is actually coming from the very edge of the universe.

      Source: This article was published on businessinsider.com by Darren WeaverJessica Orwig and Alana Kakoyiannis

      Categorized in Science & Tech

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