The foundation of the nuclear power that provides us with so much electricity is harnessing the energy that’s contained within atoms. In layman’s terms fission is the division of an atom into two and fusion is combining two into one.
Nuclear fission occurs when a large, unstable isotope is bombarded by a high speed neutron (it can be other high speed particles but normally it’s a neutron). The neutron collides with the target nucleus and splits it into two smaller isotopes releasing a lot of energy in the form of heat. 3 high speed neutrons are also produced that go on to collide with the nuclei of other isotopes thus continuing the reaction. The high speed electrons that are ejected by this process also initiate fission reactions. In most nuclear reactors Uranium-235 is the isotope they use, the energy resulting from fission is used to heat water which turns a turbine and that’s essentially how nuclear reactors produce electricity.
Fusion is what powers the sun and is unlikely to ever occur on earth because we have yet to find a way to contain such a massive amount of energy. The fusion between two nuclei with lower masses than Iron-56 generally releases energy while the fusion of nuclei heavier than iron requires energy. Our sun is currently fusing the nuclei of Deuterium and Tritium (Hydrogen-2 and Hydrogen-3) to form Helium isotopes which releases several times the amount of energy produced by fission. When all the Hydrogen isotopes are used up, the sun will start to fuse the nuclei of the Helium that’s there. The sun will keep fusing nuclei together until eventually the core is made of solid iron at which point it will die and turn into a neutron star. Larger stars have the energy to make isotopes heavier than iron, and when they die a supernova fires the matter that the star has spent it’s life creating across the galaxy. The carbon that makes up life as we know it first came into existence at the heart of a star like that. So for us to live, it meant a star had to die.
“Russian Doll” Galaxy Clusters Reveal Information About Dark Energy
Astronomers have used data from NASA’s Chandra X-ray Observatory, ESA’s Planck and a large list of optical telescopes to develop a powerful new method for investigating dark energy, the mysterious energy that is currently driving the accelerating expansion of the universe.
The technique takes advantage of the observation that the outer reaches of galaxy clusters, the largest structures in the universe held together by gravity, show similarity in their X-ray emission profiles and sizes. More massive clusters are simply scaled up versions of less massive ones.
“In this sense, galaxy clusters are like Russian dolls, with smaller ones having a similar shape to the larger ones,” said Andrea Morandi of the University of Alabama at Huntsville, who led the study. “Knowing this lets us compare them and accurately determine their distances across billions of light years.”
By using these galaxy clusters as distance markers, astronomers can measure how quickly the Universe was expanding at different times since the Big Bang. According to Einstein’s theory of general relativity, the rate of expansion is determined by the properties of dark energy plus the amount of matter in the Universe, where the latter is mostly made up of unseen material called dark matter.
If the assumed cosmological parameters (e.g., the properties of dark energy or dark matter) are incorrect, then distant clusters will not appear to be similar, that is their sizes will be larger or smaller than expected. The cosmological parameters are then adjusted so that all of the different clusters, with different masses and different distances, appear to be similar. The process is akin to determining the unknown weight of an object by adding or subtracting known weights to a balance scale until the two sides balance.
These latest results confirm earlier studies that the properties of dark energy have not changed over billions of years. They also support the idea that dark energy is best explained by the “cosmological constant,” which Einstein first proposed and is equivalent to the energy of empty space.
“Although we’ve looked hard at other explanations,” said co-author Ming Sun, also of the University of Alabama at Huntsville, “it still appears that dark energy behaves just like Einstein’s cosmological constant.”
The researchers studied 320 galaxy clusters with distances from Earth that ranged from about 760 million light years to about 8.7 billion light years. This spans the era where dark energy caused the once-decelerating universe to accelerate, a discovery that shocked many astronomers when it was made almost two decades ago.
To determine more precise results than with the Chandra X-ray data alone, the researchers combined this data with information on the expansion rate of the universe from optical observations of supernovas, and work from Planck on the cosmic microwave background, the leftover radiation from the Big Bang.
“The nature of dark energy is one of the biggest mysteries in physics, so it’s crucial to invent new tools for studying its properties, since different methods can have very different assumptions, strengths and weaknesses,” said Morandi. “We think this new technique has the ability to provide a big leap forward in our understanding of dark energy.”
A paper describing these results appeared in the April 11th, 2016 issue of the Monthly Notices of the Royal Astronomical Society journal and is available online. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.
LOWER IMAGE….X ray
May is here! My birthday is coming up and I still don’t know what to do for it. It’s during our finals week too but it doesn’t really matter because most of my classes are AP and my teachers won’t require us to take finals. And speaking of AP classes, my first one is on Tuesday and I’m so not ready. I also have APUSH on Friday and SAT on Saturday, which I haven’t even prepared for because there’s just so much going on and I’m not going to study for it until after the APUSH test. Ha, good luck with that. I also got my ACT essay score the other day. I dropped by a lot of points from the one I took in February. *cries* I got a 30+ on my ACT though and I’m content with it but I might have to take it again in June to make up for my writing score. And there goes more of my money~
I finally bought Mildliner highlighters after seeing everywhere (lol) and I have no regrets. Well, except for the fact that the shipping was the same price as them. I still love them nonetheless. And ugh, I hate bad lighting. T^T
The LHC is now
about to resume operation after being shut down since December for
annual maintenance. If its next run confirms the existence of the new
particle, that could open the long-sought passage to ‘the new physics’ –
and, hopefully, answer some big, longstanding questions…
ARE WE ALONE? SETTING SOME LIMITS TO OUR UNIQUENESS
Are humans unique and alone in the vast universe? This question– summed up in the famous Drake equation–has for a half-century been one of the most intractable and uncertain in science.
But a new paper shows that the recent discoveries of exoplanets combined with a broader approach to the question makes it possible to assign a new empirically valid probability to whether any other advanced technological civilizations have ever existed.
And it shows that unless the odds of advanced life evolving on a habitable planet are astonishingly low, then human kind is not the universe’s first technological, or advanced, civilization.
The paper, published in Astrobiology, also shows for the first time just what “pessimism” or “optimism” mean when it comes to estimating the likelihood of advanced extraterrestrial life.
“The question of whether advanced civilizations exist elsewhere in the universe has always been vexed with three large uncertainties in the Drake equation,” said Adam Frank, professor of physics and astronomy at the University of Rochester and co-author of the paper. “We’ve known for a long time approximately how many stars exist. We didn’t know how many of those stars had planets that could potentially harbor life, how often life might evolve and lead to intelligent beings, and how long any civilizations might last before becoming extinct.”
“Thanks to NASA’s Kepler satellite and other searches, we now know that roughly one-fifth of stars have planets in ‘habitable zones,’ where temperatures could support life as we know it. So one of the three big uncertainties has now been constrained.”
Frank said that the third big question–how long civilizations might survive–is still completely unknown. “The fact that humans have had rudimentary technology for roughly ten thousand years doesn’t really tell us if other societies would last that long or perhaps much longer,” he explained.
But Frank and his coauthor, Woodruff Sullivan of the astronomy department and astrobiology program at the University of Washington, found they could eliminate that term altogether by simply expanding the question.
“Rather than asking how many civilizations may exist now, we ask ‘Are we the only technological species that has ever arisen?’: said Sullivan. “This shifted focus eliminates the uncertainty of the civilization lifetime question and allows us to address what we call the ‘cosmic archaeological question’—how often in the history of the universe has life evolved to an advanced state?”
That still leaves huge uncertainties in calculating the probability for advanced life to evolve on habitable planets. It’s here that Frank and Sullivan flip the question around. Rather than guessing at the odds of advanced life developing, they calculate the odds against it occurring in order for humanity to be the only advanced civilization in the entire history of the observable universe. With that, Frank and Sullivan then calculated the line between a Universe where humanity has been the sole experiment in civilization and one where others have come before us.
“Of course, we have no idea how likely it is that an intelligent technological species will evolve on a given habitable planet,” says Frank. But using our method we can tell exactly how low that probability would have to be for us to be the ONLY civilization the Universe has produced. We call that the pessimism line. If the actual probability is greater than the pessimism line, then a technological species and civilization has likely happened before.”
Using this approach, Frank and Sullivan calculate how unlikely advanced life must be if there has never been another example among the universe’s twenty billion trillion stars, or even among our own Milky Way galaxy’s hundred billion.
The result? By applying the new exoplanet data to the Universe as a whole, Frank and Sullivan find that human civilization is likely to be unique in the cosmos only if the odds of a civilization developing on a habitable planet are less than about one in 10 billion trillion, or one part in 10 to the 22th power.
“One in 10 billion trillion is incredibly small,” says Frank “To me, this implies that other intelligent, technology producing species very likely have evolved before us. Think of it this way. Before our result you’d be considered a pessimist if you imagined the probability of evolving a civilization on a habitable planet were, say, one in a trillion. But even that guess, one chance in a trillion, implies that what has happened here on Earth with humanity has in fact happened about a 10 billion other times over cosmic history!”
For smaller volumes the numbers are less extreme. For example, another technological species likely has evolved on a habitable planet in our own Milky Way galaxy if the odds against it are better than one chance in 60 billion.
But if those numbers seem to give ammunition to the “optimists” about the existence of alien civilizations, Sullivan points out that the full Drake equation—which calculates the odds that other civilizations are around today—may give solace to the pessimists.
“The universe is more than 13 billion years old,” said Sullivan. “That means that even if there have been a thousand civilizations in our own galaxy, if they live only as long as we have been around—roughly ten thousand years—then all of them are likely already extinct. And others won’t evolve until we are long gone. For us to have much chance of success in finding another “contemporary” active technological civilization, on average they must last much longer than our present lifetime.”
“Given the vast distances between stars and the fixed speed of light we might never really be able to have a conversation with another civilization anyway,” said Frank. “If they were 50,000 light years away then every exchange would take 100,000 years to go back and forth.”
But, as Frank and Sullivan point out, even if there aren’t other civilizations in our galaxy to communicate with now, the new result still has a profound scientific and philosophical importance. “From a fundamental perspective the question is ‘has it ever happened anywhere before?’” said Frank. “And it is astonishingly likely that we are not the only time and place that an advance civilization has evolved.”
According to Frank and Sullivan their result has a practical application as well. As humanity faces its crisis in sustainability and climate change we can wonder if other civilization-building species on other planets have gone through a similar bottleneck and made it to the other side. As Frank puts it “We don’t even know if it’s possible to have a high-tech civilization that lasts more than a few centuries.” With Frank and Sullivan’s new result, scientists can begin using everything they know about planets and climate to begin modeling the interactions of an energy-intensive species with their home world knowing that a large sample of such cases has already existed in the cosmos. “Our results imply that our biological, and cultural evolution has not been unique and has probably happened many times before. The other cases are likely to include many energy intensive civilizations dealing with crises on their planets as their civilizations grow. That means we can begin exploring the problem using simulations to get a sense of what leads to long lived civilizations and what doesn’t.”
Frank and Sullivan’s argument hinges upon the recent discovery of how many planets exist and how many of those lie in what scientists call the “habitable zone” – planets in which liquid water, and therefore life, could exist. This allows Frank and Sullivan to define a number they call N(ast). N(ast) is the product of N*, the total number of stars; f(p), the fraction of those stars that form planets; and n(p), the average number of those planets in the habitable zones of their stars.
They then set out what they call the “Archaelogical-form” of the Drake equation, which defines A as the “number of technological species that have ever formed over the history of the observable Universe.”
Their equation, A=N(ast)*f(bt), describes A as the product of N(ast) – the number of habitable planets in a given volume of the Universe – multiplied by f(bt) – the likelihood of a technological species arising on one of these planets. The volume considered could be, for example, the entire Universe, or just our Galaxy.
AP Physics 1 Exam is coming up in a few days. My notebook has been finalized and tomorrow I’ll be doing practice FRQ questions for preparation. Keep up the great work guys and best of luck to those taking their exams. ( :