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The Most Energetic Mystery in the Universe

March 25, 2009 on 1:05 pm | In Astronomy, Physics, black holes | 25 Comments

When we look out at galaxies, we find the most energetic particles we’ve ever found anywhere in the Universe coming from their centers. Why?

Because as far as we can tell, all galaxies, at their centers, have huge, supermassive black holes! When matter (like a star, globular cluster, intra-galactic gas, etc.) gets too close to one of these black holes, it gets ripped apart, and settles into a disk around the black hole. This disk is called an accretion disk:

Like everything in a strong gravitational field that moves, these particles radiate (give off high-energy photons), fall in towards the center of the black hole, and sometimes get accelerated and shot out of the galaxy!

For a galaxy like ours, with a black hole a few million times as massive as our Sun, we can get extremely energetic particles out: up to 1018 eV, which is 70,000 times more energetic than the LHC!

But our black hole is kind of a commoner — a weakling, even — when you look at other galaxies. There are huge galaxies out there, such as active galaxies and quasars, where instead of a few million times as massive as our Sun, their black holes are billions or even tens of billions times as massive as our Sun:

Well, in theory, the energies of these particles can be thousands or even tens of thousands of times higher than what our galaxy can produce! We’re talking about energies of 1022 eV, which is not only insane, it’s impossible!

Why? Because there’s a maximum energy that particles traveling through the Universe can have. There’s a bath of leftover light from the Big Bang permeating the entire Universe: the CMB. If you smash a particle with too much energy into one of these CMB photons (which is unavoidable as you travel millions of light years), it causes these high-energy particles to slow down until they’re below the “speed limit”. (Okay, it’s an energy limit, but it’s really close enough.)

And unlike cops that pull you over, the light that fills outer space slows you down until you’re below the cosmic energy limit: 5.7 x 1019 eV. Well, do we see a cutoff there?

Maybe. The AGASA experiment says no, there is no cutoff, but the Pierre Auger Observatory says yes, there is one. Who’s right? On one hand, we’ve definitely seen events where we’ve measured more energy than should be allowed. It may mean our theories need revising, or it may mean that there’s something super-energetic happening in our own backyard that we don’t know about. Or — on the other, more boring hand — perhaps we’ve just done a bad job of measuring things at very high energies. Whatever the case, explaining these events that exceed the cosmic energy limit of the Universe is, in fact, the most energetic mystery in the Universe!


A Little Sun in Your Life… Dire Consequences?

March 20, 2009 on 1:18 pm | In Astronomy, Physics | 18 Comments

I really get a kick out of reading The Straight Dope. What started as a weekly column in a Chicago newspaper has grown into a nationwide phenomenon and a small empire, and is often full of fascinating questions and extremely well-researched and knowledgeable answers.

But doesn’t anyone there know to contact me if you’ve got an astrophysics question? Today’s column, which will be nationally syndicated, declares that they cannot answer the following question:

If the pink grapefruit sitting in my fruit bowl spontaneously turned into a grapefruit-sized sun, what would happen to my flat, London, and the rest of the world? If I put it somewhere safe, could I enjoy not paying for central heating? Or would it end life as we know it by melting through my floor, into the African textile shop, through the subway system, and finally to a fiery chasm in the middle of the earth where it would make all volcanoes erupt and kill everything, before coming out the other side and changing the way all the planets spin?

Well, I may be no Cecil Adams, but I can certainly answer this one. Let’s take a look at how our Sun actually works, and then scale it down to be grapefruit-sized.

The Sun is a giant ball of mostly hydrogen gas. It’s extraordinarily massive — about 300,000 times as massive as Earth — and tremendous powerful. The Sun gives off what most people would call an unfathomable amount of energy, but in scientific notation, it’s about 4 x 1026 Watts, which is at least fathomable, although it’s absolutely tremendous. This means that even at the surface of the Earth, 150 million kilometers away, that means we have 129 Watts of solar energy striking us over every square foot that receives sunlight.

But what’s truly exciting, at least for me, is the way the Sun creates its energy. To understand it, we have to go down to the tiniest atomic levels, and look at the hydrogen atoms themselves:

Because the pressure at the center of the Sun is so high, due to the gravitational pressure of having 300,000 Earths pushing in at the core, the nuclei of these hydrogen atoms, protons, get pushed together with a tremendous force. The force is so large that it causes these nuclei to fuse together, in a process called nuclear fusion. With a little math, I can figure out that in order to create the amount of energy the Sun gives off, it has to fuse together about 3.6 x 1038 atoms of hydrogen every second! That little atomic reaction, happening over and over, trillions of times every nanosecond in the Sun’s core, is what produces all the heat, light, and energy we’ve ever received from the Sun.

Now, the person who asked this question wanted to know about having a little stable grapefruit-sized Sun.

Well, here’s a big downer for you: this thing ain’t gonna be stable. If you want to have nuclear fusion going on at the core of this grapefruit-sized ball of hydrogen, you’re going to need a tremendous amount of pressure to push the atoms at the center together. There are only two ways to handle it that we know of, and neither one of them will give you an answer that you’ll like, although they’re both fascinating.

The first way is to artificially increase the pressure, like lasers (shown here) would do. Practically, you wind up getting less energy out than you have to put in to increase the pressure to obtain fusion, which is another disappointment. Scientists working on this call it inertial confinement fusion, and so far, it has never yielded more energy than it took to get it going. So this way looks like a dud. But there’s another way to get nuclear fusion…

You can increase the pressure tremendously — albeit for a very short time — by setting off a small explosion around the hydrogen core, compressing it and causing ignition. There’s a problem with this way, too. The resulting fusion reaction is uncontrolled and runs away, igniting everything. This is commonly known as a hydrogen bomb.

Either way, you give off a tremendous amount of energy, your initial “grapefruit” gets blown apart like a super-powerful exploding grenade, and depending on how much of the hydrogen in there actually managed to fuse would determine what happened. If you scaled down the Sun so that the grapefruit worked on exactly the same scale, you’d only get about 100 million atoms fusing together, or about 100 microJoules of energy. Enough energy to push the hydrogen gas away, but not even enough energy to light a match. But, if you managed to fuse the entire grapefruit into helium, you’d get the energy equivalent of a 160 kiloTonne explosion, or about 11 times the energy of the atomic bomb dropped on Hiroshima, in your fruit bowl.

Without the entire mass of the Sun to insulate this nuclear explosion from the rest of the Solar System, this grapefruit-sized ball isn’t going to last long. Either way, you’re better off getting a heat lamp for your desk, and paying your electric bill.


Unsolved Mysteries? When like charges attract!

March 18, 2009 on 2:29 pm | In Physics | 26 Comments

Attraction and repulsion are two of the simplest concepts in electricity and magnetism: like charges repel and opposite charges attract. (Two steps forward, two steps back.) For electricity, this is how positive and negative charges work:

Two positive charges will repel each other, two negative charges will repel each other, but one positive and one negative charge will attract one another. Simple enough, right? Except, everything is made up of atoms, which have positive and negative charges all throughout them. Certain materials are excellent conductors, which means that positive and negative charges are relatively free to move throughout a material. So if I bring a negatively charged rod close to a neutral conductor, the following happens:

The positive charges line up on the side closest to the rod (because they’re attracted to it) and the negative charges line up on the side farthest from the rod (because they’re repelled). Since the “opposite” charges are closer and the “like” charges are farther, this means that the force from the opposite charges is slightly stronger, and so overall, the negatively charged rod attracts the neutral conductor.

Now, here’s the weird thing: what if you charged up the metal with some negative charges? Would it repel the rod, since negative charges repel? Or would it still attract the rod, since the “opposite” charges are closer than the “like” charges? Well, the answer is both! Check it out!

What I’ve graphed here is Force vs. distance for a negatively charged rod brought close to a negatively charged conducting piece of metal. When the distance is large, they repel each other. But when you bring them close enough, the fact that the opposite charges are closer becomes more important than the fact that there are more like charges, and they attract! There’s even one perfectly balanced point where the force is exactly zero!

And of course, that’s just for electricity. Do magnets do the same thing?

Absolutely! North repels north, south repels south, but north and south attract each other. Magnets make powerful magnetic fields; the stronger the magnet, the stronger the field. What’s really neat, though, is that if you apply a strong enough magnetic field to some materials, like iron, they magnetize, too!

Well, if you bring a weak iron magnet’s North pole close to a strong magnet’s North pole, what do you think will be more important? The fact that the weak magnet is made of iron, and can be magnetized, or the fact that the North pole repels the other North pole? Let’s go down to the molecular level to find out…

Weak magnets have little tiny molecular magnetic moments pointing in many directions. Overall, though, there will be more pointing in one direction than any other, and that’s how your material is “magnetized.” But if you bring a strong magnet close enough, it applies a strong enough magnetic field, and will re-magnetize the weak magnet material to attract the strong magnet! So, is it the same deal as the electric charges? Let’s have a look:

It’s exactly the same! Far away, they repel, close in, it magnetizes and attracts, and yes, there’s a point right in the middle where it balances perfectly, and the force is exactly zero!

So the next time someone tells you that like charges repel each other, you’ll know the exception to the rule!


Random Ethics Question: Project Paperclip

March 3, 2009 on 1:13 pm | In Astronomy, Physics, Politics | 18 Comments

Sometimes, when I come home from a long day at work and need to unwind, I start reading BBC News, and occasionally the news archives are more interesting than the actual present news.

Last night, I came across a really interesting read from 2005, about Project Paperclip, which was the US Government’s plan to bring the former Nazi scientists to America and use their knowledge and expertise to further the scientific and military enterprises we had going on here, and also to deny the Soviets that knowledge.

But this required giving amnesty to Nazis (and sometimes even former SS officers) like Werner Von Braun, Arthur Rudolph, Kurt Debus, and Hubertus Strughold. The atrocities that these men and their subordinates were responsible for are well-documented, and include the death of 20,000 slave laborers producing Von Braun’s V-2 missiles, freezing inmates and putting them into low-pressure chambers, and performing human experiments at Dachau and Auschwitz. Truly, these are some of the most despicable things that human beings have ever done to one another.

And yet, the Germans had an incredible amount of scientific, aeronautic/aerospace and military knowledge that we did not. Some examples? Supersonic rockets, nerve gas, jet aircraft, guided missiles, stealth technology, and hardened armor. All in 1945. So what was the ethical thing to do? What was the smart thing to do? And overall, what was the right thing to do? US Air Force Major-General Hugh Knerr’s opinion was the prevailing one:

If we do not take the opportunity to seize the apparatus and the brains that developed it and put the combination back to work promptly, we will remain several years behind while we attempt to cover a field already exploited.

So, for better or worse, about 700 Nazi scientists were put to work for the United States.

The technological advancements and scientific breakthroughs were numerous and swift, and over the next 25 years, Werner Von Braun had masterminded the Apollo program and the Moon landings, Arthur Rudolph had designed the Saturn V rocket, Hubertus Strughold designed NASA’s life support systems, and countless other technologies such as Cruise Missiles, the B-2 Stealth Bomber, and scramjets came as outgrowths of Nazi research. So as a counterpoint to one of the worst atrocities in human history, we also have one of the greatest achievements in human history:

That’s the story of what we did and one of the steps we took to get there. Did we do the right thing? Did we do the just thing? Did we do the smart thing? For me, the answers are yes, no, and yes. And I, for one, am glad I didn’t have to be the one to make that decision. What do you think?

And this last week, so much happened in space news that we not only have a carnival, we have a carnival sideshow as well; enjoy!


A Myth from Your Dentist?

March 2, 2009 on 2:41 pm | In Physics, Random Stuff | 57 Comments

One of the beautiful things about facebook is reuniting and catching up with old friends that you haven’t seen in a very long time. Caroline was one of those people for me, someone I knew in high school and thought was awesome, and just lost touch with when we went off to our separate colleges. Well, Caroline has a few “scientific” interests that she shared with me:

That’s right, folks. She’s clearly interested in the science of clean teeth. Specifically, she wanted to know about Ionic Toothbrushes, and whether they really do anything useful or whether it’s solely a marketing ploy. (Although, personally, I’m pretty sure that Caroline is much more likely to fall for the McConaughey marketing ploy.) She says:

I knew someone who used an ionic brush to brush their teeth by opposite polarity, because plaque has a + charge. Then i told my dentist friend who discussed it w/ his collegues, and they agreed the only way to rid of plaque was by mechanical removal. Is the ionic brush a scam?

So, I did what any reasonable person would do. I went online to look for an explanation of how it works. Here’s what I found:

Is it clear yet? No? Looks like I’ll have to give it the ol’ SWAB scientific treatment here, with a little bit of science you can do in your office. The idea is that plaque is stuck to your teeth via the electromagnetic force, which is true. Plaque is mostly made of bacterial cells, and as you may have learned, all cell membranes have a positive charge on their outer surface.

You can test this! Take two pieces of scotch tape, and tape them down to the desk/table. Lift them up quickly, and they’ll rip electrons up off of the table, giving them both negative charges.

You can either move them close to each other, and watch them repel one another. Or, you can bring one of the pieces close to something with a cell membrane, like your hand. It will attract your skin, which tells you that the cell membranes on your skin are positively charged!

So now that you’re convinced that plaque bacteria (above, and eww) are positively charged on their surface, and they stick to your tooth enamel, how do we get it off? Well, brushing your teeth is a great idea, it certainly helps, but most people aren’t thorough enough to do a good job of cleaning their teeth with mechanical power alone. So what do we do? We put negative ions in your mouth, to help get the plaque to let go from your teeth. People don’t like the idea of ions in their mouth, so we give it a different name: fluoride. Which is great for not only toothpastes and mouthwashes, but also as an additive to water in general, so that when you drink tap water, it helps clean your teeth!

So now, what about this magic ionic toothbrush? The idea is that electrically charged things will be more likely to stick to whatever has a bigger charge. So if your tooth is negatively charged, it attracts plaque. If the toothbrush head has a bigger negative charge, the plaque will go to it instead of your teeth. Simple idea, right?

The big question, of course, is how effective is it? You still need to brush your teeth, of course. But it doesn’t work nearly as well as a fluoridated toothpaste does. The charge stays localized on the toothbrush, instead of covering your mouth like a sudsy, fluoridated toothpaste would. But if you have no toothpaste, the ionic brush will, in principle, work better than a regular brush on its own. Take note that this means the explanation of how the ionic brush works on Caroline’s site is not right.

But if you are, like me, someone who brushes their teeth with toothpaste every day, will this help? Well, their advertising says “up to 48% more plaque removed” followed by an asterisk. What does that asterisk mean? It doesn’t say. My recommendation is that if you want to use less toothpaste (or you can’t use it, for some reason), this is a good option. But otherwise, save your money and just use toothpaste (and drink your fluoridated water) like everyone else with healthy teeth.

On a personal note, I’ve still got all 32 teeth and have only had one cavity in the past 10 years. Brushing with a fluoride toothpaste, flossing every day, and drinking 3-4 litres of tap water a day are my only secrets. I don’t believe anecdotes as proof, but there it is anyway; anyone know anything more about whether this is more effective than a placebo?


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