Monday, February 18, 2013

The Oh-My-God Particle

One of the two Fly's Eye Cosmic Ray Detectors.

The Oh-My-God particle was an ultra-high-energy cosmic ray—most likely a proton—detected on October, 1991 in the skies over western Utah. Its observation by the University of Utah's Fly's Eye Cosmic Ray Detector was a shock to astrophysicists, who estimated its energy to be approximately 50 J. In other words, a subatomic particle with kinetic energy equal to that of a baseball traveling at about 90 kilometers per hour.
   The particle was traveling at almost the speed of light. Assuming it was a proton, its speed was only about 1.5 quadrillionth of a meter per second less than the speed of light. In other words, if it were in a race with a beam of light, the Oh-My-God particle would fall behind only one centimeter every 220,000 years.
   The energy of this particle is some 40 million times that of the highest energy protons that have been produced by the Large Hadron Collider. However, only a small part of this energy would be available for an interaction with another proton or neutron. Most of the energy would remain as kinetic energy. The effective energy available for such an interaction is still 50 times greater than the collision energy of the Large Hadron Collider.
   Applying special relativity to such a fast particle yields some incredible results. Time passes more slowly as velocity increases, and for anyone hypothetically travelling on the back of this particle time would nearly stop. For example, a trip to the Andromeda Galaxy, which is more than two million light years away, would have a perceived travel time of only three and a half minutes. Special relativity also tells us that there is a length contraction in the direction of motion. If the Earth were somehow able to match the speed of the Oh-My-God particle, it would pancake down to a thickness of less than four hundredths of a millimeter!
   The University of Utah experiment relied on two telescopes searching the sky for the characteristic flashes of ultraviolet light that are produced when a cosmic ray collides with a molecule in Earth’s atmosphere and creates a shower of secondary particles. The two telescopes were covered in photomultiplier tubes and looked like the compound eyes of a fly. By capturing almost all the light in the shower, they were able to make a good measurement of the particle’s energy.
   These ultra-high-energy cosmic rays are very rare. Since the first observation, only about fifteen similar events have been recorded to confirm the phenomenon. What cosmic process transforms an ordinary particle into an Oh-My-God particle? A supernova or supermassive black hole might explain it, but when astronomers followed the impact track back to its source they found nothing unusual in that direction.

Monday, February 11, 2013

The Water Bear

The tardigrade is also known as the water bear.

A polyextremophile is an organism that can survive many types of extreme environments. One of the most complex polyextremophiles is the tardigrade, which can live in just about every environment possible here on earth, plus some not on Earth (more on that later). Tardigrades are about a millimeter long when fully grown. They are short and plump with eight tubular legs, each with 4-8 bear-like claws. Given that they also move like a lumbering bear, tardigrades have earned the nickname water bear.
   Tardigrades typically live in marine, fresh water, or semiaquatic environments, but you can also find them in the mosses and lichens found in forested areas. As long as there is some water around, they can thrive. They feed on the fluids found in plant and animal cells. Their mouth is able to pierce the cell walls so that they can then suck out and ingest the inner parts of the cell. 
   Tardigrades can survive being completely desiccated for nearly 10 years as well as exposure to high levels of chemical toxins. They can survive extreme heat (150 °C) for a few minutes and extreme cold (-200 °C) for a few day. When exposed to extreme cold their body composition changes from 85% water to only 3% which keeps their body from being damaged by ice crystal formation. 
   The can survive extreme pressures far greater than that found at the Mariana trench. In 2007, tardigrades were sent into space on the Russian/EU satellite Foton-M3 for ten days. Even after being exposed to the vacuum of space for this long, most of the samples survived after being rehydrated back on Earth, some of which had also been fully exposed to the Sun’s radiation. Tardigrades were also sent into space on the final flight of Space Shuttle Endeavour where experiments showed that cosmic radiation and microgravity did not significantly affect their survival, confirming their usefulness in space research.
   You’re probably wondering just how these creatures could be so resilient. They rely on cryptobiosis—a state of suspended animation that they can enter in response to adverse environmental conditions where all metabolic processes stop. Their bodies dehydrate into a dense, mummified disc called a tun. They can remain in this state indefinitely until their environment becomes hospitable once again. When this happens, the tun plumps back up and the tardigrade return to its previous metabolic state.

Monday, February 4, 2013

Dangers of a Vacuum

The vacuum chamber that Jim LeBlanc was in
when his spacesuit lost all pressure.

Recently, a reader asked “What happens to the human body in a vacuum? For example, if an astronaut removed his space suit.”
   This reminds me of a scene from the movie 2001: A Space Odyssey. In the movie, HAL has figured out that Dave is planning to disconnect him when he returns to the ship, so he refuses to let Dave back in. Dave is forced to go in through the unpressurized emergency airlock, but there’s a problem: he doesn’t have his space helmet. 

  Terrifying, but Kubrick got the science right. Short-term exposure to the vacuum of space would not make your body explode or freeze solid as some movies have depicted. If you don’t try to hold your breath, exposure to space for about 15 seconds would cause no permanent injury. Holding your breath would be bad, though, because in a vacuum your lungs collect gas from your bloodstream and expands with the drop in pressure. Holding your breath would cause your lungs to overinflate and possibly rupture. This is similar to how scuba divers need to exhale when rising to the surface or risk damaging their lungs. 
   Temperature would not be an immediate problem because although space is very cold, a vacuum is a perfect insulator. You would only gradually radiate away your body heat. Exposure to direct sunlight would give you a sunburn. Your saliva and tears would quickly evaporate and you might have eardrum troubles.
   After about 15 seconds, oxygen-deprived blood from the lungs reaches the brain causing you to lose consciousness. 
   At such low pressures, your body fluids will boil away. Moist surfaces such as the eyes, mouth and airways experience this immediately. Fluids inside your body also start to vaporize. This happens rapidly in the lungs and under the skin. Bubbles of water vapor that form in the bloodstream will interrupt the circulation. This is called ebullism. No one knows how long the human body can withstand the vacuum of space—perhaps a couple of minutes. 
   In 1965, this actually happened to Jim LeBlanc while working at the NASA Manned Spacecraft Center (now called the Johnson Space Center). He was testing a space suit in their vacuum chamber when the tube that was pressurizing his suite came loose and his suit was almost completely depressurized within seconds. He stayed conscious for about 14 seconds and they began repressurizing the chamber right after he passed out. After regaining consciousness, he recalled that he could hear and feel the air leaking out of his suit, and the last thing he remembered was the saliva on his tongue starting to boil.