Monthly Archives: August 2012

Getting Hot and Heavy with Hydrogen

Deep within the cores of stars and the atmosphere of giant gas planets, intense pressure converts atoms into an unusual state physicists call degenerate matter. A normal atom is made up of a nucleus of protons and neutrons surrounded by a cloud of electrons. In degenerate matter, atoms become so squished that the tidy collections of nuclei and electrons break down into a slurry of sub-atomic particles. Hundreds of miles within Jupiter and Saturn lies a thick layer of a type of degenerate matter known as metallic hydrogen.

A sea of liquid hydrogen sloshes around below Jupiter’s surface.
Source: http://www.lpi.usra.edu/education/explore/solar_system/background/

Hydrogen on Earth exists as a gas, unless super-cooled into a liquid. You may have seen science class demonstrations with a different super-cooled gas, liquid nitrogen. The liquid would have evaporated continuously into a dense fog, like a b-movie special effect, and frozen anything that came into contact with it. Your teacher might have used liquid nitrogen to freeze bananas into such a brittle state that they could be shattered them with a hammer. Nitrogen atom are tiny, and like all elements that are gases at room temperature, it takes very little energy to make the atoms so agitated that they bounce around as a gas (instead of the relative stillness of liquid or solid matter). Liquid nitrogen requires temperatures below -300°F, and smaller atoms like helium and hydrogen need to be cooled even further (lower than -400°F) to become liquids.  For reference, the coldest (naturally occurring) temperature ever recorded on Earth was about -129°F.

When you add in the intense pressure of gas planets, though, the rules change. And I mean INTENSE pressure. At sea level on Earth, you’d feel a pressure of one atmosphere, or atm. At the bottom of the Mariana trench, six and a half miles under the sea, the pressure reaches over 1000 atm. About 6000 miles deep inside Jupiter (still over 30,000 miles from the core), the pressure reaches two million atmospheres. At this pressure, hydrogen atoms are crammed close together into a liquid state (even though they’ve been heated to a temperature of 17,000°F). The pressure is so high that atoms are forced to stick together and they can’t move apart the way they would if you heated them that high on Earth.

Normally, there’s a limit to how dense you can pack atoms – they can’t get any closer than the distance between the nuclei and electrons. Imagine a group of people each spinning a ball on a string above their head.  The people can’t get any closer than the length of the strings or the balls will collide – and nuclei can’t get any closer than their buzzing electron shells will allow. However, if you squish a bunch of ball-spinning people or atoms into a small space, they are forced into each other. Balls go bouncing off, and so do electrons.

Larger atoms, like iron, give up electrons all the time under normal temperature and pressure. They have plenty of electrons to spare, and the outermost electrons are far away (relatively speaking) from the charged protons in the nucleus. Positively charged protons in the nucleus attract the negatively charged electrons and hold them in the atom, but the distance between nucleus and electrons in larger atoms makes it easier for the electrons to go flying off to greet their neighbors. In fact, this is what makes an element conductive. The computer you’re reading this on right now depends on the fact that some elements’ atoms have no problem releasing electrons in a river of current. Insulators, on the other hand, hold tight to all of their electrons and prevent the flow of current. Hydrogen atoms only have one electron, and they are loath to give it up under normal conditions.

Iron’s outer electrons are shielded from the positive charge of the nucleus by all the electrons below them. Hydrogen only has one electron.
Source: http://www.historyforkids.org/scienceforkids/chemistry/atoms/

However, when smushed together by the crushing pressure of a gas giant’s atmosphere, hydrogen atoms are forced to release it into a big soupy mess of protons and electrons (hydrogen doesn’t have any neutrons). This hydrogen soup is called metallic hydrogen because it’s highly conductive, a key property of metals.

Click for a video overview of how metallic hydrogen is made inside gas giants

The currents that swirl around the metallic hydrogen seas in Jupiter and Saturn are what give these planets their magnetic fields (which on Earth is produced by a molten iron core). The magnetic field of Jupiter is so strong that it’s likely that hundreds of Earths could fit just in the metallic hydrogen layer of the planet.

Metallic hydrogen has only survived creation in the lab briefly and in tiny amounts, but physicists theorize that it could be used as a clean fuel or a superconductor if they could just get it to stick around. Liquid hydrogen is already used as a rocket propellant, and converting from liquid hydrogen to metallic hydrogen fuel would allow us to pack 30-40 times the amount of fuel in the same space. Years from now a metallic hydrogen engine could drive spacecraft out to Jupiter where they stop by for a quick refuel before heading out into the galaxy.

Further reading:
WiseGeek – What is Metallic Hydrogen?
Metallic Hydrogen college lecture notes – 1 & 2

What goes munch in the night?

A historical reenactment of a night eating rampage. Ice cream, chips, and granola bars are my typical fodder.

Food goes mysteriously missing in my house all the time. Cookies and cupcakes don’t last more than a few days, and forget keeping anything chocolate around. The latest casualty was a Costco-sized bag of tortilla chips. The evidence of their demise is scattered around the kitchen in the morning, and on more than one occasion, I have woken surrounded by granola bar wrappers and with chocolate on my face. Despite my best intentions and strictest diet plans, I am undone by the monster that emerges while I sleep. Sleep-me devoured my husband’s birthday cake – by the time I realized what I was doing only one scant piece remained. Sleep eating beleaguers a fair number of people, ranging from total wakefulness and recall (that late night cookie binge I berate myself over even as it’s happening) to waking up in the morning surrounded by chocolate wrappers with no idea what happened. Two different disorders flank each end of the spectrum: sleep related eating disorder and night eating syndrome. Both are chronic, lasting months to years, and often coincide with weight gain obesity.

On the unaware while eating side of the spectrum, you have sleep-related eating disorder (SRED). Patients generally can’t remember their episodes of night bingeing and, like sleepwalkers, are mostly unconscious during the event (my husband calls these episodes “werewolfing”). Other sleep disorders, like sleepwalking, obstructive sleep apnea, and restless leg syndrome, are often present alongside SRED. SRED patients consume food normally during the day, but are driven from their beds at night by an involuntary urge to eat. They make their way to the kitchen where, all while mostly unconscious, they binge on high calorie, high carbohydrate food like peanut butter, bread, and ice cream. They may even prepare an entire meal while asleep – obviously not the safest task with clumsy, sleepy fingers. SRED patients have also been known to eat inedible, toxic, or just plain weird things like soap, raw pasta, coffee grounds, or cat food.

Night eating syndrome (NES) patients, in contrast, are mostly awake during their episodes and can remember them come morning. NES was first brought to light in 1955, in patients with treatment-resistant obesity. It’s is characterized by eating a significant number of calories between dinner and sleeping (at least 25%), waking in the night to eat compulsively, and decreased hunger in the morning. Interestingly, one of the theories explaining NES is a disconnect in sleeping/waking and eating patterns. One study found NES patients had the same caloric intake and bedtime as controls, but their meal times were delayed. Animal studies that disconnected genes controlling sleeping/waking and eating found similar symptoms to NES.

Your sleep/wake and eating cycle are circadian rhythms – physical, mental, and behavioral changes that follow a 24 hour cycle. A short quiz from Phillips.com shows my circadian rhythms are slightly delayed from the norm 

Sleep eating behavior rarely falls neatly into one of these two disorders. It’s a spectrum – patients can have episodes ranging anywhere between full consciousness and sleep – making studying and treating the problem complicated. Night eating disorders do have a lot in common, though. SRED and NES are both found more often in obese populations. Whether sleep eating causes obesity or not is still up for debate, but it certainly make it harder to lose weight (as I can attest). NES also associates strongly with depression or anxiety. Both disorders have a genetic component and can be passed down in families.

Doctors treating a suspected sleep eater (wherever they lie on the spectrum) start by giving the patient a special questionnaire addressing hunger, caloric intake, familial history, sleep habits, and how long the problem has been going on. The doctor can confirm the diagnosis by performing a sleep study. Patients bring in foods they’d normally consume at night to a sleep lab, and their wakefulness and eating habits are monitored overnight. Both disorders can be treated with serotonin modulation, like taking SSRIs (commonly prescribed for anxiety and depression). Serotonin acts on the hypothalamus, which controls sleeping/waking cycles and feeding behavior. The effectiveness of serotonin modulating drugs also ties back to the high carb intake of sleep eaters – high carb food items increase the availability of tryptophan, which the body converts into serotonin. Sleep eaters might eat high carb foods because their serotonin levels are low. Topiramate, an anti-seizure medication that causes appetite reduction, can also be used to treat NES and SRED. However, topiramate comes with its share of unpleasant side effects, including dizziness, headache, nausea, and skin numbness or tingling. SRED is often successfully treated by addressing any other sleep disorders the patient may have (excluding sleepwalking) or discontinuing any drugs that induce night eating as a side effect. Sedatives, unfortunately, can often exacerbate night eating, especially in NES cases.

My most successful treatment strategy is a combination of avoidance and food stashing. I’m (mostly) vegan during my waking hours, but if there’s ice cream in the house when I go to sleep it will be gone by the morning. When I buy snacks for my friends, I have to make them take home the leftovers or buy things I won’t be tempted by. Luckily, my sleep eating self is vegetarian and hates yogurt cluster cereal. The food I can’t live without, I have my husband hide. Somewhere in my house is a host of gourmet dark chocolate bars, safe from my nocturnal rampages. Life’s a little more boring without being able to keep cinnamon toast crunch and gelato in the house, but at least I can wake up in the morning to minimal food casualties.

Sources/further reading:
Howell, Shenk, and Crow – “A review of nightime eating disorders”
Sleep Medicine Reviews (2009) 13, 23e34

Winkelman, Johnson and Richards – “Sleep related eating disorder”
Handbook of Clinical Neurology (2011), Vol. 98 (3rd series)

Circadian Rhythms Quiz