Blog Post 5: Complex Thermodynamics

Welcome back everyone,

The single most important thing in finding the correct sized black hole to harvest for energy is the amount of mass that it should contain. In this blog post, I will outline black hole thermodynamics. Thermodynamics is essential to black holes, and black holes are very essential to the formation of the universe, in fact they are sometimes called galactic engines, due to super massive black holes being at the center of many active galaxies.

Moving on, what exactly is thermodynamics, and how does it relate to black holes? Well basic thermodynamics is in essence a law that dictates that energy flows from an area of higher concentration to an area of lower concentration. Thus, when applying this concept to black holes we can say that it is the relationship between a black holes temperature and the cosmic background temperature. The cosmic background temperature is 2.7 Kelvin right now, but in 10, 15, 20 billion years it will much cooler, until it reaches ridiculously close to absolute zero. However, if we stay in the present, this means that after a black hole is created if it is hotter than the current cosmic background radiation, the black hole will create more energy, than it absorbs (after the initial creation) or in other words, it will start to radiate its mass away in the form of energy, until it fades.

In simpler terms, Black holes release more energy when they are hotter than the area surrounding them (space), and release net negative energy when they are in an area that is hotter than them.

Now, we have developed equations that tell us that smaller black holes are hotter than large ones and radiate their energy away quicker. But how can we prove this theory? Well we can use a very interesting property of black holes. Black holes have negative specific heat capacity. Using this information we performed a very complex thermodynamics experiment – we burned a candle.

The specific heat of an object is the amount of heat per unit mass required to raise the temperature by one degree Celsius. However, black holes have negative specific heat capacity. Therefore they need to lose energy in the form of mass, to raise their temperature. And when they lose mass, they emit energy in the form of hawking radiation. Thus, by adding energy to candles, an object with positive specific heat capacity, you can simulate what happens when you take energy away from a black hole. And we found that larger candles take longer to burn, meaning that larger black holes take longer to radiate their mass away.

Thus the two systems run, exactly opposite to each other. But they have one common property – time. Time is constant in both. Which means that if it takes longer for the larger mass of the candle to melt, it will take longer for a larger black hole to radiate away. What this means to us scientists, well we can potentially harvest smaller black holes and gain energy from them. Their fuel source could be garbage even!

Dr. Chinmay Patel (PhD in Astrophysics)

Professor at Stanford University

Links:

Ball, Philip (Dec 3, 2013). Could we harness energy from black holes? Retrieved From: <http://www.bbc.com/future/story/20131203-could-black-holes-provide-energy>

Anderson, Ryan (November 19, 2009). Black Hole Drive could power future Starships. Retrieved From: <http://www.universetoday.com/45571/black-hole-drive-could-power-future-starships/>

Jones, Zimmerman, Andrew (2010). What is Hawking Radiation? Retrieved From: < http://physics.about.com/od/astronomy/f/hawkrad.htm>

123HelpMe.com. "Black Holes: The Power Source for Future Space Travel?" Retrieved From: <http://www.123helpme.com/view.asp?id=43865>

Whiting, Jim. (2011). Mysteries of the universe: Black Holes. New York, USA. Publisher: Creative Education. Book.

DeGrasse, Tyson. (2007). Galactic Engines. Death by Black Hole and Other Cosmic Quandaries. (pg. 268-274). New York, USA. Publisher: Norton. Book.

Begelman, Mitchell. (2010). Gravity Triumphant. Gravity’s Fatal Attraction: Black Holes in the Universe. (pg. 1-22). New York, USA. Publisher: Cambridge University Press. Book.

#Chinmay