Category: jets

Ask Ethan: How Do Hawking Radiation And Relativistic Jets Escape From A Black Hole?

“Everything you read about a black indicates that “nothing, not even light, can escape them”. Then you read that there is Hawking radiation, which “is blackbody radiation that is predicted to be released by black holes”. Then there are relativistic jets that “shoot out of black holes at close to the speed of light”. Obviously, something does come out of black holes, right?”

When it comes to black holes, the cardinal rule is that there exists an event horizon: a region from which nothing inside can ever escape. Once you cross over, you can never get out. No matter how fast you move, how quickly or what direction you accelerate in, or even if you travel at the speed of light, your inevitable destiny lies at the central singularity. So how, then, are things like relativistic jets and Hawking radiation emitted from black holes? The key to understanding them lies in examining the conditions that occur outside the event horizon, in the region near (but not exactly at) the black hole itself. This is the critical environment where spacetime is curved, matter achieves relativistic speeds, and the quantum fields themselves are affected by relativity.

Hawking radiation and relativistic jets may be real, but they don’t break the laws of physics to exist! Find out how they really do escape on this edition of Ask Ethan.

Most cooks have experienced the unpleasantness of getting splattered with hot oil while cooking. Here’s a closer look at what’s actually going on. The pan is covered by a thin layer of hot olive oil. Whenever a water drop gets added – from, say, those freshly washed greens you’re trying to saute – it sinks through the oil due to its greater density. Surrounded by hot oil and/or pan, the water heats up and vaporizes with a sudden expansion. This throws the overlying oil upward, creating long jets of hot oil that break into flying droplets. These are what actually hit you. This is a small-scale demonstration, but it gets at the heart of why you don’t throw water on an oil fire. (Image credit: C. Kalelkar and S. Paul, source)


The Vapor Cone.

A vapor cone, also known as shock collar or shock egg, is a visible cloud of condensed water which can sometimes form around an object. A vapor cone is typically observed as an aircraft, or object, flying at Transonic speeds. ( slightly slower than the speed of sound) 

The Pressure – Temperature dependence.

As the aircraft approaches the speed of sound, the air pressure around the object drops, and thereby the air temperature drops. If the temperature drops below the dew point, water in the atmosphere condenses to form a cloud in the shape of the shockwave.

Red Bull Stratos and the Vapor Cone.

Remember that epic jump where Felix Baumgartner, as a part of the Red Bull Stratos project broke the sound barrier ( reached Mach 1.25 ) during his descent? But why weren’t vapor cones seen around Felix’s body? Or were they?


Vapor cones are formed only near the ground, where plenty of wet air persists. But when Felix broke the sound barrier, there was no wet air that surrounded him that would enable the formation of Vapor cones.

Have a Good day!

PC: twistedsifter

This is a Bonus post from the series. It‘s purpose is primarily to bring out the essence of pressure-temperature dependence that allows us visualize flow in a F1 car

When you are in the combat zone, agility of a fighter jet is of utmost importance. But as an engineer, if you have already fiddled around with the wing structure your next option would be to fiddle around with the direction of the thrust.

Thrust Vectoring

Thrust vectoring is primarily used for directional control in rockets and jets. And one achieves this by manipulating the direction of thrust .


This generates the necessary moments (and forces) that enable the directional control of the aircraft. 


An aircraft traditionally has three “degrees of freedom” in aerodynamic
maneuverability; pitch, yaw and roll. **

The number of “dimensions” of
thrust vectoring relates directly to how many degrees of freedom can be
manipulated using only the vectored engine thrust.

Therefore, 2D
vectoring allows control over two degrees of freedom (typically pitch
plus either roll or yaw) while 3D controls all three.

Lockheed Martin F35B

The F-35B short takeoff/vertical landing (STOVL) variant is the world’s first supersonic STOVL stealth aircraft.


It achieves STOVL by swiveling its engine 90 degrees and directing its thrust downward during take off/lvertical landing mode.


In the following gif you can witness the transition from a 90 degree tilted engine towards a forward thrust engine during flying.


Unlike other variants of the Lockheed Martin F-35 the F-35B has no landing hook. And as a result, witnessing its landing is rather pretty special.


But nevertheless, this is one of those posts which addresses a topic that has been a the
gold mine for research. If this sort of thing fascinated you, there have been a lot of research conducted by NASA do check them out.

Have a great day!

*Rockets – How to turn during flight ?

** Aviation 101 : Pitch Roll and Yaw