Tag Archives: Vortex

What is a Black Hole?

You’ve probably heard of black holes, those mysterious cosmic vacuum cleaners that tear apart and suck up everything around them. These exotic objects make for excellent science fiction and have a reputation for being incredibly complicated. While they can live up to their complex reputation, at a basic level they are actually not too difficult to wrap your head around!


The black hole from the blockbuster Interstellar, which hired astrophysics guru Kip Thorne as a consultant to keep scientific accuracy through much of the movie.

rocket19Jumping up in the air on Earth is a short-lived journey. An average person starts their upward flight with a speed of about 7 miles per hour. Our planet’s gravity quickly overwhelms that momentum, and the jumper lands. However, if someone could jump at 25,000 miles per hour, they could escape Earth’s gravitational pull and continue into space! Every planet and star has a special speed requirement to escape its gravity. We call this speed the escape velocity. Larger objects have higher escape velocities; it would take a monstrous 133,000mph takeoff to break free of Jupiter’s gravitational pull. The sun would shut down any jump slower than 1.4 million mph!

A black hole has so much gravity that not even light, the fastest thing in the universe, can escape it. Light travels at a whopping 670,000,000 mph. As we have seen, the bigger the planet or star, the faster something has to go to overcome its gravity. So black holes must be HUGE, right? Well, sort of.

SparkfunEverything you have ever seen on Earth is made out of atoms. While many people are aware that atoms are made up of protons, neutrons, and electrons, it might be more accurate to say they are made up of nothing. The most common atom in the universe is hydrogen. It is made up of one proton and one electron and is 99.9999999996% completely empty space. To think of it another way, if a hydrogen atom were the size of our planet, the proton would be just over a tenth of a mile wide, the electron would be about three inches across, and they would be separated by about 4000 miles. Most of our universe is empty!

Classic diagram of an atom. All of the parts are drawn FAR too large, which makes sense because if they were to scale they would all be too small to see! Image credit: Sparkfun

Black holes have a LOT of mass, which is why they have so much gravity. So much, in fact, that atoms are actually crushed to fill in the empty space. Sometimes a dying star has enough mass (and gravity) to crush atoms, but not quite enough to keep light from escaping. In these cases, a neutron star is born. These strange objects contain as much mass as the sun, but are squeezed into a space smaller than New York City. Put another way, a soup can of the stuff would weigh about as much as the mountain that AstroCamp lives on!

TahquitzBlack holes are so massive that not even light can break free from their gravity. Inside a black hole, the immense gravitational pull crushes atoms and even neutrons themselves down into a tiny speck called a singularity. This tiny point of matter is even smaller than an atom. It can range tremendously in mass, from about twice as heavy as the sun for a smaller black hole, to millions of times the mass of the sun!

Everything that we know about space comes from the light that galaxies and stars and other things give off. However, black holes don’t let light escape, so how do we find them? Well, there are a couple of ways. One is to wait for the black hole to get in between us and a distant object. Since gravity can bend light, this results in gravitational lensing, where the black hole distorts images of the things behind it, a bit like a carnival mirror.

Grav Lens

Simulation of a black hole causing gravitational lensing on the Milky Way. Note that it is not actually moving the stars, just bending the light to change how we see it! Credit: Andrew Hamilton

The black hole at the center of our galaxy was found another way: by looking at how stars in its neighborhood are moving. They whiz around in circles as if pulled by an immense central object, but we can’t see anything there. Calculating the mass needed to move the stars that fast reveals the invisible culprit: a black hole! See for yourself:
Sag A

Vortex Table: The Trampoline of Science!

Gravity is everywhere!  Anything that has mass exerts a gravitational force, including you and me!  Why can we not feel that force?  We are in the presence of a massive object that pulls on us more than we could ever pull on each other, and leaves our personal gravitational pull negligible.  That’s right, I am talking about the Earth!  In the absence of a large object with mass however, even tiny specs of dust and atoms of gas can feel a force pulling them together.

What does gravity have to do with a stretchy vortex table?  According to Einstein’s Theory of Relativity, the universe is not actually flat, but a stretchable fabric called spacetime.  Gravity, in this theory, can be represented as curvature in the fabric of spacetime.  In the diagram below, the Earth is causing the 2-Dimensional grid to stretch into the 3rd Dimension. In our 3-Dimensional universe, we can only imagine how gravity would stretch spacetime into the next dimension: the 4th Dimension!


A simulation of what the curvature of spacetime might look like. Credit: Wikipedia, Johnstone

Our Vortex Table is a great model for how gravity affects spacetime.  Any mass in the center of the table causes a small curvature in the fabric, which automatically attracts any other object placed on the table.  It is easy to see that the heavier the mass in the center, the greater the downward slope of the table, and therefore, the greater the gravitational pull on other objects.


Objects with different masses can bend spacetime in different ways. This view from the bottom of the table looks very similar to the simulation above.

The formation of stars is caused entirely by the gravitational force of attraction and can be modeled on the Vortex Table.  Clouds of dust and gas in the universe, called nebulae, are where stars are formed. The gas in a nebula is pulled together by the force of gravity to form a dense patch of gas called a protostar, which attracts even more gas and dust to become a full star.


The life cycle of a star, as illustrated on the back of an AstroCamp sweatshirt!

The formation of a star and its Solar System is not the only thing we can model on our awesome stretchy table.  When an extremely massive star dies, it becomes a black hole.  A black hole is a very dense and very massive, causing a huge curvature in spacetime.  Black holes have so much gravity that light can’t escape, so we have difficulty detecting them directly. To find black holes, astronomers look for the stuff around it, such as stars orbiting something invisible, or material that is getting accelerated to very high speeds.


The vortex table lives up to its name.

Simulating a black hole with fabric is difficult…Imagine the vortex table stretched so far down that the hole goes down into infinity!  The resulting slope can affect stars and planets more than 50,000 lightyears away, about the radius of our galaxy. Scientists theorize that there is a supermassive black hole at the center of every galaxy, which is what holds everything together.  Look familiar?

Galaxy Comparison

The image on the left is from the vortex table. The one on the right is a spiral galaxy called M74. Photo credit: NASA

Gravity and the Vortex Table

When a Line Isn’t a Line or Who’s Line is it Anyway?

What is the shortest path between two points?  I bet most of you said a line, and in a lot of circumstances you would be correct.  The problem is that this is only true if you are using a flat space like a sheet of paper.  When your space begins to curve, you need to become more creative.  Let’s take the cities of New York and Tokyo as an example.  The shortest distance between them would be a straight line going through the Earth, but that’s no help to planes that need to stay above the ground.  So airlines need to figure out a more complex path to make the journey as efficient as possible.  This path is called a great circle! For our New York to Tokyo flight you need to travel north almost past Alaska to travel on the great circle.
Here is a fun site that you can use to map great circles connecting airports around the world: The Great Circle Mapper 

Now you might think that outer space would be an escape from these silly curved geometries, but you would be very wrong.  Einstein’s theory of General Relativity showed us that space is very far from flat.  Any object with mass will warp space much like a weight will warp a trampoline.  The heavier the object, the greater the warping.  This is the basic principle of gravity!  One of the interesting effects of this curving of space is that light will behave like our airplane and always follow the shortest path between two points, which often isn’t a line. That is what our vortex table is meant to show.  The marbles are trying to go from one side of the metal ball to the other.  If the ground was flat, they could simply go right next to it, but in our curved fabric space, the shortest path is a nice even circle several inches from the metal ball.

In space, we have even more extreme cases.  For example, the light from a star might be split going around an object like a black hole.  Some of the light goes around to the left, some of the light goes around to the right.  After navigating the black hole, the two beams of light might eventually converge when they get to the Earth.  A telescope detecting these two beams would see two identical stars on either side of the black hole, one on the right one on the left.  In reality, there is only one star behind the black hole, but the telescope doesn’t know any better.  We call this gravitational lensing, just one of the mind-bending things that can happen in space.  Here is a diagram to make things slightly less clear than mud. The gray stars are what you see, the black is what is real.


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