Tag Archives: Black Hole

The Life and Death of Stars

Did you know that stars live and die just like other living things?…Okay, maybe not just like them. But they do have a beginning, middle, and end. All stars start out the same way, from a nebula. A nebula, otherwise known as a “star nursery”, is a cloud of gas and dust out in space. Nebulae will then start to clump up due to the massive amounts of gravitational pull. This clumping creates protostars, which are basically spherical masses of the gas and dust that are collecting even more gas and dust from the nebula.

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Once the gravity of the protostars becomes great enough, the process of fusion will begin, turning the protostar into a star. A star is defined to be a self-luminous gaseous spheroidal celestial body of great mass which produces energy by means of nuclear fusion reactions. Fusion is the act of turning lighter elements into heavier ones which can only occur under great pressures.

Depending on the original mass of the nebula and protostar, a star can be of any number of sizes. For our purposes, let’s stick with an average sized star (like our Sun),  a massive star, and a supermassive star.

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For a Sun-like star, once it has completed fusing hydrogen into helium it will become unstable and swell in size, becoming a red giant. As a red giant, it will have a thin outer shell of some hydrogen gas, and an inner core of mostly helium. Once the helium runs out, it will become extremely unstable and puff out it’s shells of hydrogen and helium, becoming a planetary nebula. One example of this is the Ring Nebula (M57). Left in the center is a white dwarf star, which is named so due to how hot and luminous it is. When the white dwarf radiates its energy away, it will fade, becoming a brown (or black) dwarf star.

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For a massive and supermassive star: they will go through the fusion process, become unstable, puff out a shell, swell to a red supergiant, start the next round of fusion, and so on and so forth, creating heavier and heavier elements. Once the massive and supermassive star become extremely unstable they will go supernova. A supernova is the largest explosion in space, which is very bright and ejects most of its mass.

stars 6When this happens for a massive star, a neutron star will be left behind. A neutron star is a celestial object with very small radius (typically 18 miles/30 km) and very high density, composed mostly of closely packed neutrons. Neutron stars also tend to rotate extremely quickly and emit regular pulses of radio waves and other electromagnetic radiation, earning them another name, pulsars.For a supermassive star, it will follow the same path of a massive star, but with one key difference. Instead of leaving a neutron star behind after the supernova, it will leave behind a black hole. A black hole is simply a region of space having a gravitational field so intense that no matter or radiation can escape.

Supernovae create the heaviest elements in our universe, which are the building blocks to life as we know it. Without this constant cycle of creation and destruction, we would have nothing. So the next time you look up in the sky, be thankful to that glowing orb of incandescent gas and all of the gas and dust that came before it.

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:
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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


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