Tag Archives: Stars

Stellar Evolution Part 3: Supergiant and Supernova

Most stars on the main sequence are relatively average: not too big and not too small. But every so often, a star begins its life as an absolute monster: a supergiant.

Supergiant

These supergiants do join the main sequence, but due to the sheer amount of gravitational force and pressure, they burn through the hydrogen in their cores in a fraction of the time that smaller stars do. They quickly leave the main sequence and expand in size to become thousands of times larger than the sun. Like smaller stars, these supergiants begin helium fusion in their cores and begin hydrogen fusion in shells around the core. But unlike smaller stars, which stop their fusion at this point, supergiants form several layers throughout the star of differently fusing gases, giving it an onion-type look.

Supergiant stellar evolution

Fusion in the core will eventually reach iron. At this point, nuclear fusion no longer produces energy, and so it stops. Without outward radiation pressure, the intense gravity causes the star to collapse. Protons and electrons get forced together in the core, turning it into a rigid sphere of neutrons. As the outer layers reach the limits of the neutron core, they rebound off and get propelled outward with huge amounts of energy. These shockwaves tear the star apart in a supernova.

Supergiant stellar

Credit: NASA, ESA, and G. Bacon (STScI) 

All that remains is the rigid sphere of neutrons, known as a neutron star. However, some supergiants are so massive that even the neutron star continues to collapse, creating an object so dense that it creates a singularity, also known as a black hole. Supergiants are rare in our universe, but their existence is crucial. Supernovas are so energetic that they create all of the elements heavier than iron, and many star systems, including our own, are made from the remnants of these explosions. Without them, life itself wouldn’t exist.

Written By: Scott Yarbrough

Additional Resource: Mouser

Stellar Evolution Part 2: Main Sequence Stars

When a protostar’s core reaches 15,000,000 degrees Celsius, nuclear fusion begins in its core. This ignition marks the star’s birth as it becomes a main sequence star.

Stars part 2

Main sequence stars have a ton of variety. They range from cooler red stars to hotly burning blue ones, and their size can range from a fraction of our sun’s mass up to several hundred times as large. The only thing that matters for the main sequence is the presence of hydrogen fusion in the core. Hydrogen fusion takes hydrogen ions and turns them into helium, creating massive amounts of energy in the process. The outwards radiation pressure resists the force of gravity, preventing the star from collapsing any further.

Stars Hydrogen Fusion

But once the core runs out of hydrogen, the star starts to contract again briefly, until a shell of hydrogen around the core becomes hot enough to fuse into helium. When this happens, the radiation pushes the outer layers of the star far out into space, turning the star into a red giant. The core continues to collapse, however, continuing to heat up until it reaches 200,000,000 degrees Celsius. At this point, the helium that now makes up the core begins to fuse into carbon. Eventually, the helium will also run out. When this happens, the outer layers of the star continues to expand and cool down until finally all that is left is a planetary nebula with the remnant of the core at the center. We call this remnant a white dwarf.

Stars Planetary Nebula

You may be surprised to not hear the word “supernova” being thrown around. This is because supernovae only occur in incredibly large stars. For most of the main sequence stars, their deaths will be relatively calm and quiet, going out not with a bang, but with a sigh.

Written By: Scott Yarbrough

 

Stellar Evolution Part 1: Nebulae and Protostars

In the vast emptiness of space, there are floating clouds of gas and dust called nebulae. These clouds are stellar nurseries, filled with material that will one day become multiple solar systems. stellar evolution When part of a nebula is slightly more densely packed than the rest, gravity is stronger in that region. It begins to pull the surrounding gas inwards. This increases gravity, which pulls even more stuff in. As this happens, the gas molecules rub against one another, heating up due to friction. When the gas heats up, it begins to give off light, illuminating the nebula with brilliant colors. Eventually, this region of the cloud takes on a rough spherical shape. The gas begins to ionize, separating electrons from their nuclei as the sphere heats up even further as it continues to collapse due to the massive gravitational forces at play. This spherical shape is known as a protostar! Stellar Evolution Stars This protostar will continue to collapse and heat up, eventually becoming a main-sequence star. For that to happen, nuclear fusion must begin in the core. When it starts, outwards radiation pressure is so strong that it prevents gravity from causing the star to collapse any further. We’ll talk about the life — and death — of main-sequence star in a future blog post, so keep your eyes open! Written By: Scott Yarbrough

Measuring the Brightness of Stars

There are countless stars that we can see in our night sky, and all of them are unique. Some are dim, barely visible without a telescope. Others are bright and can be seen even in the most light-polluted areas. We measure the brightness of these stars using the magnitude scale.

brightness of stars

The magnitude scale seems a little backwards. The lower the number, the brighter the object is; and the higher the number, the dimmer it is. This scale is logarithmic and set so that every 5 steps up equals a 100 times decrease in brightness. So magnitude 10 is 100 times dimmer than magnitude 5, which is 100 times dimmer than magnitude 0.

brightness of stars scale

Our sun — the brightest thing in our sky — is magnitude -26.7. Other objects like the moon or nearby planets have negative magnitudes, and other stars vary greatly. The dimmest objects humans can see with the naked eye is around 6; any dimmer and we need to use a telescope.

What we’ve been talking about is apparent magnitude. It measures the brightness of stars and other celestial objects as they are as viewed from Earth, without taking into account distance or actual luminosity. It’s fine for describing what things look like from here, but it isn’t very good at describing how much light those objects are actually emitting. Our moon is incredibly bright to us, but if it were farther away from us, its brightness would decrease a lot.

To better compare the brightness of objects to each other, we use the absolute magnitude scale. The logarithmic scale is the same, but we calculate what an object’s apparent magnitude would be if it were exactly 10 parsecs away from Earth (about 33 light-years away). This way, we eliminate distance as a factor for comparing the brightness of space objects.

brightness of stars gif

As you can see, the brightness measurement of stars is a little more complicated than it first appears. It may also be difficult to really visualize the difference in brightness. But it’s an easy task to find a catalog of stars, go outside, and experience it yourself!

Written By: Scott Yarbrough

The Geminid Meteors

Nothing is more exciting than looking up and seeing a shooting star streak across the night sky. But we all know it’s not really a star falling from the heavens, but rather a giant ball of rock, ice and dust skimming through the atmosphere.

This December we will be able to witness one of the most famous and spectacular meteor showers of the year. The Geminid Meteors will be in view between December 4th and December 16th. However, it will peak on the night of December 13th at roughly 10:00 PM, with the possibility of sighting about 120 meteors per hour.

meteors

Unlike most other meteor showers, these meteors don’t come from a comet flying through Earth’s atmosphere. Instead, they come from the asteroid 3200 Phaethon.

meteors 1Due to 3200 Phaethon’s highly elliptical orbit and maximum distance from the sun, takes about 1.4 years to orbit it. It has a debris trail in orbit and once a year, Earth runs into this dusty path, which intersects our planet’s path through space. It gets extremely close to the sun, only 13 million miles from it (Earth is about 93 million away from the sun).

Unfortunately, December’s supermoon may wash out all but the brightest meteors. But, facing south can be helpful to view them, since this is where they appear to emerge from. With or without the supermoon be sure to check it out, it’ll be a sight worth seeing!

Written By: Mimi Garai

Look up and Constellations

A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere. They typically represent animals, mythological people, gods or creatures. There are 88 modern constellations, but just because those are the ones that are recognized doesn’t mean that one you make up is less valid.

The stars that constellations are comprised of are not necessarily stars that are near each other. So how do they appear that way? It’s all about perspective.

constellations

Take for example, The Big Dipper, an asterism in Ursa Major. An asterism is a smaller part of a constellation, usually with more noticeable stars. The Big Dipper is composed of seven bright stars: Alkaid, Mizar, Alioth, Megrez, Phecda, Merak, and Dubhe. Together, they appear to be in the shape of a spoon (use your imagination). However, they are all different distances away from Earth as well as from each other. Their distances from Earth respectively are roughly: 104 ly, 78 ly, 82.5 ly, 80.5 ly, 83 ly, 79.5 ly, and 123.6 ly.  

constellations gif

But if you simply change your perspective, or location from which you’re looking at them, then the picture changes! Unfortunately, since we are all on Earth, our perspective can not move enough to make a big difference.

Written by: Mimi Garai

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.

stars 5

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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stars 3

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.

stars 1

stars

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.

Where Do Stars Come From?

Where do stars come from? The short answer is: gravity. All objects with mass experience gravitational attraction to each other. That includes you & the Earth, you & me, every person on our planet, and every star in the cosmos. So, why aren’t we pulled in all directions? Gravity depends on two things: mass and distance. The bigger an object is, the stronger its influence. The farther it is from you, the less you’re affected by its pull. Stars have plenty of mass, but they’re so far away that their gravitational effect on us is negligible. You and I could stand next to each other, but we just aren’t massive enough to pull significantly on each other compared to the much stronger attractive force Earth exerts on our bodies.

Orion Nebula

The Great Orion Nebula, visible to the naked eye as part of Orion’s dagger, is a massive space-cloud system and a productive stellar nursery. Image credit: UMass/2MASS/IPAC

In deep space, it’s a different story. In the absence of larger gravitational influences, even dust particles pull each other closer. It’s this quiet, dark, and delicate dance that gives rise to the stars we see in the night sky. Nebulae are massive space clouds of gas and dust. Within these clouds, turbulence makes some areas denser than others. When a dense knot of dust reaches critical mass, it collapses under its own gravitational pull, heating up and becoming a protostar. This spinning collection of hot, dense debris drags nearby particles along with its rotation, and an embryonic solar system is formed.

Einstein’s theory of relativity describes spacetime as a three-dimensional fabric that can be stretched in a fourth dimension. The way that massive objects stretch the fabric of spacetime explains their gravitational pull on each other. That’s tough to visualize, but a two-dimensional model that stretches in 3D helps us to wrap our heads around the idea.  

LNvortex
Particles of water vapor model the behavior of dust in a nebula.

When we place a heavy sphere in the center of a sheet of stretchy fabric, it pulls the surface down. Drop marbles or BBs onto the fabric and they spiral around and around before coming to rest at the lowest point. The same thing happens with water vapor: it spirals to the spot where the gravitational potential is lowest– the heavy object in the middle.

This model of spacetime provides a simple, fairly accurate illustration of the way individual stars form in nebulae.

Written By: Caela Barry

Angular Momentum Makes Science FUN!

Woohooo! Science is fun! What you just saw is a classic demonstration of something called Conservation of Angular Momentum. This concept can be difficult to grasp, and is certainly a mouthful. Let’s break it down and see if we can understand what is happening!

Kyle Spin
A good place to start is the last word. Momentum is a mathematical quantity (technically it’s a vector) that can be calculated by multiplying something’s mass by its speed. Something that is heavy and fast has more momentum than something heavy and slow, light and fast, or especially light and slow.

Angular momentum is just momentum in a circle. This can be calculated by multiplying the momentum by its distance from the center of the circle that it is traveling in, or the radius. This is a little harder to understand, but if two things have the same momentum, the one that is traveling in a bigger circle will have the larger angular momentum. If two objects are at the same radius, the one that has the larger momentum has a larger angular momentum.

Angular MomentumWhy do we care? Mostly because angular momentum is a conserved quantity. You may have heard of Conservation of Energy before, a principle that simply states that energy can not be created nor destroyed. Conservation of Angular Momentum works the same way, and as we saw that it is basically mass tim es velocity times radius. Since mass isn’t something that we see appear or disappear very often, this really only means two things can change: its speed and the size of its circle.

The total amount of angular momentum has to stay the same. That’s the conservation part. So if you have something at a large radius and bring it closer, the speed has to go up to compensate. There are several good real life ways to see this. Watch the beginning and the end of a game of tetherball, and you should notice a dramatic difference. Similarly, figure skaters often go into dizzying routines where they bring their arms in and start to spin faster and faster!

Matthew Bate Star CollapseThis same thing can happen on a cosmic scale. One cool example is in our solar system. Jupiter is well known for being the biggest planet, but it also has the shortest day at just under 10 hours long! Jupiter formed from a huge gas cloud that was slowly spinning. As it collapsed into a planet, it had to spin faster because of conservation of angular momentum! Even cooler: this process is still happening. Even as we speak, Jupiter is still shrinking at a rate of about 2 cm per year, which isn’t a lot…but still means that the planet is speeding up!

The animation on the left shows a star forming by a similar process. Credit Matthew Bate

There is another much more exotic example: Neutron stars! We have written about these before, which you can read here. In short, neutron stars form when stars much larger than our sun explode and leave a collapsed core behind. These neutron stars are only about 10 miles in diameter; a stark contrast with our sun’s 800,000 mile diameter. Stars spin too, and you can probably see where this is going. Even though the sun rotates just over once a month, conservation of momentum would demand that it spin faster if it were to shrink in such dramatic fashion. As a result, slow neutron stars spin about once every 8 seconds. Fast ones, known as pulsars, can spin around at over 700 times per second! Just be glad that doesn’t happen in the chair!

neutron-star_8914_600x450

Neutron stars don’t look like much, but usually reside within these cool molecular clouds that were part of their stellar outer layers during their previous phases. Credit NASA/ESA/HST

How Many Stars are Out There?

The numbers used in Astronomy are truly staggering.  For starters, the Earth is about 25,000 miles around. The nearest star to us is–obviously–the sun, which is 93 million miles away. To travel that distance, you would have to circle the Earth nearly 4000 times! The larger the numbers get, the harder it gets to understand what they mean.

For example, if someone is a millionaire, they have at least a million dollars. If someone is a billionaire, they have at least a billion dollars. What is the difference between that million and billion? A factor of one thousand! That means that to be a billionaire, you have to make a million dollars one thousand times! Getting to trillions is similarly outrageous. To be a trillionaire, you would have to make a million dollars ONE MILLION TIMES!

Moving back to astronomy, the numbers naturally get even more difficult to understand! We learned from the video that our galaxy has around 300 billion stars! Remember how big a billion was!? Even when Max was typing 3,050,374 zeroes per day, he still had to go on for 270 years to type that many zeroes! Take into account that there are an estimated 100 billion galaxies in our universe, and things really start to get out of hand.

We estimate that the number of stars in the universe is around 70,000,000,000,000,000,000,000. Thats 70 sextillion, or 70 thousand million million million if that helps! For Max to type out that many zeroes would take 62,871,248,000,000 years (62 trillion!). Keep in mind that the accepted age of the universe is only 13.8 billion years. It would take Max over 1,000 times the age of the universe, just to type out the number of zeroes that there are stars in the universe!

Perhaps Neil Degrasse Tyson said it best: “There are more stars in the universe than grains of sand on any beach, more stars than seconds have passed since Earth formed, more stars than words and sounds ever uttered by all the humans who ever lived”.

And it isn’t particularly close.  http://www.naturalhistorymag.com/universe/201367/cosmic-perspective?page=2

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We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!

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