What it Takes to be a Star
More than 100 billion stars exist in our galaxy, yet on a clear night only about 3,000 of them are visible to the naked eye. Here are some more illuminating facts about stars!
What Are Stars?
Our own Sun is a star! Stars are bright, huge balls of gas. They get super hot and bright by burning one gas, hydrogen, into another gas, helium, in a process called nuclear fusion.
Even though our own star, the Sun, is easy to see, all of the other stars at night are many many light-years away which is why they look like dots of light to our own eyes.
How Are Stars Born?
Stars form in dense billows of gas and dust particles called GIANT MOLECULAR CLOUDS.
- Gravity constantly pulls the dust particles together, while pressure constantly pushes them apart, until the molecular cloud cools.
- The dust particles then gather into clumps called PROTOSTARS.
- Gathering creates heat, and some protostars become so hot that they release energy (a process called thermonuclear fusion).
- This gathering and releasing balances a protostar, and it begins evolving into a star like the Sun.
- A protostar that is too small to become a star is called a BROWN DWARF. It produces heat for a few million years.
Star Bright
Make a wish on the first star you see at night!
Star light, star bright,
First star I see tonight,
I wish I may, I wish I might,
Have the wish I wish tonight.
Ever said this nighttime prayer? Some stars do shine more brightly than others.
- A bright star, as seen from Earth, is either closer to us than other stars or produces more energy鈥攐r both.
- Astronomers rate star brightness by magnitude. Magnitude 1 is about 100 times brighter than magnitude 6.
- Stars with a magnitude of 6 or less can be seen with the naked eye.
- The brightest star seen from Earth, Sirius, is magnitude 鈥1.46
All Stars Are Not White
The color of a star indicates the temperature at its surface. The hottest stars are blue. The coolest stars are red. (Think of a candle flame. The hottest area is blue!) Astronomers have sorted star colors into classes. More stars are red than any other color
A Rainbow of Colors!
| Class | Color | Temperature | Star |
| 0 | Blue | 30,000 to 60,000 K | Delta Orionis |
| B | Bluish white | 10,000 to 30,000 K | Rigel |
| A | White | 7,500 to 10,000 K | Sirius |
| F | Yellowish white | 6,000 to 7,500 K | Fomalhaut |
| G | Yellow | 5,000 to 6,000 K | Sun |
| K | Orange | 3,500 to 5,000 K | Arcturus |
| M | Red | 2,000 to 3,500 K | Betelgeuse |
Star temperature is measure donthe KELVIN SCALE:
0 (zero) K = -459.67掳 Fahrenheit = -273.15掳 Celsius
Types of Stars
A star can shrink or grow. Small stars last longer than large stars.
Stars usually begin as dwarf stars. These are small, but they can last for millions (even billions) of years.
A star can shrink or grow.
Small stars last longer than large stars.
Stars usually begin as dwarf stars. These are small, but they can last for millions (even billions) of years. The Sun is a dwarf star.
- DWARF stars can become giants, supergiants, or hypergiants.
- A GIANT star can be 200 times as wide as the Sun and 1,000 times as bright.
- A SUPERGIANT star can be 1,000 times as wide as the Sun and 10 million times as bright.
- A HYPERGIANT star can be 2,100 times as wide as the Sun and up to 40 million times as bright. (Hypergiant stars last only a few million years.)
Big Red
Betelgeuse is a red supergiant star that is 14,000 times brighter than the Sun and about 20 times as massive. If it were where the Sun is now, it would extend past Jupiter.
Big Blue
Hypergiant Eta Carinae is called a luminous blue variable (LBV) because it emits lots of energy, is extremely hot, and varies in brightness.
Do Stars Die?
Yes, stars do die, just as people do. When stars run out of fuel, they die. How this happens depends on their mass.
- A WHITE DWARF is a small, dense, dying star that releases an expanding gas shell called a PLANETARY NEBULA. Stars the size of the Sun will eventually become white dwarfs. Scientists think that white dwarfs become black dwarfs.
- BLACK DWARFS. A black dwarf star emits no light. (There are no known black dwarfs in the universe.)
- A large star can collapse in an explosion called a SUPERNOVA when it dies. (When a hypergiant does this, it鈥檚 called a HYPERNOVA.)
- Gas and debris are violently ejected and the core of the star shrinks into a NEUTRON STAR.
- A neutron star is small (6 to 12 miles wide) but dense: One teaspoonful of a neutron star would weigh as much as a small mountain on Earth. A neutron star spins very fast鈥攁s much as hundreds of times per second.
- A PULSAR is a type of neutron star that emits energy in pulses, sort of like a light beam from a lighthouse.
- When a massive star dies and collapses, it can form a STELLAR BLACK HOLE. The gravity of a black hole is so strong that it even pulls in light.
Black Holes
Don鈥檛 be fooled. Black holes are not empty space. They are extremely dense objects with lots of matter squeezed into a very small area.
As a result, the gravity is so strong that nothing, no even light, can escape!
Finding black holes is challenging. Most are invisible, so the only way to find them is by observing their gravitational effects on surrounding objects!
- A MID-MASS BLACK HOLE has a mass of hundreds to thousands of Suns.
- A SUPERMASSIVE BLACK HOLE, with a mass millions to billions of times greater than that of the Sun, is thought to be at the center of most large galaxies
In May of 2020, scientists reported on a new black hole! Google 鈥HR 6819鈥 and you鈥檒l learn about a system made of two stars plus a black hole. This black hole is closer to Earth than another black hole so it鈥檚 an exciting discovery!
How to Stargaze
To see the most stars in the night sky, you鈥檒l need very dark skies and cloudless nights. In cities and towns, there is usually too much light pollution to see a lot of stars. But in the country鈥檚 darkest skies, you could see countless stars blanketing the sky above you.
See if you can take a drive out to the country or go camping. Check the weather first to make sure that it will be a clear night. Then just look up! You will need to wait about 20 minutes for eyes to get used to the dark and really see the stars above.
Now, when you stare at the stars, you鈥檒l be one of the handful of kids who know that 鈥淭winkle, twinkle, little star鈥 is a nice lullaby for babies but also that stars are really massive balls of gas鈥攕uper hot and burning bright!