You probably know of some ordinary types of stars in space. Our Sun for instance. Other examples of stars you may or may not know. There are several different star types and the following will help if you want to use your home telescope or binoculars with a star chart to locate them in the sky.
How many types of stars are there in the universe? The Hertzsprung-Russell diagram identifies three distinct types of stars. These are the faint small stars (white dwarfs), main sequence stars, and the giants. Most are ‘main sequence’ stars, of which our Sun is one.
There are several other names referring to star types that can cause confusion. The following looks at the names of star types that you might find mentioned and how they fit in the scheme of the three distinct types. It also gives examples and where to look to see these.
Types of stars in space
The following describes the different types of stars in the universe that are within these three main types (+ some more).
As well as their spectral class (shown in the Hertzsprung-Russell diagram), these can be further classified by luminosity…
Luminosity Classes of Stars in Space
|Symbol||Class of Star||Example|
|0||Extreme, luminous supergiants|
|Ib||Less luminous supergiants||Antares|
|sd||Subdwarfs||Kapteyn’s Star (HD 33793)|
|wd or D||White dwarfs||Sirius B|
1. Dwarf Stars
We start with the main sequence types, which fuse hydrogen to form helium in their cores. These are ‘young’ stars known as dwarf stars and include yellow dwarf and red dwarf stars.
Apart from our sun, other main-sequence stars include Sirius A and a further 90% of stars known in the Universe. The Hertzsprung-Russell diagram (above) shows the broad range of these types in terms of temperature and luminosity.
Sirius A is the brightest star in the night sky, though it is not always as bright as some of the solar system planets, e.g. Jupiter, Venus, Mars, and Mercury, as seen from Earth at certain times. It is a spectral type A and is in the white spectrum range.
It is mostly of carbon and oxygen (generated from helium fusion).
In the blue spectral range is Beta Centauri, which along with its ‘neighboring’ triple star Alpha Centauri (Alpha Centauri A, B, & C) is prominent in the Southern Hemisphere skies. The two are ‘pointer stars’ that direct observers to the Crux constellation (AKA Southern Cross).
Dwarf stars fit into the luminosity class of V (see table). The Roman numeral ‘V’ is the luminosity class for main sequence stars.
2. Yellow Dwarf star
Is the Sun a red giant? No, our Sun that illuminates our day is what is known as a yellow dwarf. (No need for a telescope or sky map here).
The proper name for our Sun’s type, however, is a g type main sequence star, shown in the diagram. These can range in color and aren’t necessarily yellow.
So our Sun is a G spectral type – (this category covers stars of a mass equivalent to 80–125% of our Sun’s size).
Our Sun has an expected lifespan of about 10 billion (1010) years. It’s expected to last another 7 billion years, which is good for life on Earth.
These G types have temperatures ranging between 4,900 and 6,000 Kelvin (K; 8360ºF–10,340ºF) and their light derives from the nuclear fusion of hydrogen into helium, like other main sequence stars.
Other ‘yellow dwarfs’ include Alpha Centauri A and B, Tau Ceti, and 51 Pegasi.
3. Red Dwarf
These are low mass stars, that are the longest-lived and the most common type of star in the Milky Way. But, they are not easily seen. They are very faint stars.
Temperature wise these are cooler than our Sun since they reach only 3800 K (6,380ºF).
Proxima Centauri (AKA Alpha Centauri C) is an example of a red dwarf.
Named after the astronomer, E. E. Barnard, Barnard’s star is a low-mass red dwarf within our Milky Way. The place to point your telescope for observing Barnard’s Star is near the celestial equator. In the northern hemisphere, it is best seen in summer (June) high in the sky in the constellation Ophiuchus. Its neighbors are Sagittarius, Scorpius, and Libra.
Barnard’s Star is smaller and older than our Sun of 4.5 billion years old). It has been described as a flare star, which is one that has bursts of brightness at random but relatively rare times, as in the one seen in 1998.
4. Red Giant Stars
A red giant star is a dying star.
These types have run out of hydrogen. Red giant stars fit into the luminosity class of either II or III.
Examples of a red giant include Aldebaran (Alpha Tauri) in the constellation Taurus and Mira (Omicron Ceti) in Cetus, in the northern sky.
5. Blue giant
Stars that are blue giants are large and extremely hot. They burn helium and are in a phase that follows the main sequence.
Blue giant stars fit into the luminosity class of either II or III (with II the brighter of the two).
6. Supergiant Stars
These are the biggest and most luminous of the stars seen from Earth. Their temperature can range from about 3,450 K to over 20,000 K (red to blue spectrum).
Although rare and short-lived they are super bright. Supergiant stars fit into the luminosity classes of 0, Ia, or 1b.
Examples in the blueish-white spectrum or B type include Rigel in the constellation Orion and Deneb in Cygnus, both are the brightest stars in each. You can see these with your naked eye.
Betelgeuse is an example of a red supergiant that’s found in the constellation Orion. For perspective, it is 1000x the size of and 14,000x brighter than our Sun. Both Rigel and Betelgeuse are in the luminosity class of Ia.
Look for Betelgeuse and Rigel in the constellation of Orion. But keep in mind that Betelgeuse has been acting weird lately and may at times be dim – more on this at Space.com.
Another stand out red supergiant star in the Milky Way is Antares. Although less luminous than Betelgeuse being in the class Ib, it stands out like Mars with its reddish coloring.
You’ll find Antares in the constellation Scorpius.
7. White Dwarfs
A white dwarf is a star that has exhausted its nuclear fuel. These are small dense stars comprised of carbon. Their surface temperatures are high ranging from hot.
White dwarf stars fit into the luminosity class of wd or D.
Its sister star, Sirius A, is a main sequence star of spectral type A.
White dwarfs explained…
8. Neutron Stars
You’re not able to see these with the typical instruments. These are very dense small celestial objects with a radius of about 12-18 miles (20-30 km), of mostly packed neutrons. They are thought to be a collapsed center, remnant of a giant star. It’s a stage at the end of the stars existence.
Example: SR J0108-1431 in the constellation Cetus (the Whale), in the northern sky is the closest neutron star to us. This example is a pulsar, which is neutron star that is highly magnetized and rotates, emitting a beam of electromagnetic radiation.
9. T tauri Star
This is a class of variable stars that are relatively young (< 10 million years). The temperature at the core of these is two low for hydrogen fusion. How are they powered? Gravitational energy driven by contraction of the star is their source of power.
The nearest T Tauri stars to us are in the Taurus molecular cloud in the constellations Taurus and Auriga, and the ρ-Ophiuchus (pronounced rho oh-fee-ook-ee) molecular cloud of the constellation Ophiuchus, both about 400 light years away. More than 200 T Tauri stars are estimated in the Rho-Ophiuchus molecular cloud.
10. Variable Stars
These stars are so named because they change in brightness (as seen from Earth). The cause can be intrinsic (e.g. the star itself shrinking and expanding) or extrinsic (e.g. another celestial object eclipses it). There are around 42,000 variable stars.
Examples are R And in the constellation Andromeda and T Aqr in the constellation Aquarius.
11. Runaway Stars
A runaway star is one moving at a speed and direction through space abnormal to the surrounding interstellar matter, which includes the gas, dust, and cosmic radiation. An example of a runaway star is GD 50, which is a white dwarf star, smaller than our Earth by with slightly more mass than our sun.
12. Hypervelocity Stars
These are stars that move at high velocities. In 2005, one was recorded that moved at a velocity of 2 million mph. It was coined an ‘Outcast’ star, ejected by the Milky Way. They are associated with black holes.
13. Intergalactic Stars
These are sometimes termed rogue stars because they are not gravitationally bound to any galaxy.
14. Halo Stars
This is a group of globular clusters and field stars. These encircle the outer edge of spiral galaxies including the Milky Way in an area called the ‘halo zone’. They are thought to be the oldest stars in the galaxy.
What is a protostar? As the name suggests (proto- meaning first or earliest), it is an early stage — a forming star. It’s basically a gas mass that’s contracting.
Hope you enjoyed these interesting facts about stars. There is so much to learn about the Universe. When you wish upon a star, what type will it be?
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