You see the Milky Way as a hazy band of lights stretching across the night sky. Here’s what to know about the Milky Way, especially in the number of stars and what we can or can’t see as backyard astronomers.
The Milky Way is made up of various types of matter, including stars, gas, and dust. Dark matter comprises about 90% of the galaxy’s mass. This type of matter is not visible since it does not interact with light. The remaining 10% of the mass is visible, such as stars, gas, and dust.
What is the most common star in the Milky Way?
It’s estimated that around 70% of the stars in the Milky Way are red dwarfs. The most common type of star in the Milky Way galaxy is a red dwarf star. These stars are typically less massive and cooler than our Sun.
It is estimated the Milky Way contains somewhere between 100 billion and 400 billion stars and the red dwarfs make up 70% of these, though there are several different star types of interest including giants and yellow dwarfs, like our Sun.
The Milky Way also contains white dwarfs and neutron stars, among many others.
What formed the Milky way
Scientists postulate that the Milky Way formed around 13.6 billion years ago. The theory is that it started as a small, dense cloud of gas and dust that collapsed under its own gravity, eventually forming a rotating disk.
The Milky Way size and shape
The Milky Way is a barred spiral galaxy containing billions of stars, planets, and other celestial objects.
One of the biggest challenges for us observers to comprehend is its sheer size. The galaxy is estimated to be around 100,000 light-years in diameter, which means that it would take light 100,000 years to travel from one end of it to the other.
The other thing to comprehend is that the Milky Way is not static. It’s constantly evolving and changing, with stars being born, dying, and moving all the time.
The Milky Way is shaped like a disk with a central bulge. The disk is about 1000 light-years thick and is surrounded by a halo of stars that extends up to 100,000 lightyears from the center of the galaxy.
It’s said that major events shaped its current form.
What’s at the center of the Milky Way
At the center of the Milky Way is a dense concentration of stars, which is called the Central bulge.
See the bulge in the center in this image, which shows the various components of the Milky Way.
SMC: Small Magellanic Cloud; LMC: Large Magellanic Cloud. Image credit: Pablo Carlos Budassi (CC BY-SA 4.0)
Outside the center bulge, the Milky Way is made up of the following structures:
- Galactic halo
The spherical region surrounding it that is made up of old stars and globular clusters. - Galactic disk
The flattened region contains most of the Milky Way’s stars, gas, and dust. By the way…It’s not perfectly flat. Studies reveal that the disk becomes increasingly warped in parts far away from the Milky Way’s center. - Spiral arms
These are thought to have formed through the gravitational interactions between stars and gas in the disk. There are four of these, and Earth orbits in our solar system within one, namely the Orion Arm.
Our home, Earth, is located in the Orion Arm, a relatively quiet part of the Milky Way, far from the central bulge and the most active regions of star formation in the spiral arms.
Visible Features to backyard astronomers
The feature most prominent to us amateur observers is the Milky Way’s galactic plane. Most of the galaxy’s stars and gas exist on this plane. It’s what we see as the light and cloud band across the night sky and what we know as the ‘Milky Way’.
Other visible features of the Milky Way are dark constellations. This is not a traditional constellation recognized by astronomers, but rather a region of the sky that appears dark to the naked eye.
The southern hemisphere gives the best views of the Milky Way and among the visible features depicted from this southern perspective are dark constellations.
Cultural significance: One example, in the southern hemisphere, is the Dark Emu. Named by the traditional people of Australia, it is a dark constellation and subject of aboriginal mythology. The Incas also recognized dark constellations in the Milky Way.
You’ll also see open clusters, which are groups of stars visible to the naked eye as fuzzy patches of light within the Milky Way. Try looking through your telescope to see more detail. These are relatively young, with ages typically ranging from a few million to a few billion years.
Some of these objects are in the Messier catalog. The Pleiades cluster, for example, is a Messier Object that’s easy to find and is located within the Milky Way galaxy. It is a relatively nearby open star cluster that is visible to the naked eye in the night sky from Earth.
As a backyard astronomer in the southern hemisphere, you can also get to see the large and small Magellanic Clouds.
Magellanic clouds
The Magellanic Clouds are two irregular dwarf galaxies that orbit the Milky Way galaxy and are members of the Local Group. They are named after the Portuguese explorer Ferdinand Magellan, whose crew first observed them during their voyage around the world in the early 16th century.
The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are seen from the southern hemisphere with the naked eye in dark skies. They appear as faint, fuzzy patches of light and are often described as looking like two small clouds.
Emission nebulae
Many emission nebulae are located within the Milky Way galaxy, including the famous Orion Nebula, the Lagoon Nebula, and the Eagle Nebula, among others.
We see these nebulae with the naked eye as faint, fuzzy patches of light in the night sky, and they can be seen from Earth with the aid of decent telescopes or binoculars.
Emission nebulae are clouds of ionized gas that emit light at various wavelengths, including visible light. They are often associated with regions of active star formation, where the intense radiation from young, hot stars ionizes the surrounding gas.
Other fascinating features include the following but don’t expect to see these using amateur astronomy gear.
Streams around the Milky Way
We cannot see the streams wrapping the Milky Way with our naked eyes, but astronomers have been able to study these using advanced telescopes and imaging techniques, including telescopes that can detect different types of light, such as infrared and radio waves.
By studying the streams, astronomers learn more about the structure and history of our galaxy, as well as the process of galaxy evolution through mergers and interactions.
Sagittarius Stream
The Sagittarius Stream is a long, complex structure of stars that wrap around the Milky Way galaxy in an orbit that nearly crosses the galactic poles. It consists of tidally stripped stars from the Sagittarius Dwarf Elliptical Galaxy, resulting from the process of merging with the Milky Way over a period of billions of years.
Helmi Stream
The Helmi Stream is a long, narrow structure made up of stars that wrap around the Milky Way galaxy in an orbit that is nearly perpendicular to the plane of the galaxy. It is thought to be the remnant of a small dwarf galaxy that was disrupted and absorbed by the Milky Way billions of years ago.
Magellanic stream
The Magellanic Stream is a long, ribbon-like structure made up of gas that wraps around the Milky Way galaxy in an orbit that is nearly perpendicular to the plane of the galaxy. It is thought to have been formed by the gravitational interaction between the Milky Way and the Small and Large Magellanic Clouds, two small satellite galaxies that orbit the Milky Way.
Gamma-ray bubble
We can’t see the gamma-ray bubble as a backyard astronomer. We rely on astronomers using the Fermi Gamma-Ray Space Telescope and other instruments to tell us about this phenomenon, first discovered in 2010
They tell us that the gamma-ray bubble comprises high-energy gamma rays that extend above and below the plane of our galaxy for tens of thousands of light-years.
The gamma-ray bubble is thought to be the result of a burst of star formation that occurred in the Milky Way’s central region several million years ago. The burst of star formation produced massive stars that exploded as supernovae, releasing large amounts of energy in the form of gamma rays. Over time, the gamma rays from these explosions accumulated in the region around the galactic center, creating the bubble-like structure that we observe today.
Observing the Milky Way Galaxy
To better understand the Milky Way Galaxy, professional astronomers use both ground-based and space-based telescopes to study the galaxy. Ground-based telescopes are located on Earth and can provide high-resolution images of the Milky Way’s visible features.
Space-based telescopes, such as the Hubble Space Telescope, can observe the galaxy without the interference of Earth’s atmosphere and provide clearer images.
Another technique used to study the Milky Way is radio astronomy. Radio telescopes can detect radio waves emitted by celestial objects, including the Milky Way. This method allows astronomers to study the galaxy’s structure and magnetic fields.
In addition to telescopes and radio astronomy, scientists also use computer simulations and models to study the Milky Way. These simulations can help researchers understand the galaxy’s formation, evolution, and behavior.
Current Understanding of the Milky Way Galaxy
The galaxy’s dynamics are governed by the gravitational forces of its various components. The stars in the disk orbit around the galactic center in a roughly circular path, while the stars in the bulge and central bar move in more complex orbits. The spiral arms are regions where gas and dust are compressed, leading to the formation of new stars.
Unanswered Questions
Despite our current understanding of the Milky Way, there are still many unanswered questions about its structure and evolution.
For example, scientists are still trying to determine the precise number of spiral arms and their locations. Additionally, the nature of dark matter, which makes up most of the galaxy’s mass, remains a mystery.
Another area of active research is the origin of the Milky Way’s disk and bulge. Scientists are trying to understand how these structures formed and evolved over time.
Some theories suggest that they formed from the merging of smaller galaxies, while others propose that they formed from the collapse of gas and dust in the early universe.