Giant Molecular Clouds – The Stellar Nursery

Giant Molecular Clouds are the birth place of stars. They’re often referred to as stellar nurseries and even the giver’s of life. Without these amazing and awesome occurrences in space; there’d be no stars, no planets, no solar systems and no life. Sorry, humans. Sorry, E.T. Sorry, Mr. Spock.

What Are Giant Molecular Clouds Made of?

Molecular Clouds are a type of interstellar clouds which depending on their density and size, can create and give birth to stars! Giant Molecular Clouds are mostly made up of hydrogen. Hydrogen is the element needed to begin the process of fusion, which is the beginning of a star’s life cycle.

Giant Molecular Clouds contain massive quantities of gas and dust, enough to create hundreds of thousands of stars.



Photo by Luis Argerich


Giant Molecular Clouds Give Birth to Stars?

Yeah, Giant Molecular Clouds are the mommies and daddies to stars. They’re so big, contain so much gas and have so much mass that they can eventually begin to collapse on itself – starting the baby (star) makin’ process.

This birthing process begins by a Giant Molecular Cloud’s mass getting so large that its gravity starts to collapse on itself. Think of it as all of the matter on the outer part of its cloud getting pulled in towards the inner sections of its matter.



“Core collapse scenario” by R.J. Hall – Illustration by contributor (After Modelling Supernovae with PHOENIX.). Licensed under CC BY 2.5 via Wikimedia Commons –


Because this inner matter has nowhere to go, even though the outer matter is pushing on it, it compresses to the point of collapse, which creates a baby protostar and that eventually turns into a main sequence star. Main sequence stars use its hydrogen molecules to start the fusion process, launching the star’s life cycle.

Where do Giant Molecular Clouds Hang Out?

Giant Molecular Clouds make up a small portion (about 1%) of the matter that makes up the space between stars within a galaxy, referred to as the Interstellar Medium. Think of this as all the emptiness between stars, star clusters, solar systems, etc it’s the empty voids of space.



“Cepheus B” by X-ray: NASA/CXC/PSU/K. Getman et al.; IRL NASA/JPL-Caltech/CfA/J. Wang et al. – NASA Image of the Day. Licensed under Public Domain via Wikimedia Commons –


Most molecular clouds, both small and giant molecular clouds hang out around the center of a galaxy. In the Milky Way, most molecular clouds are located in a ring formation around the center of the galaxy between 11,000 and 24,000 light years from the center of the Milky Way.



Photo by NASA Goddard Space Flight Center


In the Milky Way, it’s estimated that there are about 6,000 molecular clouds. They spend all day and all night pumping out baby stars, resulting in new stars, solar systems and maybe even life.

Giant Molecular Clouds hang out mostly in the spiral arms of a spiral arm galaxy, so they must form, create and die within around 10 to 100 million years. The reason why this has to happen in this astronomically short period of time is because it takes roughly 10 to 100 million years for all of the Giant Molecular Cloud’s mass, matter and materials to pass through the arm region of the spiral arm galaxy.



Photo by NASA’s Marshall Space Flight Center


How Big Are Giant Molecular Clouds?

Bigger than your brain can even comprehend. Giant Molecular Clouds are thought to be as big as 100 to even 600 light years in diameter. That’s HUGE!

To put that into Earth terms and perspective; 100 to 600 light years is equivalent to 587,862,537,318,360 to 3,527,175,223,910,164 miles, in diameter.

The Earth’s diameter is 7,917 miles…

Giant Molecular Clouds can have masses of up to 6,000,000 solar masses, which is the standard astronomical unit of measurement equal to that of one Sun (our solar system’s star). So these massively large Giant Molecular Clouds can easily be 6 million times the mass of one of our Suns.



“Part of the Taurus Molecular Cloud” by ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin. – Licensed under CC BY 3.0 via Wikimedia Commons –


Giant Molecular Clouds can be so large that they literally span the entire area of a constellation. Imagine looking up into the night’s sky and seeing the stars of a constellation and how far away they are from Earth. Now imagine how far away those stars are from one another. They can be hundreds of light years or many quadrillions of miles across.

Because Giant Molecular Clouds are so big, we often refer to the ones close to us by the names of the constellations that they cover. For example, here is the Orion Molecular Cloud Complex, one of my favorite constellations and molecular clouds.



“Orion Head to Toe” by Rogelio Bernal Andreo – Licensed under CC BY-SA 3.0 via Wikimedia Commons –


Giant Molecular Clouds are cold, freezing cold. They can range from roughly -440 to -370 degrees Fahrenheit, equivalent to roughly 10 to 50 degrees Kelvin.

These massive collections of dust and gasses don’t actually emit their own light, of course the stars they create emit light, but molecular clouds on their own, aren’t usually observable. They appear dark when looking through a regular optimal telescope.

Here’s a great example of how a Giant Molecular Cloud can block out the visible light by its dense molecules. The dark center of this image is the Molecular Cloud cataloged as Barnard 68.



“Barnard 68” by ESO – Licensed under CC BY 4.0 via Wikimedia Commons –


How Small Are Small Molecular Clouds?

Small Molecular Clouds are usually much smaller than that of their “big brothers”, the Giant Molecular Clouds.

While Giant Molecular Clouds can be hundreds of light years across, Small Molecular Clouds are usually only 1 light year across and typically between 2 and 50 solar masses.

Small Molecular Clouds are also referred to as Bok globule and are pretty much the same thing are Giant Molecular Clouds, dense formations and collections of cosmic dust and gasses. They contain hydrogen, cabon oxides and helium.

Something interesting, Bok globule or Small Molecular Clouds usually give birth to double or multi-star systems! We call these solar twins! Others call them binary star systems.

What’s an Example of a Multi-Star System?

Our Solar System’s closest neighboring star is actually a multi-star system. Alpha Centauri, which is a bad ass star system.

Alpha Centauri A and Alpha Centauri B give off the visual appears of a binary star system. However, if you look closely enough, it’s actually a multi-star system. There is a third star in this system named Proxima Centauri. See the little red circle in the image below for Proxima Centauri.



“Alpha, Beta and Proxima Centauri” by Skatebiker – See above for details. Licensed under CC BY-SA 3.0 via Wikipedia –


Because this multi-star system is so close to our Solar System, and because this is a multi-star system, it appears to be the brightest star (system) in the nights sky. However, it’s actually more than just one star, so it may or may not be the “brighest star” (singular) in the night’s sky.

In fact, for many years, prior to the discovery of Proxima Centauri, we believed that Alpha Centauri A was the closest star to our Solar System’s star, the Sun at 4.37 light years away. However, upon discovering Proxima Centauri with higher powered telescopes, we know that Proxima Centauri is our closest neighbor at 4.24 light years away.

Proxima Centauri is still roughly 24,925,371,582,298 miles away from our Sun, which is still 24 trillion miles away.



Featured image by Stuart Rankin,

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