What Is An Interstellar Cloud? (EXPLAINED!)

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The term “interstellar” literally means between the stars and describes the regions of space between solar systems. These areas contain sparse collections of gas, dust, and plasma. Interstellar clouds are the areas where this space material is more highly concentrated and the place where many stars are born.

Continue reading to explore interstellar clouds, how they are formed, what they are made of, and why they are important to us.

How Are Interstellar Clouds Formed?

Interstellar clouds are denser-than-average regions of space where gas, dust, and plasma gather in the areas between star systems. They exist in the interstellar regions of space, i.e., the areas of space between galaxies and star systems, and can stretch for thousands of light years.

They form in areas where gas and dust are more highly concentrated. This could be leftover material from the big bang or concentrated clouds created by a star’s end-of-life process (such as a supernova explosion).

We can determine the chemical composition of interstellar clouds by studying the radiation they emanate from radio waves to gamma rays.

Most of the interstellar clouds that scientists observe are large and easy to spot, but there are likely millions of other smaller clouds that we are yet to discover. There is 85% of our Universe that we cannot see, and scientists believe that some of these areas could contain Interstellar clouds.

Are We Inside An Interstellar Cloud?

Looking at the Milky Way, you’ll see a littering of dark strips. These are caused by interstellar clouds, where the collections of gas and dust are too dense for light to pass through effectively.

Our local interstellar cloud is also known as “local fluff.” It is an “Emission Type Nebula” consisting of supernova remnants mixed with cold neutral atoms. Emission nebulae are so-called because they emit their own light via the ionizing radiation of young stars within them.

The ionized particles in our local interstellar cloud are exceptionally hot, with some reaching temperatures exceeding 1,000,000 degrees Celsius. However, the overall temperature is relatively low because the particles are spread out at an average of 0.3 particles per cubic centimeter, which means you could stand right in the middle of it and barely feel any heat at all.

Due to the sparsity of our local interstellar cloud, it is dim and difficult to see (even with our best scientific instruments). Still, we know that the cloud spans a width of around 30 light-years, and we are slowly moving through it, and we’ll leave it entirely in approximately 20,000 years.

This is because our Sun moves in a different direction from the interstellar cloud. As we move through the cloud, our Sun utilizes its magnetic field to push ionized particles around our entire solar system. This creates a “magnetotail” in the wake of its path, and we can see these tails across the Universe.

We can’t see the magnetotail of our own solar system because we are inside it, which makes it challenging to observe.

However, the Sun’s magnetic field moves only the ionized particles. Other neutral particles pass right through our solar system as we travel through the interstellar cloud – these particles can help us determine the local cloud’s movement and direction.

In doing this, we can better understand the space environment around us and help protect astronauts traveling into space.

What Are Interstellar Clouds Made Of?

“Interstellar medium” is any material found between stars. This consists of roughly 99% interstellar gas and 1% interstellar dust. This material is very low density with only one atom per cubic cm (compared to 10^19 atoms per cubic cm on Earth)

Interstellar clouds describe the regions of this interstellar medium where the gas and dust clump together in higher concentrations. And we can see these regions because their density makes it harder for light to pass through, and thus, they appear darker.

The composition of these clouds is relevant to astronomers because their makeup can cause “red shifting.” Astronomers use the term redshift to describe the effect of mass on light wavelengths. When light passes through interstellar clouds, its wavelength is stretched or “shifted” towards the red end of the color spectrum.

Common gases found within interstellar clouds are hydrogen and nitrogen, known to cause a red shift through Rayleigh Scattering. The presence of these gases is also crucial for star formation.

Are Stars Born In Interstellar Clouds?

Scientists generally agree that stars are born within interstellar clouds, but there is yet to be a universal understanding of how this occurs.

We know that stars form within dense concentrations of gas and dust known as nebulas or interstellar clouds. These clouds can be leftover collections of gas and dust from the big bang or the remnants of a supernova explosion.

Universal gravitational law states that every particle in the Universe exerts a force of attraction on every other particle. In an interstellar cloud, this means that over time the particles will begin to clump together; as the mass grows, so does its gravitational field.

Eventually, this mass reaches a critical point where its gas pressure crosses the cloud’s (or nebula’s) gravity. When this happens, the cloud begins to collapse in on itself; this triggers nuclear fusion with the cloud’s most abundant element (molecular hydrogen), which then gives birth to a star.


We are currently traveling through an interstellar cloud, otherwise termed “local fluff.” Clouds like this are regions of space with a denser concentration of material, making it possible for star formation. Many of these clouds are leftover material from the big bang or can be created from the remnants of dying stars.

Our Sun protects us from ionized particles while the neutral ones zoom right past our planet. And, as we travel in different directions, we will one day leave this interstellar cloud altogether.


Interstellar cloud – Wikipedia

Star Formation (uoregon.edu)

(6) Where And How Are Stars Born? – YouTube

Are We Actually In A Nebula? – YouTube

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