Why do galaxies have different shapes

This would be an example of our human-centered biases. Although many of them do resemble the Milky Way, others come in wildly different shapes and forms. Before we go any further, let's take a step back and talk about what all galaxies have in common.

Galaxies are complex systems held together by gravity. They're made up of gasses, stellar dust and millions — sometimes even billions — of stars, which are accompanied by their own planets and asteroid belts. Yet similarities aside, every galaxy has a unique story to tell. The history of each one is reflected in its shape. Scientists divide galaxies up into a handful of appearance-based categories.

The Milky Way is what's known as a spiral galaxy, meaning that it looks like a broad, flattened disc with a slight bulge protruding outward at its center. That arrangement is the product of rotation speed, time and gravity. To learn more, we talked to astrophysicist Raja GuhaThakurta, Ph.

It's a field that invites a lot of debate. Nonetheless, it's widely thought that most spiral galaxies begin their lives as spinning clouds of gas and dust. The speed at which they rotate matters a great deal. According to GuhaThakurta, massive, rapidly rotating clouds are more likely to become spiral galaxies. Gravity attempts to pull these spinning, amorphous bodies into flattened planes. Over time, the clouds are forced to contract because of gravity and loss of energy due to friction.

And due to a principle called the conservation of angular momentum , when a spinning object contracts, it rotates more rapidly. You can see this in action at your local skating rink. Experienced ice skaters know to increase their twirl speed by drawing their arms inward. The same physical forces also effect the look of the pointed "arms" that can be seen around the rims of such galaxies.

Rapidly rotating systems tend to have a ring of small, tight arms. In contrast, those that move more slowly have longer, loosely wrapped ones. To understand why, GuhaThakurta recommends trying a little home experiment: "Imagine stirring your coffee. Put a dollop of cream somewhere other than the center.

You'll notice that the cream will form a spiral pattern," he says. The processes and variables that were present in the creation of the galaxies and stars shed light on the formation of the universe in its present and future state. The heavens that look so familiar to us are actually an ever-changing and dynamic environment. Galaxies and stars form, evolve and change as surely as we do over our lifetime.

This life span is on a far greater scale, however, than we can easily fathom. Whereas evolution and processes of creating galaxies and stars are an ongoing operation, which to the untrained eye is nearly imperceptible, science has enabled us to get a greater understanding of the processes. In a seemingly lifeless cloud of gas and small objects, a galaxy is about to be born. That seemingly empty, cold mass of gaseous clouds holds the essential ingredients of a future galaxy.

This almost empty stagnant environment contains all the matter and energy to create a huge galaxy containing hundreds of thousands of powerful stars and planets.

There are several forces at work in huge primordial gas clouds. Gravity and centrifugal force being the most importent. With centrifugal force from the original Big Bang and moving at a half million miles per hour, this large area of gasses is spinning in unison. There are several theories on how this primordial gas comes together to form a galaxy.

The second theory claims galaxies were formed by several smaller clouds of gas merging into one. The third theory states that galaxies were formed by numerous small gas clouds merging into one. The centrifugal force of the spinning gas cloud along with the gravitational pull within the clouds work together to give a galaxy its shape.

All galaxies began with an elliptical shape, which is mostly a result of the centrifugal force of the spinning gas cloud. Like pizza dough being spun into the air the gas cloud flattens to a thin disk shape.

Only the small center of the galaxy retains a spherical shape do to its slow rate of rotation and density. This is an example of slow angular velocity at the center of the galaxy. Many Galaxies evolve into much more complex shapes. There are four types of galaxies. These four types or groupes are devided by their shape.

This classification system was developed by the astronomer Hubble and is named the Hubble classification. The four types of galaxies are spiral , barred spiral , elliptical , and irregular galaxies. A typical spiral galaxy contains about one hundred billion stars and is approximately one hundred thousand light years across.

Kaufman p. They are characterized as well as classified by the thickness of the central bulge. The spiral arms are made up of millions of relatively young stars in a constant orbit around the center of the galaxy.

Our Milky Way galaxy is an example of such a spiral galaxy. A barred spiral galaxy is charaterized by a destinct bar running through its nucleus. Like the spiral galaxy , the barred spiral galaxy has a central bulge containing the majority of mass in the galaxy.

The spiral arms in both a spiral galaxy and a barred spiral galaxy are formed by density waves that move threw the forming galaxy. He categorized galaxies in three ways:.

Spiral: Galaxies such as our own Milky Way that have a recognizable disklike shape, with arms that spread out from a rotating galactic center. Elliptical: Galaxies that form a single, signature ovoidal cloud, with irregular rotations. Irregular: Galaxies that hold to no particular recognizable shape or structure with no nucleus or discernible rotation pattern, essentially chaotic blobs of stars.

However, scientists have made great strides in theoretical and computational modelling of galaxies as they change over these long timescales, enabling our understanding of galaxy evolution to constantly progress. The Antennae Galaxies have been colliding and merging into a single galaxy for roughly million years.

This image combines X-ray, infrared, and visible light to show how the collision is making new stars and churning the gas in the galaxies into marvelous shapes. The physical processes involved in galaxy formation and evolution form an incredibly complex puzzle, operating at a extraordinary scale.

Scientists at the Institute for Theory and Computation ITC are working on this puzzle by combining simulations with real world observations to piece together the history of the Universe and to predict the fate of galaxies like the Milky Way. Our Milky Way and the Andromeda Galaxy are giant spiral galaxies hurtling towards each other at kilometers per second. In about 4 billion years, the two will meet. These two ghostly giants will pass through each other, but their gravity will stretch and pull the other until they merge into one massive elliptical galaxy.

Astrophysicists believe that the Sun will be pushed to the outskirts of the new galaxy, known as Milkomeda , with a chance of being ejected into deep intergalactic space. We see such mergers taking place today. The Antennae Galaxies are two spiral galaxies that have collided, resulting in increased star formation. It is believed that these galaxies will also eventually coalesce into a large elliptical galaxy.

By studying the shape and history of galaxies, we are also studying our future. Support Our Science. Utility Menu News Events.

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