What makes galaxy

Some believe that galaxies formed from smaller clusters of about one million stars, known as globular clusters , while others hold that galaxies formed first, and later birthed globular clusters. It's also difficult to figure out how many of a given galaxy's stars formed in situ from its own gas , versus forming in another galaxy and joining the party later. By letting astronomers peer into the universe's farthest reaches—and earliest moments—instruments such as NASA's James Webb Space Telescope should help resolve lingering questions.

All rights reserved. Galactic clusters and mergers Some galaxies occur alone or in pairs, but they are more often parts of larger associations known as groups, clusters, and superclusters.

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Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help. It has very strong gravity that pulls in everything around it. Photo by Ian Norman. There are many galaxies besides ours, though.

The The Hubble Space Telescope was launched in It orbits Earth and takes amazing pictures of stars, planets, and other galaxies. Some scientists think there could be as many as one hundred billion galaxies in the universe. This is the picture taken by the Hubble Space Telescope showing thousands of galaxies. Even the tiny dots are whole galaxies.

Stars are made of gas, but between the stars — in the so-called interstellar medium — large amount of gas reside as well. In small galaxies, there can be as much interstellar gas as star gas, while the fraction decreases with the size of the galaxy. The interstellar medium is divided into different phases. Some regions are diffuse and extremely hot, with temperatures of millions of degrees. In these regions, the gas is ionized , meaning that most atoms have had one or more electrons ripped off due to the high temperature.

The hotter the gas is, the higher the pressure, and the more it expands this is the same mechanism that makes a hot air balloon rise. This is where new stars are formed! In the Big Bang, practically only hydrogen and helium atoms were created, which I wrote more about in the article The Big Bang — an eyewitness account. Today about two percent of the total gas mass has been turned into metals, and about one third of these metals have clumped together as dust.

When a star is born, a disk of gas and dust forms around it. Dust may clump together, forming rocks that in turn, make bigger rocks that can eventually end up as planets. In the total mass budget, the planets play a diminishingly small role, but they are probably necessary for the existence of life, so they are quite exciting nonetheless.

Since the discovery of the first planets outside our Solar System a mere 25 years ago, it has become apparent that most stars have planets. We know now of more than 4, exoplanets i. In the center of most galaxies resides a 'supermassive black hole'. These black holes can weigh millions or billions times the mass of the Sun in astronomy everything is so massive that measuring stuff in grams or kilograms becomes impractical, so instead we use Solar masses, which is approximately the same as two billion billion trillion kilograms.

Sometimes these quasars can evacuate the galaxy of gas to such an extent that it quenches the formation of new stars. Dark matter differs from 'normal' matter in that it only interacts gravitationally. This means that it neither is affected by, nor exerts, electromagnetic or nuclear forces, so it cannot emit light, and it cannot collide with other things.

We cannot see it; we only see the effect it has on things that we can see, as it interacts gravitationally with the luminous matter. The normal matter can cool and become a dense galaxy, but the dark matter has a harder time clumping together, and is therefore located in a much larger 'halo' around the visible part of the galaxy.

Thus, what we see as a galaxy is in fact but a fraction of what a galaxy actually is. This figure shows the approximate dimensions of the components of the Milky Way. Galaxies come in a variety of shapes and appearances, but in general, we can organize them into three classes:.

Astronomers aren't certain exactly how galaxies formed. After the Big Bang, space was made up almost entirely of hydrogen and helium. Some astronomers think that gravity pulled dust and gas together to form individual stars, and those stars drew closer together into collections that ultimately became galaxies.

Others think that the mass of what would become galaxies drew together before the stars within them were created. Astronomers are also refining their techniques of measuring the mass of individual galaxies, such as this study that used the three-dimensional movements of several galaxies to better narrow down the Milky Way's mass. In the early s, many astronomers thought that the entire universe lay within our galaxy, the Milky Way.

Others, such as Harlow Shapley, a scientist and head of the Harvard College Observatory, argued that the spiral-shaped blobs thought to be dust and gas were separate and called them "island universes. It wasn't until , when Edwin Hubble identified several special pulsing stars called Cepheid variables and realized that they lay outside of the known span of the Milky Way.

These celestial objects were completely unique collections of stars at distances well beyond our home galaxy. After Hubble measured the distance to individual galaxies, he went on to measure their Doppler shift — how much light from the galaxies was stretched out due to their motion. He determined that galaxies all around the Milky Way are moving away from us at terrific speeds. The farther away the galaxies are, the faster they are fleeing.

Because of this, he was able to determine that the universe itself is expanding , and years later, astronomers determined that the expansion is accelerating. Most galaxies have black holes at their centers that can produce a tremendous amount of energy, which astronomers can see over great distances. Material circling the black hole may be accelerated outward by its jets.