Galaxies
Describe how galaxies are formed.
The universe is made of clusters of galaxies, and clusters of clusters of galaxies, called super clusters. Galaxies are comprised of tens of millions of stars. Between the stars, there are interstellar clouds of gas and dust. The smallest galaxies are called dwarfs while the largest are called giants.
Our Milky Way Galaxy is one of three large galaxies in the Local Group of Galaxies. The other large galaxies are the Andromeda Galaxy, and Messier 33, also in the Local Group are many dwarf galaxies. Several of these dwarf galaxies orbit around the large galaxies. The Milky Way has two prominent satellite galaxies, called the Large and Small Magellanic Clouds.
The Local Group is a few million light-years across. Larger clusters of galaxies can contain hundreds of galaxies. Galaxies within a cluster are bound together by their gravitational pulls. They each orbit around a common centre of mass. Because the density of galaxies is high within clusters, galaxy collisions can occur.
The largest nearby cluster of galaxies is the Virgo Cluster. The Virgo Cluster contains about a thousand galaxies, and spans about ten million light-years. The enormous gravity of the Virgo Cluster makes it the centre of a larger structure, called the Local Super cluster. This collection of nearly 100 clusters stretches across a hundred million light-years.
Describe the radiation emitted by galaxies.
We see fluorescent light emitted by gas ionized by hot stars. These gas clouds are the site of newly born stars. The light from both stars and gas is dimmed to some extent by dust within the galaxy's interstellar medium. Galaxies contain a black hole at the centre so the dense central galaxy provides material which accretes onto the black hole which releases a large amount of gravitational energy. Part of the energy in this plasma is emitted as x-rays, gamma rays and visible light.
Explain what is meant by the term Active Galactic Nucleus (AGN)
The universe is made of clusters of galaxies, and clusters of clusters of galaxies, called super clusters. Galaxies are comprised of tens of millions of stars. Between the stars, there are interstellar clouds of gas and dust. The smallest galaxies are called dwarfs while the largest are called giants.
Our Milky Way Galaxy is one of three large galaxies in the Local Group of Galaxies. The other large galaxies are the Andromeda Galaxy, and Messier 33, also in the Local Group are many dwarf galaxies. Several of these dwarf galaxies orbit around the large galaxies. The Milky Way has two prominent satellite galaxies, called the Large and Small Magellanic Clouds.
The Local Group is a few million light-years across. Larger clusters of galaxies can contain hundreds of galaxies. Galaxies within a cluster are bound together by their gravitational pulls. They each orbit around a common centre of mass. Because the density of galaxies is high within clusters, galaxy collisions can occur.
The largest nearby cluster of galaxies is the Virgo Cluster. The Virgo Cluster contains about a thousand galaxies, and spans about ten million light-years. The enormous gravity of the Virgo Cluster makes it the centre of a larger structure, called the Local Super cluster. This collection of nearly 100 clusters stretches across a hundred million light-years.
Describe the radiation emitted by galaxies.
We see fluorescent light emitted by gas ionized by hot stars. These gas clouds are the site of newly born stars. The light from both stars and gas is dimmed to some extent by dust within the galaxy's interstellar medium. Galaxies contain a black hole at the centre so the dense central galaxy provides material which accretes onto the black hole which releases a large amount of gravitational energy. Part of the energy in this plasma is emitted as x-rays, gamma rays and visible light.
Explain what is meant by the term Active Galactic Nucleus (AGN)