Intergalactic Medium and Quasars

Intergalactic Medium

• The universe is not primarily composed of galaxies, but rather a vast intergalactic medium (IGM).
• The IGM is a vast expanse of gas and dust, primarily hydrogen and helium, spread throughout the universe.
• Galaxies are considered “rare islands” in the vast ocean of the IGM.
• The IGM serves as a source of raw materials for galaxies.
• Gravity draws gas from the IGM into galaxies, feeding their star formation.

Quasars

• Quasars are the most powerful objects in the universe.
• They are incredibly bright, shining with the power of a trillion stars.
• Quasars are found in the centers of some galaxies, acting as a central source of energy.
• They are small in comparison to galaxies, roughly the size of a grain of sand compared to the Amazon River.
• They can significantly affect their host galaxies, reshaping the surrounding cosmos.
• Quasars are powered by supermassive black holes.
• They are highly efficient engines of energy conversion, converting matter into energy 60 times more effectively than stars.

Quasar Discovery & Nature

• In the 1950s, astronomers detected mysterious radio waves originating from various points in the sky. These were termed “quasi-stellar radio sources” or “quasars”.
• Quasars appear as points of light, similar to stars, in radio waves.
• They emit high-energy X-rays, radio waves, and flicker.
• Because of their high speeds (30% the speed of light), quasars are believed to be distant objects.
• The distance to these objects implies that they are not stars but active galactic cores billions of light-years away.
• Quasars are thousands of times brighter than the Milky Way galaxy.

Quasar Evolution & Distribution

• Quasars are more common in the early universe.
• Their numbers peaked about 10 billion years ago.
• This suggests a period of heightened activity during the early universe, as galaxies and the universe were still forming.

Black Hole Powering

• The extreme luminosity of quasars cannot be explained by star formation alone.
• The immense energy output is attributed to supermassive black holes at the center of galaxies.
• The energy comes from the accretion disk, a massive disk of gas orbiting the black hole.
• The gravitational pull of the black hole creates friction and heat in the accretion disk, converting matter into energy.

Impact of Quasars & Stellar Formation

• The massive energy output from quasars can impact the surrounding gas, heating it up.
• This heated gas prevents the formation of new stars.
• Cold gas is required for star formation, as it readily collapses under gravity.
• Quasars also expel gas from galaxies, depleting their fuel supply for star formation.
• This process, while seemingly detrimental, could be beneficial for the development of life, as excessive star formation can lead to intense supernova activity, potentially sterilizing planets.

The Milky Way & Quasars

• It is unknown if the Milky Way went through a quasar phase.
• Studying distant quasars can provide insights into the history of the Milky Way.
• The Milky Way’s supermassive black hole, Sagittarius A*, may have grown to its current size (4 million times the sun’s mass) through a past quasar phase.
• Sagittarius A* could become a quasar in the future, possibly triggered by the merger of the Milky Way with Andromeda.

The Future of Quasars & Galaxies

• Galaxy mergers often lead to the formation of double quasars, as the supermassive black holes in each galaxy coalesce.
• This event provides fresh fuel for the black holes, increasing their activity.
• The merging of supermassive black holes would create a powerful and spectacular event.

Explore the fascinating concepts of the intergalactic medium (IGM) and quasars in this quiz. Learn about the composition of the universe, the role of the IGM, and the incredible power of quasars. This knowledge is vital to understanding the dynamics of galaxies and their formation.