Largest map of universe

•  Astronomers have created the first map of the large-scale structure of the universe based entirely on the positions of quasars.
• These quasars are so far away that their light left them when the universe was between three and seven billion years old, long before the Earth even existed.
• During the first two years of the Sloan Digital Sky Survey’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars.
• The telescope’s observations gave the team the quasars’ distances, which they used to create a three-dimensional map of where the quasars are. However, to use the map to understand the expansion history of the universe they used technique of “baryon acoustic oscillations” (BAOs).
• BAOs are the present-day imprint of sound waves which travelled through the early universe, when it was much hotter and denser than the universe we see today. However, when the universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place. These frozen waves are left imprinted in the three- dimensional structure of the universe.

What are Quasars?

• Quasars are extremely distant objects in our known universe. They are the furthest objects away from our galaxy that can be seen.
• Quasars are extremely bright masses of energy and light. The name quasar is actually short for quasi-stellar radio source or quasi-stellar object.
• Quasars emit radio waves, x-rays and light waves. Quasars appear as faint red stars to us here on Earth.
• A quasar is believed to be a supermassive black hole surrounded by an accretion disk. An accretion disk is a flat, disk-like structure of gas that rapidly spirals around a larger object, like a black hole, a new star, a white dwarf, etc.
• When a galaxy, star or gas is absorbed into a quasar in such a way, the result is a massive collision of matter that causes a gigantic explosive output of radiation energy and light. This great burst of energy results in a flare, which is a distinct characteristic of quasars.
• The light, radiation and radio waves from these galaxies and stars being absorbed into a black hole travel billions of light years through space. When we look at quasars which are 10-15 billion light years away, we are looking 10-15 billion years into the past.

How Quasars are helpful?

• Quasars are the incredibly bright and distant points of light powered by super-massive black holes.
• Because quasars are so bright, we can see them all the way across the universe
• That makes them the ideal objects to use to make the biggest map yet
• The amazing brightness of quasars is due to the super-massive black holes found at their centres.
• As matter and energy fall into a quasar’s black hole, they heat up to incredible temperatures and begin to glow. It is this bright glow that is detected by a dedicated 2.5-metre telescope on Earth

By: Vishal