Our Future Night Sky is Dark
Do not worry, this title is not philosophical, it is purely technical. It is a conclusion from the current estimation of cosmological parameters. The observational cosmology has entered in the era of high precision measurements. Now we are able to cover all the electromagnetic spectrum form radio to X-rays. We have telescopes for each band, some on the ground and some are orbiting to the Earth. Recently, we have move towards the observations beyond EM waves. The detection of gravitational waves at LIGO has opened the window for the gravitational wave astronomy. Now, the cosmologist have a large amount of high precision data. This can be used to estimate the cosmological parameters like the current expansion rate (Hubble constant), fraction of dark matter, dark energy and other components, age of the Universe, etc.
The current estimation of the energy budget of the Universe suggest that around 95% is from dark sectors (dark energy and dark matter), and only 5% is luminous matter. Clearly, the universe is presently dominated by dark energy. This component impose a negative pressure and accelerating the expansion of the Universe. Other components impose positive gravity, and were responsible for deceleration in the expansion of the Universe. The dark matter was responsible for the clustering of baryonic matter (luminous matter) and only because of its presence all the structure we see today e.g. stars, galaxies, clusters, were formed. We can see the whole expansion history of the Universe from origin (Big Bang) to present accelerated expansion in the figure.
The accelerated expansion was first found in the observation of explosion of white dwarf star called Supernova-Ia in late 90’s. Later it was also conformed in the observation of cosmic microwave radiation and Baryon acoustic oscillations. Now, it is a well established fact that the Universe is dominated by dark energy and expanding at accelerated expansion. Therefore, all objects those are not gravitationally bound with each other are going away from each other at exponentially increasing rate. This suggest that in future we will see very few objects in the night sky. Our night sky will be mostly dark, apart from moon, planets, stars from the Milky Way, and other gravitationaly bounded object.
By
Dr. Avinash Singh
Department of Physics,
Kalinga University, Naya Raipur
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