We are not the only galaxy that means we are the only being in this big huge universe. There are several other planet and galaxies in this huge universe. Milky Way galaxy is the home of our Solar System. It is a
barred spiral galaxy about 100,000-120,000 light-years in diameter containing
about 300 ± 100 billion stars. It may contain at least as many planets. Its
thickness is about 1,000 light-years. The age of our galaxy is about 13.2
billion years. Figure 1a is a mosaic of Earth-based images showing the plane of
the Milky Way galaxy.
Solar systems are thought to form from protoplanetary discs of gas and dust around newly formed stars. They form from the coalescence of clumps of material that sweep out lanes forming dark rings in the disc. Figure 1b is an image of a protoplanetary disc probably during planet formation.
The present-day formation rate of stars with the Sun’s mass is estimated to be 0.68-1.45 Msun/yr [2]. If the present rate is similar to the past rate, then about 9-19 billion solar mass stars formed between 13.2 billion years ago and the present. The lifetimes of stars depends on their mass (Figure 1c). Stars with similar masses to our Sun have lifetimes of about 10 billion years. Therefore, between 2.2 and 4.6 billion of those stars have exceeded their lifetimes and no longer exist. “A technological civilization on any planets around these stars would have been destroyed, moved to some other habitable planet around another star or continuously live in an artificial spacecraft”.
Recently a very old star with Earth-sized planets has been discovered by the Kepler spacecraft [3]. Kepler-444, a metal-poor Sun-like star has an age of 11.2 ± 1.0 Gyr and 5 planets with sizes between those of Mercury and Venus. Therefore, Kepler-444 formed when the Universe was less than 20% of its current age. This indicates there were enough heavy elements in the early history of the Universe to form terrestrial-like planets. Therefore, Earth-like planets formed throughout most the Universe 13.8 Gyr history. Figure 2d is a diagram showing a comparison of the Kepler-444 system to other planetary systems. The Solar System is located in the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm (Figure 1e and 1f). It is about 28,000 light-years from the galactic center; located about 75,000 light years from the farthest edge and about 25,000 light years from the nearest edge (Figure 1e). The light we see today from the galactic center and nearest edge was emitted long before civilization began about 12,000 years ago.So the above data help us to find out that we are not the only one in big universe. We have brothers and sisters too maybe!!!!
Solar systems are thought to form from protoplanetary discs of gas and dust around newly formed stars. They form from the coalescence of clumps of material that sweep out lanes forming dark rings in the disc. Figure 1b is an image of a protoplanetary disc probably during planet formation.
The present-day formation rate of stars with the Sun’s mass is estimated to be 0.68-1.45 Msun/yr [2]. If the present rate is similar to the past rate, then about 9-19 billion solar mass stars formed between 13.2 billion years ago and the present. The lifetimes of stars depends on their mass (Figure 1c). Stars with similar masses to our Sun have lifetimes of about 10 billion years. Therefore, between 2.2 and 4.6 billion of those stars have exceeded their lifetimes and no longer exist. “A technological civilization on any planets around these stars would have been destroyed, moved to some other habitable planet around another star or continuously live in an artificial spacecraft”.
Recently a very old star with Earth-sized planets has been discovered by the Kepler spacecraft [3]. Kepler-444, a metal-poor Sun-like star has an age of 11.2 ± 1.0 Gyr and 5 planets with sizes between those of Mercury and Venus. Therefore, Kepler-444 formed when the Universe was less than 20% of its current age. This indicates there were enough heavy elements in the early history of the Universe to form terrestrial-like planets. Therefore, Earth-like planets formed throughout most the Universe 13.8 Gyr history. Figure 2d is a diagram showing a comparison of the Kepler-444 system to other planetary systems. The Solar System is located in the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm (Figure 1e and 1f). It is about 28,000 light-years from the galactic center; located about 75,000 light years from the farthest edge and about 25,000 light years from the nearest edge (Figure 1e). The light we see today from the galactic center and nearest edge was emitted long before civilization began about 12,000 years ago.So the above data help us to find out that we are not the only one in big universe. We have brothers and sisters too maybe!!!!
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