Question

What is a dark matter and how can it been seen by us and what is a nebula blast?

Answer 1

Visible matter = all the stars, suns and solar system makes up only $5\%$ of the universe

Dark matter : Scientists found out that the galaxies does not have enough matter which can provide gravity enough to make spiral and stable galaxy. They found out that there is some matter which is invisible to humans and which helps in stability and shaping of the galaxies and this matter is known as dark matter. We cannot see it because it does not interact with light. Properties of dark matter are yet to be known. It is mysterious to all the scientists.

This colorful bubble is a planetary nebula called NGC 6818, also known as the Little Gem Nebula. It is located in the constellation of Sagittarius (The Archer), roughly 6,000 light-years away from us. The rich glow of the cloud is just over half a light-year across - humongous compared to its tiny central star - but still a little gem on a cosmic scale.

When stars like the sun enter "retirement," they shed their outer layers into space to create glowing clouds of gas called planetary nebulae. This ejection of mass is uneven, and planetary nebulae can have very complex shapes. NGC 6818 shows knotty filament-like structures and distinct layers of material, with a bright and enclosed central bubble surrounded by a larger, more diffuse cloud.

Scientists believe that the stellar wind from the central star propels the outflowing material, sculpting the elongated shape of NGC 6818. As this fast wind smashes through the slower-moving cloud it creates particularly bright blowouts at the bubble’s outer layers.

Hubble previously imaged this nebula back in 1997 with its Wide Field Planetary Camera 2, using a mix of filters that highlighted emission from ionized oxygen and hydrogen. This image, while from the same camera, uses different filters to reveal a different view of the nebula.