How do you classify a spiral galaxy?

Spiral galaxies are classified as Sa/SBa, Sb/SBb or Sc/SBc (classic/barred) according to the tightness of their spiral, the clumpiness of their spiral arms, and the size of their central bulge. These differences can be traced back to the relative amounts of gas and dust contained within the galaxies.

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Then, what are the most plentiful galaxies in the universe?

Elliptical galaxies are the most abundant type of galaxies found in the universe but because of their age and dim qualities, they're frequently outshone by younger, brighter collections of stars. Elliptical galaxies lack the swirling arms of their more well-known siblings, spiral galaxies. Moreover, can we see black hole from earth? Scientists can't directly observe black holes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation. We can, however, infer the presence of black holes and study them by detecting their effect on other matter nearby.

Could there be life in the galaxies nearest to the Milky Way?

The galaxies that are nearest to the Milky Way are mostly small galaxies that aren't very bright. This is not to say that there couldn't be life in these galaxies. However, the most favorable galaxies for life are probably those like the Milky Way-big, bright spiral galaxies. Do wormholes in space exist? Einstein's theory of general relativity mathematically predicts the existence of wormholes, but none have been discovered to date. A negative mass wormhole might be spotted by the way its gravity affects light that passes by.

You can also ask is time travelling possible?

In Summary: Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second.