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9 votes

Why does Helix Nebula look like an eye?

Look at Helix Nebula NGC 7293 (Aquarius) on the left and Ring Nebula M57 (Lyra) on the right. Both are of the planetary nebula type, and very similar. This NASA video, based on Hubble Space Telescope ...
Albert's user avatar
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3 votes

How can $\Omega_m<1$ indicate an infinitely expanding universe?

I studied that if $\Omega=\frac{\rho}{\rho_c}$, which is the sum of the three is greater than one, the universe eventually collapses, if exactly one, its flat and if less than 1, it keeps expanding. ...
Sten's user avatar
  • 4,694
3 votes

Why does Helix Nebula look like an eye?

Prior to the formation of the Helix Nebula, there was a star similar to our own Sun in its post-main sequence stage. Eventually, this star consumed its entire fuel supply, which caused fusion to cease ...
4NT4R3S's user avatar
  • 1,015

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