Answer:
negative growth, rapid growth, slow growth and zero growth
Explanation:
Answer:
b. flat rotation curves in spiral galaxies
Explanation:
Dark matter accounts for majority of the matter in the universe (about 85%). It is considered to be composed of subatomic particles which are yet to be discovered. Dark matter cannot be observed because it does not emit light that can be detected. Only its gravitational effect is visible.
Astronomers when calculated the mass of the visible matter and tried to account for the observed speed of stars in the galaxy, there was a mismatch. To understand what caused this mismatch, astronomers gave name to the invisible matter as the Dark Matter.
The expected velocity of stars should decrease away from the near the center of the galaxy but a constant velocity of stars was observed that is a relatively flat rotation curve was obtained.
Thus, flat rotation curves in spiral galaxies in an evidence of Dark Matter.
-- Earth is one planet is a "Solar System", that consists of everything
that's gravitationally hooked to the Sun ... one star. This system contains
7 other other significant planets, more than 100 of their moons, and huge
numbers of comets, asteroids, dwarf planets, and countless bodies in a
giant shell that are so small and so far away that we can only see a few
of them so far. Every one of these items orbits the sun. The ones that
are farthest out may take thousands of years to complete one orbit.
That's the 'kingdom' of ONE star ... the sun.
-- It's very likely that there are similar gatherings of different-size objects
around MOST stars ... maybe ALL stars. Those objects are tremendously
difficult for us to see. We're just beginning to be able to see the most massive
planets that go with other stars, and already, something like a thousand of them
have been discovered. We know that they're there, but we can't see things like
their actual size or surface markings yet.
-- Stars are clumped in gatherings of several billion, called 'galaxies'.
Our sun is one of an estimated 300 to 400 billion stars in one galaxy,
which we call the "Milky Way Galaxy".
-- Astronomers estimate that there are billions of other galaxies.
So there are billions of billions of other stars, and most of them may
have several planets.
That's an awful lot of OTHER physical systems out there, that contain
other planets and moons.
Having trouble wrapping your mind around all of that ? Don't worry,
you're not the only one. It's easy for us to talk about it, but impossible
for our minds to actually understand it. It's just too big.
