The universe is estimated to contain ___ galaxies, each with approximately ___ stars.

100 billion galaxies; 100 billion stars

True or False: The Earth is the largest planet in the universe.

False; the Earth is one of the eight planets and is relatively small compared to many other celestial bodies.

The Big Bang Theory is also referred to as the ___ hypothesis.

Expanding universe

True or False: The steady-state theory posits that the universe has a definite beginning and end.

False; the steady-state theory suggests that the universe does not have a beginning or an end.

The Big Bang event is estimated to have occurred ___ billion years ago.

13.7 billion years ago

True or False: The universe has stopped expanding since the Big Bang.

False. The universe continues to expand even to the present day.

Stars are primarily composed of ___ and ___.

Hydrogen gas and helium

True or False: The apparent motion of stars from east to west is due to the rotation of the Earth on its axis from east to west.

False. The apparent motion is due to the rotation of the Earth on its axis from west to east.

The initial temperature of the gas clouds in which stars form is approximately ___°C.

-173°C

True or False: A protostar emits light.

False. A protostar does not emit light; it is a dark, dense mass of gas.

The red-giant phase occurs when a star exhausts its core hydrogen and begins converting it into ___ in the core.

Helium

True or False: A star's future after the red-giant phase is independent of its initial mass.

False. A star's future after the red-giant phase depends on its initial mass.

A star with a mass greater than 1.44 times the solar mass will end its life as a white dwarf. True or False?

False. A star with a mass greater than 1.44 times the solar mass will not become a white dwarf; it will end its life as a neutron star or black hole.

The process that occurs when the core of a red giant star shrinks and helium is converted into carbon is known as ___.

Nuclear fusion

A supernova explosion produces energy equivalent to that released by the Sun in ___ years.

100 years

True or False: A neutron star is less dense than a white dwarf star.

False - A neutron star is denser than a white dwarf star.

The first image of a supermassive black hole was obtained by the Event Horizon Telescope on ___ date.

10th April 2019

True or False: A black hole is formed when a massive star's core survives a supernova explosion.

True

Black holes are formed from the indefinite contraction of ___ under the action of their own gravity.

Neutron stars

True or False: Black holes can be observed directly through visible light.

False. Black holes cannot be seen because they do not allow light to escape.