1. Which of the following statements is/are correct?
1. The universe is mostly consisted by the baryonic matter.
2. Only 5 percent of the universe is the normal matter.
3. The dark energy can be a property of space or a kind of dynamical energy fluid.
Select the correct option using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Correct Option: (b)
Explanation:
Dark energy and matter
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein’s gravity theory, the version that contains a cosmological constant, makes a second prediction: “empty space” can possess its own energy.
Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energyof- space would appear. As a result, this form of energy would cause the universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the
universe.
Another explanation for how space acquires energy comes from the quantum theory of matter. In this theory, “empty space” is actually full of temporary (“virtual”) particles that continually form and then disappear.
Another explanation for dark energy is that it is a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the universe is the opposite of that of matter and normal energy. Some theorists have named this “quintessence,” after the fifth element of the Greek philosophers. But, if quintessence is the answer, we still don’t know what it is like, what it interacts with, or why it exists. So, the mystery continues.
It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter (baryonic matter) - adds up to less than 5% of the universe. In short, we are unsure about what’s there in 95% of the universe.
2. Which of the following conditions are prerequisite for a celestial body to qualify a planet as per the International Astronomical Union?
1. It must orbit a star.
2. It must have a spherical shape.
3. It must have at least one moon.
Select the correct option using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Correct Option: (a)
Explanation:
Planets
The most recent definition of a planet was adopted by the International Astronomical Union in 2006. It says a planet must do three things:
It must orbit a star (in our cosmic neighbourhood, the Sun).
It must be big enough to have enough gravity to force it into a spherical shape.
It must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun.
Moons, also known as natural satellites — orbit planets and asteroids.There are more than 200 moons in our solar system. Most orbit the giant planets — with Saturn and Jupiter leading moon counts — but even smaller worlds like Pluto can have five moons in orbit. Both Mercury and Venus do not have any moon but they are planets. Hence, having moons does not qualify a planet.
3. Which of the following statements regarding the dark matter are correct?
1. The evidences indicate that the dark matter cannot be baryonic matter.
2. It is dark because the light cannot escape from it.
3. The dark matter may predate the Big Bang.
Select the correct option using the codes given below:
(a) 1 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2, and 3
Correct Option: (c)
Explanation:
Dark Matter
For the first 150 million years after the Big Bang, there were no galaxies or stars or planets. The universe was featureless. As time passed, the first stars formed. Stars collected into galaxies. Galaxies began to
cluster together. Those clusters are made up of the galaxies and all the material between the galaxies. Clumps of matter in smashed into each other, and the planets in our solar system began to form around the sun.Something must hold our solar system, galaxies and clusters of galaxies together. And gravity is that “glue.”In some clusters, the space between galaxies is filled with gas so hot, scientists cannot see it using visible light telescopes. The gas only can be seen as X-rays or gamma rays. Scientists look at that gas and measure how much there is between galaxies in clusters. By doing this, they discovered that there must be five times more material in the clusters than we can detect. The invisible matter that we can’t detect is called “dark
matter.”
The nature of dark matter is unknown. A substantial body of evidence indicates that it cannot be baryonic
matter, i.e., protons and neutrons.
The favoured model is that dark matter is mostly composed of exotic particles formed when the universe was a fraction of a second old.
Such particles, which would require an extension of the so-called Standard Model of elementary particle physics, could be WIMPs (weakly interacting massive particles), or axions, or sterile neutrinos.
The non-baryonic candidates can be grouped into three broad categories: hot, warm and cold.
Hot dark matter refers to particles, such as the known types of neutrinos, which are moving at near the speed of light when the clumps that would form galaxies and clusters of galaxies first began to grow.
Cold dark matter refers to particles that were moving slowly when the pre-galactic clumps began to form, and warm dark matter refers to particles with speeds intermediate between hot and cold dark matter.
The name dark matter refers to the fact that it does not appear to interact with observable electromagnetic radiation, such as light.Dark matter interacts with the rest of the universe only through its gravity.
The new study done by the researchers of the John Hopkins university reveals that the dark matter existed even before the Big Bang. The theory says that after the Big bang, dark matter influenced the way regular matter clumped together. This resulted in the formation of galaxies and the clusters.
4. Which of the following statements is/are correct?
1. Singularities are regions of space where the curvature of spacetimebecomes infinite.
2. Within the event horizon, the escape speed is less than the speed of the light.
3. All black holes contain singularities.
Select the correct option using the codes given below:
(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2, and 3
Correct Option: (c)
Explanation:
Black hole
The basic structure of a black hole consists of a singularity hidden by an event horizon.
Within the event horizon, the escape speed (vesc) exceeds the speed of the light (c) and an object is trapped forever. Outside the event horizon, vesc< c and the object is able to escape.
The ‘event horizon’ is the boundary defining the region of space around a black hole from which nothing (not even light) can escape.
5. Which of the following statements regarding the Schwarzschild radius is/ are correct?
1. The Schwarzschild radius of an object is inversely proportional to the mass.
2. Any object whose radius is smaller than its Schwarzschild radius is called a black hole.
3. It was discovered by Einstein during solving the theory of general relativity in 1916.
Select the correct option using the codes given below:
(a) 2 only
(b) 1 and 3 only
(c) 3 only
(d) 1, 2, and 3
Correct Option: (a)
Explanation:
Schwarzschild radius
The Schwarzschild radius (sometimes historically referred to as the gravitational radius) is a physical parameter that shows up in the Schwarzschild solution to Einstein’s field equations, corresponding to the radius defining the event horizon of a Schwarzschild black hole. It is a characteristic radius associated with every quantity of mass.
The Schwarzschild radius was named after the German astronomer Karl Schwarzschild, who calculated this exact solution for the theory of general relativity in 1916.
The Schwarzschild radius of an object is proportional to the mass.A small mass has an extremely small Schwarzschild radius.
Any object whose radius is smaller than its Schwarzschild radius is called a black hole.The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body (a rotating black hole operates slightly differently). Neither light nor particles can escape through this surface from the region inside, hence the name “black hole”.