< General Studies Home Page < Space

Content

• Galaxy
• Our Solar System
• Planeta, Dwarf Plants & Other Celestial Bodies
• Moon
• Planets with Highest Number of Moon
• Asteroids
• Gravitational Lensing
• Sun
• Life Cycle of Stars: Stars – Dwarf Stars – Neutron Stars – Black Holes

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1)  Galaxy

• Galaxies are like building blocks of Universe.
• A galaxy is huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by their gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle.
• When we look up at the stars in the night sky, we see other stars in the Milky Way.
• There are many galaxies besides ours. Some scientists estimate the total number of galaxies to be as much as one hundred billion.

2) OUR SOLAR SYSTEM

• Planets
  • 8 (My Very efficient mother just served us nuts)
  • Venus is considered as ‘Earth’s twin‘ because its size and shape are very much similar to that of earth
  • Pluto: Till recently (August 2006) was called a planet. However, in a meeting of International Astronomical Union, a decision was taken that Pluto like other celestial objects (Ceres, 2003 UB₃₁₃) discovered in recent past may be called a dwarf planet’.

Inner Planet : Mercury, Venus, Earth, Mars (very close to sun, made of rocks). They are called inner planets as they lie between the sun and the belt of asteroids. They are also called terrestrial planets, meaning earth like as they are made up of rock and metals, and have relatively high densities.

Outer Planet: Jupiter, Saturn, Uranus, Neptune. They are called outer planets. They are also known as Jovian or Gas planets. Jovian means Jupiter like. Most of them are much larger than the terrestrial planet and have a thick atmosphere, mostly of helium and hydrogen.

• The difference between terrestrial and Jovian planets can be attributed to the following conditions.
  1. The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location.
  2. The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds are not all that intense to cause similar removal of gases from the Jovian planets.

The terrestrial planets are smaller and their lower gravity could not hold the escaping gas.

3) PLANETS, DWARF PLANTS AND OTHER CELESTIAL BODIES

4)  MOON

• It is Earth’s only natural satellite
• Size: 1 km (Radius)
• Distance: 3,84,400 km away from earth
• Only one side visible
  • The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on earth.

5)  PLANETS WITH HIGHEST NUMBER OF MOON

• SATURN

6)  ASTEROIDS

• Apart from the stars, planets and satellite, there are numerous tiny bodies which also move around sun. These bodies are called asteroids. They are found between orbits of Mars and Jupiter. Scientists are of the view that asteroids are parts of a planet which exploded many years back.

A) Near Earth Asteroid:

• About Near Earth Objects
  • NEOs are comets and asteroids nudged by the gravitational attraction of nearby planets into orbits which allows them to enter the Earth’s neighborhood. They occasionally approach close to the Earth as they orbit the sun.
  • NASA’s Center for Near-Earth Object Study (CNEOS) determines the times and distances of these objects as and when their approach to the Earth is close.
• Significance of Near-Earth Objects:
  • Scientific interest in comets and asteroids is largely due to their status as relatively unchanged remnant debris from the solar system formation process over 4.6 billion years ago. Therefore, they can give clue regarding original conditions which led to formation of planets.
  • Further, an asteroid is considered as one of the existential dangers for life on earth. Therefore, it’s important to study these near-earth objects and prepare to ward off any future hit.
• When is an Asteroid considered PHA (Potentially hazardous asteroid)?
  • Asteroids with a minimum orbit intersection distance (MOID) of about 05 AU (i.e. roughly 7,480,000 km or less and a diameter more than 150 meters is considered PHAs.
  • Note: It is not necessary that asteroids classified as PHAs will necessarily impact the earth. It only means that there is a possibility of such threat.

B)  Psyche

• About Psyche Asteroid:

• • Psyche is one of the asteroids in the asteroid belt. What makes the asteroid unique is that it appears to be the exposed nickel-iron core of an early planet, one of the building blocks of our solar system.
• About Psyche Mission:
  • The Psyche Mission is a NASA space mission launched on 13^th Oct 2023 to explore origin of planetary cores by orbiting and studying the metallic asteroid Psyche in 2029. The mission consists of Psyche Aircraft.
• Significance:
  • Understanding the Core of a Planet: Deep within rocky terrestrial planets – including Earth – scientists infer the presence of metallic cores. But these remain unreachably far below the planets’ rocky mantles and crusts. Psyche offers a unique window into the violent history of collisions and acceleration that created terrestrial planets.
  • Science Goals include:
    • Understand a previously unexplored building block of planet formation: Iron cores.
    • Look inside terrestrial planets, including Earth, by directly examining the interior of a different body, which otherwise couldn’t be seen.
    • Explore a new type of world made of metal (and not of rock and ice)
  • Science Objectives:
    • Understanding Psyche – Whether it is a core, or if it is an unmelted material, relative ages of psyche’s surface
  • Deep Space Optical Communication (DSOC): The Psyche mission is also testing a sophisticated new laser communication technology that encodes data in photons at near-infrared wavelength (rather than radio waves) to communicate between a probe in deep space and Earth.

7)  GRAVITATIONAL LENSING

• Basics
  • Gravity bends the time-space around us. And since light travels through space, it also bends while passing through this bent time space.
  • This bending of light creates the same effect as the bending of light through a glass lens and the phenomenon is called gravitational lensing (i.e. lensing effect created by gravity). Einstein first predicted gravitational lensing in 1912 and is an effect of his theory of general relativity.

• It is clearly observable when gravitational force is high (i.e. bending of space-time is high) such as in case of large galaxies or cluster of galaxies. Thus, large galaxies can behave like large natural telescopes.
• Applications
  • Scientists use this phenomenon to study distant stars/galaxies in Universe which would otherwise have been difficult to see even by the most powerful space telescopes. The image of the distant object would be magnified if there is a gravitational source (like a large galaxy) in the path.
  • The phenomenon also helps us in understanding the origin of a galaxy/star as we can observe light from distant stars when there were still getting formed.
    • For e.g. NASA under its TEMPLATES initiative is using gravitational lensing to study how galaxies are forming stars and how the star formation is distributed across galaxies.
• It also helps us in studying of super massive blackholes at cosmological distance.

8) Sun

A) Basics About Sun

• Distance: 150 million km away from earth
• Radius: 696,000 km

B)  Sun’s Structure – 3 Atmospheric LAYERS

• Sun has six layers. The core, radiative zone and convection zone consist of the inner layers or the parts of the sun which is not visible. Photosphere, Chromosphere and Corona comprise of the sun’s atmosphere or outer layer.
• Inner Layer
  1. Core: It is the innermost layer of sun. The Core is Plasma, but its movement is extremely similar to gas. The temperature in Sun’s core is nearly 15-million-degree Celsius. 
  2. Radiative Zone: It is the second layer of sun and sits outside the core. This zone has temperature of millions degree Celsius. The layer serves as a passage for all the energy that is released by the core.
  3. Convection Zone: It is the outermost layer and completely surrounds Radiative zone. In this layer, all the hot material found near the center of the Sun rises cools down and drops back into the radiative zone to get more heat. This is the movement that creates sunspot and Solar flares.
• Outer Layers:
  1. Photosphere is the deepest layer of the sun that we can observe directly. It reaches from the surface to about 250 miles above that. Temperature varies from about 6700-degree Celsius to 3,700-degree celsius. Most of the photosphere is covered by granulations (caused by convection current) of the plasma within the Sun’s convective zones. 
  2. Chromosphere: The chromosphere is a layer in the Sun between about 250 miles and 1300 miles above the solar surface (the photosphere). The temperature in the chromosphere varies between (3700 (lowest temperature) at the bottom to 7700-degree C at the top), so in this layer (and higher layers) it actually gets hotter if you go further away from the sun, unlike in the lower layers, where it gets hotter if you go closer to the centre of the sun.
  3. Transition Zone: The transition region is very narrow (60 miles / 100 km) layer between the chromosphere and the corona where the temperature rises abruptly from about 7700-degree celsius to 5,00,000-degree C)
  4. Corona: It is the outermost layer of the Sun, starting at about 13,00 miles above the solar surface (the photosphere). The temperature in the Corona is 5,00,000-degree celsius or more upto a few million-degree celsius. It can’t be seen with naked eyes except during a total solar eclipse or with use of a coronagraph. It doesn’t have any upper limit.

C) Understanding Solar Winds

• The solar wind is a stream of charged particles released from the upper atmosphere of the sun, the Coron The solar wind streams plasma (a mix of positively and negatively charged particles) and particles from the sun out into space.
• Cause
  • The temperature of Corona reaches upto 1.1-million-degree celsius (2-million-degree Fahrenheit).
  • As rising heat and pressure push that material away from the Sun, it reaches a point where gravity and magnetic field are too weak to contain it. That point, known as the Alfven Critical Surface, marks the end of Solar Atmosphere and beginning of Solar Wind.
• Why does the property of solar winds change with time?
  • The sun’s activity shifts over the course of its 11 year cycle, with sun spot numbers, radiation levels, and ejected material changing over time.
  • The wind also differs based on where on the sun it comes from and how quickly that portion is rotating.
  • As the plasma material leaves the sun, carried by solar wind, it becomes more gas-like.
• How does it affect the earth?  
  • As the wind travels off the sun, it carries charged particles and magnetic clouds. This is constantly hitting our planet with interesting effects.
  • If the solar wind reached the earth’s surface, its radiation would do severe damage to any life that might exis They can affect Earth’s satellite and the Global Positioning Systems (GPS).
  • But earth’s magnetic field acts as shield, redirecting the material around the planet so that it streams beyond it.
  • The force of the wind stretches out the magnetic field so that it is smooshed inward on the sun-side and stretched out on the night side.
  • Solar Storms (Coronal Mass Ejections – CMEs)
    • Sometimes, especially during the active period of the cycle – known as the solar maximum, the sun spits out large burst of plasma known as Coronal mass ejections (CMEs). These have stronger effect than the standard solar wind.
    • When the solar wind carries CMEs and other powerful bursts of radiation into a planet’s magnetic field, it can cause the magnetic field on the back side to press together, a process known as Magnetic Reconnection.
    • Charged particles in case of magnetic reconnection stream back towards the planet’s magnetic poles, causing beautiful displays known as the aurora borealis in the upper atmosphere.
  • About Auroras
    • In the north the phenomenon is called the aurora borealis or the northern light. In the southern hemisphere, it’s the aurora australis, or southern lights.
    • Even though the earth’s magnetic field stretches symmetrically from the north to the south, recent satellite images of the entire planed showed mismatched auroras happening at the same time in the two hemispheres.
    • Why? Our magnetic field is squeezed asymmetrically by solar winds approaching from an angle, twisting and displacing the northern and southern lights in different forms and locations.
    • Useful video to understand Auroras: https://youtu.be/PgIKsuZ3RZU

9)  Life Cycle of Stars: Stars – Dwarf Stars – Neutron Stars – Black Holes

A) Life Cycle of a Star

• • Where a star ends up at the end of its life depends on the mass it was born with.
    • Stars with lots of mass may end their lives as black holes or neutron stars.
    • A low or medium mass star (with mass less than 8 times the mass of sun) will become a white dwarf.

B)        Medium Stars – > Red Giant -> White Dwarf -> Black Dwarf

• CHANDRASHEKHAR LIMIT 
  • The Chandrashekhar Limit, named after the Indian astrophysicist Subrahmanyam Chandrashekhar, is the maximum mass that a stable white dwarf star can have. It is an important concept in astrophysics, particularly in the study of stellar evolution. Chandrashekhar discovered that if a white dwarf’s mass exceeds approximately 4 times the mass of Sun (Known as Chandrashekhar mass), the pressure generated by the electrons is no longer sufficient to counteract gravity. As a result white dwarf becomes unstable and collapse under its own weight.

C) Neutron Star

• Neutron Star: It is formed by catastrophic collapse of the core of a massive star. While a white dwarf is supported by electron degeneracy pressure, neutron stars are supported by neutron degeneracy pressure.
• How is Neutron Star formed: In its dying phase, when a star with a core containing mainly iron exhausts all its fuel, it collapses under gravity and explodes as supernova. The extreme high pressure causes protons and electrons to combine together to form neutron (thus forming a neutron star). They energy released during the process blows away the outer layer of the star.
• Would a neutron star further collapse into blackhole? -> It would depend on the mass of the neutron star’s core. If the mass is less than three solar masses it remains as a neutron star, but if the star’s mass more than about 3 solar masses, then it collapses further to form a black hole.
• The highest possible mass of a neutron star is not very well known, but it can’t be theoretically more than 3 solar masses (beyond which, it should be a black hole). The maximum mass for a neutron star, which has been precisely measured so far, is around 1 solar mass.
• The neutron stars are among the densest objects in the universe. They have a radius of 10-20 km but carry a weight of upto 2.5 times the mass of Sun.
• A big difference between Neutron star and Black Hole is that neutron star has a hard surface unlike that of a black hole.

D) Black Hole

• Why in news?
  • Ferocious black holes reveal ‘time dilation’ in early universe (July 2023: Source: The Hindu)
  • Spotting black holes (Sep 2023: Source – The Hindu)
• What is a Black Hole?
  • A Black hole is a place in space where gravity pulls so much that even light can’t get out. This strong gravity is because matter has been squeezed into a tiny space. This can happen when a star is dying.
  • Since, no light is emitted from them, they are invisible.
  • They are generally detected by telescopes by analyzing the behavior of stars that are very close to this black hole.
  • How large is a black hole?
    • A black hole can be as small as an atom (but having the mass of a mountain) and they can be very large as well.
    • Stellar is a kind of blackhole whose mass is around 20 times the mass of sun. There are many many steller blackholes in our Milky Way Galaxy.
    • “Supermassive” are the largest black holes. These black holes have masses that are more than 1 million suns together. Every large galaxy contains a supermassive blackhole at its center. The Supermassive blackhole at the center of the Milky Way galaxy is called Sagitarrius. It has a mass of 4 million suns and would fit inside a very large ball that could hold a few million earths.

Quasars: Quasars are a subclass of active galactic nuclei (AGNs), extremely luminous galactic cores where gas and dust falling into a supermassive black hole emit electromagnetic radiation across the entire electromagnetic spectrum. They are among the brightest objects in the Universe. Note: All Quasars are AGN, but not all AGN are Quasar

• • The boundary of black hole is called event horizon which acts as one way towards the black hole and allows nothing to get out of it.

• Singularities and Blackhole
  • In 1915 Karl Schwarzschild noticed that Einstein’s then new-general theory of relativity predicted the existence of strange objects known as “singularities”. They were places where his new equation describing gravity seemed to go haywire. Inside them there was a bizarre place where time stopped, and space became infinite. Over the years evidence have piled up explaining that singularities do exist in our universe as black holes.
• Spotting black holes: How do we identify blackholes?
  • A blackhole is identified by the gravitational force it exerts on nearby stars.

Astronomers have found systems in which a visible star orbits around an unseen companion. One cannot conclude that the companion is blackhole always; it might merely be a star that is too faint.

• • • If the unseen companion happens to be a black hole, then because of its high gravity it will start pulling matter off the surface of the visible star. This matter start falling towards the blackhole in a characteristic spiral path. In the process it also emits X-Rays which can be detected from earth.
    • From the observed orbit of visible star one can determine the lowest possible mass of the black hole.
• Recent Updates about Blackholes
  1. Scientists have discovered oldest black hole yet (Nov 2023)
     • A study published in Nov 2023 have confirmed that supermassive blackholes existed at the dawn of the universe. NASA’s JWST and Chandra X-Ray Observatory have teamed up to confirm this observation.
     • Given the age of the Universe is 13.7 billion years old, the age of this black hole is 13.2 billion years. Further, this blackhole is whopper – 10 times bigger than the black hole in our milky way galaxy. It is believed to weigh from 10% to 100% the mass of all the stars in its galaxy.
     • How was it formed?
       1. The researchers believed that the black hole was formed from colossal clouds of gas that collapsed in a galaxy next door to one with stars. The two galaxies merged, and the black hole was formed.
     • Role of Chandra X-Ray Observatory: The fact that Chandra X-Ray detected it confirms without doubt that it is a black hole. With X-rays you discover the gas that is being gravitationally pulled into the black hole, sped up and it starts glowing int the X-Ray.
     • This one is considered quasar since it is actively growing, and the gas is blindingly bright.
  2. Ferocious Blackholes reveal time dilation in Early Universe (July 2023)
     • Scientists have used observation of a ferocious class of black holes called quasars to demonstrate “time dilation” in the early Universe, showing how time then passed only about a fifth as quickly as it does today. The observation stretches back to about 12.3 billion years ago, when the universe was roughly 1/10^th of its present age.

Quasars were used as a “clock” in the study to measure time in the deep past. The researchers used observations involving the brightness of 190 quasars across the universe dating to about 1.5 billion years after the Big Bang even that gave rise to the Cosmos. They compared the brightness of these quasars at various wavelengths to that of quasars existing today, finding that certain fluctuations that occur in a particular amount of time today did five times more slowly in the most ancient quasars.