Gravitational force is responsible for the rotation of every object around other bigger objects than itself. Because of this force, our moon rotates around earth, earth rotates around sun, sun rotates around the black hole sagittarius A* present in the centre of our milky way galaxy.

Now the question is, can moons also have their sub moons?

 The answer of this question requires lots of research and investigation. With current knowledge, we can only predict about any result with the help of some theories and laws of physics.

Here, a question arises in everyone's mind that why moon revolves earth and not revolves around the sun when sun creates greater gravitational attraction than any other object in our solar system?

This question can be answered and understand by assuming space-time as a fabric. Let's consider whole space-time as a fabric and all other astronomical bodies as balls of different sizes on that fabric.

Because of their variable masses, all the different balls will create different curve in that fabric and because of that curve all the lighter bodies starts getting attracted towards heavier bodies than itself. Same phenomenon takes place in the universe where all those balls are different astronomical bodies.

Now the answer of the above question is Hill sphere.

Hill sphere is the space around any astronomical body where any heavier body can influence a lighter body than itself. This is also known as Roche sphere. This is explained by George William Hill and Edouard Roche so it is known by their names.

Now, the radius of earth's Hill sphere is 1,500,000 km and the distance of our moon from earth is about 3.5 lakh km, this means moon comes inside the earth's Hill sphere which means no other body can force moon to revolve around it.

Somehow, the distance between earth and moon increases to more than 1,500,000 than moon will change it's orbit and starts rotating the sun.

Now, moon also have it's own Hill sphere whose radius is 60,000 km which means if any body will come this close to moon then it will start orbit the moon but if that object is present outside the moon's Hill sphere then it will start orbiting the Earth and not the moon.

All the satellites send from the on the moon also orbit the moon in it's Hill sphere and can be said it's sub moons. Until now, we didn't found any natural sub moon of our moon and if any natural sub moon of our moon does exist than it will not orbit the moon for consist time.

This means it will either gets attracted towards moon or earth's surface because of tidal courses takes place between earth and moon. This means our moon can't keep any sub moon.

There is more than 200 moons only in our solar system but the fact are there is only four moons (Titan, Enceladus, and two more) only in our solar system whose sub-moon can theoretically exist but still we didn't found any sub moons of those four moons.

In our solar system there are unlimited moons but unfortunately we can't see most of them with our latest technology. The first moon which is discovered outside our solar system was discovered in 2018. This means we need lots of upgrades find any sub moon.

Saturn just knock down Jupiter in number of moons, after the discovery of 20 new moons by scientists, Saturn now have 82 moons where Jupiter have 79 moons. All these new moons are orbiting Saturn just like it's old moons but with variety of time period to complete their rotation around Saturn.

Two of them takes 2 years to complete a rotation around the Saturn where other 18 takes more than 3 years. One of the new moons have farthest known orbit around Saturn.

All these new moons are nearly similar in size whose diameter is around 5 kilometres. Seventeen of the new moons orbit Saturn backward — or in retrograde — compared to the planet's other natural satellites.

How do we even know Saturn has moons?

Although most planets of the Solar system are visible to the naked eye and have been known to humans since antiquity, it wasn't until Galileo Galilei turned a telescope on Jupiter in 1610 that we discovered Earth was not alone in having an orbiting companion.

Galileo saw Jupiter's four largest moons and could make out what we now know are Saturn's rings. Decades later, with better telescopes, Christian Huygens and Giovanni Domenico Cassini observed Saturn's moons.

It became clear that the giant planets are surrounded by multitudes of satellites, resembling smaller versions of the Solar system.

By the middle of the 19th century, telescopes had improved enough that the first eight moons of Saturn – including Titan, the largest one – had been viewed directly.

The introduction of photographic plates, which enabled the detection of fainter objects with long-exposure observations, helped astronomers increase their count of Saturn's moons to 14.

The retrograde moons have orbits resembling some of Saturn's other already-known moons. And after observing them, scientists are predicting that they are pieces of a big moon who orbits Saturn in past.

The moons were discovered by a team led by Scott S. Sheppard at the Carnegie Institution for Science and using the Subaru Telescope on Hawaii’s Mauna Kea.

It was a long journey (literally) to the next big improvement in our view of Saturn's moons. Many of the smaller moons were not discovered until the Voyager fly-by missions in the 1980s and the more recent 13-year stopover of the Cassini spacecraft in Saturn's orbit.
Until these closer visits, we knew little about the moons aside from the fact that they existed.
One of Cassini's goals was to explore Titan, which is the only moon in the Solar system with a thick, smoggy atmosphere. Another was to take a look at Saturn's other mid-sized moons, including frozen Enceladus, which may hold an ocean of liquid water beneath its icy crust.

Cassini also discovered much smaller moons, so-called "shepherd moons" that interact with Saturn's rings by carving gaps and wavy patterns as they pass through a rubble of rocks and snowballs.

These close-up observations from space advanced our understanding of individual moons that stay near to Saturn. Recently, many more moons have been found in orbits much further from the planet.

These more distant moons could only be detected with large optical telescopes such as the Subaru telescope at Mauna Kea in Hawaii. The telescope is equipped with sensitive cameras that can detect some of the faint objects separated by millions of kilometres from Saturn.

To confirm that these objects are indeed associated with Saturn, astronomers have to observe them over days or even months to reconstruct the shape and size of the moon's orbit.

Such observations revealed a population of moons that are often described as "irregular" moons. They are split into three distinct groups: Inuit, Gallic, and Norse. They all have large, elliptical orbits at an angle to those of moons closer to the planet.

Each group is thought to have formed from a collision or fragmentation of a larger moon. The Norse group consists of some of the most distant moons of Saturn, which orbit in the opposite.

Once again this discovery of Saturn new moons proves that, here is many hidden things in our solar system. This things were hidden until now because of only one reason "we were lacking of technology to discover them".

On the basis of images and data collected by NASA's Cassini mission, scientists from USA and Germany proposed a paper, in which they proposed that Saturn's moon Enceladus have same organic molecules and which were responsible for life on earth.

In search for life in this universe, now a moon of Saturn named as Enceladus attracted the attention of scientists towards itself. For searching life, scientists tries to detect the same  molecules which were present on earth when life starts originating here.

Enceladus is the sixth largest moon of Saturn of diameter of 500 km which is actually ten times smaller than Titan which is the largest moon of Saturn. Enceladus is the most reflective heavenly body in our solar system due to the clean ice present over it's surface.

NASA has collected some data with the help of image collected by Cassini spacecraft which ends on September 15, 2017. On the basis of this data, scientists of USA and Germany has confirmed that they have detected some kind of organic molecules which can play a role of precursor molecule of life.

The elements were found to be nitrogen- and oxygen-bearing organic compounds and they are quite abundant in Enceladus.

The shocking fact is, new molecules are nothing but the ingredients of amino acids whose capability is known to everyone.
The research paper, published in Monthly Notices of the Royal Astronomical Society, says that they could be the ideal precursors for the synthesis of 'biologically relevant organic compounds in the warm depths of Enceladus' ocean'.

The similar components are part of the chemical reactions on earth which produces amino acids, the building blocks of life. The materials ejected form core of Enceladus after mixing with it's subsurface water and released in space in form of ice grains and water vapour.

Scientists are predicting that these hydrothermal vents on the ocean surface leads to provide the energy which fuels chemical reaction. This supply of energy leads to formation on amino acids.

"If the conditions are right, these molecules coming from the deep ocean of Enceladus could be on the same reaction pathway as we see here on Earth. We don't yet know if amino acids are needed for life beyond Earth, but finding the molecules that form amino acids is an important piece of the puzzle," said Nozair Khawaja, who led the research team of the Free University of Berlin.

Actually scientists has detected the organic material in the ice grains releases by Enceladus and they are using CDA's mass spectrometer measurement to determine the composition of organic material in the grains.

These organic molecules are firstly dissolved in the ocean of Enceladus from where they get evaporated and starts floating in the space and NASA’s Cassini has that CDA's mass spectrometer which detect those organic molecules just before condensing into ice form.

This discovery clearly proves that enceladus have a reactive ocean where there a great probability of finding of any other type of life relevant compounds or molecules or even there is a chance that we will able to detect some kind of microbial life on enceladus.

There are many probability related to microbial life or organic molecules but from above discovery, it is clear that enceladus is one of those celestial bodies near us where life may be originating.

Today a huge part of society believes that "there is no life outside the earth". For supporting there views they raise a point that water is one of the most important component for life and there is no water in liquid state on any other heavenly body in universe.

The fact is, scientists have already discovered a waterworld which made up of only water which is in liquid. Now, two teams of astronomers have discovered the largest water reservoir ever detected in the universe.

This water reservoir is not only the largest one but is also the farthest reservoir of water ever found. This water surrounds a feeding black hole which is also known as quasar, present at 12 billion light years away from earth.

The amount of this water in this reservoir is 140 trillion times all the water present in earth's ocean.

According to Matt Broadford a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif, "The environment around this quasar is very unique in that it's producing this huge mass of water". Matt Broadford leads one of the two teams which discover this water reservoir.

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•What happens if you falls into a Black Hole?

Lets know about Quasars:

Quasar is a extremely luminous active galactic nucleus (AGN), in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk.

With time, the gasses attracted by the gravitational pull black hole and it is emitted out in the form of electromagnetic radiation. This electromagnetic radiation is enormous in amount and can be observed in electromagnetic spectrum.

It is now known that quasars are distant but extremely luminous objects, so any light which reaches the Earth is redshifted due to the metric expansion of space. Quasars are believed—and in many cases confirmed—to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, as suggested in 1964 by Edwin Salpeter and Yakov Zel'dovich.

Light and other radiation cannot escape from within the event horizon of a black hole, but the energy produced by a quasar is generated outside the black hole, by gravitational stresses and immense friction within the material nearest to the black hole, as it orbits and falls inward.

The brightest quasar in the sky is 3C273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a medium-size amateur telescope), but it has an absolute magnitude of −26.7.

Both groups of astronomers studied a particular quasar called APM 08279+5255, which harbours a black hole 20 billion times more massive than the sun and produces as much energy as a thousand trillion suns.


Astronomers expected water vapour to be present even in the early, distant universe, but had not detected it this far away before. There's water vapour in the Milky Way, although the total amount is 4,000 times less than in the quasar, because most of the Milky Way’s water is frozen in ice.

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Water vapour is a important proof to reveal the facts about these strange body (quasar). In case of this quasar, water vapour surrounds the outline area of black hole which exists some hundred light years.

Presence of this water vapour indicates, this quasar is wetting the gas in X-rays and infrared radiation, and that the gas is unusually warm and dense by astronomical standards.

Although the gas is at a chilly minus 63 degrees Fahrenheit (minus 53 degrees Celsius) and is 300 trillion times less dense than Earth's atmosphere, it's still five times hotter and 10 to 100 times denser than what's typical in galaxies like the Milky Way.

Astronomers measures the gasses like carbon monoxide and water vapour around this quasar and they conclude that "there enough gas is present to feed that hungry black hole until it grows six times of its present size".

According to them they can't predict that when it is going to happen but there is a chance for some gasses to condense and form a star or another phenomenon can takes place in which some of the gasses may ejected out from quasar.

How it sounds that 'scientists are trying to measure the ghost'?
But yes they are taking help of cosmos to measure the actual mass of ghost particle also known as "Neutrino".

A neutrino is a Fermion that interacts only via the weak subatomic force and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small that it was long thought to be zero. The mass of the neutrino is much smaller than that of the other known elementary particles.

Here we are going to discuss that how a team of scientists, for the first time have set an upper limit on the mass of the lightest of the three different types of neutrino. Those are sometimes called “ghost particles” because they’re so difficult to detect.

 Scientists with the Karlsruhe Tritium Neutrino experiment, or KATRIN, said  they’ll be taking measurements “well into the next decade” and hope to produce “high-impact results.

Weak interactions create neutrinos in one of three leptonic flavors: electron neutrinos νe), muon neutrinos (νμ), or tau neutrinos (vτ), in association with the corresponding charged lepton.

Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavors. A neutrino created with a specific flavor has an associated specific quantum superposition of all three mass states.
Neutrinos are created by various radioactive decays, including the following:

* In beta decay of atomic nuclei or hadrons,
* In natural nuclear reactions such as those that take place in the core of a star,
* Artificial nuclear reactions in nuclear reactors, nuclear bombs, or particle accelerator,
* During a supernova,
* In the spin-down of a neutron star,
* when accelerated particle beams or cosmic rays strike atoms,.

The majority of neutrinos detected in the vicinity of the Earth are from nuclear reactions in the Sun.

As neutrinos are abundant but tiny and elusive, we needed every piece of knowledge available to calculate their mass, and our method could be applied to other big questions puzzling cosmologists and particle physicists alike."

Calculating mass of neutrino takes more than half a million computing hours to process the data; this is equivalent to almost 60 years on a single processor," said cosmologist Andrei Cuceu from University College London.

But Grace did it: the supercomputer returned a mass for the lightest of the three neutrons of 0.086 electron volts (with a lower limit of zero), or around 1.5 × 10-37 kilograms.

The team also calculated a combined mass for the three neutrinos - 0.26 electron volts. Both these results have a confidence interval of 95 percent.

Universe is huge right?

In fact it is so huge that we are not able to measure its whole size as we have been only able to see a limited part of universe known as observable universe. This observable universe contains billions of galaxies, stars and other heavenly bodies.

Now the question rises is, is this universe is endless? Is there is anything exist in outside the universe? And we have only a single answer of this question "The multiverse".

Multiverse is a hypothetical concept according to which "there are multiple universes in existence".

In 1952, Erwin Schrodinger in his lecture in Dublin warned his audience because he thinks, what he is going to say is a type of joke for most of his audience. He said that when his equations seemed to describe several different histories, these were "not alternatives, but all really happen simultaneously".

Hence form there the  birth of concept of multiverse takes place.
We have seen that the movies and comics are using this concept very widely as they give different name for multiverse like multiple dimensions, parallel universe, parallel reality, alternative timeline and many more.

But physics community is totally divided on this topic. Some says multiverse must exist and some says it is just a hypothetical concept.
Scientist community don't take multiverse as a topic for debate or research.

But this doesn't mean that scientists never try to find any evidence for multiverse. In 2010, scientist named as Stephen M Feeney analysed the data collected by Wilkinson microwave Anisotropy probe (WMAP) and regarding to that data he claimed to find the evidence of collision of our universe with other in distant past.

After this, when the plank satellite take part in this discovery and didn't found such collision as it does not detect any gravitational pull on our universe due to any other universe.

Max Tegmark ( a cosmologist) has provided a taxonomy of universes beyond the familiar observable universe. The four levels of Tegmark's classification are arranged such that subsequent levels can be understood to encompass and expand upon previous levels. They are briefly described below.

Level 1. The existence of our universe

This is based on predictions of chaotic inflation according to which the existence of an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions.

According to chaotic inflation theory, the space ( Multiverse) is expanding and most interesting thing is this expansion will continue forever.

But here are some areas in the universe which stop expanding due to some reasons and form some bubbles and these are named as embryonic universe.

There is no limitations about the shape and size of these bubbles. The main thing is, the shape of these bubbles will decide the physical constant of that particular universe but the laws of physics will remain same in each and every bubbles.

Level 2. Oscillatory and Fecund universe

A cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles.

Forexample, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a Big Bang and ending with a Big Crunch; in the interim, the universe would expand for a period of time before the gravitational attraction of matter causes it to collapse back in and undergo a bounce.

Level 3. Many world interpretation of Quantum Mechanics

Here, we can't predict about any result as every event is taking place in some universe. According to the MWI, each of these possible observations corresponds to a different universe.

For understanding this, if we throw a dice in air and trying to find the different probabilities then accordingly quantum mechanics, each and every number can come but in different universes. This means, if we get 1 then other five possibilities are going to take place in different universes.

Level 4. Ultimate ensemble

This is Tegmark's own hypothesis also known as ultimate mathematical universe hypothesis.
This level considers all universes to be equally real which can be described by different mathematical structures.

We can say that in this level of multiverse everything is possible means, what we are thinking write now is happening somewhere in some kind of universe which means our each new thought is creating a new universe.

Now after discussing about these levels, you may feel very awkward to read about the theories which says our universe is empty at any place form where we can escape out from our universe and in same way enter in other universes. This theory also explains us about more than 4 dimensions ( at least 10).

But we should not forget that all these are just  ideas, theories or mathematical solutions and it will take centuries to reach at some destination. Hence we can conclude only one thing "multiverse is not a topic for debate as we can take it as a reality so we will find something".

How Stars are formed?

Have you ever question yourself, how these "bulbs of universe" (Stars) formed?

They are present in number of millions and billions hence, they are forming each and every second because the process of star formation is time consuming. Star formation is the process in which the dense region of interstellar space which is also referred as "stellar nurseries" collapses and form stars.

Lets know more about interstellar clouds first:

In the universe, lots of stellar remnants, and diffuse interstellar medium of gases and dusts are present. Our milky way galaxy is composed of about 70% of hydrogen gas and in rest 30% a huge amount of helium is present. But our interstellar medium is also rich in heavy elements released from stars.

These regions of heavy density take a shape of cloud which is further referred as diffuse nebulae which later converts into nebulas with high density and this is the site for formation of a star.

These dense nebulas are also called molecular nebula because most of the Hydrogen content in these nebulas exist in molecular form(H2).
The main reason of star formation is, cloud collapse.

But the question rises in mind is, what lead these cloud to collapse?

This question can be answered by using virial theorem. This theorem states that to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy.

In large clouds, the kinetic energy of gas pressure is insufficient to support it then the phenomenon of gravitational collapse takes place. The mass above which a cloud will go under such gravitational collapse is known as jeans mass which depends on the temperature and density of cloud.

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•What is dark matter and dark energy?

•The String Theory!

During cloud collapse dozens to ten thousands of stars form more or less simultaneously which is observable in so-called embedded clusters.

The end product of a core collapse is an open cluster of stars. As the cloud collapses, the material at the centre begins to heat up, Known as a protost, it is this hot core at the heart of the collarapsing cloud that will one day become a star.

Molecular clouds may collide with each other, or a nearby supernova explosion can be a trigger, sending shocked matter into the cloud at very high speeds. (The resulting new stars may themselves soon produce supernovae, producing self-propagating star formation).

Alternatively, galactic collisions can trigger massive starbursts of star formation as the gas clouds in each galaxy are compressed and agitated by tidal forces.

The black holes present in the centre of the galaxy also show its effects on star formation.

In newly formed galaxies, the black hole is small hence the process of star formation is faster as compare to those old galaxies in which a huge black hole is sitting in the centre of the galaxy ejecting radio-frequency-emitting particles at near-light speed can also block the formation.

Star formation takes approximately a billion years and between this time that start goes into different phases. One of the most longest and famous phase is formation of a protostar.

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A protostellar cloud will continue to collapse as long as the gravitational binding energy can be eliminated. This excess energy is primarily lost through radiation.

However, the collapsing cloud will eventually become opaque to its own radiation, and the energy must be removed through some other means.

The dust within the cloud becomes heated to temperatures of 60–100 K, and these particles radiate at wavelengths in the far infrared where the cloud is transparent. Thus the dust mediates the further collapse of the cloud.

Here one noticeable point is that the mechanism of formation of low mass and high mass star is totally different in comparison.

Major discoveries about star formation in the far reaches of the Universe. This is important as far away galaxies are seen far back in time, because of the huge distances their light has needed to reach us.

Studying starlight from the most distant objects Hubble has observed gives clues about how stars formed in the early years of the Universe, and how they have changed over time.

Nowadays, scientists are trying to find the oldest star of universe because by studying these oldest star we can predict the early time of our universe.

Today we are capable to see the formation of stars with the help of evolved telescopes and hence we can know anything about Stars now.