Evolution of a Star

INTRODUCTION:

Stellar evolution is the process by which a star changes over the course of a time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years to least massive which are considerably longer than the age of the universe. All stars are born from collapsing clouds of gas and dust, often called Nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main sequence star. Depending on their mass, they reach the end of their evolution as whitedwarf, neutron star or black hole.

                         

NEBULA:

—  Nebula is a cloud of hydrogen gas and dust. It is a birthplace of stars. A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of the stellar evolution. For a low mass star, it lasts about 500000 years. Protostars are usually surrounded by dust, which blocks the light they emit, so they are difficult to observe in the visible spectrum.

                                                    

AVERAGE STAR:

—  After a part of nebula gains sufficient mass, it begins to collapse under its own gravity. As a result, the increased pressure in the core triggers nuclear fusion of hydrogen into helium. This stops further gravitational collapse and the star is officially born. The size of the star at this point will set the course for the rest of its life. The star with the mass between 0.5 to 8 times the mass of our sun is considered as an ‘average star’.

                                                

RED GIANT:

—  A Red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The most common red giant is stars on the red giant branch that are still fusing hydrogen into helium core.

PLANETARY NEBULA:

—   All planetary nebulae form at the end of intermediate massed star's lifetimes. They are a relatively short-lived phenomenon, lasting perhaps a few tens of thousands of years, compared to a considerably longer phases of stellar evolution. Once all of the red giant's atmosphere has been dissipated energetic ultraviolet radiation from the exposed hot luminous core, called a planetary nebula nucleus (PNN), ionizes the ejected material. Absorbed ultraviolet light then energises the shell of nebulous gas around the central star, causing it to appear as a brightly coloured planetary nebula.

                                 

WHITE DWARF:

—  A white dwarf is a very dense star that is the end stage of average star life. After the star runs out of helium, the star will try to combine carbon, which the star can’t combine. So the gas spreads apart from the star leaving behind a carbon dense white dwarf. When the white dwarf runs out of its remaining energy it loses its brightness and becomes a brown dwarf.

                           

MASSIVE STARS:

—  Massive stars are born, just like average stars out of clouds of dust called nebula. When a nebula collects enough mass it begins to collapse under its own gravity. The internal pressure created by this collapse is enough to trigger fusion of hydrogen deep in its core. When nuclear fusion begins a star is born. When a star is considered massive if it is at least 8 times more massive than our sun.

RED SUPERGIANT:

—  They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares are the brightest and best known red super giants, indeed the only first magnitude red supergiant stars. They are much cooler than the sun and are observed to rotate slowly or very slowly.

SUPERNOVA:

—  A supernova is an event that occurs upon the death of certain type of stars. A supernova is the explosion of a star. It is the largest explosion that takes place in space. The most recent directly observed supernova in the milky way was Kepler’s supernova in 1604.

NEUTRON STARS:

—  Neutron stars are created when giant stars die in supernovas and their cores collapse, with the proton and electrons essentially melting into each other to form neutrons. Neutron stars rotate extremely rapidly after their formation due to the conservation of angular momentum.

BLACK HOLES:

—  Black holes are incredibly massive but cover only smaller region. Virtually noting can escape from them. Under classical physics even light is trapped by a blackhole. A black hole can be formed by death of a massive star. A black hole is a region of a space-time exhibiting such strong gravitational effects that nothing can escape from it.

HR DIAGRAM:

The Hertzprung-Russell diagram is a graphical tool that astronomers use to classify stars according to their luminosity, special type, color, temperature and evolutionary stage.

Stars are stable phase of hydrogen burning lie along the main sequence  according to their mass. After a star uses up all the hydrogen in its core, it leaves the main sequence and moves towards the red giant branch. The most massive stars may also become red supergiants, in the upper right corner of the diagram.

The lower left corner is reserved for the white dwarfs.

Submitted by:

Ezitha Monteiro

Delvita Veigas

Divyashree

Keerthana

I M Sc Physics

Reference

Internet

Journal

From the southern sky - Phoenix

The southern sky

Phoenix

Phoenix constellation lies in the southern sky. It was named after the phoenix, the mythical bird that rises from its own ashes.

The constellation was originally introduced by the Dutch astronomer and cartographer Petrus Plancius from the observations of the Dutch navigators Frederick Houtman and Pieter Dirkszoon Keyser in the late 16th century. It is a relatively small constellation, but it is the largest among the 12 constellations created and named by Plancius. It was first depicted on his globe in 1598 and later appeared in Johann Bayer’s atlas Uranometria in 1603.

Phoenix constellation is easy to see for anyone in Australia and South Africa during southern hemisphere summer, but generally can’t be observed by anyone living north of the 40th parallel, and lies pretty low in the sky for observers north of the equator.

Phoenix contains several notable deep sky objects, among them the Phoenix Cluster of galaxies, the black hole candidate HLX-1, and Robert’s Quartet, a compact galaxy group.

Phoenix is the 37th constellation in size, occupying an area of 469 square degrees. It is located in the first quadrant of the southern hemisphere (SQ1) and can be seen at latitudes between +32° and -80°. The neighboring constellations are Eridanus, Grus, Fornax, Hydrus, Sculptor and Tucana.

Phoenix belongs to the Johann Bayer family of constellations, along with Apus, Chamaeleon, Dorado, Grus, Hydrus, Indus, Musca, Pavo, Tucana and Volans.

Phoenix contains five stars with known planets and does not have any Messier objects. The brightest star in the constellation is Ankaa (Alpha Phoenicis) with an apparent magnitude of 2.40. There is one meteor shower associated with the constellation -the Phoenicids-which occurs around December 5 every year

French explorer and astronomer Nicolas Louise de Lacatle charted and designated 27 starts with the Bayer designation Alpha through to omega in 1756, of these he labelled two stars close together lambda and assigned omicron, psi and omega to three stars.

MAJOR STARS IN PHOENIX

1. Ankaa – α Phoenicis (Alpha Phoenicis)

2. β Phoenicis (Beta Phoenicis)

3. γ Phoenicis (Gamma Phoenicis)

4. κ Phoenicis (Kappa Phoenicis)

5. ζ Phoenicis (Zeta Phoenicis)

6. ν Phoenicis (Nu Phoenicis)

7. SX Phoenicis

Brightest star - Ankaa or Alpha Phoenicis

Ankaa is the brightest star in the constellation. Its name comes from the Arabic al- ‘anqā’, which means “the phoenix.” It is also sometimes known as Nair al- Zaurak, or “the bright star of the skiff” (an-na’ir az-zawraq in Arabic).

Alpha Phoenicis is a spectroscopic binary star approximately 85 light years distant. The system has the combined stellar classification K0.5 IIIband a combined apparent magnitude of 2.377. The two components in the system orbit each other with a period of 3848.8 days (or 10.5 years). The primary star, as the spectral class indicates, is an orange giant.

Water on Mars

Water on Mars

Introduction

Mars is the fourth planet from the Sun and the second smallest planet in the Solar system after Mercury. Have you heard the big news!?

NASA has reported there is water on Mars. Let’s travel to the Mars now..

Using an imaging spectrometer on NASA’s Mars Reconnaissance Orbiter(MRO), researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet.

These dark, narrow 100 meter-long streaks called ‘recurring slope lineae’(RSL) flowing downhill are inferred to have been formed by contemporary flowing water. Recently, planetary scientists detected hydrated salts on these slopes at Hale crater, corroborating their original hypothesis that the streaks are indeed formed by liquid water.

Another view of ‘recurring slope lineae’ or RLSs, flowing out of a mountainside on Mars.

Almost all water on Mars today exists in small quantities as vapour in the atmosphere and occasionally as low volume liquid brines in shallow Martian soil. The only plane where water ice is visible at the surface is at the north polar ice cap.

Scientists have also travelled deep underground into mines and found microorganisms related to ancient species that once lived in watery environments much close to the surface. Such migrations raise the possibility of the same thing happening on Mars- as the water retreated, life moved deeper underground.

However, while the find is tantalizing for astrobiologists eager to find alien life, it is also a bit of tease. It will be decades before astronauts can visit the surface of Mars and likely much longer before we can drill a mile beneath the dusty surface. So we may not see any expeditions in our lifetime.

Observations of the Red planet indicate that rivers and oceans may have been prominent features in its early history. Billions of years ago, Mars was warm and wet world that could have supported microbial life in small regions. But the planet is smaller than Earth, with thinner atmosphere. Over the time, as liquid water evaporated, more and more of it escaped into space, allowing less to fall back to the surface of the planet.

More than five million cubic kilometres of ice has been identified at or near to cover the whole planet to a depth of 35 meters.

Although there are some extremophile organisms that survive in hostile condition on Earth, including stimulations that approximate Mars, plants and animals generally cannot survive the ambient conditions present on the surface of Mars. Surface gravity of Mars is 38% of Earth. Researches are going on this area.

Submitted by

Students

1^st M.Sc. Physics

Reference

• Internet
• Journal

SPECTRUM

Spectrum

Introduction

A spectrum is a condition that is not limited to a specific set of values but can vary, without steps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colours in visible light after passing through a prism.  As scientific understanding of light advanced, it came to apply to the entire electromagnetic spectrum.

In the 17th century, the word spectrum was introduced into optics by Isaac Newton, referring to the range of colours observed when white light was dispersed through a prism. Soon the term referred to a plot of light intensity or power as a function of frequency or wavelength, also known as a spectral density plot.

The term spectrum was expanded to apply to other waves, such as sound waves that could also be measured as a function of frequency, frequency spectrum and power spectrum of a signal.

Electromagnetic spectrum

Electromagnetic spectrum refers to the full range of all frequencies of electromagnetic radiation and also to the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. Devices used to measure an electromagnetic spectrum are called ‘spectrograph’ or ‘spectrometer’. The visible spectrum is the part of the electromagnetic spectrum that can be seen by the human eye. The wavelength of visible light ranges from 390 to 700nm. The absorption spectrum of a chemical element or chemical compound is the spectrum of frequencies or wavelengths of incident radiation that are absorbed by the compound due to electron transitions from a lower to a higher energy state.

Light from many different sources contains various colours, each with its own brightness or intensity. A rainbow, or prism, sends these component colours in different directions, making them individually visible at different angles. A graph of the intensity plotted against the frequency is the frequency spectrum of the light. When all the visible frequencies are present equally, the perceived colour of the light is white, and the spectrum is a flat line.

In radio and telecommunications, the frequency spectrum can be shared among many different broadcasters. The radio spectrum is the part of the electromagnetic spectrum corresponding to frequencies lower below 300 GHz, which corresponds to wavelengths longer than about 1 mm. The microwave spectrum corresponds to frequencies between 300 MHz (0.3 GHz) and 300 GHz and wavelengths between one meter and one millimeter.

Mass spectrum

A plot of ion abundance as a function of mass to charge ratio is called a mass spectrum. It can be produced by a mass spectrometer instrument. The mass spectrum can be used to determine the quantity and mass of atoms and molecules.

Energy spectrum

In physics, the energy spectrum of a particle is the number of particles or intensity of a particle beam as a function of particle energy. Examples of techniques that produce an energy spectrum are alpha particle spectroscopy, electron energy loss spectroscopy, and mass analyzed ion kinetic energy spectrometry.

Discrete spectrum

In physics, particularly in quantum mechanics, some differential operator have discrete spectra, with gaps between values. Common cases include the Hamiltonian and the angular momentum operator.

Spectrogram

In acoustics, a spectrogram is a visual representation of the frequency spectrum of sound as a function of time or another variable.   An apparatus used for recording and measuring spectra, especially as a method of analysis.

Splitting of white light

Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). This speed change causes the light to be refracted and to enter the new medium at a different angle. The degree of bending of the light's path depends on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media. 

Light of different colours to  be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow. This can be used to separate a beam of white light into its constituent spectrum of colours.

Reference

·        Wikipedia

SUBMITTED BY: 

Ahallya K V

Akshatha G

Akhila K

Athira V

Amal George

CAN YOU HEAR ME?

CAN YOU HEAR ME?

The Magic called Sound

What is it like, when you accidentally press the mute button of your TV remote, while watching an electrifying cricket match? Even though you still can watch the match, you certainly lose interest in the game without sound. If this is so, then think of a time when the whole world will fall into a mute mode. No one can even contemplate a soundless world.

The world we survive is full of sound. The world we live in is full of sound. The chirping of birds, whistling of wind, roaring of animals, splashing of water- these are all parts of rhythms of nature. Not only natural sounds, but man- made sounds like the honking of horns too become an inevitable part of our lives. In short, man and sound are inseparable.

Sound is the music of life

Sound, in its simplest sense, is an energy made by vibrations.

When an object vibrates, it creates the movement in the air particles. These particles get in contact with others close to them, and make them vibrate too. As this continues, it becomes a bigger process, with more and more air particles bumping into each other. This movement creates what is known as sound waves. It keeps going until the object runs out of energy. We hear the sound when our ears are within the range of the vibrations.

The speed of sound

The speed of sound primarily depends on the medium through which the waves travel. For instance, sound waves travels faster in water, than in air. But in the medium of steel , it’s even faster . In an ideal gas, speed of sound depends only on its temperature and composition.

There are fixed rates for the speed of sound wave. In dry air at 20⁰C the speed of sound is 343 meters per second. Now takes the case of water. Here, sound travels four times faster, at an approximate rate of 1,484 m/s . But in solids like iron, it reaches around 5,120 m/s !

The speed of light is 2.99792458 x 10⁸m/s, almost 870,000 times faster than the speed of sound! This is the reason why you see lightning before you hear the thunder.

Why is it said that Super Sonic aircraft surpass the speed of sound?

Supersonic speed refers to a speed greater than that of sound. A bullet fired from a modern day gun is said to have this kind of speed. Another important example is the supersonic air craft. They are flights which travel faster than the sound that is audible to human ears.

An Indian example of Supersonic flight is the HAL Tejas, which is still in service.   

Star facts:-

·       Study of sound

Acoustics is the scientific study of sound waves.

·       Phobias

While ‘Acousticophobia’ refers to the fear of noise, ‘melophobia’ refers to the fear of music!

·       Smaller is louder

Smaller objects vibrate faster, creating higher frequency sounds. This is why the sound of your voice being higher than your father’s

·       New Science

Cymatics is a relatively younger branch of science that stu dies geometric forms created by Sound waves.

·       Loud Enough

Loudness depends on how loud or soft the sound is; it is measured in decibels (dB). It has been found that at 125dB, a sound becomes painful to human ears.

·       Healing Effect

One of the techniques that uses sound waves to heal wounds is the ‘MIST’ therapy.

Sound Level Meter

The Sound level meter, a hand held instrument with microphone, is commonly used tool for acoustic measurements.

·       Far- Reaching

It is said that whales communicate with each other underwater, their sound waves travel up to 800km.

Sound need medium to pass through

We know that, our Diwali crackers bursts with sound. But do we think such big explosions and collisions of the massive objects in space creates sound? Well, there are no sounds coming from them. The reason behind this strange phenomenon is that, there is no ‘medium’outside the the Earth to travel through. Air is not the only medium through which sound waves can travel. It can pass through liquid and solids too.

Hearing Range of animals varies greatly

As matter of fact, no two species of animals look alike,or behave alike.Similarly, the abilities and senses of animals vary too, from species to species.

One cannot expect a monkey to have the hearing ability of an elephant, nor can auditory ability between a marine mammal and terrestrial animal be compared. Generally, it is seen that larger animals hear and use low frequency sounds while smaller ones have with higher frequencies. However, there are always exceptions, as in the case of spadefoot toads that can easily pick up low frequency sounds. These animals live in desert habitats.

Similar to animals, birds and insects too have peculiar auditory features that help them adapt to surroundings.

Birds are known for their musical communication

How many of us have seen birds that don’t make sounds? Not many. Birds are in fact, most known for their ability to make sound, be it sweet chirping, or harsh caws.

There are different frequencies at which birds’ sound come out . There are others too that can sing at high frequencies, like warblers, sparrows, waxwings, kinglet etc. It is believed that one can never stop a bird from learning its own species’ song.

Sound around us

What is Ultra sound?

We have heard that most humans can hear the sounds between 20 and 20000 hertz. Ultra sounds are above this limit, or specifically above 20000 Hz. They are not different rom normal sound in terms of physical properties. But the only difference is that they can be heard and produced by only a few animals like bat, moth,dolphins etc and not by humans. In other words, the range of ultrasound begins where our sonic range ends.

The uses of ultrasound can be seen in electronic, navigational, industrial, medicinal and security applications.

Ultra sounds are useful in SONAR

SONAR is the short form for SOund NAvigation and Ranging. It is an ultrasonic system used in ships and other vessels for navigation, and locating objects underwater.

As we know, Sound waves travel faster than light through water. However , ordinary sound waves cannot travel longer distances , only ultrasonics waves can. Due to their high frequency and short wavelength, ultrasonic waves penetrate water to very long distances and it is this feature that is utilized in Sonar.

Fig. Illustration that shows the work of a SONAR

Ultrasounds are useful in medicine

Fig. Ultrasound scanning

Some of the important applications of ultrasonics can be seen in the field of medicine. Ultrasonography or ultrasonic scanning is one of it, which uses high frequency sound waves to produce images of internal organs, vessels and tissues. This type of scanning is used to diagnose the condition of organs such as liver, kidneys, gallbladder.

Then there is something called obstetric ultrasound. It is a technique used during pregnancy to create images of a baby inside the womb.

Another public health application of ultrasounds is dental care. It enables the equipment called ‘descalers’ to remove plaque from teeth.

Fig. Ultrasound Scanning machine

Noise, noise, everywhere

Noise pollution or Sound pollution refers to the term of excessive and troublesome sound that effects all living things on Earth. Commonly, noise is discussed in terms od decibels (dB), which is also the measure of loudness or intensity of sound. There are different kinds of noise around us today, and one of it is environmental noise. Roughly speaking, it is the accumulation of all the noise present in the specified environment

It is said that plants have the ability to control adverse effect caused by the noise pollution. Hence , grow more and more plants, thus we can stay healthy and present a beautiful , calm environment to our future.

SUBMITTED BY:

Thushara R B

Yogini E

Pradeep A

Sahana D

(Ist M Sc)

Reference:

TELL ME WHY?

JOURNAL- JUNE 2017

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