The News:

Andrew Howell, formerly of the Physics Division at Lawrence Berkeley National Laboratory and now at the University of Toronto, and Peter Nugent, an astrophysicist with Berkeley Lab's Computational Research Division said in a report, which appeared in the September 21 issue of Nature, as lead authors that a Supernova called SNLS-03D3bb in galaxy 4 billion light years away, is found to be more than twice as bright as most Type Ia supernovae, has much less kinetic energy but startlingly appears to be half as massive as a typical Type Ia supernova. In other words, it simply has overgrown the famed Chandrasekhar Limit!

"Chandrasekhar's 1931 model of stellar collapse was elegant and powerful; it won him the Nobel Prize," says Nugent. "But it was a simple one-dimensional model. Just by adding rotation one can exceed the Chandrasekhar mass, as he himself recognized," he added.

The Background:

What is Chandrasekhar's limit?

The Chandrasekhar's limit was first discovered and calculated by the Indian physicist Subrahmanyan Chandrasekhar in 1930. It is stated as follows:

In theory, the greatest possible mass of a stable cold star, above which it must collapse and become a black hole is 1.4 times the mass of our Sun. In other words, it is the the largest mass a white dwarf can attain.

How it came about?

In 1930, Chandrasekhar as a young undergraduate, setting out to Cambridge, Britain from India in pursuit of higher studies, calculated this remarkable thing on ship on his maiden voyage! There are many remarkable things about his work as is a heart rending controversy.

First, he applied Einstein's special theory of relativity to his study of the end stage in evolution of stars, when it is still not comprehended by many scientists. Even the renowned physicist, Stephen Hawking, hailed as ‘Second Einstein’, gave an account of Subramanian Chandrasekhar’s work in his classic popular science bestseller “A Brief History of Time”.

Second, his work predicted the existence of a stellar phenomenon that is simply fascinating, despite not being characterised further by him. His papers on the field are published between 1931 and 1936.

Now comes the pinching fact that when Chandrasekhar eventually presented this work in a Royal Society meeting in 1935, it was ridiculed and put down by Arthur Eddington, a scientist of reckoning in those days. The prejudice driven approach by Eddington and others embittered him and eventually left to the United States and remained there at the University of Chicago for the rest of his career.

Thanks to Arthur I. Miller, his novel "Empire of the Stars" gives a moving account of these things. Later, many scientists agreed with the opinion that the autocracy of Eddington might have delayed the progress of astrophysics by some 1 or 2 decades!

What happened now?

Scientists have found that the supernova is brighter but puzzlingly the ejecta of supernova are slower than typical Type Ia supernovae. This led to the conclusion that the supernova is resulted from a white dwarf star, that has super Chandrasekhar Limit mass. This does not mean the Limit is challenged yet. There are many possibilities. One, It's possible that a very rapidly spinning star could afford to be more massive without explosion. It's also possible that two white dwarfs, with a combined mass well over the Chandrasekhar limit, could collide and explode. Nevertheless, scientists warn that others should be careful when incorporating the Chandrasekhar limit in their work.

The heat of nuclear fusion in a star's core pushes the outer shells of the star outward against collapsing under gravity. As the star dies, the thrust vanishes and the star collapses back into its own core under its own gravity. At this stage, the electron degeneration starts and exerts pressure against collapse. If the star has a mass below the Chandrasekhar limit, this collapse is countered by electron degeneracy pressure and a stable white dwarf is born. If a star had a mass above the Chandrasekhar limit, the electron degeneracy pressure would be unable to resist the force of gravity, and collapse would ensue. The star's density would increase far beyond that of a white dwarf, leading to formation of a neutron star, black hole.

The News:

Scientists in US have developed new ultra-precise clocks that may outsmart the existing atomic clocks in precision and economy and would render obsolete, the technology behind high precision clocks that reigned for 50 years. Moreover, eventually, it may force scientists to give a new definition to the second itself.

The Background:

Evolution of measurement is simply an engaging reading for even a person with a non-science background. People in ancient times are smart enough to naturally divide the flow of time based on the duration of day and night combined together. By the turn of eighteenth century, the modern measures of time are spreading around the world. The history and evolution of time measurement is beyond the scope of article.

We, humans need very precise measure of time many a time. For example, in sports, the hundredth of a second decides the winners in many athletic events. Apart from such things, which have a direct bearing on us or command our interest, there are matters that interest scientists and commonly pass unnoticed by most of us, where fractions of a second to the order of millions are important. For example, Earth and Astronomical studies, GPS (Geographical Positioning System), Inter-planetary Navigation etc command precisions of time beyond the need of every day life.

As the science progressed, very accurate clocks developed. The first atomic clock was built in 1949 at the U.S. National Bureau of Standards (NBS). The first accurate atomic clock, based on the transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. This led to the internationally agreed definition of the second being based on atomic time.

Conventional Atomic clock work by measuring the ticks of cesium atoms exposed to microwave radiation. When microwaves were tuned to the natural frequency of ionized cesium gas, the electrons iside them get excited to change states. These to and fro transitions constitute the ticks for atomic clock. In actual clocks, there are complex feedback and monitoring mechanisms to measure the cesium oscillator. After this innovation, in 1967 the International System of Units (SI) has defined the second as the “time required for 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the Caesium-133 atom”. Besides, other units like the volt and metre also depend on the definition of the second as part of their own definitions.

Now, everything may change soon, as the maser based microwave referencing of cesium atoms is giving way to laser based referencing of ions of atoms like Mercury, Strontium or Ytterbium. The laser referencing allows scientists to use frequencies of 100,000 times higher than microwaves.

For physicists, a billionth of a second is just too long a time between ticks of a clock. How else would it be, when their precise clocks shows a real dif¬ference between time shown by a clock in a hill station and another at sea level? Einstein’s theory of relativity shows that time itself passes more quickly when gravity is reduced! And rest assured, it is proved!

Current Scenario:

Mr. Bergquist, a physicist with the Na¬tional Institute of Standards and Technology in Boulder, Colora¬do, USA works with extremely accu¬rate device. He and others have demonstrated the current better way to make atomic clocks. The new clock could at least be 100 times more accurate than the standard clock could ever be.

Still, can’t fathom the effect of this accuracy? Take this: The current standard atomic clock, by their margin of error, will neither gain nor lose a sec¬ond in about 70 million years, whereas the new clock pushes that period out to a whopping 400 million years!

• An Introduction to Scalars and Vectors
• Components of Vectors
• Fundamentals of Vectors

• Motion Along a Straight Line

• An Introduction to Waves
• Basic Properties of Waves
• Deriving the Wave Equation
• Determining the Speed of a Wave
• Different Types of Waves
• What is the Doppler Effect
• Doppler Effect in Light
• The Doppler Effect for Sound Waves

• The Law of Reflection
• The Necessity of Reflection
• Introduction to Curved Lenses
• Photons and the Compton Effect

• Einstein’s Theory of Special Relativity

• Einstein’s Theory of General Relativity

• Relativity Concepts and Controversies
• The Lorentz Transformations and the Theory of Relativity

• Understand Scientific Units and the International System of Measurement

• Newton’s Three Laws of Motion
• Newton’s Law of Gravity

• What is the Photoelectric Effect
• What is the Visible Light Spectrum

• What are Particles

• Succeed With Your Physics Degree
• A Physics Degree and Employment

• The Nobel Prize

• Making Physics Fun

• The Difficulties of Quantum Mechanics