Showing posts with label Astronomy. Show all posts
Showing posts with label Astronomy. Show all posts

5 Quotes By Stephen Hawking On Black Holes

stephen hawking black holes quotes universe astrophysics

Stephen Hawking [1942-2018] was an English cosmologist and author who is most well known for his theory of black holes. Hawking is known for postulating the black hole thermal radiation. Hawking also made important contributions to the big bang theory of the universe.

Following are five noteworthy quotes on black holes by Stephen Hawking:

1. I used to think that information was destroyed in black holes. But the AdS/CFT correspondence led me to change my mind. This was my biggest blunder, or at least my biggest blunder in science.

2. Black holes ain't as black as they are painted. They are not the eternal prisons they were once thought. Things can get out of a black hole, both to the outside, and possibly to another universe. So if you feel you are in a black hole, don't give up. There's a way out.

stephen hawking black holes quotes astrophysics for students

3. Einstein was wrong when he said "God does not play dice." Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen.

4. My discovery that black holes emit radiation raised serious problems of consistency with the rest of physics. I have now resolved these problems, but the answer turned out to be not what I expected.

5. It is said that 'fact is sometimes stranger than fiction', and nowhere is this more true than in the case of black holes. Black holes are stranger than anything dreamt up by science fiction writers.

Why Astronomer Carl Sagan Was An Agnostic?

carl sagan astronomy science and religion quotes

Carl Sagan was a renowned American astronomer who is best known for his show, Cosmos: a personal voyage. Sagan, an expert in the field of exobiology, persuaded NASA for Mars missions and to search for exoplanets with signs of life.

When asked about his religious belief, Carl Sagan did not assertively pick a side. He did not know for sure if there was a God. Carl was also uncomfortable about being labeled an atheist. That is why, Sagan claimed to be agnostic—to not hold any belief about God's existence.

In an interview, Carl Sagan described his unique idea of God, as a set of physical laws that govern the universe, which is the same as what Albert Einstein also believed.

However, Carl Sagan was an open critic of blind belief. At one point, Sagan also believed that religion or God was unnecessary in modern day society.

"Where did God come from?" Carl Sagan asks believers. "If we say that God always existed, why not save a step, and conclude that the Universe always existed?" Carl argues.

Carl Sagan adds that science has enlarged our picture of the universe. In some respects, science has far surpassed religion in delivering awe. "The Universe is much bigger than our prophets said, grander, more subtle, more elegant", Sagan wrote in the book Pale blue dot.

Carl Sagan also criticized the idea of perfection - that God is perfect. He wrote in the book Contact - "Why didn't God start the universe out in the first place so it would come out the way he wants? Why's he constantly repairing and complaining? God is not good at design or execution".

Despite writing extensively not in favor of religion, Carl Sagan never described himself as an atheist, as boldly as contemporaries like Richard Feynman did. Carl Sagan was an agnostic because according to him: "Extraordinary claims require extraordinary evidence."

richard feynman atheist carl sagan agnostic
Richard Feynman was an atheist

"To be certain of the existence of God and to be certain of the nonexistence of God seem to me to be the confident extremes in a subject so riddled with doubt and uncertainty as to inspire very little confidence indeed". Carl Sagan adds.

On the other hand, Feynman had said: I call myself an atheist. Agnostic for me would be trying to weasel out and sound a little nicer than I am about this.

Who Proposed The Idea of Black Hole?

black hole history science astrophysics for students

The black hole is a great source of mystery and inspiration for scientists and writers alike. These are abnormalities in space where the gravity is so strong that not even light, traveling at an enormous speed of 300,000 km/sec, can escape.

How did the idea of black hole come about?

In 1915, more than a hundred years ago, Albert Einstein published a theory of space and time or "spacetime" in which one of the crucial predictions was the bending of light as it approached a massy body, like the sun or a black hole.

That light bent in the presence of mass was confirmed in an experiment led by English astronomer Arthur Eddington in 1919. After this observation, Einstein's general relativity was taken more seriously, as it resurrected the original idea of black hole – which was published way back in 1784!

It was English astronomer John Michell who suggested the existence of a body so big that even light could not escape. As a result, such an object could not be seen directly but its gravitational effects on nearby bodies could be measured.

At that time, the term black hole did not exist. Astronomers instead used the term "dark stars" which is a pretty cool name to describe a stellar body hiding in plain sight.

In 1916, Karl Schwarzschild used Einstein's field equations of general relativity to calculate the radius up to which any object of mass must be "cramped" to make it a black hole. This is called the Schwarzschild radius.

For example: Earth crushed to the size of a pea would turn into a black hole.

black hole history astrophysics for students

Although the theory of general relativity implied the existence of a monstrous space object capable of trapping light in its grasp, Einstein wrote in a paper that a star would "never shrink" to zero size.

When will black hole form

A new development occurred in 1930. Indian physicist Subrahmanyan Chandrasekhar calculated how a star could actually shrink or collapse if it "ran out of hydrogen" or other nuclear fuels to burn.

Consequently, there come various stages in the star's life cycle. Upon collapse, the star may become a white dwarf - like our sun will - too feeble to burn bright in our skies.

Chandrasekhar predicted that a white dwarf with mass greater than "a limit" will be subject to further gravitational collapse, evolving into a different type of stellar remnant - a denser neutron star.

What would it take to form a black hole then? In 1939, American physicist Robert Oppenheimer produced a paper titled, "On Continued Gravitational Attraction" and in it calculated that a star would have to be at least three times as massive as the sun to become black hole.

Birth of black hole

The paper by Oppenheimer was the key factor in the rejuvenation of astrophysical research in the United States in the 1950s - mainly by John Archibald Wheeler.

In fact, the term black hole was coined in 1967 by Wheeler during a talk he gave at the NASA Goddard Institute of Space Studies. Not even light could escape from it, it was undetectable - hence, "black" hole.

One also could not tell from the outside what was inside the black hole. This means that the black hole contains a lot of information which is hidden from the outside world and Wheeler called this, "A Black Hole Has No Hair".

But in 1971, English mathematical physicist Roger Penrose described a way for information to be transferred from rotating black hole to an outside particle. Three years later, another method for the same was provided by cosmologist Stephen Hawking, as in Hawking radiation.

At around the same time in America, physicist Kip Thorne, one of Wheeler's doctoral students, developed the general relativistic theory of thin accretion disks around black holes, a flattened band of spinning matter around the event horizon.

Something you may have already seen in artist's impressions of the black hole:

black hole disc astrophysics for students

Thorne compiled many theoretical results about the black holes in a 1994 book for non-scientists, titled Black Holes and Time Warps. It was a widely recognized book on the subject and translated into six languages.

Cut to present

The phenomenon of black hole captured the attention of some of the greatest minds in history and continues to surprise us even more in mainstream media.

Most recently, in the 2014 film "Interstellar" by director Christopher Nolan. Physicist Kip Thorne was also closely involved in the making and acted as executive producer.

Interstellar was a huge success - the science fiction movie project not only generated a fortune at the box office but also a new public interest regarding the black holes.

In 2019, the first picture of a black hole in Messier 87 was released based on data from 2017. It was compiled by the event horizon telescope - a collective effort of scientists from over 20 countries made it possible to see the distant space object by converting the entire planet Earth into a giant virtual telescope!

The image of black hole confirmed how lucky we are as a species at this particular time, with the capacity of the human mind to comprehend the universe, to have built all the science and technology to see it in glorious action.

On a fun ending note, black holes have come a long way - from gigantic mass eating monsters in space to the shape of a doughnut!

Why Carbon Did Not Form In The Big Bang?

why carbon did not form in big bang astronomy big bang failed creation carbon physics science nuclear physics

Where did all the chemical elements in the periodic table come from? Physicists theorized that elements can be created inside dying stars and astronomers confirmed this by observation.

Essential elements like carbon, nitrogen, oxygen and iron are created towards the end of a star’s life cycle. Much heavier and precious elements like Gold are formed in supernova explosions.

Shortly after the big bang, the explosion that birthed the universe, there was 92% hydrogen and 8% helium atoms. Simple elements came into existence quick, obvious, but what about the rest of them?

Why did nature have to wait for early stars' death in hundreds of millions of years time to produce carbon, oxygen, etc.?

Two reasons: One, by the time simple atoms formed, the universe had already cooled enough. Second, there was hardly any disposable helium.

We know, hydrogen has 1 nucleon, a proton, and helium has 2 protons and 2 neutrons, so 4 nucleons. The reactions to yield heavier elements would be:

H + He or He + He

Giving out nuclei with 5 and 8 nucleons respectively, both highly unstable.

For example: The resulting beryllium-8 has half life of only 8.19×10−17 seconds. Stable beryllium has 5 neutrons and 4 protons.

Thus, beryllium-8 would immediately decay into two stable helium nuclei, if ever it came into being.

Besides, hydrogen and helium are themselves incredibly stable. It turns out that nature preferred stability over creation of heavy elements.

Soon, gigantic lumps of hydrogen began forming due to sophisticated engineering by gravity. The lumps were spherical, because again… nature likes stability.

The first stars made light in extreme conditions upon converting hydrogen to helium, because of Einstein's energy mass equivalence.

why stars shine why carbon did not form in big bang how stars make light astronomy big bang failed creation carbon physics star life cycle supernova nuclear physics

Towards the end, most hydrogen in the star is converted to helium. There is abundance of helium nuclei to combine with beryllium-8 in just the right time to become carbon-12.

Ultimately, it boils down to the amount of disposable helium, even if the pressure and temperature conditions are met. The collapsing star makes more elements like nitrogen, oxygen, iron and nickel as it dies.

In the big bang, helium was unavailable for extensive use. Whereas, in the star, formation of carbon is possible in the triple alpha process. And since life on earth is carbon based, we are children of the stars.

First Images From NASA's Webb Telescope Revealed

first image nasa james webb telescope hubble deep field image

First image (credit: NASA, ESA, CSA) by the Webb Telescope is of galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago, the time when our planet Earth just began to form. Surrounding the cluster are tiny unseen objects of the universe as they were 13 billion years ago, shortly after the Big bang.

SMACS 0723, a massive object, is bending the light rays coming from the distant galaxies behind it. The Webb telescope has brought those galaxies into sharp focus. This phenomenon is called gravitational lensing and is based on Einstein's theory of relativity.

The image was taken by Webb's near-infrared camera and took about 12.5 hours to be assembled from a collection of images taken at various wavelengths. When the Hubble Space Telescope took a similar deep field image it took several weeks!

The first deep field was unveiled by the president of the United States Joe Biden during a White House event. “It’s hard to even fathom,” he commented.. “It’s astounding. It’s an historic moment for science and technology, for America and all of humanity.”

Thousands of galaxies that have come into Webb's infrared view for the first time would fit in a single grain of sand held at arm's length by someone on the ground. These images will help astronomers to calculate the compositions of the earliest galaxies.

The telescope, named after the longest serving NASA administrator, took over 30 years for completion and could revolutionize our understanding of the universe. Its infrared capabilities will allow humans to see back in time to the first galaxies and study their evolution.

hubble vs webb telescope first image deep field nasa

Webb is the official successor of the Hubble space telescope. Its operations are led by NASA with its partners: ESA (European Space Agency) and CSA (Canadian Space Agency). The camera that took this image was built by the University of Arizona and Lockheed Martin’s Advanced Technology Center.

Why James Webb Telescope Is Better Than Hubble

james webb space telescope launch 22 december successor of Hubble telescope

The James Webb space telescope (JWST) is named after the longest serving NASA administrator and is the official successor to the Hubble space telescope. JWST is the costliest astronomy project having spent nearly three decades in the making.

The largest and the most powerful telescope in the world is scheduled to be launched in December 2021 after many delays since completion. The JWST will be able to look back in time closer to the Big Bang than ever before.


JWST was built by NASA in collaboration with European Space Agency and Canadian Space Agency. It will explore the universe in the infrared region, something that Hubble space telescope is incapable of doing. The mirror size is 6.5 meters - three times the size on the Hubble telescope but it weighs half of Hubble.


To make observations in the infrared part of the electromagnetic spectrum, JWST must be kept under 50K or −223°C which is extremely cold. It uses a cryocooler and a large five-layer sunshield to block light and heat from the Sun, Earth and Moon to maintain a stable temperature.


The objectives of JWST include detecting clues to the origins of the universe, like observing infant galaxies and their evolution. As well as locating earth like planets outside the solar system and study the origins of life.
Hubble space telescope is capable of observing events that happened in space some 500 million years after the Big Bang, whereas Webb telescope can go back even further to around 100 million years after that event.


JWST has a near infrared camera for observation of faint extrasolar planets very close to the bright stars. It also has a near infrared spectrograph capable of measuring spectrum of faint stars and galaxies. A fine guidance sensor helps the telescope stay pointed at whatever it is commanded to look at.


It was scheduled to launch before but accidental tears in the delicate sunshield in 2018 delayed the project. Controversy also erupted over naming of the telescope as activists alleged that James Webb had discriminated against LGBTQ scientists during his term.

james webb telescope big bang hubble telescope

The mirror in JWST will be folded before launch. It is made up of 18 hexagonal segments - shaped so to join without gaps in between them. The mirror will unfold after the launch and it will take at least two weeks before the telescope becomes operational in orbit.

How it works

When picture of a galaxy is taken we see it the way it was millions of years ago because light takes time to travel. It is like finding a picture of a child dated from 1900 but if that child was still alive, they would be among the oldest people on the planet.

As the light travels, it becomes red-shifted due to expansion of the universe. So, objects at extreme distances are easier to see in the infrared. We can see these objects the way they were millions of years ago, that is, when that galaxy was fairly young.
JWST's infrared capabilities will allow humans to see back in time to the first galaxies for the first time. Infrared astronomy will also help us to learn how stars and galaxies have evolved over time. By overcoming all the challenges, JWST is set to launch in December 2021.

Who discovered that we are made from star stuff?

Hans Bethe Starstuff contemplating the stars Carl Sagan

Astronomer Carl Sagan popularized the phrase "We are made of star stuff" when he said: Nitrogen in our DNA, calcium in our teeth, iron in our blood and carbon in our food; were made in the interiors of collapsing stars.

However, most people wouldn't know the name of that scientist who actually found it out. It was German American physicist Hans Bethe (1906-2005) who wrote it in a paper titled "Energy Production in Stars" as early as in 1939.

In 1930s, at the time when European scientists were debating quantum mechanics, Bethe migrated to United States and contemplated the stars. He thus became the first person to figure out that conversion of hydrogen into helium was the primary source of energy in a star.

The process is called nuclear fusion in which many nuclei combine together to make a larger one. It so happens that the resultant nucleus is smaller in mass than the sum of the ones that made it. So, by virtue of Einstein's equation E=mc², the mass is converted to energy.

When a star would eventually run out of hydrogen (its primary fuel) it would start converting helium into carbon, nitrogen, oxygen and so on, in order to keep itself hot.

However, those reactions themselves will halt at some point and the star would no longer be able to support itself against its own gravity and it will die in an explosion.

Therefore, it was proposed that most of the material that we're made from, came out of the dead stars which spewed out those chemical elements into the universe for further use. Hence, we are made of star stuff.

Bethe's groundbreaking paper not only helped in understanding the inner workings of the stars but also solved the age-old questions like: 'How do stars shine?' 'Where did the chemical elements come from?'

He won the 1967 Nobel Prize in physics for this theory of stellar nucleosynthesis. Bethe would continue to do research on supernovae, neutron stars, black holes and other problems of astrophysics well into his late nineties.

Carl Sagan Hans Bethe Cornell Astrophysics
Carl Sagan and Hans Bethe share the stage at Cornell

Now, Carl Sagan, who was earlier at Harvard University, joined Cornell in 1976 and became immediate colleagues with Hans Bethe who had been at Cornell since coming to America in 1935. While Bethe was a professor of physics, Sagan was a professor of Astronomy.

It was unfortunate that the general public still did not know about stellar nucleosynthesis despite Bethe discovering it some 40 years ago and winning the highest prize for it a decade ago. Carl Sagan changed this.

Their common interests in science and politics brought them even closer. Bethe was also a fan of Sagan's 1980 show Cosmos: A personal voyage. In one of the episodes, when Sagan said "We are made of star stuff", he immortalized Bethe's work in television history.
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