Astronomy

Black Holes – New Discoveries

J B S Haldane

Gamma rays from outer space are in the news. Recent satellite and telescope discoveries have located their origin. In the process, new light is visible on black holes. The idea of a black hole has its origin in a theoretical work of a great Indian Scientist, Subrahmanyan Chandrasekhar.

One of the most interesting findings in astronomy has been that black holes cannot hide any more! Though it is said that not even light can escape a black hole, its presence is indicated by the emission of gamma rays and X-rays. As a black hole pulls the surrounding gas into it, the radiation that follows it, gives it away.

It is believed that there is a huge black hole in the centre of our galaxy, the Milky Way. It is equivalent to an unimaginable three million solar masses, spread across a diameter of 16 million km. Though the black hole in our galaxy is the largest, it requires a telescope with a resolution 10,000 times better than the Hubble Space Telescope to resolve it. Two Harvard theorists recently constructed a computer model that simulates the emission from a black hole. The observations are proving them correct. The size and spin of the black hole are being measured by observing the black hole area in sub-millimeter band (0.2 to 1.5mm) and the infrared regions of the spectrum. Several telescopes on Earth were effectively ‘joined’ together to form one as large as the Earth to resolve the target’s features.

If the massive black hole in our galaxy is seen as a glutton, a super massive black hole in the spiral galaxy, NGC 1097, which is 45 light years away, looks as if it were on a strict diet. Near-infrared rays rather than gamma rays detected the dietary habit of this black hole. Images taken by the European Southern Observatory’s Very Large Telescope in Chile have shown incredible details of just a filamentary structure of matter swirling down to the black hole at the centre of the spiral galaxy.

The astronomers had to mask the blinding light from the stars to register the black hole area, which was 25 times fainter than the faintest object the naked eye could see. The image revealed 300 star-forming regions. May be the black hole is ‘fasting’, whetting its appetite in anticipation of a feast of the stars, when they become fat and old after a couple of billions of years!

The Chandra X-ray telescope has revealed black holes not as a violent villain but as a caring hero of a new generation of stars! It has found the new stars orbiting within alight year from the Milky Way’s central black hole. It is as though several deer are happily grazing within the reach of a lion! Chandra has also found black holes, which may be described as middle weight champions to keep company with their heavy-and light-weight counterparts existing merrily with several starbursts. And the Hubble Space Telescope has found a disk of blue stars around a black hole in the neighbouring Andromeda galaxy. Perhaps there is a ‘live-and-let live’ policy in the cosmos!

More curious is the finding by SWIFT of a super massive black hole without a home Viz. a massive galaxy. The host galaxy, it is explained, may be exclusively made up of unexplained dark energy. Equally puzzling is the statement by a scientist of the Lawrence Livermore Laboratory (US) that there is no such thing as a black hole at all! According to George Chapline, black holes are actually stars made out of dark energy formed by the collapse of massive stars.

Ideas about black holes are changing fast nowadays. Even the famous Stephen Hawking has taken a U-turn in his ideas. He is no longer holding that nothing escapes a black hole, as in his revised view, information can be extracted from what escapes from a black hole!

chandra-satellite

The Betrayal Of Chandra

A great Indian scientist, Subrahmanyan Chandrasekhar (1910-1995), indicated through his theoretical work, the existence of black holes. Young Chandrasekhar, a post-doc from Cambridge (UK), had hit upon the revolutionary idea that stars at the end of their life become white dwarf. These are stars that have exhausted most or all or their nuclear fuel and have collapsed into a very small size near the end of their final stage. Chandrasekhar concluded that the mass of a white dwarf could not exceed 1.4 times that of the Sun. this is today known as the Chandrasekhar limit.

Chandra got a golden opportunity to present his views to scholars. He made a presentation at the Royal Astronomical Society in London in 1935. he expected applause and admiration but what he got was exactly the opposite. Arthur Eddington, then 53, famous for his discovery of the bending of light as predicted by Einstein, launched a ‘disgraceful and cruel attack’ on the young man. Chandra could just not believe how a respected scientist could sink so low.

Eddington was so powerful that even famous personalities in science like Niels Bohr, Pauli and Rosenfeld dared not oppose him. Even Chandra’s supervisor, Ralph Fowler, backed out, though many knew that the young Indian was right. Eddington could just not stomach the idea of Chandra, as it would have demolished his own pet theories. Petty jealousy won the day.

A disappointed and betrayed Chandra left England for the United States, where he got a permanent position in the Yerkes Observatory of the Chicago University. Britain’s loss became America’s gain. For Chandra, the transition was a blessing in disguise. The liberal atmosphere of Chicago brought out the best in him. Within ten years of his arrival, he was made a Fellow of the Royal Society (1944). In 1983 he shared the Nobel Prize for physics with Willy Fowler. That year his famous Mathematical Theory of Black Holes appeared in print.

One significant conclusion from Chandra’s works is that stars more massive than the Sun must either explode or form black holes. Some scientists still think that Chandra should not be given ‘too much credit’ for his theoretical work, which indicated the existence of black holes. But as Miller points out there is a logical sequence between the Chandrasekhar Limit and the eventual black holes. True, many others like Robert Oppenheimer and Gary Snyder had also predicted the life pattern of massive stars ending up as black holes. But the starting point of it all Viz. the collapse of a massive star beyond the limit envisaged by Chandra is the crucial deduction.

Four years after Chandra passed away, NASA launched an X-ray satellite in 1999, named after him to probe the Universe in X-rays. Chandra, the satellite has given the best view yet of the X-ray Universe. The findings are giving almost every month amazing results that dramatically prove Chandra right. X-astronomy has confirmed the collapse of the massive stars and the existence of black holes. Chandra, the satellite, has revealed the presence of many previously undetected black holes in the Milky Way and in nearby galaxies, including possibly a new class of black holes called intermediate black holes.

Chandra has dramatically revealed yet another proof of the scientist’s theory. The satellite recently discovered a neutron star, where such black holes were expected in a dense cluster of young stars more massive than the Sun, much to the surprise of astronomers: It is considered possible that extremely massive stars blow off their mass so effectively during their life that they leave only neutron stars after they explode as supernova. The discovery of a neutron star may limit the range of stellar masses that lead to the formation of stellar black holes. Exceeding the Chandrasekhar limit may thus give surprises but the limit stays on.

There is hardly any parallel in the history of science to the betrayal by a British scientist. But things have changed. Prof Martin Rees, British Astronomer Royal, for example is all praise for Chandra. Rees says Chandra probably thought longer and deeper about our Universe than anyone since Einstein. Notwithstanding the betrayal, Chandra did not become a bitter and angry man. In the words of the great astronomer, Hans Bethe (1906- 2005) Chandra was a “….first-rate astrophysicist and a beautiful and warm human being”.

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