What Is a Black Hole?

An artist's drawing shows a large black hole pulling gas away from a nearby star. Image Credit: NASA E/PO, Sonoma State University, Aurore Simonnet


A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.

Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.


How Big Are Black Holes?

Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object.

Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way.

An artist's drawing shows the current view of the Milky Way galaxy. Scientific evidence shows that in the middle of the Milky Way is a supermassive black hole. Image Credit: NASA/JPL-Caltech
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The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.


How Do Black Holes Form?

Scientists think the smallest black holes formed when the universe began.

Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.

Scientists think supermassive black holes were made at the same time as the galaxy they are in.


This image of the center of the Milky Way galaxy was taken by the Chandra X-ray Observatory. Image Credit: NASA/CXC/MIT/F.K. Baganoff et al.
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If Black Holes Are "Black," How Do Scientists Know They Are There?

A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.


Could a Black Hole Destroy Earth?

Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.

This artist's drawing shows a supermassive black hole in the center of a galaxy. The black hole is surrounded by a cloud of material that is spiraling into it. Image Credit: NASA E/PO, Sonoma State University, Aurore Simonnet
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Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now.

The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.


How Is NASA Studying Black Holes?

NASA is using satellites and telescopes that are traveling in space to learn more about black holes. These spacecraft help scientists answer questions about the universe.

world record of century

Sachin Tendulkar finally hits 100th international century

                                   

NEW DELHI: Indian cricket icon Sachin Tendulkar, treated like God by his fans, ended the long and tiring wait for his 100th international century on Friday at Dhaka's Shere Bangla National Stadium.

Sachin hits 100th ton

Tendulkar, the leading run scorer in the history of both Test and one-day cricket, achieved the most-coveted ton by taking a single off Shakib Al Hasan against Bangladesh in Asia Cup. Tendulkar's century came off 138 balls and was studded with 10 fours and a six.

"I can't think of anything at this stage, it has been a tough phase for me," Tendulkar told Neo Cricket channel after his innings. "I started off the season well but was luckless. It does not matter how many hundreds you score, you still have to grind it out."

"When I got the 99th century, no one spoke about it. I guess it was the media which started it. Everywhere I went people were talking about my 100th hundred," he said.

He was finally out for 114, caught behind off Mashrafe bin Mortaza, who then ran over to shake his hand.

The master blaster's 99th century had come against South Africa on March 12, 2011, at Nagpur during the World Cup. Friday's century was Tendulkar's 49th in one-dayers; he has 51 Test centuries.

Tendulkar, who was left stranded on 99 international hundreds for a year and four days, played Test series against England, the West Indies and Australia. He also featured in the recently concluded triseries in Australia but his bid to become the first batsman to score 100 international hundreds remained unfulfilled, although he came close on a few occasions.

Tendulkar has set a benchmark unlikely to be surpassed in his lifetime, with his closest rival, Ricky Ponting, on 68 international centuries and approaching the twilight of his career at the age of 37.

Since his international debut at 16 against archrival Pakistan in 1989, Tendulkar has been compared to not only top batsmen of his era like Brian Lara and Inzamam-ul-Haq, but also to Australian great Donald Bradman as the best batsman ever.

Bradman, who retired in 1948 with an average of 99.94 runs, said Tendulkar reminded him of his own playing style.

Tendulkar has defied age and injury at every stage of his career. Whenever injuries threatened to stall his career, he pushed his body to the limit, and sometimes even beyond. Even the most threatening of all his injuries - the painful tennis elbow (in 2004) - couldn't break him. He cried out in agony, waited with hope for almost a year, tackled it with determination and ultimately conquered it like only he can.

In February 2010, Tendulkar became the first in world cricket to score a double hundred in one-day internationals, while in December 2010 he became the first to score 50 Test tons, both landmarks achieved against the best pace attack in world cricket - South Africa.

Wisden, regarded as the bible of cricket, named Tendulkar as the leading cricketer in the world for the year 2010.

In 2007, Wisden had identified Tendulkar as the player to have won such an award for 1998 - had it been instituted then.

Tendulkar, who realised his long-cherished dream when India won the World Cup in April 2011, was also named in Wisden's 2009 Test XI, at his accustomed number four position.

His passion for the game not only keeps him going, but also gives him the opportunity to reinvent himself. Each time he goes out on to the field he seems to be raising the bar for himself.