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2011 NOBEL PRIZE IN PHYSICS October 4, 2011

Posted by jcconwell in Astronomers, Cosmology, supernova, white dwarf.
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The Royal Swedish Academy of Sciences said American Saul Perlmutter would share the 10 million kronor ($1.5 million) award with U.S.-Australian Brian Schmidt and U.S. scientist Adam Riess. Working in two separate research teams during the 1990s – Perlmutter in one and Schmidt and Riess in the other – the scientists raced to map the change in the  universe’s expansion over time. They were measuring the change in  Hubble’s Constant,  by analyzing a particular type of supernovas, Type Ia, or exploding stars.

SN 1994D in NGC 4526. in lower left

Type Ia supernovas are thought to be caused by a white dwarf star exceeding its maximum mass, the Chandrasekar limit, of about 1.4 Solar masses, collapsing and detonating into a supernova. Since this collapse occurs at the same mass limit , it’s though all Type Ia supernova are equally bright.

They found that the light emitted by more than 50 distant Ia supernovas was weaker than expected, a sign that the universe was expanding at an accelerating rate, the academy said.

“For almost a century the universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago,” the citation said. “However the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the universe will end in ice.”

Perlmutter, 52, heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and University of California, Berkeley.

Schmidt, 44, is the head of the High-z Supernova Search Team at the Australian National University in Weston Creek, Australia.

Riess, 41, is an astronomy professor at Johns Hopkins University and Space Telescope Science Institute in Baltimore, Maryland.

Schmidt said he was just sitting down to have dinner with his family in Canberra, Australia, when the phone call came.

“I was somewhat suspicious when the Swedish voice came on,” Schmidt told The Associated Press. “My knees sort of went weak and I had to walk around and sort my senses out.”

The academy said the three researchers were stunned by their own discoveries – they had expected to find that the expansion of the universe was slowing down. But both teams reached the opposite conclusion: faraway galaxies were racing away from each other at an ever-increasing speed.

The discovery was “the biggest shakeup in physics, in my opinion, in the last 30 years,” said Phillip Schewe, a physicist and spokesman at the Joint Quantum Institute, which is operated by the University of Maryland and the federal government.

Rare Outburst of the Recurrent Nova U Scorpii Begins January 28, 2010

Posted by jcconwell in Nova, stars, supernova, white dwarf.
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Artists rendition of the recurrent nova RS Oph Credit: David Hardy/PPARC

(From Universe Today): Today, two amateur astronomers from Florida detected a rare outburst of the recurrent nova U Scorpii, which set in motion satellite observations by the Hubble Space Telescope, Swift and Spitzer. The last outburst of U Scorpii occurred in February of 1999. Observers around the planet will now be observing this remarkable system intensely for the next few months trying to unlock the mysteries of white dwarfs, interacting binaries, accretion and the progenitors of Type IA supernovae.

One of the remarkable things about this outburst is it was predicted in advance by Dr. Bradley Schaefer, Louisiana State University, so observers of the American Association of Variable Star Observers (AAVSO) have been closely monitoring the star since last February, waiting to detect the first signs of an eruption. This morning, AAVSO observers, Barbara Harris and Shawn Dvorak sent in notification of the outburst, sending astronomers scrambling to get ‘target of opportunity observations’ from satellites and continuous coverage from ground-based observatories. Time is a critical element, since U Sco is known to reach maximum light and start to fade again in one day.

Subrahmanyan Chandrasekhar October 20, 2009

Posted by jcconwell in Astronomers, Astronomy, white dwarf.
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One Hundred years ago, yesterday, October 19, 1910, Subrahmanyan Chandrasekhar was born.

Subrahmanyan Chandrasekhar

Subrahmanyan Chandrasekhar

Arguably the greatest astrophysicist of the twentieth century, his name is in every astronomy book. From the upper mass limit of a white dwarf, Chandrasekhar’s limit, to the orbiting Chandra X-ray telescope, he left his mark on the very concepts and vocabulary that physicists and astronomers use today.

Chandrasekhar was the nephew of Sir Chandrasekhara Venkata Raman, who won the Nobel Prize for Physics in 1930. Chandrasekhar was educated  at the University of Madras, and at Trinity College, Cambridge. From 1933 to 1936 he held a position at Trinity.

By the early 1930s, scientists had concluded that, after converting all of their hydrogen to helium, stars lose energy and contract under the influence of their own gravity. These stars, known as white dwarf stars, contract to about the size of the Earth, and the electrons and nuclei of their constituent atoms are compressed to a state of extremely high density. Using the new theory of Quantum Mechanics, Chandrasekhar determined what is known as the Chandrasekhar limit—that a star having a mass more than 1.44 times that of the Sun does not form a white dwarf but instead continues to collapse. Later it was found that more massive stars cores collapse blows off its gaseous envelope in a Type II supernova explosion, leaving a neutron star. An even more massive star continues to collapse leaving a black hole. Type Ia supernova use the same mechanism in a different way.If a binary star system has a white dwarf stealing matter from its companion, and it exceeds Chandrasekhar limit, the white dwarf will collapse and detonate. For this contibuttion he was awarded the 1983 Nobel Prize in Physics

Chandra  receives Nobel prize (1983)

Chandra receives Nobel prize (1983)

These calculations contributed to the eventual understanding of supernovas, neutron stars, and black holes, and the production of the elements in the periodic table.