6. Dramatic Changes

Dramatic Change in Stars

2015-03-05. Astronomers Watch a Supernova and See Reruns. By Dennis Overbye, The New York Times.

2012 Jan 11. Hubble Solves Mystery on Source of Supernova in Nearby Galaxy. News Release Number: STScI-2012-06, Hubblesite.  Summary: Using NASA's Hubble Space Telescope, astronomers have solved a longstanding mystery on the type of star, or so-called progenitor, that caused a supernova in a nearby galaxy. The finding yields new observational data for pinpointing one of several scenarios that could trigger such outbursts. Based on previous observations from ground-based telescopes, astronomers knew that a kind of supernova called a Type Ia created a remnant named SNR 0509-67.5, which lies 170,000 light-years away in the Large Magellanic Cloud galaxy. The type of system that leads to this kind of supernova explosion has long been a high importance problem with various proposed solutions but no decisive answer. All these solutions involve a white dwarf star that somehow increases in mass to the highest limit. Astronomers failed to find any companion star near the center of the remnant, and this rules out all but one solution, so the only remaining possibility is that this one Type Ia supernova came from a pair of white dwarfs in close orbit.

2011 Oct 24. NASA Telescopes Help Solve Ancient Supernova Mystery. JPL News.  Excerpt:A mystery that began nearly 2,000 years ago, when Chinese astronomers witnessed what would turn out to be an exploding star in the sky, has been solved. New infrared observations from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE, reveal how the first supernova ever recorded occurred and how its shattered remains ultimately spread out to great distances. The findings show that the stellar explosion took place in a hollowed-out cavity, allowing material expelled by the star to travel much faster and farther than it would have otherwise. "This supernova remnant got really big, really fast," said Brian J. Williams, an astronomer at North Carolina State University in Raleigh. Williams is lead author of a new study detailing the findings online in the Astrophysical Journal. "It's two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we've been able to finally pinpoint the cause." …The observations also show … that a white dwarf can create a cavity around it before blowing up in a Type Ia event. A cavity would explain why the remains of RCW 86 are so big. When the explosion occurred, the ejected material would have traveled unimpeded by gas and dust and spread out quickly. Spitzer and WISE allowed the team to measure the temperature of the dust making up the RCW 86 remnant at about minus 325 degrees Fahrenheit, or minus 200 degrees Celsius. They then calculated how much gas must be present within the remnant to heat the dust to those temperatures. The results point to a low-density environment for much of the life of the remnant, essentially a cavity….

2010 May. Hypervelocity Stars -Observations-  Lecture by Dr. Warren Brown, Harvard Smithsonian Center for Astrophysics

2010 Feb 22. From the Clash of White Dwarfs, the Birth of a Supernova. By Dennis Overbye, NY Times. Excerpt: ...For the last 20 years, astronomers seeking to measure the cosmos have used a special type of exploding star, known as Type 1a supernovas, as distance markers. They are thought to result when stars known as white dwarfs grow beyond a certain weight limit, setting off a thermonuclear cataclysm that is not only bright enough to be seen across the universe but is also remarkably uniform from one supernova to the next. Using them, two teams of astronomers a little more than a decade ago reached the startling and now widely held conclusion that some “dark energy” was speeding up the expansion of the universe.
But astronomers, to their embarrassment, have not been able to agree on how the white dwarf gains its fatal weight and explodes, whether by slowly grabbing material from a neighboring star or by crashing into another white dwarf.
In a telephone news conference on Wednesday and a paper published Thursday in the journal Nature, Marat Gilfanov and his colleague, Akos Bogdan, both of the Max Planck Institute for Astrophysics in Garching, Germany, said that for at least one class of galaxies in the universe, the roundish conglomerations of older, redder stars known as ellipticals, these supernovas are mostly produced by collisions.
“We have revealed the source of the most important explosions in cosmology,” Dr. Gilfanov said, adding that until now “we didn’t know exactly what they were.”...

2009 Nov 6. Supernova fits into a new class. By David Perlman, Chronicle Science Editor.  Excerpt: (11-05) 19:12 PST SAN FRANCISCO -- A bizarre exploding star that left its embers glowing invisibly in the distant sky .... The record examined by Dovi Poznanski, a UC Berkeley researcher, revealed that the short-lived but violent cosmic explosion in a far-off galaxy 135 million light-years away could be an entirely new class of supernovae.... This unique supernova, dubbed SN2002bj, was the first one found that was apparently caused when helium gas flowed from one tiny but immensely massive white dwarf star to another dwarf star orbiting close by. The result was a true thermonuclear explosion that died away in days rather than months, the Berkeley astronomers said, and its formation differed sharply from standard supernova models.
...Poznanski calculated that at the explosion's most powerful moment, it must have flared 10 billion times brighter than our sun, although nowhere near as bright as normal supernovae that can blaze 10 times more powerfully than that. ...The story of SN2002bj's detection actually started with a competition involving two amateur astronomers: Tim Puckett of Atlanta, who operates his own automated high-tech observatory in the little Georgia town of Ellijay (population 1,119), and Jack Newton, who has a high-tech robot telescope in Portal, Ariz. (population 80). They lead an amateur World Supernova Search Team, whose 28 members - from Canada to South Africa - use their high-powered telescopes to scan the skies every clear night. The team has discovered no fewer than 206 supernovae in the past 15 years.
Puckett and Newton discovered SN2002bj at the same time the night it flared, and immediately reported it to the International Astronomical Union's Central Bureau for Astronomical Telegrams at the Harvard Smithsonian Astrophysical Observatory in Cambridge, Mass., on April 18, 2002.
Alex Filippenko, a senior UC astronomer whose team also hunts for supernovae with a robot telescope system at Lick Observatory atop Mount Hamilton, also reported detecting the stellar explosion on the same night - but just a little later. "It really was a dead heat," Filippenko said of the discovery. But he conceded that Puckett and Newton beat him technically" by three and a half hours because Puckett's observatory is located where the time is three hours ahead and where the sun sets much earlier....

2008 November/December. Blown apart. BY KEAY DAVIDSON.  Excerpt: ...Saul Perlmutter ... "Our brains are...so good at seeing patterns that we sometimes see patterns that aren't there."
Perlmutter and his colleagues have spent two decades looking for patterns in the night sky-specifically, patterns in the spatial distribution of distant, dying stars that suddenly brighten, and then fade. They hope to resolve an ancient puzzle: How will the universe end? Eleven years ago, in the autumn of 1997, they uncovered a big piece of the puzzle. But their discovery was so unexpected that they worried the patterns were illusory. They checked and rechecked their data, searching for some subtle error that might have misled them. A mistake would make them look like fools. But if they waited too long to report their results, rival teams might beat them to announcing the discovery and perhaps to winning a Nobel Prize.
Their shocking discovery was "dark energy," a mysterious repulsive force that apparently makes the universe expand faster and faster over time. Dark energy now threatens to undermine fundamental beliefs about physics, cosmology, perhaps even the nature of scientific discovery....
...when Perlmutter arrived at Berkeley as a graduate student in physics in the early 1980s, he hoped to do research "that would address a deep philosophical question." His doctoral adviser was physicist Richard A. Muller, who was planning to use robotic telescopes to look for supernovae and a hypothetical star called Nemesis, which Muller suspected triggered mass extinctions on Earth by steering comets toward the inner solar system every 26 million years. Perlmutter joined that project, where physicist Carl Pennypacker was developing a robotic telescopic search at Berkeley's Leuschner Observatory in Lafayette. Over the next few years, their hard-working robot observer detected 20 "nearby" supernovae. Although the mystery star was never found, the supernova investigations opened the long, winding road to a historic discovery....

2008 December 4. Study Illuminates Star Explosion From 16th Century. The New York Times.  Excerpt: NEW YORK (AP) -- More than 400 years after Danish astronomer Tycho Brahe challenged established wisdom about the heavens by analyzing a strange new light in the sky, scientists say they've finally nailed down just what he saw.
It's no big surprise. Scientists have known the light came from a supernova, a huge star explosion. But what kind of supernova?
A new study confirms that, as expected, it was the common kind that involves the thermonuclear explosion of a white dwarf star with a nearby companion.
...The story of what's commonly called Tycho's supernova began on Nov. 11, 1572, when Brahe was astonished to see what he thought was a brilliant new star in the constellation Cassiopeia. The light eventually became as bright as Venus and could be seen for two weeks in broad daylight. After 16 months, it disappeared.
Working before telescopes were invented, Brahe documented with precision that unlike the moon and the planets, the light's position didn't move in relation to the stars. That meant it lay far beyond the moon. That was a shock to the contemporary view that the distant heavens were perfect and unchanging.
...The direct light from the supernova swept past Earth long ago. But some of it struck dust clouds in deep space, causing them to brighten. That ''light echo'' was still observable, and the new study was based on analyzing the wavelengths of light from that....

2008 May 21. X-RAY OUTBURST LEADS TO ALL-OUT STUDY OF SUPERNOVA. by Robert Sanders.  NASA's Swift satellite caught the rare birth of a supernova earlier this year, allowing astronomers to rapidly deploy ground-based telescopes to follow its evolution and learn about normal stellar explosions. UC Berkeley astronomers have analyzed the data to conclude that the original star was more than 30 times the mass of the sun, but only slightly larger, when its core ran out of fuel and imploded, blowing the star to smithereens.

2008 May 14. DISCOVERY OF MOST RECENT SUPERNOVA IN OUR GALAXY. NASA RELEASE: 08-126. Excerpt: WASHINGTON  -- The most recent supernova in our galaxy has been discovered by tracking the rapid expansion of its remains. This result, using NASA's Chandra X-ray Observatory and the National Radio Astronomy Observatory's Very Large Array, will help improve our understanding of how often supernovae explode in the Milky Way galaxy.

2006 July 21. Hypervelocity stars. New Scientist magazine podcast leads with an interview Dr. Warren Brown discussing hypervelocity star discoveries. Companion article: "Black Holes Don't Eat Everything" -- cover-story of the July 22, 2006 issue of New Scientist magazine.

2006 Jan 27. Podcast interview on Hypervelocity Stars. Fraser Cain, of the space-news site Universe Today interviews Dr. Warren Brown regarding the early hypervelocity star discoveries.

 

Archive: Past Articles for Chapter 6

NOTICE: On the 2009 edition of the GSS CD-ROM, supernova images in the folder ChangingCosmosImages > 6FindingSupernova > snLightCurvesSN1994i
are missing.
They are now posted for you to download in a zip compressed file at snLightCurveSN1994i.zip (2.7 Mb)

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