BA: AstroAlert: Type Ia supernova in M101! (SN 2011fe)

[Ann]

Well, rosettastoned, first the supernova seemed to stall at magnitude 11.0, then it jumped to magnitude 10.5 and seemed to stall there. Then it jumped to magnitude 10.3, where it seemed to stall. Then it rose to magnitude 10.0, then to 9.9. Then it remained there for a really long time, then it faded to 10.0, then it plunged to 10.5. And then it seemed to stall at 10.5! On Tue, 27 Sep 2011 23:52:49 GMT, it was still 10.5.

Look at these stepped gables on the Hanseatic buildings of the city of Bruges in Belgium ( or Flanders). The light curve of the supernova resembles such stepped gables to me!







Ann

[Beyond]

Ann of brown gables. You must be the sequel.

[rosettastoned]

Alrighty then, it's a type gabled Ia of hanseatic origin (Could it be connected to the October-fest, somehow?)

[Ann]

So, rosettastoned, you're from Norway! Nice to see you here at Starship Astersisk*!

Yes, our stepped gabled type Ia of hanseatic origin, which (who?) may possibly have visited the Oktoberfest and had a few too many beers to give him such a step-gabled personlity in the first place, is now stuck on a pretty broad step at magnitude 10.5. On Wed, 28 Sep 2011 23:37:02 GMT, SN 2011fe still hovered there.

I know you won't believe me, but - the house was blue!!

Ann of brown gables, eh? Couldn't the gables be blue? I guess not. Back in hanseatic times, and even in the days of Anne of Green Gables, blue gables were a no-no. In one of the later Anne books, she and her friends have promised to paint somebody's house. I think the house was going to be painted green, as is fitting in a book about a character from Green Gables. But somehow or other - and I don't remember the details at all - the house ends up being painted blue. The whole thing becomes a magnificent scandal, and people come travelling from relatively far away to see the hideous house, the blatantly blue building! Imagine a blue house becoming the sort of juicy tidbit that you think you are going to tell your grandchildren about!




Beyond, you now have 1955 posts. That makes me nostalgic, since 1955 was the year I was born!

Ann

[Beyond]

Blimey, Anne was always getting into trouble. My mother liked to watch her, but the show just wasn't my cup of tea. Or coffee, or cocoa, etc. etc.

[Ann]

Can you believe that on Thu, 29 Sep 2011 22:53:54 GMT, the supernova was still 10.5? How long is it going to hover at that magnitude?

Ann

[Ann]

Photo: William Wiethoff

Ladies and gentlemen, I'm offering you this...splendid...supernova... Sn 2011 fe!!!! Lete's hear it for the supernova!!

Ladies and gentlemen, what would you say is the magnitude of this magnificent monstrosity of a mega-explosion in a Messier Object? Do I hear 10.7? Do I hear 10.6?

No, ladies and gentlemen! On Sat, 01 Oct 2011 03:40:01 GMT, SN 2011fe was still 10.5!!!!

HOORAY!

















Ann

[Beyond]

ooh, Ann splurged for the bubbly stuff. Since we are seeing the super nova w-a-y after the event via photons, could it be that the little rascals are having a bit of 'fun' with us? It has already been shown that photons behave differently when scientists are observing just them. It does seem that an explosion (of any size) just doesn't behave this way. Just one of the unsolved mysterys of life.

[Ann]

ooh, Ann splurged for the bubbly stuff. Since we are seeing the super nova w-a-y after the event via photons, could it be that the little rascals are having a bit of 'fun' with us? It has already been shown that photons behave differently when scientists are observing just them. It does seem that an explosion (of any size) just doesn't behave this way. Just one of the unsolved mysterys of life.

I guess!

Because now, less than twelve hours after I wrote my last post about the supernova, it has now dropped to magnitude 10.8!!!

I suppose some of the photons caught some of the other photons and said "Tag, you're it" or whatever you say when you're playing tag in English!

And I guess the photons from the supernova are playing tag in English. If not, I'll bet they're playing tag in Turkish.

You know this Pioneer 10 plaque which carried a message from humanity to whatever intelligent species this little spacecraft might encounter out there? Some years later, one of the Voyager probes carried a golden long-playing record with a lot more messages to E.T. Among other things, every nation that belonged to the United Nations sent a message to the aliens in their own language - well, in their own earthly language, not E.T.'s tongue. But who knows if E.T. doesn't speak the same language as we do, or at least the same language as some of us do? The Turkish representative at the U.N. recorded the following message for the aliens:

Hello, all Turkish-speaking friends!

So I guess the phtons from Supernova 2011fe which have been arriving at such irregular speeds have been playing tag in either English or Turkish!

Ann

[Beyond]

Actually, who really knows what photons do on their long journeys? It's not like we can actually watch them on their long journeys, so maybe they do play photon games, out there in the vastness of space. What ever they do, i would have to assume that they do it in 'photonese'. Maybe that's why i don't understand most of what i see.

[neufer]

now, less than twelve hours after I wrote my last post about the supernova, it has now dropped to magnitude 10.8!!!

Perhaps the erratic/step function nature that you talk about has to do mostly
with the fact that your numbers are not being updated on timely basis.

<<SN 2011fe is a star which perished in a Type Ia supernova event that is currently visible from Earth. The star was discovered by the Palomar Transient Factory (PTF) survey on 24 August 2011 during an automated review of images of the Messier 101 from the nights of 22 and 23 August 2011. The star, formerly a white dwarf, is located in Messier 101, the Pinwheel Galaxy, 21 million light years from Earth. It was observed by the PTF survey very near the beginning of its supernova event, when it was approximately 1 million times too dim to be visible to the naked eye. It is the youngest type Ia ever discovered. About 13 September 2011, it reached its maximum brightness of apparent magnitude +9.9 which equals an absolute magnitude of about -19, equal to 2.5 billion Suns. At +10 apparent magnitude around 5 September, SN 2011fe was visible in small telescopes. As of 30 September the supernova is at +11 apparent magnitude in the early evening sky after sunset above the northwest horizon.

The Palomar Transient Factory is an automated telescopic survey that scans the sky for transient and variable astronomical events. Information is fed to the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Lab, which computes the information to identify new star events. After the initial observation of the SN 2011fe event, telescopes were used in the Canary Islands (Spain) to identify the emission spectrum of light emitted at various stages of the event. Following this, the Hubble Space Telescope, the Lick Observatory in California, and the Keck Observatory in Hawaii were used to observe the event in greater detail.

Although SN 2011fe was initially very faint, it brightened rapidly. On the day it was first imaged, 24 August 2011, it was 1 million times too dim to be visible to the unaided eye. One day later, it was 10 thousand times too dim. The next day it was 6 times brighter than that. On 25 August, the EVLA radio telescope failed to detect radio emissions from SN 2011fe. While such emissions are common for other types of supernovae, they have never been observed for Type Ia's.

Two possible candidates were proposed for the precursor system; however, subsequent analysis appears to rule them out.

Type Ia supernova events occur when a white dwarf star accretes enough additional matter to exceed the Chandrasekhar limit and collapse, triggering runaway fusion and a supernova explosion. Because this collapse happens at a consistent mass, the resulting explosions have very uniform characteristics, and are used as "standard candles" to measure the distance to their host galaxies. The exact brightness and behavior of a Type Ia supernova depends on the metallicity of its parent star (the fraction of the star composed of elements heavier than hydrogen and helium before its evolution into a white dwarf). Because the SN 2011fe event was detected so early, astronomers can gain a more accurate measurement of its initial composition and of its evolution during the supernova explosion, and so refine their models of Type Ia supernova events (resulting in more precise distance estimates for other Type Ia supernova observations).

Type Ia supernova standard candles may help provide evidence to support the hypothesis of dark energy and the accelerating expansion of the universe. A better understanding of type Ia supernova behavior may in turn allow theoretical models of dark energy to be improved.>>

[neufer]

You know this Pioneer 10 plaque which carried a message from humanity to whatever intelligent species this little spacecraft might encounter out there? Some years later, one of the Voyager probes carried a golden long-playing record with a lot more messages to E.T. Among other things, every nation that belonged to the United Nations sent a message to the aliens in their own language - well, in their own earthly language, not E.T.'s tongue. But who knows if E.T. doesn't speak the same language as we do, or at least the same language as some of us do? The Turkish representative at the U.N. recorded the following message for the aliens:

Hello, all Turkish-speaking friends!

So I guess the photons from Supernova 2011fe which have been arriving at such irregular speeds have been playing tag in either English or Turkish!

Distribution of the Turkic languages across Eurasia

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<<The Turkic languages constitute a language family of at least thirty five languages, spoken by Turkic peoples across a vast area from Eastern Europe and the Mediterranean to Siberia and Western China, and are considered to be part of the proposed Altaic language family.

The total number of Turkic speakers is over 250 million, including speakers of a second language. The Turkic language with the greatest number of speakers is Turkish proper, or Anatolian [and Balkan] Turkish, the speakers of which account for about 40% of all Turkic speakers.

Characteristic features of Turkish, such as vowel harmony, agglutination, and lack of grammatical gender, are universal within the Turkic family. There is also a high degree of mutual intelligibility between the various Oghuz languages, which include Turkish, Azerbaijani, Turkmen, Qashqai, Gagauz, and Balkan Gagauz Turkish.>>

Parrot page from "Codex Cumanicus"

<<The Codex Cumanicus was a linguistic manual of the Middle Ages, designed to help Catholic missionaries communicate with the Cumans, a nomadic Turkic people. It is currently housed in the Library of St. Mark, in Venice (Cod. Mar. Lat. DXLIX).

The "Cuman Riddles" (CC, 119-120; 143-148) are a crucial source for the study of early Turkic folklore. Andreas Tietze referred to them as "the earliest variants of riddle types that constitute a common heritage of the Turkic-speaking nations."

Among the riddles in the Codex are the following excerpts:

Aq küymengin avuzı yoq. Ol yumurtqa.
"The white kibitka has no mouth (opening). That is the egg."

Kökčä ulaχïm kögende semirir. Ol huvun.
"my bluish kid at the tethering rope grows fat, The melon."

Oturğanım oba yer basqanım baqır canaq. Ol zengi.
"Where I sit is a hilly place. Where I tread is a copper bowl. The stirrup.">>

[Ann]

I liked that Turkish stuff, Art. Not least the riddles. So they had blue melons in Turkey, then?

As for the supernova, SN 2011fe, the latest report from http://www.rochesterastronomy.org/supernova.html says that on Tue, 04 Oct 2011 03:13:49 GMT, the magnitude of the supernova was 10.9. It's clearly fading now, but slowly.

Ann

[Ann]

Here you can see a light-curve in three colors of SN 2011fe from AAVSO, American Association of Variable Star Observers.

As you can see, the supernova is fading, and its decline is steepest in blue light. This is typical of supernovae type Ia. According to http://www.skyandtelescope.com/communit ... 68728.html, the magnitude of SN 2011 is about 11.1 now, and it is fading by about 0.1 magnitude every two days.

Ann

[neufer]

Here you can see a light-curve in three colors of SN 2011fe from AAVSO, American Association of Variable Star Observers.

As you can see, the supernova is fading, and its decline is steepest in blue light. This is typical of supernovae type Ia. According to http://www.skyandtelescope.com/communit ... 68728.html, the magnitude of SN 2011 is about 11.1 now, and it is fading by about 0.1 magnitude every two days.

So what happened to your "stepped gables on the Hanseatic buildings of the city of Bruges"

[Ann]

Here you can see a light-curve in three colors of SN 2011fe from AAVSO, American Association of Variable Star Observers.

As you can see, the supernova is fading, and its decline is steepest in blue light. This is typical of supernovae type Ia. According to http://www.skyandtelescope.com/communit ... 68728.html, the magnitude of SN 2011 is about 11.1 now, and it is fading by about 0.1 magnitude every two days.

So what happened to your "stepped gables on the Hanseatic buildings of the city of Bruges"

Well, like you said... those darn people at http://www.rochesterastronomy.org/supernova.html hardly ever update! (Or they're so busy updating all other supernovae over - shouldn't that be below?- magnitude 17.0 that they don't have time for the real supernova-show! And hey... they don't even limit their attention to active supernovae, since today they even added a suspected nova, magnitude 18.7, in the Andromeada galaxy!)

P.S. This was apparently my 2000th post... Hooray!

Ann

[Beyond]

Hooray! That's it tisk-tisk. You had more of a celebration for the 1a when it hit 10.5. I'm tempted to give you a , but I'll be nice and refrain.

[Ann]

Ah! Supernova 2011fe has finally taken another step down! Or make that, http://www.rochesterastronomy.org/supernova.html has belatedly updated this supernova!

On Wed, 10/12/2011 05:11:47, Sn 2011fe was down to magnitude 11.2.

It's losing steam, I think!









Ann

[Ann]

On Tue, 18 Oct 2011 00:05:27 GMT, SN 2011fe was down to magnitude 11.6.

It's all downhill now.

Ann

[bystander]

Astronomy Without A Telescope – The Progenitor Problem
Universe Today | Steve Nerlich | 2011 Nov 26

[i]DEM L71 - a Type 1a supernova remnant. Analysis of the outer shockwave and inner ejecta indicate the remnant material does not greatly exceed 1 solar mass - and it contains a high iron to silicon/oxygen ratio. This all suggests that the progenitor star was a compact white dwarf. But, apart from that, the steps that led up to the explosion are a mystery (Credit: NASA/Chandra)[/i]

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[i]Surprisingly, the white dwarf merger scenario seems the more likely cause of Type 1a supernovae, based on current (though largely circumstantial) evidence. (Credit: Bad Astronomy/Discover)[/i]

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With so much of our current understanding of the universe based on Type 1a supernovae data, a good deal of current research is focused upon just how standard these supposed standard candles are. To date, the weight of analysis seems reassuring – apart from a few outliers, the supernovae do all seem very standard and predictable.

However, some researchers have come at this issue from a different perspective by considering the characteristics of the progenitor stars that produce Type 1a supernovae. We know very little about these stars. Sure, they are white dwarfs that explode after accumulating extra mass – but just how this outcome is reached remains a mystery.

Indeed, the final stages preceding an explosion have never been definitively observed and we cannot readily point to any stars as likely candidates on a pathway towards Type Ia-ness. In comparison, identifying stars that are expected to explode as core collapse supernovae (Types Ib, Ic or II) is easy – core collapse should be the destiny of any star bigger than 9 solar masses.

Popular theory has it that a Type 1a progenitor is a white dwarf star in a binary system that draws material off its binary companion until the white dwarf reaches the Chandrasekhar limit of 1.4 solar masses. As the already compressed mass of predominantly carbon and oxygen is compressed further, carbon fusion is rapidly initiated throughout the star. This is such an energetic process that the comparatively small star’s self-gravity cannot contain it – and the star blows itself to bits.

But when you try to model the processes leading up to a white dwarf achieving 1.4 solar masses, it seems to require a lot of ‘fine tuning’. The rate of accretion of extra mass has to be just right – too fast a flow will result in a red giant scenario. This is because adding extra mass quickly will give the star enough self-gravity so that it can partially contain the fusion energy – meaning that it will expand rather than explode.

Theorists get around this problem by proposing that a stellar wind arising from the white dwarf moderates the rate of infalling material. This sounds promising, although to date studies of Type 1a remnant material have found no evidence of the dispersed ions that would be expected from a pre-existing stellar wind.

Furthermore, a Type 1a explosion within a binary should have a substantial impact on its companion star. But all searches for candidate surviving companions – which would presumably possess anomalous characteristics of velocity, rotation, composition or appearance – have been inconclusive to date.

An alternative model for the events that lead up to a Type 1a are that two white dwarfs are drawn together, inexorably inspiralling until one or the other achieves 1.4 solar masses. This is not a traditionally favoured model as the time required for two such comparatively small stars to inspiral and merge could be billions of years.

However, Maoz and Mannucci review recent attempts to model the rate of Type 1a supernovae within a set volume of space and then align this with the expected frequency of different progenitor scenarios. Assuming that between 3 to 10 % of all 3-8 solar mass stars eventually explode as Type 1a supernovae – this rate does favour the ‘when white dwarfs collide’ model over the ‘white dwarf in a binary’ model.

There is no immediate concern that this alternate formation process would affect the ‘standardness’ of a Type 1a explosion – it’s just not the finding that most people were expecting.

Type-Ia supernova rates and the progenitor problem, a review - Dan Maoz, Filippo Mannucci

• arXiv.org > astro-ph > arXiv:1111.4492 > 18 Nov 2011

<< Previous

[bystander]

Closest Type Ia Supernova in Decades Solves Cosmic Mystery
Lawrence Berkeley National Laboratory | 2011 Dec 14

[i]The Palomar Transient Factory caught SN 2011fe in the Pinwheel Galaxy in the vicinity of the Big Dipper on 24 August, 2011. Found just hours after it exploded and only 21 million light years away, the discovery triggered the closest-ever look at a young Type Ia supernova. (Credit: B. J. Fulton, Las Cumbres Observatory Global Telescope Network)[/i]

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Type Ia supernovae (SN Ia’s) are the extraordinarily bright and remarkably similar “standard candles” astronomers use to measure cosmic growth, a technique that in 1998 led to the discovery of dark energy – and 13 years later to a Nobel Prize, “for the discovery of the accelerating expansion of the universe.” The light from thousands of SN Ia’s has been studied, but until now their physics – how they detonate and what the star systems that produce them actually look like before they explode – has been educated guesswork.

Peter Nugent of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) heads the Computational Cosmology Center in the Lab’s Computational Research Division and also leads the Lab’s collaboration in the multi-institutional Palomar Transient Factory (PTF). On August 24 of this year, searching data as it poured into DOE’s National Energy Research Scientific Computing Center (NERSC) from an automated telescope on Palomar Mountain in California, Nugent spotted a remarkable object. It was shortly confirmed as a Type Ia supernova in the Pinwheel Galaxy, some 21 million light-years distant. That’s unusually close by cosmic standards, and the nearest SN Ia since 1986; it was subsequently given the official name SN 2011fe.

Nugent says, “We caught the supernova just 11 hours after it exploded, so soon that we were later able to calculate the actual moment of the explosion to within 20 minutes. Our early observations confirmed some assumptions about the physics of Type Ia supernovae, and we ruled out a number of possible models. But with this close-up look, we also found things nobody had dreamed of.”

“When we saw SN2011fe, I fell off my chair,” says PTF team member Mansi Kasliwal of the Carnegie Institution for Science and the California Institute of Technology. “Its brightness was too faint to be a supernova and too bright to be nova. Only follow-up observations in the next few hours revealed that this was actually an exceptionally young Type Ia supernova.”

Because they could closely study the supernova during its first few days, the team was able to gather the first direct evidence for what at least one SN Ia looked like before it exploded, and what happened next. Their results are reported in the 15 December, 2011, issue of the journal Nature.

Confirming a carbon-oxygen white dwarf

Scientists long ago developed models of Type Ia supernovae based on their evolving brightness and spectra. The models assume the progenitor is a binary system – about half of all stars are in binary systems – in which a very dense, very small white-dwarf star made of carbon and oxygen orbits a companion, from which it sweeps up additional matter. There’s a specific limit to how massive the white dwarf can grow, equal to about 1.4 times the mass of our sun, before it can no longer support itself against gravitational collapse.

“As it approaches the limit, conditions are met in the center so that the white dwarf detonates in a colossal thermonuclear explosion, which converts the carbon and oxygen to heavier elements including nickel,” says Nugent. “A shock wave rips through it and ejects the material in a bright expanding photosphere. Much of the brightness comes from the heat of the radioactive nickel as it decays to cobalt. Light also comes from ejecta being heated by the shock wave, and if this runs into the companion star it can be reheated, adding to the luminosity.”

By examining how SN 2011fe’s brightness evolved – its so-called early-time light curve – and the features of its early-time spectra, members of the PTF team were able to constrain how big the exploding star was, when it exploded, what might have happened during the explosion, and what kind of binary star system was involved.

The first observations of SN 2011fe were carried out at the Liverpool Telescope at La Palma in the Canary Islands, followed within hours by the Shane Telescope at Lick Observatory in California and the Keck I Telescope on Mauna Kea in Hawaii. These were shortly followed by NASA’s orbiting Swift Observatory.

Says Nugent, “We made an absurdly conservative assumption that the earliest luminosity was due entirely to the explosion itself and would increase over time in proportion to the size of the expanding fireball, which set an upper limit on the radius of the progenitor.”

Daniel Kasen, an assistant professor of astronomy and physics at the University of California at Berkeley and a faculty scientist in Berkeley Lab’s Nuclear Science Division, explains that “it only takes a few seconds for the shock wave to tear apart the star, but the debris heated in the explosion will continue to glow for several hours. The bigger the star, the brighter this afterglow. Because we caught this supernova so early, and with such sensitive observations, we were able to directly constrain the size of the progenitor.”

“Sure enough, it could only have been a white dwarf,” says Nugent. “The spectra gave us the carbon and oxygen, so we knew we had the first direct evidence that a Type Ia supernova does indeed start with a carbon-oxygen white dwarf.”

The expected and the unexpected

“The early-time light curve also constrained the radius of the binary system,” says Nugent, “so we got rid of a whole bunch of models,” ranging from old red giant stars to other white dwarfs in a so-called “double-degenerate” system.

Kasen explains that “if there was a giant companion star orbiting nearby, we should have seen some fireworks when the debris from the supernova crashed into it.” A red giant would have made the supernova brighter by several orders of magnitude early on. “Because we didn’t observe any bright flashes like that, we determined that the companion star could not have been much bigger than our sun.”

Nor was there much chance the companion was another white dwarf in a double-degenerate system, unless it had somehow avoided being torn apart and littering the surroundings with debris. A shock wave plowing through that kind of rubble would have produced a burst of early light the observers couldn’t have missed. So unless the companion was positioned almost exactly between the exploding star and the observers on Earth, closer to it than a 10th the diameter of our sun – an unlikely set of circumstances – the white dwarf’s companion had to be a main-sequence star.

While these observations pointed to a “normal” SN Ia, the way the white dwarf exploded held surprises. Typical of what would be expected, early spectra obtained by the Lick three-meter telescope showed many intermediate-mass elements spewing out of the expanding fireball, including ionized oxygen, magnesium, silicon, calcium, and iron, traveling 16,000 kilometers a second – more than five percent of the speed of light. Yet some oxygen was traveling much faster, at over 20,000 kilometers a second.

“The high-velocity oxygen shows that the oxygen wasn’t evenly distributed when the white dwarf blew up,” Nugent says, “indicating unusual clumpiness in the way it was dispersed.” But more interesting, he says, is that “whatever the mechanism of the explosion, it showed a tremendous amount of mixing, with some radioactive nickel mixed all the way to the photosphere. So the brightness followed the expanding surface almost exactly. This is not something any of us would have expected.”

PTF team member Mark Sullivan of the University of Oxford says, “Understanding how these giant explosions create and mix materials is important because supernovae are where we get most of the elements that make up the Earth and even our own bodies – for instance, these supernovae are a major source of iron in the universe. So we are all made of bits of exploding stars.”

“It is rare that you have eureka moments in science, but it happened four times on this supernova,” says Andy Howell, coleader of PTF’s SN Ia team: “The super-early discovery; the crazy first spectrum; when we figured out it had to be a white dwarf; and then, the Holy Grail, when we figured out details of the second star.”

Howell adds, “We’re like Captain Ahab … except our white whale is a white dwarf. We’re obsessed with proving they cause supernovae, but the evidence has been eluding us for decades.” This time, he says, “We got our whale … and we lived.”

“This first close SN Ia in the era of modern instrumentation will undoubtedly become the best-studied thermonuclear supernova in history,” the PTF team notes in their Nature paper, and “will form the new foundation upon which our knowledge of more distant Type Ia supernovae is built.”

Two decades after the Berkeley-Lab-based Supernova Cosmology Project, led by 2011 Nobel Prize-winner in Physics Saul Perlmutter, proved that Type Ia supernovae could be used to measure the expansion history of the universe, Berkeley Lab astrophysicists and computer scientists have finally gotten a close-up look at what these remarkable cosmic mileposts really look like.

Supernova 2011fe from an Exploding Carbon-Oxygen White Dwarf Star - Peter E. Nugent et al

• Nature 480 344 (15 Dec 2011) DOI: 10.1038/nature10644
  arXiv.org > astro-ph > arXiv:1110.6201 > 27 Oct 2011

Astronomers Find New Clues to Supernova Origins
WM Keck Observatory | 2011 Dec 14

Scientists Publish New Findings about the ‘Supernova of a Generation'
University of California, Santa Barbara | 2011 Dec 14

Solving a supernova mystery
Carnegie Institution for Science | 2011 Dec 14

Supernova Caught in the Act
National Science Foundation | 2011 Dec 14

The "Supernova of a Generation" Shows Its Stuff
California Institute of Technology | 2011 Dec 14

[bystander]

Hubble images help pin down identity of August supernova’s companion star
University of California, Berkeley | 2011 Dec 15

In August, as amateurs and professionals alike turned their telescopes on the nearest Type Ia supernova discovered in decades, University of California, Berkeley, research astronomer Weidong Li focused instead on what could not be seen.

Li, who died on Monday, Dec. 12, pulled up images of the northern sky taken over the past nine years by the Hubble Space Telescope in search of the star and its binary companion as they looked before the supernova explosion. But his initial disappointment when he saw no star at all quickly turned to excitement.

Because the Hubble telescope is so sensitive, the fact that it did not detect any stars in the area in the Big Dipper told Li and his colleagues that neither the pre-supernova “progentitor” star – presumably a white dwarf – nor its companion were bright. In fact, Li’s analysis of the archival high-resolution Hubble telescope data suggests that the companion to the Aug. 24 supernova could not have been a bloated red giant or a bright helium star, which would have been visible.

Instead Li and his colleagues conclude in a paper published in the Dec. 15 issue of the journal Nature that the companion was most likely a normal star like the sun, a somewhat evolved star called a subgiant, or perhaps a white dwarf.

Li’s discovery about the supernova’s origins is helping astronomers understand more about the explosive mechanisms of Type Ia supernovae, which are the foundation of discoveries for which three scientists – including UC Berkeley physics professor Saul Perlmutter – last weekend were awarded the 2011 Nobel Prize in Physics.

“Our paper is the first ever to exclude directly some of the major candidates for Type Ia supernovae,” said coauthor Joshua Bloom, UC Berkeley associate professor of astronomy.

The team’s finding fits with new theoretical modeling of the exploding white dwarf by the supernova’s discoverers: Peter Nugent, head of the Computational Cosmology Center at Lawrence Berkeley National Laboratory, and his colleagues, including physicists from UC Berkeley. They also published their conclusions in the Dec. 15 issue of Nature.

Type Ia supernovae indicate accelerating expansion of universe

Type Ia supernovae are bright and visible across huge cosmic distances, which allowed Perlmutter, his Nobel laureate colleagues and their teams to employ them as “standard candles” to measure the universe. In 1998, these studies revealed that the expansion of the universe is accelerating, and such acceleration is now widely believed to require the presence of a mysterious “dark energy.”

“The discovery of the accelerating expansion of the Universe has revolutionized physics, and the repulsive dark energy may provide key clues to the long-sought quantum theory of gravity,” said coauthor Alex Filippenko, who was a member of both of the teams that made the Nobel Prize-winning discovery and a UC Berkeley professor of astronomy. “But the actual origins of Type Ia supernovae have remained mysterious, and various aspects of the explosion are not well understood.”

Astronomers believe that the star that explodes to produce a Type Ia supernova is a white dwarf composed primarily of carbon and oxygen, but the white dwarf presumably explodes because it pulls matter from a binary companion that astronomers to date have been unable to identify.

An opportunity to study such explosions at close hand came on Aug. 24, when Nugent, while looking at data from the Palomar Transient Factory (PTF), which searches for short-lived events in space, spotted a remarkable object in the nearby Pinwheel Galaxy (Messier 101) some 21 million light years away. Subsequently named SN 2011fe, it garnered worldwide attention as the nearest such supernova in the past 25 years. Although its brightness was 40 times too faint for the eye to see, for a month the supernova could be easily viewed through binoculars, a rare occurrence among amateur astronomers and the general public.

“These are the sorts of important events that the Palomar Transient Factory was designed to uncover,” said PTF principal investigator Shrinivas Kulkarni, a professor at the California Institute of Technology.

Li immediately thought of looking for the original star and its companion in past Hubble data, seeing it, he said, as “a golden opportunity to investigate the properties of the progenitor system through direct imaging.”

Within two days, Li and about 30 collaborators from around the world were able to obtain images of the supernova from the 10-meter Keck Telescope in Hawaii and its adaptive optics system. Using these high-resolution images, they pinpointed the exact location of the supernova, but when they saw nothing there, they used the red, green and blue wavelength observations from the telescope to set a stringent limit on how bright the progenitor and its companion could be.

The authors then were able to exclude the presence of a red giant and most types of helium stars, leaving a faint white dwarf or a subgiant star as likely companions.

Next steps include using more sensitive telescopes, such as the planned James Webb Space Telescope, to detect the faint surviving companion star.

“That will give us another opportunity to reveal more secrets about this supernova and ultimately help us understand the explosion physics of Type Ia supernovae, and possibly refine them as an even better cosmological distance ladder,” Li said.

Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe - Weidong Li et al

• Nature 480 348 (15 Dec 2011) DOI: 10.1038/nature10646

A Supernova with a View
Weizmann Institute of Science | 2011 Dec 15

[Ann]

That's really very very interesting. To me, the most intriguing detail by far is that the companion of the exploding white dwarf was not a red giant.

Personally, I think astronomers have been a little too enamored of red giants. I remember the shock that ripped through the astronomical community when it was found that the progenitor of SN 1987A was not a red giant, but a blue star. Common wisdom, up until then, had been that supernovae always involved red giants. Either it was the red giant itself that exploded as a supernova, or else it was a red giant that fed matter to a white dwarf so that it exploded.

Well, the nearest and best-studied supernova type II had no red giant involved, and the nearest and best-studied supernova type Ia had no red giant involved.

I'm not saying that red giants can't be the progenitors of supernovae, and I'm not saying that they can't feed white dwarfs so that they explode. Personally I'm convinced that both scenarios happen frequently.

But I find it so interesting, nevertheless, that the red giants are not a necessary requirement for a supernova. They are not the holy grail that solves the supernova mystery.

Ann

[bystander]

Journal Club: When White Dwarfs Collide
Universe Today | Steve Nerlich | 2012 Jan 21

Today's article outlines how Type 1a supernovae may arise from the collision of two white dwarfs - and how this may be a much more common cause than we had previously supposed.

[url=http://www.universetoday.com/88465/astrophoto-supernova-ptf11kly-in-m101-by-rick-johnson/][b][i]Supernova PTF11kly in M101. Credit: Rick Johnson[/i][/b][/url]

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There is growing interest about the nature of the events that precede Type 1a supernovae. We are confident that the progenitor stars of Type 1a supernovae are white dwarfs – but these stars have generally very long lives, making it difficult to identify stars that are potentially on the brink of exploding.

We are also confident that something happens to cause a white dwarf to accumulate extra mass until it reached its Chandrasekhar limit (around 1.4 solar masses, depending on the star’s spin).

For a long time, it had been assumed that a Type 1a supernova probably arose from a binary star system with a white dwarf and another star that had just evolved into a red giant, its outer layers swelling out into the gravitational influence of the white dwarf star, This new material was accreted onto the white dwarf until it hit its Chandrasekhar limit – and then kabloowie.

However, the white-dwarf-red-giant-binary hypothesis is currently falling out of favour. It has always had the problem that any Type 1 supernovae has, by definition, almost no hydrogen absorption lines in its light spectrum – which makes sense for a Type 1a supernovae arising from a hydrogen-expended white dwarf – but then what happened to the new material supposedly donated by a red giant partner (which should have been mostly hydrogen)?

Also, the recently discovered Type 1a SN2011fe was observed just as its explosion was commencing, allowing constraints to be placed on the nature of its progenitor system. Apparently there is no way the system could have included something as big as a red giant and so the next most likely cause is the merging (or collision) of two white dwarfs.

Other modeling research has also concluded that the two white dwarf merger scenario maybe statistically more likely to take place than the red giant accretion scenario – since the latter requires a lot of Goldilocks parameters (where everything has to be just right for a Type 1a to eventuate).

This latest paper expands the possible scenarios under which a two white dwarf merger could produce a Type 1a supernovae – and finds a surprising number of variations with respect to mass, chemistry and the orbital proximities of each star. Of course, it is just modeling but it does challenge the current assertion at the relevant Wikipedia entry that white dwarf mergers are a second possible, but much less likely, mechanism for Type 1a supernovae formation.

So – comments? Anyone want to defend the old red-giant-white-dwarf scenario? Does computer modeling count as a form of evidence?

How the merger of two white dwarfs depends on their mass ratio: orbital stability and detonations at contact - Marius Dan et al

• arXiv.org > astro-ph > arXiv:1201.2406 > 11 Jan 2012

Earliest-yet observation of August supernova nails it
University of California, Berkeley | via EurekAlert | 2012 Jan 11

The Contributor to SN 2011fe
Universe Today | Jon Voisey | 2012 Jan 08

A Stellar Discovery
University of California, Berkeley | Timothy Lesle | 2012 Jan 03

Constraints on the Progenitor System of the Type Ia Supernova SN 2011fe/PTF11kly - Weidong Li et al

• Nature 480(7377) 348 (2011 Dec 14) DOI: 10.1038/nature10646
  arXiv.org > astro-ph > arXiv:1109.1593 > 07 Sep 2011

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[Ann]

For me as a non-lover of red things, it has been interesting and somewhat frustrating to see astronomers invoke red stars to explain all supernovae. Supernova 1987A demonstrated that non-red giants can explode as core-collapse supernovae, and the comparatively nearby Type Ia in Messier 101 apparently demonstrates that no big red star was involved in the explosion.

It is of course compelling evidence against the red giant theory that Type Ia supernovae are defined as supernovae with no hydrogen in their spectra - so how could they get that way if they are forced to explode by having hydrogen dumped on them?

But I can see another problem if supernovae Type Ia are made by two colliding white dwarfs. White dwarfs come in different varieties and have different masses, but the supernovae Type Ia are often extremely similar. How can they get that way if the explosions involve different amounts of mass?

Ann