STScI: Hubble Solves Mystery on Nearby Supernova Source

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STScI: Hubble Solves Mystery on Nearby Supernova Source

Post by bystander » Thu Jan 12, 2012 4:32 am

STScI: Hubble Solves Mystery on Nearby Supernova Source
NASA STScI | HubbleSite | 2012 Jan 11
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.

"We know that Hubble has the sensitivity necessary to detect the faintest white dwarf remnants that could have caused such explosions," said lead investigator Bradley Schaefer of Louisiana State University (LSU) in Baton Rouge. "The logic here is the same as the famous quote from Sherlock Holmes: 'When you have eliminated the impossible, whatever remains, however improbable, must be the truth.'"

The cause of SNR 0509-67.5 can best be explained by two tightly orbiting white dwarf stars spiraling closer and closer until they collided and exploded.

These results are being reported today at the meeting of the American Astronomical Society in Austin, Texas. A paper on the results will be published in the January 12 issue of the science journal Nature.

For four decades the search for Type Ia supernovae stellar progenitors has been a key question in astrophysics. The problem has taken on special importance over the last decade with Type Ia supernovae being the premier tools for measuring the accelerating universe.

Type Ia supernovae are tremendous explosions of energy in which the light produced is often brighter than a whole galaxy of stars. The problem has been to identify the type of star system that pushes the white dwarf's mass over the edge and triggers this type of explosion. Many possibilities have been suggested, but most require that a companion star near the exploding white dwarf be left behind after the explosion.

Therefore, a possible way to distinguish between the various progenitor models has been to look deep in the center of an old supernova remnant to search for the ex-companion star.

In 2010, Schaefer and Ashley Pagnotta of LSU were preparing a proposal to look for any faint ex-companion stars in the center of four supernova remnants in the Large Magellanic Cloud when they discovered that the Hubble Space Telescope had already taken the desired image of one of their target remnants, SNR 0509-67.5, for the Hubble Heritage program, which collects images of especially photogenic astronomical targets.

In analyzing the central region they found it to be completely empty of stars down to the limit of the faintest objects that Hubble can detect in the photos. Schaefer reports that the best explanation left is the so-called "double degenerate model" in which two white dwarfs collide.

There are no recorded observations of the star exploding. However, researchers at the Space Telescope Science Institute in Baltimore, Md., have identified light from the supernova that was reflected off of interstellar dust, delaying its arrival at Earth by 400 years. This delay, called a light echo, of the supernova explosion also allowed the astronomers to measure the spectral signature of the light from the explosion. By virtue of the color signature, astronomers were able to deduce it was a Type Ia supernova.

Because the remnant appears as a nice symmetric shell or bubble, the geometric center can be accurately determined. These properties make SNR 0509-67.5 an ideal target to search for ex-companions. The young age also means that any surviving stars have not moved far from the site of the explosion.

The team plans to look at other supernova remnants in the Large Magellanic Cloud to further test their observations.

An absence of ex-companion stars in the type Ia supernova remnant SNR 0509−67.5 - Bradley E. Schaefer & Ashley Pagnotta
Astronomers Discover Origin of Thermonuclear Supernova
Louisiana State University | 2012 Jan 11
http://www.phys.lsu.edu/SNprogenitor/

SNR 0509-67.5
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ScienceShot: No Star Left Behind

Post by bystander » Mon Aug 20, 2012 6:39 pm

ScienceShot: No Star Left Behind
Science NOW | Ken Croswell | 2012 Aug 17
Contrary to expectations, the brightest supernova in recorded history left no star in its wake, say astronomers who have searched the celestial wreckage (shown). In 1006, observers watched a star explode in the constellation Lupus that shone about a dozen times more brilliantly than Venus ever does. The explosion was a Type Ia supernova, the most luminous variety, which occurred when a small, dense star known as a white dwarf blew up about 7000 light-years from Earth. Such a supernova is supposed to result when a larger companion star dumps material onto the white dwarf, triggering a runaway nuclear reaction that annihilates the small star. However, as astronomers will report in The Astrophysical Journal, a thorough search for the companion, which should have survived the explosion, has turned up nothing. This finding dovetails with a similar nondetection in a nearby galaxy and suggests the explosion arose instead when two white dwarfs that were in orbit around each other merged and blew up—hinting that more Type Ia supernovae may stem from double white dwarfs than astronomers had thought.

Hunting for the progenitor of SN 1006: High resolution spectroscopic search with the FLAMES instrument - Wolfgang E. Kerzendorf et al
SN 1006
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Supernova 1006 lived fast and left no companion behind

Post by bystander » Thu Sep 27, 2012 6:39 pm

Supernova 1006 lived fast and left no companion behind
Scientific American | Kelly Oakes | 2012 Sep 26

Cause of Supernova SN 1006 Revealed
University of Barcelona | 2012 Sep 27

No surviving evolved companions of the progenitor of SN 1006 - Jonay I. González Hernández et al
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Re: STScI: Hubble Solves Mystery on Nearby Supernova Source

Post by Ann » Fri Sep 28, 2012 12:27 am

This is certainly very interesting, but I'm still reeling from what seems to me like the "perfect" explanation for many of the Type Ia supernovae. The idea would be that the white dwarf that is going to explode has a nearby, puffed-up giant companion. Gas streams from the companion onto the white dwarf, whose rotation is "spun up" as a result of having gas falling onto it. As the companion dumps more and more gas on the white dwarf, the dwarf rotates ever faster, while the companion shrinks and gets fainter.

Eventually the companion has been "bled dry". It has no gas left to give to the now very massive white dwarf. The companion has become small and very dim. Compare the scenario with the star Algol! A bright B-type main sequence star is "stealing gas" from an emaciated red giant. Although the red giant is still larger than the B-type star, it is also much fainter, and it contains only about one fourth as much mass as the main sequence component, even though the giant must once have been the more massive star.

Let's return to the white dwarf stealing gas from its evolved companion. The white dwarf might be spun up to the point where its mass exceeds its Chandrasekhar limit, so that it should really already have exploded as a Type Ia supernova. But because of the centrifugal forces in the rapidly rotating star, the mass of the star does not "press down on the center of it" with enough force to make it explode.

But when the former red giant has been "bled dry" to the point that it can give no more gas to the wildly rotating white dwarf, the mechanism that is speeding up the rotation of the degenerate star is turned off, and the star's rapid rotation will gradually slow down. But at a certain point the rotation will have slowed down to the point where the centrifugal forces can no longer counteract the great mass of the white dwarf. Therefore it will explode, and since it contains more mass than the Chandrasekhar limit technically allows, it will explode as a very brilliant Type Ia supernova.

When astronomers then search for the companion of the white dwarf that exploded, they will likely find nothing. The companion is still there, but it is so small, faint and shriveled that astronomers aren't likely to detect it.

It seems to me that this scenario might explain a large number of Type Ia supernovae, certainly many of the more brilliant ones. And just because astronomers can't find the companion of the white dwarf doesn't mean it isn't there, it if has had most of its mass stolen from it and turned into a cinder.

See http://asterisk.apod.com/viewtopic.php?f=31&t=29479

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Texas: 'White Widow' Scenario for Type Ia Supernovae

Post by bystander » Fri Oct 26, 2012 10:14 pm

The White Widow Model: A New Scenario for the Birth of Type Ia Supernovae
University of Texas | McDonald Observatory | 2012 Oct 25
Image
No partner star found for Tycho's Supernova Remnant
(Credit: X-ray: NASA/CXC/Rutgers/K.Eriksen et al.; Optical: DSS)
J. Craig Wheeler has studied the exploding stars called supernovae for more than four decades. Now he has a new idea on the identity of the "parents" of one of the most important types of supernovae — the Type Ia, those used as "standard candles" in cosmology studies that led to the discovery of dark energy, the mysterious force causing the universe's expansion to speed up.

Wheeler lays out his case for supernova parentage in the current issue of The Astrophysical Journal. He explains why he thinks the parents of Type Ia could be a binary star made up of white dwarf star (the burnt-out remnant of a Sun-like star) and a particular type of small star called an “M dwarf.”

In the paper, he explains that current theories for Type Ia parents don't correctly match up with telescope data on actual supernovae.

There are two main models today that attempt to explain how Type Ia supernovae are born. One is called a “single-degenerate model,” in which a binary star is made up of a degenerate, or dead star, called a white dwarf paired with a younger star. Over time, as the stars orbit each other, the white dwarf’s gravity siphons gas from the atmosphere of its partner star until the white dwarf becomes so massive and dense that it ignites, triggering an immense thermonuclear explosion.

Wheeler wrote the first scientific paper invoking this idea in 1971. Astronomers have been trying to identify what type of star the partner must be ever since.

The other, more recent, theory for building a Type Ia supernova is known as the “double-degenerate model.” Here, it takes two white dwarfs in a binary system spiraling together and colliding to create a Type Ia supernova.

The telescope data support neither completely, Wheeler says.

Astronomers have carefully observed supernovae for decades. In the best-case scenario, a supernova is watched from the time it is discovered and becomes extremely bright, until its fades from view. Its light signature, or spectrum, changes over that time. Any models of supernova parents must reproduce an evolving spectrum that matches that of actual supernovae.

"I believe that the spectra have to be respected,” Wheeler said. "The really high-order constraint [on a supernova model] is to get the spectral evolution correct. That is, you've got to get all the bumps and wiggles, and they've got to be in the right place at the right times."

Telescope observations in the last few years have considerably narrowed the possibilities on which models work, he said, "putting tighter and tighter constraints on whether any companion star exists and what kind of star it can be."

Now, Wheeler thinks maybe a new twist on the single-degenerate model can fill the bill. He says pairing the white dwarf with an M dwarf could do the trick.

"M dwarfs are the most common star in the galaxy, and white dwarfs are the second-most common star in the galaxy,” he said. “And there's lots of M dwarf-white dwarf binary systems. Do they make Type Ia supernovas? That's another question."

In the paper, he lays out evidence why he thinks the M dwarf is a good candidate:

First, M dwarfs are dim. In recent years, astronomers using large telescopes have looked hard at the gaseous remnants left behind by Type Ia supernovae for the partner star that would be left behind after the white dwarf detonated. “One thing blows up as a supernova, the other thing's got to be left behind,” Wheeler said. “Where is it? We don't see it.”

Small, red M dwarfs are dim enough to work — even the most massive M dwarf would not show up on Hubble Space Telescope observations. And it’s even possible, Wheeler said, that the white dwarf could have devoured the entire M dwarf before the white dwarf exploded. M dwarfs don’t have heavy cores to leave behind.

Wheeler calls this scenario a "white widow system," a play on words referencing the stellar binaries known as "black widow systems," in which a neutron star eats its stellar companion. In the "white widow" case, the predator is a white dwarf.

The second reason the M dwarf is likely the white dwarf's co-parent in producing Type Ia supernovae is that M dwarfs are magnetic. “They flare, they do all sorts of crazy things,” Wheeler said. His thought experiment supposes that the white dwarf is magnetic as well. “That's the thrust of the paper, to think about what happens if both stars are magnetic,” he said.

Though astronomers studying other types of stars have included magnetic fields in their theories, "it's just a completely different part of parameter space to bring in the role of magnetic fields in the supernova game,” Wheeler said. But “it is the way nature works. Things are magnetic. The Sun is magnetic; the Earth is magnetic. The magnetic fields are there. Are they big enough to do something?"

If a magnetic white dwarf and a magnetic M dwarf are in a binary star pair, Wheeler said, their opposite magnetic poles would attract, and they would become tidally and magnetically locked into a rotation in which the same side of each always faces the other and the magnetic poles point directly at one another. In this case, the white dwarf still pulls material off of the M dwarf, but the material would build up on a single spot on the white dwarf that pointed right back at the M dwarf, irradiating it and driving off even more mass, consuming the M dwarf and leading to an eventual explosion.

White Dwarf/M Dwarf Binaries as Single Degenerate Progenitors of Type Ia Supernovae - J. Craig Wheeler
Tycho's Supernova Remnant
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Re: ScienceShot: No Star Left Behind

Post by JunoJim » Sat Nov 24, 2012 10:18 pm

I'm a newbie, but I was wondering if anyone knew or had an idea of what may be the "yellow" streaks on the upper right ofthe photo ???

Looking at other images, the cloud is separated into two masses, upper left, and lower right, I wonder if the streaks are "lightning", serving to equalize different electrical charges of the two masses ???
bystander wrote:ScienceShot: No Star Left Behind
Science NOW | Ken Croswell | 2012 Aug 17
Contrary to expectations, the brightest supernova in recorded history left no star in its wake, say astronomers who have searched the celestial wreckage (shown). In 1006, observers watched a star explode in the constellation Lupus that shone about a dozen times more brilliantly than Venus ever does. The explosion was a Type Ia supernova, the most luminous variety, which occurred when a small, dense star known as a white dwarf blew up about 7000 light-years from Earth. Such a supernova is supposed to result when a larger companion star dumps material onto the white dwarf, triggering a runaway nuclear reaction that annihilates the small star. However, as astronomers will report in The Astrophysical Journal, a thorough search for the companion, which should have survived the explosion, has turned up nothing. This finding dovetails with a similar nondetection in a nearby galaxy and suggests the explosion arose instead when two white dwarfs that were in orbit around each other merged and blew up—hinting that more Type Ia supernovae may stem from double white dwarfs than astronomers had thought.

Hunting for the progenitor of SN 1006: High resolution spectroscopic search with the FLAMES instrument - Wolfgang E. Kerzendorf et al
SN 1006

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Re: STScI: Hubble Solves Mystery on Nearby Supernova Source

Post by geckzilla » Sat Nov 24, 2012 11:24 pm

According to the info page for the image, yellow & orange represent optical data. It's only a particularly strong area of optical density. Red is radio, blue x-ray. So the question you might ask is why did the material become so compact at that particular arc in the circle, not whether or not it's some form of electricity. It looks kind of like it ran into something and smooshed together. There's an amateur explanation for you. ha
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Re: STScI: Hubble Solves Mystery on Nearby Supernova Source

Post by Ann » Sun Nov 25, 2012 6:56 am

Planetary nebulae by HST
I won't even offer my own amateur explanation to you. But I note that the shape you describe, with a bright rim, which is brighter in some places than in others, is common when it comes to planetary nebulae. Of course there is a big difference between planetary nebulae and supernova remnants, particularly when it comes to their formation. But interestingly enough, their shapes can be rather similar.

Anyway, supernovae remnants often seem to contain sharp rims. This is a Hubble Telescope picture of a part of another supernova remnant. The color is red because this filament was only detected in red hydrogen alpha light.

One supernova remnant that is made up of a series of nested rims and filaments is Simeis 147. Note that this supernova remnant is seen in visible light. It glows in red hydrogen alpha light.

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Re: STScI: Hubble Solves Mystery on Nearby Supernova Source

Post by JunoJim » Mon Nov 26, 2012 11:40 pm

Yellow is optical - lines are pretty straight - I still wonder...

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