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Fraser
2004-Oct-28, 04:44 PM
SUMMARY: Using the Hubble Space Telescope, astronomers have located what they think is the burned out star at the heart of Tycho's Supernova Remnant, which exploded in 1572. This discovery provides the first direct evidence that these kind of supernovae, called Type 1a, occur when a white dwarf consumes material from a binary companion until it reaches a certain point and explodes. They discovered the star, which is similar to our own Sun, because it's moving away from the explosion three times faster than other objects in the region - it was sling shotted away when its dancing partner vapourized.

What do you think about this story? Post your comments below.

Guest
2004-Oct-28, 06:03 PM
How is it possible that the star was not consumed in the supernova blast?! :o :ph34r:

antoniseb
2004-Oct-28, 06:22 PM
Originally posted by Guest@Oct 28 2004, 06:03 PM
How is it possible that the star was not consumed in the supernova blast?!
There were two stars very near each other. One suddenly exploded, leaving only debris, and promptly giving off 10^51 ergs of energy. The other star was a million miles across, and absorbed perhaps 10^47 ergs. This is a lot of energy, but only enough to blow away the outer layers of the star.

Another way to look at it is that the star that exploded had enough energy to blow a star apart, but the other one only got about one ten-thousandth enough energy to blow a star apart.

om@umr.edu
2004-Oct-28, 11:49 PM
Originally posted by antoniseb@Oct 28 2004, 06:22 PM
This is a lot of energy, but only enough to blow away the outer layers of the star.
Must have been another one of those homogeneous stars.

After "the outer layers of the star" were blown away, the surviving star ". . . is similar to our Sun".

Sounds fishy to me.

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2004-Oct-29, 01:21 PM
Originally posted by om@umr.edu@Oct 28 2004, 11:49 PM
Must have been another one of those homogeneous stars.
No more homogenous than the current model for the sun. Clearly is was not something like the model described in the "Iron Sun" thread in the alternative theories section.

Here's a more detailed paper on the observations.
The binary progenitor of Tycho Brahe’s 1572 supernova (http://www.arxiv.org/PS_cache/astro-ph/pdf/0410/0410673.pdf)
Don't be frightened by the 31 page length, the actual paper is about 7 pages long, the rest is figures, captions, references, etc.

Note that the paper indicates that the star, Tycho G, is similar to the sun in some ways, it is not exactly like the sun. It is an evolved G0 to G2 sub-giant with a low surface gravity, which means that it has a lot of extra heat expanding what is now its outer shell. It also has a few other peculiar spectral characteristics indicating that it absorbed some Fe and Ni from the explosion of its companion.

What spectral type was this star before the explosion? Most likely it was an F star.

The paper also points out that the velocity of Tycho G indicates that it had an orbital period of between two and seven days before the explosion.

om@umr.edu
2004-Oct-29, 01:37 PM
Originally posted by antoniseb@Oct 29 2004, 01:21 PM
It also has a few other peculiar spectral characteristics indicating that it absorbed some Fe and Ni from the explosion of its companion.


Sounds fishy to me.

Oliver
http://www.umr.edu/~om

antoniseb
2004-Oct-29, 02:49 PM
Originally posted by om@umr.edu@Oct 29 2004, 01:37 PM
Sounds fishy to me.
So read the paper. It may still sound fishy, but then you'll be able to give some explicit details as to what's in doubt about their observations and conclusions. Just adding a tone of doubt is the sort of thing the younger kids on the forum do, but not what we've come to expect from you.

om@umr.edu
2004-Oct-29, 03:48 PM
Sorry, Anton.

You are right.

I should have said your explanation, that the star "absorbed some Fe and Ni from the explosion of its companion" seems ad hoc to me.

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2004-Oct-29, 04:05 PM
Originally posted by om@umr.edu@Oct 29 2004, 03:48 PM
I should have said your explanation, that the star "absorbed some Fe and Ni from the explosion of its companion" seems ad hoc to me.
On that one, I was just paraphrasing the paper. Their point was that in the search they were looking for a star that met certain characteristics, one of which was elevated Fe and Ni levels. The actual observed levels are lower than solar levels [if I read the paper correctly], but higher than the levels expected for a halo star that just happened to be passing through the area. This was only a test of whether the star was a candidate do be the free-flying widow of the ex-white-dwarf.

Generally, I thought the paper would be one you'd latch on to, since it mentions Fe and Ni as part of the slower moving ejection debris. That being said, your model for our sun is not based on a type 1a supernova, so this object says little about the specifics of your theory.

om@umr.edu
2004-Oct-29, 04:08 PM
Anton,

I think you were paraphrasing the paper correctly.

The critical data on Fe and Ni in Tycho G are in Fig 3 and Supplementary Fig 1 of the paper.

I cannot make sense of their "Normalized flux" on the vertical axis of the line spectra in Fig. 1.

However, the caption to Fig 1 states, "We have not detected significant spectroscopic anomalies, either here or in the whole sample, and most spectra are well produced assuming solar abundances".

With kind regards,

Oliver
http://www.umr.edu/~om

VanderL
2004-Oct-29, 05:29 PM
Is the stars' speed and direction something that is caused by the suprnova event?
I would like to hear thoughts on what can accelerate a star away from a supernova, and leave the star intact. I'm not sure the star is speeding away from the site of the explosion but the fact it is "moving away three times faster" than any other star in the region, makes me wonder if this can really be caused by the suprnova event.
Any thoughts?

Cheers.

antoniseb
2004-Oct-29, 07:15 PM
Originally posted by VanderL@Oct 29 2004, 05:29 PM
makes me wonder if this can really be caused by the suprnova event. Any thoughts?
The idea expressed in the paper is that the star 'Tycho G' was orbiting the slightly heavier white dwarf with an orbital period of between two and seven days, and that one day the star changed from orbiting a white dwarf to being in the middle of a hot cloud with no white dwarf present any more to keep it bound. The effect would be similar to swinging a ball on a string around your head, and then letting go. [I'm free, I'm free!, Forget these tight ellipses, I'm gonna go in a straight line!] I don't think that any momentum added to Tycho G by shrapnel from the ex-white-dwarf would contribute substantially to its momentum.

Duane
2004-Oct-29, 07:49 PM
I second what antoniseb says, I would only add that the SN explosion would have imparted a small amount of acceleration to the star. Its current velocity is far more related to its past orbit, however.

VanderL
2004-Oct-29, 09:51 PM
Ok, I see the picture, so the star is now no longer in gravitational interaction with the supernova remnant.
That doesn't influence the integrity of the star itself?
Also the supernova is caused by a stars' collapse, does it loose more than half it's original mass? Is it known how large the mass-loss of a supernova really is (or can be)?

Cheers.

Duane
2004-Oct-29, 10:21 PM
Originally posted by VanderL@Oct 29 2004, 09:51 PM
so the star is now no longer in gravitational interaction with the supernova remnant. That doesn't influence the integrity of the star itself?


The short answer is no, but I know that won't be enough to satisfy you V, so to try and explain:

The star's integrety would have been more influenced by the close-orbiting relationship it had with the white dwarf then by is sudden "release" from the WD's gravity. Once the gravity well of the WD was removed, the intergrety of the companion would have been stronger, not weaker.


Also the supernova is caused by a stars' collapse, does it loose more than half it's original mass? Is it known how large the mass-loss of a supernova really is (or can be)?


You have asked these questions in an odd way. Remember that this is a Type 1A supernova--it arose when a white dwarf star accumulated enough material from a companion to exceed the Chandrakesar Limit of 1.4 solar masses. The progenitor star was totally disrupted by the resulting explosion--in other words, ALL of its mass was lost!

In Type II supernovas, the amount of mass lost is dependant on the starting mass of the collapsing star. A very large star will have no mass loss--it collapses into a black hole.

Guest
2004-Oct-29, 11:14 PM
Hi Duane, thanks for answering,

I thought that this type of supernova left a neutron star, but it looks as though I'm mistaken. I had the impression that neutron stars are small compact objects that are quite massive, hence the question on mass-loss.

Cheers.

Duane
2004-Oct-30, 04:51 PM
There are some studies that suggest a low-mass neutron star might remain after an explosion of a white dwarf. There are a handful of lower mass (less than ~1.4Sm) neutron stars seen orbiting companions that might have arisen this way. In all cases, the NS's are from 0.96 to 1.35 Sm, so you would be taking roughly 0.1 to 0.5 Sm lost.

VanderL
2004-Oct-31, 11:03 AM
Ok Duane,

So there are several ways to get a Supernova (the different types) and there are several different "outcomes", all depending on the mechanism and the proprties of the progenitor(s). The outcome is not always clear (companions are not always found), which makes all this supenova business very confusing for me.
To me it looks like there is no way to really verify what is going on, other than "retro-fitting" the data with the different theoretical models for the different supernova types. Is there any webpage that you know of where the mechanisms/progenitors/"offspring" can be found?

Cheers.

antoniseb
2004-Oct-31, 02:16 PM
Hi VanderL,

When a white dwarf becomes a type 1a supernova, it is very rapidly converts the carbon and oxygen in it to Iron. Some details are still fuzzy, but there is much more energy available than when Magnesium and Sulfur are being turned to iron. The White Dwarf leaves no unified remnant. It is just a rapidly expanding cloud of hot debris.

VanderL
2004-Oct-31, 09:48 PM
Hi Antoniseb,

Thanks for the explanation, so that type of supernova (Ia) never leaves an identifiable star?
Suppose the white dwarf had a companion, would it be possible for it to survive?

Cheers.

Duane
2004-Nov-01, 06:25 PM
So there are several ways to get a Supernova (the different types) and there are several different "outcomes", all depending on the mechanism and the proprties of the progenitor(s). The outcome is not always clear (companions are not always found), which makes all this supenova business very confusing for me.


Yes there are different types of supernovas, but they are really not all that hard to comprehend. There are essentially 2 main types, a Type 1A and a Type II. There are a number different sub-catagories for both types, however those all relate to the chemical differences in the progenitor stars.

A Type 1A is they type described in this article. These types of explosions always involve the transfer of mass from a companion star to the ember of a star that has already gone through its time on the main sequence. There are three basic embers of star death--a white dwarf, a neutron star and a black hole.

In the case of the white dwarf and the neutron star, when enough material collects on the surface of star, a gravity-induced reaction occurs that causes a flash over. This means that the hydrogen (mostly) that has collected on the surface experiences a period of run-away fusion, which we see as a sudden bright flash.

In some cases, a white dwarf can collect enough material to exceed a net volume of 1.4 Solar masses (Sm). When that occrs, the efffect is as described by antoniseb above--that is, the runaway fusion reaction can be so violent as to completely disrupt the unlucky progenitor. There is also a possibility that the white dwarf can leave a compact remnant behind--a small neutron star.

In most cases, the amount of material that has built up on a white dwarf does not reach the critical mass of 1.4 Sm. Instead, these stars can experience episodic explosions, as the material collected meets the thresh-hold to ignite a round of nucluer fusion, and they begin the process of collecting more mass after the event. These stars are considered as standard candles for determining distance.

The same thing can happen with a neutron star, although they can also experience much larger explosions when the "ash" of previous flashes builds up enough to ignite secondary nuclear fusion--that is, instead of fusing hydrogen, they fuse carbon. In either case, the gravity of a neutron star is so incredibly huge, that there is no danger of the neutron star being disrupted.

Type II supernovas involve very massive stars. These are known as core-collapse supernovas, and are always a 1 shot deal. These stars are so large that they go through their supply of hydrogen in a very short time as compared to stars like our sun. They will continue to fuse different elements up to the point where iron forms in the core. Once the iron accumulates to 1.4 Sm., the core collapses, triggering the bright flash we see as a supernova.

Again, different subclasses involve the different makeup of these large stars, but the triggering event is the same in all of them.

As for outcomes, the biggest single factor is the size of the progenitor star. The larger the original star, the stranger the remnant--up to the formation of a black hole. For web info on this stuff, plug in "supernova", "Type II" or something along those lines, then start reading. There's thousands of sites.


When a white dwarf becomes a type 1a supernova, it is very rapidly converts the carbon and oxygen in it to Iron.

A very quick comment on this. Antoniseb is correct that this can occur, however it only occurs on those white dwarves unlucky enough to have gathered enough material to exceed the Chadrakesar Limit of 1.4Sm. Repeater Tpe 1A involve the fusion of hydrogen.


Thanks for the explanation, so that type of supernova (Ia) never leaves an identifiable star?
Suppose the white dwarf had a companion, would it be possible for it to survive?


It is not correct to say never, rather the correct term would be usually. Of course, I am talking about the type that completely disrupts the progenitor.

It would be very likely that the companion would survive. This article is about one such survivor. In fact, I would think that the companion would almost always survive, unless it was very small or very close to the exploding white dwarf.

antoniseb
2004-Nov-01, 06:34 PM
Originally posted by VanderL@Oct 31 2004, 09:48 PM
Suppose the white dwarf had a companion, would it be possible for it to survive?
Actually, it must have a companion. That is how it increases it's mass to the exploding point, and the point of the article that started this thread is that they believe they identified the companion for Tycho's Supernova [SN1572A] which is presumed to be a type 1a, based on Tycho's observations over 16 months.

Concerning Duane's notes above, the standard candle type 1a supernovas do not appear to leave neutron stars or black holes, but most or all other types of supernovas do.