Starship Asterisk*

Air4ce wrote:I did not quite follow why it is that supernovae always have a companion star.

My (basic) understanding is that a star goes nova as a consequence of consuming its own fuel. This would appear to be an internal process, independent of a companion star.

I'm a history major. What am I missing?

Thanks all

Air4ce

Type Ia supernovae are thought to be white dwarf stars which accrete mass from a companion until they exceed the Chandrasekhar limit and then go supernova. In this case it is thought to be a merger between two white dwarfs so the supernova left nothing behind.

Where is the companion star?
It´s in anywhere.
I think that the energy of the Supernova affected to the companion star and it bursted.

bystander wrote: Stars merge atoms (fusion)

Oops! guess I was inking without thinking on that one. But still, could the white dwarf star that is going supernova pull enough mass from its companion that it ceases to be a functioning star? I’d like to understand what happens to a star whose mass is artificially reduced this way. As its mass is reduced the gravitational pressure would start decreasing and the star would expand. With the decreasing pressure the ability to fuse atoms would reduce and the expansion would stop. As the companion struggles to find an equilibrium as it continues to loose mass, what is the end game? Does it just evaporate away?

Another question that occurs to me is why do we find a companion at the scene of the crime at all? If the companion is orbiting the white dwarf, and the white dwarf’s mass gets spread out over tens of light years in a nova event, what is holding the companion in that spot? Why does it not go shooting off like a yo-yo whose string has broken?

FloridaMike wrote:

Another question that occurs to me is why do we find a companion at the scene of the crime at all? If the companion is orbiting the white dwarf, and the white dwarf’s mass gets spread out over tens of light years in a nova event, what is holding the companion in that spot?

This is a picture of the remnant of Tycho Brahe's supernova from 1572. There is actually a companion in this picture. You can see the "wake" of the companion as a small "comma" at eight o'clock. As gases from the explosion are still streaming outwards at a high speed, they "run into the companion" and form a wake around it.

The companion has most likely changed the direction it had when the supernova blew. However, both the white dwarf that exploded and the companion that survived were probably rather low-mass objects (the white dwarf certainly was). Therefore they might not have been orbiting one another at tremendous speeds, and when the white dwarf blew, the companion was not "flung away" at a really breakneck speed. I agree with you, however, that the explosion should have changed the direction of the motion of the companion. As you can see, too, the companion is not at the center of the supernova remnant. The companion has indeed moved away some distance during its 400+ years as a single star.

Ann

JohnD wrote:We have previously heard, possibly on APOD, of anomalously fast moving stars.
An example is RX J0822-4300, " currently moving away from the center of the Puppis A supernova remnant at over 3 million miles per hour " as the Wiki has it.
http://en.wikipedia.org/wiki/RX_J0822-4300
If there is a variation in the usual mechanism of a supernova that ejects the neutron star, could this have removed the remnant from SNR 0509-67.5 ?

JOhn

My answer is no, it couldn't have "removed" the remnant, and by removed I assume you mean that it's so far from the supernova location as to not be found in that particular field of view.

The expanding spherical shell of gas that we see is the front of the "blast wave" that the supernova created (not including light or neutrinos..), it would be hard to explain how the supernova ejected a companion at a higher speed than the blast wave itself.


Here's an x-ray image of Puppis A: http://heasarc.nasa.gov/docs/objects/sn ... image.html

You can see that the neutron star that got a kick is well inside the expanding shell of gas, which makes sense because it is vastly heavier than the gas. Also the progenitor star for Puppis A is estimated to have been 25 solar masses whereas the progenitor for SNR 0509-67.5 was ~1.4 solar masses. So the speed at which SNR 0509-67.5 could have "kicked" a companion would be much smaller than Puppis A which should leave it very near the center of the explosion. And if not, they simply need to search within the expanding shell for the missing companion because it wouldn't have passed it.

With this type of supernova, shouldn't the companion erupt due to the mass it gained while it was being buffeted by the supernova? I think the star's gases and dust that was blown out could have collected on the companion, therefore it gaining a lot of mass. If this were to happen, would there be a breach in the nebula?

FloridaMike wrote:

bystander wrote: Stars merge atoms (fusion)

Oops! guess I was inking without thinking on that one. But still, could the white dwarf star that is going supernova pull enough mass from its companion that it ceases to be a functioning star? I’d like to understand what happens to a star whose mass is artificially reduced this way. As its mass is reduced the gravitational pressure would start decreasing and the star would expand. With the decreasing pressure the ability to fuse atoms would reduce and the expansion would stop. As the companion struggles to find an equilibrium as it continues to loose mass, what is the end game? Does it just evaporate away?

Another question that occurs to me is why do we find a companion at the scene of the crime at all? If the companion is orbiting the white dwarf, and the white dwarf’s mass gets spread out over tens of light years in a nova event, what is holding the companion in that spot? Why does it not go shooting off like a yo-yo whose string has broken?

If a star loses enough mass then yes, it will stop fusion, and I don't think there's anything stopping it from just "evaporating away" as you put it.

As for your other question, supernovas release a tremendous amount of energy that accelerates the gas we see expanding outward, which is moving very very fast (11 million km/h for cassiopeia a from http://chandra.harvard.edu/photo/2009/casa/ with a cool movie!, 17 million km/h for Tycho's SNR http://chandra.harvard.edu/photo/2009/casa/). The yo-yo who's string breaks off shoots off in a straight line at the velocity it had just before the string broke; for stars this would be the orbital velocity. A high orbital velocity is around 500 km/s, or 1.8 million km/h, very fast! But still a tenth of the speed of the expanding shell. If you can still see the shell, the companion will be inside of it.

Also, the expanding shell of gas is only visible for around a hundred thousand years (http://curious.astro.cornell.edu/questi ... number=533) a blink of the eye in astronomical terms. We are looking at the yo-yo when its string broke at, lets say .1 seconds ago, so it's still very close to the position it was when the string broke.

TNT wrote:With this type of supernova, shouldn't the companion erupt due to the mass it gained while it was being buffeted by the supernova? I think the star's gases and dust that was blown out could have collected on the companion, therefore it gaining a lot of mass. If this were to happen, would there be a breach in the nebula?

I don't think it will gain a lot of mass. When the progenitor star blows up it ejects all of its mass out in a spherical shell, so the companion star is only going to see a small fraction of this ejected mass.

Imagine having 2 bags of flour (our 2 stars), the size of a bag of flour is what, 6 inches across? So a radius of 3 inches, lets place the second bag of flour very close to the first bag (in astronomical terms), lets say 100 radii away or 300 inches (25 feet). Note that the distance from the sun to mercury is about 83 sun radii. Now place your favorite explosive inside one of the bags of flour, when it blows up all of the flour will expand outward spherically. By the time the shell reaches the intact bag of flour it will have a surface area of 4*Pi*(300inches)^2 = 1,130,000 square inches. The intact bag of flour has a disc size of Pi*(3inches)^2 = 28 square inches. 28/1,130,000 = .000025 = .0025% of the flour will hit the intact bag.

PiTHON wrote: We are looking at the yo-yo when its string broke at, lets say .1 seconds ago, so it's still very close to the position it was when the string broke.

Thanks for helping me square my intuition with the facts!

This paper (An absence of ex-companion stars in the type Ia supernova remnant SNR 0509−67.5, Schaefer & Pagnotta, Nature V481, 164–166, (12 January 2012)

http://www.nature.com/nature/journal/v4 ... 10692.html

would seem to be the stimulation to publish this picture as an APOD just now, and the authors may be better informed detectives than some of us in investigating the Case of the Missing Super Nova.

John

Actually, it also depends on how powerful.the explosion is, too.

TNT wrote:With this type of supernova, shouldn't the companion erupt due to the mass it gained while it was being buffeted by the supernova? I think the star's gases and dust that was blown out could have collected on the companion, therefore it gaining a lot of mass. If this were to happen, would there be a breach in the nebula?

This supernova presumably resulted from two white dwarfs merging. Before the two white dwarfs merged, there is no reason to think that they received any mass to speak of before they merged, because the strong gravity of each white dwarf would have held on tightly to their highly compressed atmospheres. So they blew when they merged. Alternatively , one white dwarf might have blown first, and the gas and dust that was dumped on its white dwarf companion would have sent that one over the brink, too.

FloridaMike wrote:
Oops! guess I was inking without thinking on that one. But still, could the white dwarf star that is going supernova pull enough mass from its companion that it ceases to be a functioning star? I’d like to understand what happens to a star whose mass is artificially reduced this way. As its mass is reduced the gravitational pressure would start decreasing and the star would expand. With the decreasing pressure the ability to fuse atoms would reduce and the expansion would stop. As the companion struggles to find an equilibrium as it continues to loose mass, what is the end game? Does it just evaporate away?

I don't think that white dwarfs will usually be able to pull enough gas from a star to stop it from "functioning as a star" - that is, I don't think a white dwarf will usually be able to steal enough gas from a companion to make that star unable to keep its fusion processes going.

A few days ago Regulus and dwarf galaxy Leo 1 were the Astronomy Picture of the Day. Regulus, as it happens, has a close-in companion that might be an underweight white dwarf. This emaciated white dwarf was probably created when its progenitor evolved into a bloated red giant and started dumping gas on its smaller but more compact main sequence companion. Because the companion stayed compact and the red giant stayed bloated, more and more of the red giant's mass was transferred onto the companion. Or, to summarize - the red giant became sufficiently "diluted" that its gravity lost much of its grip on its outer layers. The diluted outer layers expanded until they were "caught" by the main sequence companion. This started "funneling" the red giant's outer atmosphere onto the companion until the companion had grown relatively massive. The red dwarf eventually shrunk into a "too light-weight" white dwarf.

But the companion didn't explode, and the red giant didn't "evaporate into nothing".

However...

There is something called the Black Widow pulsar.

http://en.wikipedia.org/wiki/Black_Widow_Pulsar wrote:

The Black Widow Pulsar (B1957+20) is an eclipsing binary millisecond pulsar that orbits with a brown dwarf companion with a period of 9.2 hours with an eclipse duration of approximately 20 minutes. When it was discovered in 1988 it was the first eclipsing binary pulsar known.[1] The prevailing theoretical explanation for the system implied that the companion is being destroyed by the gravitational environment (Roche lobe overflow) caused by the neutron star, and so the sobriquet black widow was applied to the object. Subsequent to this, other objects with similar features have been discovered, and the name has been applied to the class of millisecond pulsars with an ablating companion.

In other words, the Black Widow pulsar appears to be a tight binary system where the extreme gravity of the pulsar is destroying the companion star. The companion is now a light-weight brown dwarf, but it was probably a normal star before its pulsar companion started "eating it".

What will happen to the brown dwarf companion? Will it just "evaporate away"? I doubt it. I guess that the brown dwarf will end its days as a small compact body similar to a planet, unless it will merge with the pulsar and be destroyed that way.

Ann

I got a bit confused when I saw the image brought up through the "shown above"in the explanation until I realised that the image in the Chandra X-ray Center website is orientated differently to the APOD! The APOD also covers a smaller field-of-view. but still ing.

Ann wrote: What will happen to the brown dwarf companion? Will it just "evaporate away? I doubt it. I guess that the brown dwarf will end its days as a small compact body similar to a planet, unless it will merge with the pulsar and be destroyed that way.

Ann

Thanks Ann, truly fascinating.

What is the faint object, just below the centre of the overlay circle? Is that a background star or galaxy?

r.w.b wrote:What is the faint object, just below the centre of the overlay circle? Is that a background star or galaxy?

"The nebulous object is a random far-background galaxy of no connection." taken from http://www.phys.lsu.edu/SNprogenitor/

fletch wrote:what is that small black dot about half-way up between center of supernova at 12:00 o'clock position?

It appears when the cursor is off the image and disappears when the cursor is over the image and the ring appears. It appears to be some sort of digital artifact from processing, perhaps putting the image on APOD with the highlighted copy.

It does not appear to be anything significant to the image.