How many solar-mass stars have become planetary nebulas?

[Ann]

Over at the Observation Deck forum, Latest Sky Photography and Found images, there is a new image of a planetary nebula, the Twin Jet Nebula. The caption said:

Ordinary planetary nebulae have one star at their centre, bipolar nebulae have two, in a binary star system. Astronomers have found that the two stars in this pair each have around the same mass as the Sun, ranging from 0.6 to 1.0 solar masses for the smaller star, and from 1.0 to 1.4 solar masses for its larger companion. The larger star is approaching the end of its days and has already ejected its outer layers of gas into space, whereas its partner is further evolved, and is a small white dwarf.

I take this to mean that the small white dwarf was once a star more massive than the Sun, while its companion may contain no more mass than the Sun. However, the companion has already ejected its outer layers into space, suggesting that it, too, was definitely more massive than the Sun when it was on the main sequence.

This leads me to wonder how many white dwarfs there are in the nearby universe (say, in our galaxy) that started out as stars with no more mass than our Sun. Are white dwarfs born from solar-mass stars still a rarity in our circa 14 billion year old universe?

Ann

Ann

[Ron-Astro Pharmacist]

Over at the Observation Deck forum, Latest Sky Photography and Found images, there is a new image of a planetary nebula, the Twin Jet Nebula. The caption said:

Ordinary planetary nebulae have one star at their centre, bipolar nebulae have two, in a binary star system. Astronomers have found that the two stars in this pair each have around the same mass as the Sun, ranging from 0.6 to 1.0 solar masses for the smaller star, and from 1.0 to 1.4 solar masses for its larger companion. The larger star is approaching the end of its days and has already ejected its outer layers of gas into space, whereas its partner is further evolved, and is a small white dwarf.

I take this to mean that the small white dwarf was once a star more massive than the Sun, while its companion may contain no more mass than the Sun. However, the companion has already ejected its outer layers into space, suggesting that it, too, was definitely more massive than the Sun when it was on the main sequence.

This leads me to wonder how many white dwarfs there are in the nearby universe (say, in our galaxy) that started out as stars with no more mass than our Sun. Are white dwarfs born from solar-mass stars still a rarity in our circa 14 billion year old universe?

Ann

Ann

Owing to their short lives white dwarfs seem like they would be a bit harder to spot and quantitate after the gas shedding phase is over. Conditions like - what the star was composed of originally, how much mass it had and how many have cooled to such a temperature they are difficult to spot makes me wonder if the JWST will be used to investigate them as part of its mission. I guess I don't know its projected abilities yet or its place in the scheme of observation platforms.

As far as your question goes I ran across this answer. "Estimates say that around 6-7% of the stars are white dwarfs.
Still, it is known that around 97% of the stars are bound to end up as white dwarfs in the future (due to their mass)".

Wonder if it's accurate? It does seem too few in the 14 billion year old universe.

[geckzilla]

Considering how small they are and yet how many PN we can see, I'd have to guess that a whole lot of them do! They are not large structures, usually around a light year in diameter, but they are not at all uncommon. We can't know for sure how far away most of them are, but we know they must be relatively close due to their presumed size. I would conclude that it must be a common stage in stellar evolution because if it was rarer we'd see a lot fewer of them. They're somewhat ephemeral in nature as well, are they not?

[Ron-Astro Pharmacist]

Considering how small they are and yet how many PN we can see, I'd have to guess that a whole lot of them do! They are not large structures, usually around a light year in diameter, but they are not at all uncommon. We can't know for sure how far away most of them are, but we know they must be relatively close due to their presumed size. I would conclude that it must be a common stage in stellar evolution because if it was rarer we'd see a lot fewer of them. They're somewhat ephemeral in nature as well, are they not?

That was my thought too. (I love words; probably too much. Ephemeral was a perfect description.) Planetary nebulas don't last long in the grand scheme of things. It's kind of a privilege to witness them.

It does seem strange that there weren't more Sun-like stars earlier in the universe if the composition is 6-7% now. Could they have been recycled somehow? Other than in a Type 1a supernova. That would have meant a lot of those have occurred in the past; it seems way too many. As I was leading to earlier I wonder if better equipment in the future will be able to detect their numbers at a greater distance due to the size factor you mentioned. Astronomers have a lot of work to do - I can only imagine.

[neufer]

how many white dwarfs there are in the nearby universe (say, in our galaxy) that started out as stars with no more mass than our Sun. Are white dwarfs born from solar-mass stars still a rarity in our circa 14 billion year old universe?

"Estimates say that around 6-7% of the stars are white dwarfs.

Still, it is known that around 97% of the stars are bound to end up as white dwarfs in the future (due to their mass)".

[b][color=#0000FF]The circled stars in the above picture are white dwarfs. The entire photo covers a small region near the center of a globular cluster known as M4. Researchers using the Hubble Space Telescope discovered a large concentration of white dwarfs in M4.[/color][/b]

---

There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun.

White dwarfs are thought to be the final evolutionary state of stars (including our Sun) whose mass is not high enough to become a neutron star—over 97% of the stars in the Milky Way. (Only main sequence stars with initial masses of above 8 M_☉ have the potential to become neutron stars.)

After the hydrogen–fusing period of a main-sequence star of low or medium mass ends, a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, around 1 billion K, an inert mass of carbon and oxygen will build up at its center. After shedding its outer layers to form a planetary nebula, it will leave behind this core, which forms the remnant white dwarf. Usually, therefore, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses (M_☉), the core temperature is sufficient to fuse carbon but not neon, in which case an oxygen-neon–magnesium white dwarf may be formed.

If the mass of a main-sequence star is lower than approximately half a solar mass, it will never become hot enough to fuse helium at its core. It is thought that, over a lifespan that considerably exceeds the age (~13.8 billion years) of the Universe, such a star will eventually burn all its hydrogen and end its evolution as a helium white dwarf composed chiefly of helium-4 nuclei. Owing to the very long time this process takes, it is not thought to be the origin of the observed helium white dwarfs. Rather, they are thought to be the product of mass loss in binary systems or mass loss due to a large planetary companion.>>

[Ron-Astro Pharmacist]

Twinkle, twinkle little dwarf

How I wonder - are you a smurf ?

Out in space you are a gnome

ET says you were his home

Twinkle, twinkle little stone

Your 'lectrons all have left the zone !


- It's the weekend!!!

[Ann]

Thanks for your input, everyone! I have to give special thanks to Ron-Astro Pharmacist, who had the idea and went to the trouble of googling what percentage of stars in the universe are actually white dwarfs "today" (make that in the nearby universe, where "today" makes any sense at all).

But my question was another one. How many solar-mass stars have actually turned into white dwarfs in our 13.8 billion year old universe?

Let me be a bit more precise. By solar-mass stars, I mean stars that were born with exactly (say, within 1%) the same mass that our Sun was born with.

Ron-Astro Pharmacist, you said that 6-7% of all stars in the universe are white dwarfs. How many of the existing white dwarfs in the universe are the remnants of stars that were born with the same mass as the Sun?

Could it be that an overwhelming number of the white dwarfs in the universe are the remnants of stars that were born with more mass than the Sun?

When we see a planetary nebula somewhere in the sky, may we conclude that we are probably seeing the death shroud of a star that was born more massive than the Sun?

Is the universe old enough for an appreciable number of stars born with the same mass as the Sun to have turned into white dwarfs?

Is the typical "pre-white dwarf lifetime" of a star born with the mass of the Sun about the same as the current age of the universe?

If there is an appreciable shortage of white dwarfs born from stars with the same mass as the Sun, could that be because most G-type stars in the universe are at least a few billion years younger than the age of the universe? Perhaps a rather small percentage of all solar-mass stars that have ever existed were born before star formation peaked in the universe, some 10 billion years ago. Perhaps all solar-mass star that were born 13 billion years ago have turned into white dwarfs by now, but a solar-mass star born during the peak of star formation 10 billion years ago might just be in the process of casting off its outer layers and lighting them up as a planetary nebula. Or indeed, it might not even have progressed that far, but might still be a red giant.

Ann

[Ron-Astro Pharmacist]

Thanks for your input, everyone! I have to give special thanks to Ron-Astro Pharmacist, who had the idea and went to the trouble of googling what percentage of stars in the universe are actually white dwarfs "today" (make that in the nearby universe, where "today" makes any sense at all).

But my question was another one. How many solar-mass stars have actually turned into white dwarfs in our 13.8 billion year old universe?

Let me be a bit more precise. By solar-mass stars, I mean stars that were born with exactly (say, within 1%) the same mass that our Sun was born with Ron-Astro Pharmacist, you said that 6-7% of all stars in the universe are white dwarfs. How many of the existing white dwarfs in the universe are the remnants of stars that were born with the same mass as the Sun?

Could it be that an overwhelming number of the white dwarfs in the universe are the remnants of stars that were born with more mass than the Sun?

Ann

I think many of your questions should be left to a real astro "physicist" but there is a lot of "phun to phind" for us wanna be's.

http://science.nasa.gov/astrophysics/fo ... nd-evolve/

http://earthsky.org/space/white-dwarfs- ... dead-stars

[rstevenson]

... How many solar-mass stars have actually turned into white dwarfs in our 13.8 billion year old universe?...

Solar-mass stars like our own will have a lifetime of about 10 billion years, give or take. So your question becomes, how many such solar-mass stars were there in the Milky Way (or the universe, if you wish) prior to about 10 billion years ago? I'm not sure we can pin a number on that at all, yet.

Since white dwarfs are the end point of stars with original masses ranging from less than 1/10th solar mass to about 10 solar masses, knowing the number of white dwarfs in the Milky Way (or universe) isn't going to help you, since we can only estimate the percentage of all those white dwarfs that formed from exactly 1 solar-mass stars.

Rob

[Ann]

Rob!!! Long time no see! So good to hear from you!

And your answer is the correct one, of course. I was just wondering, since there seems to be G-type dwarfs in circa 12-billion-year-old globular clusters, which suggests that stars like the Sun could stay on the main sequence for up to 12 billion years. But since the stars in globulars are so metal-poor, they might well have started out less massive than the Sun and still appear to belong to the same spectral class as the Sun.

Ann