I read somewhere a long time ago that there is enough matter in our solar system in the form of rocks and dust to create another sun.Is this correct? Was our solar system trying to create a 2 star system?
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The vast majority of the stuff in the solar system other than the Sun itself is contained in one body, Jupiter. The total mass of the solar system is estimated to be about 1.0014 solar masses, or about one solar mass plus 1.4 Jupiter masses. (Jupiter's mass is a bit less than 0.001 solar masses.) Using the highest estimates on the mass of the Oort cloud, the total mass of the solar system, excluding the Sun itself, is about 30 Jupiter masses. These early estimates have been shown to be wrong. Current estimates are that the mass of the Oort cloud is one or two Earth masses. Even if the hypothesized planet IX does exist and is as large as some hypothesize (about five Earth masses), that will only budge the estimated 1.0014 solar masses by a tiny, tiny bit.
The smallest possible star, defined as something capable of fusing hydrogen, is about 65 to 80 Jupiter masses. The answer is no.
David Hammen
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6And a good part of that matter wouldn't be useful for forming a star as it's not useful as fusion fuel (in fact would poison the fusion process). Which is one reason stars die, their fusion process gets poisoned by heavy isotopes. – jwenting Dec 19 '22 at 08:03
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1@Panzercrisis https://www.wolframalpha.com/input?i2d=true&i=Divide%5B%5C%2840%29jupiter+mass%5C%2841%29%2C%5C%2840%29sun+mass%5C%2841%29%5D – David Hammen Dec 19 '22 at 13:33
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3@Panzercrisis The mass of the smallest possible star is typically stated in terms of Jupiter's mass rather than the Sun's mass. There are many good reasons for this. – David Hammen Dec 19 '22 at 13:35
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@Panzercrisis 0.001% --> 0.00001, I think the % sign is an error there, or it should be 0.1%. – Nick T Dec 20 '22 at 00:49
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"Using the highest estimates on the mass of the Oort cloud, the total mass of the solar system, excluding the Sun itself, is about 30 Jupiter masses." That phrasing is confusing. It fails to clearly distinguish between reality and beliefs about reality. Clearer would be "Previously, the highest estimates of the mass of the Oort cloud resulted in the total mass of the solar system, excluding the Sun itself, to be calculated as 30 Jupiter masses." – Acccumulation Dec 21 '22 at 02:50
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No. The total mass of the planets, asteroids, dust etc in the solar system is only about 0.1% of the mass of the sun. There is not nearly enough to make even a small star.
James K
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11@DaveTheWave That's not nearly enough. A better number is 0.0014 Sun masses, or about 1.4 Jupiter masses. The smallest possible star is 65 to 80 Jupiter masses, depending on who one reads. – David Hammen Dec 18 '22 at 04:24
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There's probably at least another 0.1% in the "vacuum", by which I mean the 3 to 10 atoms per cubic centimeter in the empty regions of space. By my calculations, 1 cubic light year would contain about 1,000 Earth masses (assuming those were all protons) per atom per cubic centimeter. – Michael Dec 18 '22 at 19:03
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3I'm not sure that counts as "rocks and dust". On the other hand, I'm not sure if planets count as "rocks and dust". However, no matter which way you cut it, there isn't enough "stuff" for a second star. – James K Dec 18 '22 at 20:12
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2@Michael 1000 Earth masses is a bit more than 3 Jupiter masses, so not enough stuff to cut it. Moreover, the Sun and the planets are very good at either expelling small material from the solar system or making such material drop into the Sun. (The zodiacal light falls into the latter category.) Even if what you wrote is true (which it isn't), an additional three Jupiter masses will not cut it. – David Hammen Dec 19 '22 at 13:47
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@DavidHammen Yes, I'm aware that 1000 Earth masses isn't enough to cut it... it would need to be 1000 times larger still to equal the mass of the sun. But why do you say that what I wrote isn't true? Are my calculations off on the total mass present in the "empty" space of the solar system? – Michael Dec 19 '22 at 21:47
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1@Michael I suspect your number is too large by a factor of $10^8$. The vast majority of protons in interplanetary space come from the Sun (aka the solar wind, which arises from things such as sunspots and coronal mass ejections). The density of those solar emissions drops with the square of distance from the Sun. Moreover, it is not spherically symmetrical. The majority of those particles are near the plane of the Sun's equator. (continued) – David Hammen Dec 20 '22 at 08:49
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Assuming spherical symmetry and a density of 13 protons / cubic cm at 1 AU I get $10^{-5}$ earth masses for a sphere with a radius of one light year. That is certainly overkill due to the assumption of spherical symmetry and is smaller than your calculation by a factor of $10^{-8}$. – David Hammen Dec 20 '22 at 08:51
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@DavidHammen Thanks! That makes sense. In the back of my head I was setting 1 proton / cm^3 as a lower bound, forgetting that intergalactic space is 1 proton / m^3, not cm^3! – Michael Dec 21 '22 at 16:45
Either way, what do you see as the mass of the sun, and of the rest of the system?
– Robbie Goodwin Dec 19 '22 at 02:02