Pranam Source KR IRS Jupiter Is Bigger Than Some Stars, So Why Didn't We Get a ... https://www.sciencealert.com › why-isn-t-jupiter-a-star <https://www.sciencealert.com/why-isn-t-jupiter-a-star#:~:text=So%20why%20is%20Jupiter%20a,able%20to%20fuse%20hydrogen%20either.>
On Mon, 5 Jul 2021 at 18:10, 'Siva Subramanian Perinkulam' via iyer123 < [email protected]> wrote: > > Yes. It is always better to indicate the source if known . But, many time > it is not furnished in the FB or WA fwds. So we copy and paste. > The problem comes if you raise a query!! > > SP > > Sent from Yahoo Mail for iPhone > <https://overview.mail.yahoo.com/?.src=iOS> > > On Monday, July 5, 2021, 8:07 AM, Indian Rediff <[email protected]> > wrote: > > It would be wonderful if you could also give full attribution as to where > you have retrieved this information from. That way curious folks could > choose to go deeper into the subject - and the not-so-curious, could simply > read what you have posted. > > Sai > > On Mon, Jul 5, 2021 at 5:43 AM Rajaram Krishnamurthy < > [email protected]> wrote: > > Pranam > > This is Jupiter and this is Science. > > Jupiter Is Bigger Than Some Stars, So Why Didn't We Get a Second Sun? > JANUARY 2021 > > The smallest known main-sequence star in the Milky Way galaxy is a real > pixie of a thing. It's called EBLM J0555-57Ab, a red dwarf 600 light-years > away. With a mean radius of around 59,000 kilometres, it's just a smidge > bigger than Saturn. That makes it the tiniest known star to support > hydrogen fusion in its core, the process that keeps stars burning until > they run out of fuel. > > In our Solar System, there are two objects larger than this teeny star. > One is the Sun, obviously. The other is Jupiter, like a giant scoop of ice > cream, coming in with a mean radius of 69,911 kilometres. > > So why is Jupiter a planet and not a star? > > The short answer is simple: Jupiter doesn't have enough mass to fuse > hydrogen into helium. EBLM J0555-57Ab is about 85 times the mass of > Jupiter, about as light as a star can be - if it were any lower, it would > not be able to fuse hydrogen either. But if our Solar System had been > different, could Jupiter have ignited into a star? > > Jupiter and the Sun are more alike than you know. > > The gas giant may not be a star, but Jupiter is still a Big Deal. Its mass > is 2.5 times that of all the other planets combined. It's just that, being > a gas giant, it has really low density: around 1.33 grams per cubic > centimetre; Earth's density, at 5.51 grams per cubic centimetre, is just > over four times higher than that of Jupiter. > > But it's interesting to note the similarities between Jupiter and the Sun. > The Sun's density is 1.41 grams per cubic centimetre. And the two objects > are very compositionally similar. By mass, the Sun is about 71 percent > hydrogen and 27 percent helium, with the rest being made up of trace > amounts of other elements. Jupiter by mass is about 73 percent hydrogen and > 24 percent helium. > > It's for this reason that Jupiter is sometimes called a failed star. But > it's still unlikely that, left to the Solar System's own devices, Jupiter > would even become close to being a star. > > Stars and planets, you see, are born through two very different > mechanisms. Stars are born when a dense knot of material in an interstellar > molecular cloud collapses under its own gravity - spinning as it goes in a > process called cloud collapse. As it spins, it spools in more material > from the cloud around it into a stellar accretion disc. > > As the mass - and therefore the gravity - grows, the core of the baby star > is squeezed tighter and tighter, which causes it to grow hotter and hotter. > Eventually > it becomes so compressed and hot, the core ignites, and thermonuclear > fusion kicks off. > > According to our understanding of star formation, once the star has > finished accreting material, a whole lot of accretion disc is left over. > This is what the planets are made of. > > Astronomers think that, for gas giants like Jupiter, this process (called > pebble accretion) starts with tiny chunks of icy rock and dust in the disc. > As they orbit the baby star, these bits of material start to collide, > sticking together with static electricity. Eventually, these growing clumps > reach a large-enough size - around 10 Earth masses - that they can > gravitationally attract more and more gas from the surrounding disc. > > From that point, Jupiter gradually grew to its current mass - about 318 > times the mass of Earth, and 0.001 times the mass of the Sun. Once it had > slurped up all the material that was available to it - at quite a remove > from the mass required for hydrogen fusion - it stopped growing. > > So, Jupiter was never even close to growing massive enough to become a > star. Jupiter has a similar composition to the Sun not because it was a > 'failed star' but because it was born from the same cloud of molecular gas > that gave birth to the Sun. There is a different class of objects that can > be considered 'failed stars'. These are the brown dwarfs, and they fill > that gap between gas giants and stars. > > Starting at over about 13 times the mass of Jupiter, these objects are > massive enough to support core fusion - not of normal hydrogen, but > deuterium. This is also known as 'heavy' hydrogen; it's an isotope of > hydrogen with a proton and a neutron in the nucleus instead of just a > single proton. Its fusion temperature and pressure are lower than the > fusion temperature and pressure of hydrogen. > > Because it occurs at a lower mass, temperature and pressure, deuterium > fusion is an intermediate step on the way to hydrogen fusion for stars, as > they continue to accrete mass. But some objects never attain that mass; > these are known as brown dwarfs. > > For a while after their existence was confirmed in 1995, it was unknown > whether brown dwarfs were underachieving stars or overambitious planets; > but several studies have demonstrated that they form just like stars, from > cloud collapse rather than core accretion. And some brown dwarfs are even > below the mass for deuterium burning, indistinguishable from planets. > Jupiter is right on the lower mass limit for cloud collapse; the smallest > mass of a cloud collapse object has been estimated at about one Jupiter > mass. So if Jupiter had formed from cloud collapse, it could be considered > a failed star. But data from NASA's Juno probe suggest that, once upon a > time at least, Jupiter had a solid core - and that is more consistent with > the core accretion formation method. > > Modelling suggests that the upper limit for a planet mass, forming via > core accretion, is less than 10 times the mass of Jupiter - just a few > Jupiter masses shy of deuterium fusion. So, Jupiter isn't a failed star. > But thinking about why it isn't one can help us better understand how the > cosmos works. In addition, Jupiter is a stripy, stormy, swirly butterscotch > wonder in its own right. And without it, we humans may not have even been > able to exist. That, however, is another story, to be told another time. > > KR IRS 5721 > > -- > You received this message because you are subscribed to the Google Groups > "iyer123" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/iyer123/CAL5XZoo%2B50zugmBLjsYFLr4AnnCbaLrLoZ8BTrMLyG9uawbSSw%40mail.gmail.com > <https://groups.google.com/d/msgid/iyer123/CAL5XZoo%2B50zugmBLjsYFLr4AnnCbaLrLoZ8BTrMLyG9uawbSSw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "iyer123" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/iyer123/CAHqYaCr52jHWWtpgrdT-6qYzqYs4W604UPZYGyh80xx-CiCgtg%40mail.gmail.com > <https://groups.google.com/d/msgid/iyer123/CAHqYaCr52jHWWtpgrdT-6qYzqYs4W604UPZYGyh80xx-CiCgtg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "iyer123" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/iyer123/856653164.3294992.1625488794272%40mail.yahoo.com > <https://groups.google.com/d/msgid/iyer123/856653164.3294992.1625488794272%40mail.yahoo.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Thatha_Patty" group. 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