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You might wonder why the next major step in nuclear fusion in stars involves three helium nuclei and not just two. Although it is a lot easier to get two helium nuclei to collide, the product of this collision is not stable and falls apart very quickly. It takes three helium nuclei coming together simultaneously to make a stable nuclear structure. Given that each helium nucleus has two positive protons and that such protons repel one another, you can begin to see the problem. It takes a temperature of 100 million K to slam three helium nuclei (six protons) together and make them stick. But when that happens, the star produces a carbon nucleus.

Stars in your little finger

Stop reading for a moment and look at your little finger. It’s full of carbon atoms because carbon is a fundamental chemical building block for life on Earth. Each of those carbon atoms was once inside a red giant star and was fused from helium nuclei in the triple-alpha process. All the carbon on Earth—in you, in the charcoal you use for barbecuing, and in the diamonds you might exchange with a loved one—was “cooked up” by previous generations of stars. How the carbon atoms (and other elements) made their way from inside some of those stars to become part of Earth is something we will discuss in the next chapter. For now, we want to emphasize that our description of stellar evolution is, in a very real sense, the story of our own cosmic “roots”—the history of how our own atoms originated among the stars. We are made of “star-stuff.”

Becoming a giant again

After the helium flash, the star, having survived the “energy crisis” that followed the end of the main-sequence stage and the exhaustion of the hydrogen fuel at its center, finds its balance again. As the star readjusts to the release of energy from the triple-alpha process in its core, its internal structure changes once more: its surface temperature increases and its overall luminosity decreases. The point that represents the star on the H–R diagram thus moves to a new position to the left of and somewhat below its place as a red giant ( [link] ). The star then continues to fuse the helium in its core for a while, returning to the kind of equilibrium between pressure and gravity that characterized the main-sequence stage. During this time, a newly formed carbon nucleus at the center of the star can sometimes be joined by another helium nucleus to produce a nucleus of oxygen—another building block of life.

Evolution of a star like the sun on an h–r diagram.

Evolution of a Star like the Sun on an H–R Diagram. In this plot the vertical axis is labeled “Luminosity (LSun),” and goes from 1.0 near the bottom to 10,000 near the top. The horizontal axis is labeled “Surface Temperature (K),” and goes from 9000 on the left to 3000 on the right. The main sequence is drawn as a diagonal red line beginning at L ~ 40 on the left down to T ~ 4000 at the bottom. The evolutionary path of the star is drawn as a black line. Beginning at L = 1 and T = 5500, the line moves upward away from the main sequence. This portion of the line is labeled “(a),” and is described in the caption. The line continues upward to L ~ 1000 and T ~ 3000 to point “(b),” labeled “Core helium flash.” From point b, the line (now dashed) moves downward to L ~ 100 and T ~ 5000 and labeled “(c),” and is described in the caption. From c, the line moves upward again. This portion of the line is labeled “(d),” and is described in the caption. The line culminates in a series of waves near L = 5000 and T ~ 3500 and is labeled “Helium shell flashes.”
Each stage in the star’s life is labeled. (a) The star evolves from the main sequence to be a red giant, decreasing in surface temperature and increasing in luminosity. (b) A helium flash occurs, leading to a readjustment of the star’s internal structure and to (c) a brief period of stability during which helium is fused to carbon and oxygen in the core (in the process the star becomes hotter and less luminous than it was as a red giant). (d) After the central helium is exhausted, the star becomes a giant again and moves to higher luminosity and lower temperature. By this time, however, the star has exhausted its inner resources and will soon begin to die. Where the evolutionary track becomes a dashed line, the changes are so rapid that they are difficult to model.

Questions & Answers

Evil space aliens drop you and your fellow astronomy student 1 km apart out in space, very far from any star or planet. Discuss the effects of gravity on each of you.
Shell Reply
are you doing a test?
donot
what is quantum physics
sanjeev Reply
Quantum mechanic or physics is a branch of physics which deals with the dynamics of smallest things of all like atoms subatomic particles and elementary particles.
Ronaldo
Correct.....
Adam
Yes
ashish
what is circumstellar matter
sakshi Reply
where the Pluto has been gone
sanjeev Reply
pluto hasnt gone,its stiĺl on kuiper belt with others
1412
it have not gone anywhere it is still present on it's position in kuipler belt
YOG
does anyone know the smallest thing in the whole universe I know I'm taking a general test
BHUMI Reply
Quarks... Think so.. 🤔
Pavan
higgs Bo particle .. think so.
sakshi
higgs boson particle
sakshi
A.) Your brain...
Andy
i guess andy should go and check his brain
Amritansh
can anybody think that what is present before big bang?
YOG Reply
I Don't Think Time Existed Before The Big Bang, So Talking About Anything Before The Big Bang Is Useless.....
Adam
but we have to think that what is present before big bang by which this whole universe is formed
YOG
because something can't create from nothing
YOG
it is thought by the scientists that 2 parallel universe collided with each other and got mixed in a point which exploded and formed the big bang It is thought that this process of big bang is continuous which means it will be repeated after a certain time interval
BHUMI
2 parallel universe collided with each other and got mixed in a point which exploded and formed the big bang, it is thought that this process of big bang is continuous which means it will be repeated after a certain time interval
BHUMI
before the big bang 2 parallel universe collided with each other
BHUMI
We Don't Know For Sure If That's The Case, We Need To Establish What Is Nothing?
Adam
One big crunch before big bang..just like now.. Our universe will end with big crunch or by expand.. More expand.. Much more since planets get separated 🖖 from its own core... I don't know more.. 😉
Pavan
how those two parallel universes came into existence
sakshi
no one knows what came before. The theory exists only because the numbers for expansion (calculated via redshift, measuring the CMB, etc) add up.
Jacie
We used to think that there were 3 possible endings to the universe - expanding , oscillating (cycle of crunch, then expand, the crunch again), and the steady-state theory (multiple places where matter enters the universe.
Jacie
However, the expanding model is the only valid one left. Dark energy and dark matter are speeding the process of expansion up exponentially. the process had been slowing down up till now. this means that there's no going back (or big crunch) and disproves the oscillating universe theory
Jacie
👍👍
Ashish
we also measured the density of objects and that is decreasing, meaning that all space objects (predominantly referring to galaxies) are moving farther away from each other. this means that the universe is not staying the same and disproves the steady-state theory.
Jacie
Oh yeah, and the steady-state theory stated that the universe has stayed the same and will not change Fun fact: the steady-state theory was first disproved when we discovered a quasar from really far away (meaning that the light reaching us was old and we saw into the past). It was so different
Jacie
and therefore disproved the theory
Jacie
Well Said.....
Adam
As for before the big bang, I find the application of entropy to a multiverse an interesting hypothesis. From the Law of Entropy, systems, left alone, will devolve to their least organized state. In the multiverse hypothesis, universes are popping in and out of existence all the time.
Damon
Time is relative, just frequency of events relative to other events. With no events, there is no time. If the big bang was an event that happened, then there must have been time before the big bang and something must have caused it to happen.
Toby
That's Pre Bang Physics, Strictly Speculation At This Point.....
Adam
Time is relative and critical to this question. As we don't really know what went before, we will need to make some assumptions. Before the big bang, I believe that there was dinner and a movie.....
Andy
before Big Bang there were matters and anti matters so this is a Theory of matters and anti matters it is believed that there was a battle between matter and antimatter in which matter won and that is certainly the reason that why we study States of matter all forms of matter
Amritansh
but if antimatter would have won what would be the nature of universe
sakshi
If Anti Matter Would've Won, The Universe Would've Look Exactly The Same As It Does Now.....
Adam
bc antimatter did win
Jacie
very slightly tho
Jacie
we can actually explain how universe came into existence by the theory of Quantum gravity. matter won over Anti matter because of neutrino there is present research going on neutrino or sterile neutrino it could be the answer I think once we find the cnu background radiation or cosmic neutrino bac
Ronaldo
can we make quantum universe by quantum level bigg bang explosion.
Prabhakar Reply
what do u mean by quantum universe?
rutuja
see quantum mechanics is a theory like we use general relativity for the study and characteristics of big objects in the same way we use quantum mechanics for the small objects study. This is called quantum mechanics and the object or thing in the universe on which we apply it is quantum universe
BHUMI
string theory is more appropriate for universe
YOG
pls explain about her hoags galaxy
sakshi Reply
Hoags Galaxy Is A Non Typical Galaxy, Of A Type Known As Ring Galaxy.....
Adam
o wow
Rohit
what are theories for the formation of asteroids. kindly someone tell
shamaun
what is nebula
sakshi
its a stellar nursury
Ashish
nebulae is a cloud of dust and various other gases . All the stars are born from nebulae and several stars die and form nebulae for eg, cats eye nebulae or Orion nebulae
BHUMI
how does it far between moon and earth?
Nyan Reply
About 240,000 Miles From Earth Or 380,000 Kilometers.....
Adam
do anyone know about the new celestial phenomenon called STEVE
sakshi Reply
I don't believe i have. Can you elaborate?
josh
No, never heard. Thank you for the information!
donot
scientists have observed mysterious lights in sky , they call them STEVE . They assume that it has to do with electrons and protons from a region around the earth called magnetosphere
sakshi
ohooo
Mad
explain about space weather pls?
sakshi
Atmospheric Optical Phenomenon.....
Adam
?
sakshi
Hot Gas In The Sky..... Strong Thermal Emission Velocity Enhancement Or STEVE Also Called "Sky Glow".....
Adam
pls tell me briefly about multiuniverse theory
sakshi Reply
we doesn't know what is beyond this world or how is space time actually..so there are many ideas put forward by scientists. 1.infinite universe 2.bubble universes 3.daughter universes 4.mathematical universes 5.parallel universes these are just different concepts ..
Mad
No Evidence Or Data Exist For Multiverse Hypothesis, That's Why They're About 9 Different Interpretations Of It.....
Adam
Theories are formed on imaginations and evidences which can be theoritical and logical. yes there are evidences for Multiverse theory. thsts why many Scientists bekieve in it.
Udit
yeah
Mad
evidence?
Mad
Then Why Are They Called Hypothesis?
Adam
according to the super position law everything have equal chance that it can be present but we can't see every state of it so it is possible that multiverse are present but we can only see one universe but it is true that our universe have many copies if it called multiverse
YOG
Can we done biggbang explosion at quantam level
Prabhakar Reply
Is bigbang really exist?
donot
that's just a concept na?
Mad
i mean that's the thing we believe had the beginning..but no solid proofs
Mad
big bang is just a theory or idea of some scientists no body precisely knows how it occurred it may be correct or wrong...... but it is now just an idea not any experiment is conducted to support it....
Zunain
yeah yeah
Mad
The Big Bang Theory Is The Best Explanation We Have For The Early Stages Of The Universe, All Our Data Supports The Big Bang Theory, And The Hypothesis Was Proposed By George Lemaitre A Belgian Catholic Priest And Astronomer, It Did Not Become A Theory Until Edwin Hubble The Astronomer Observed The
Adam
Expansion Of The Universe In 1929, Hypothesis Is An Educated Guess, Theory Has Data And Experiments To Back Up It's Claim..... So Any Time You See The Word Theory, That Means Their Is Evidence To Support The Theory.....
Adam
ooh
Mad
thanks martinez it really help us
1412
your explanation
1412
You're Very Welcome.....
Adam
A Couple Of Examples Would Be, Germ Theory, Atomic Theory, Theory Of Relativity, Theory Of Evolution And Plate Tectonics Theory And Quantum Theory And Cell Theory Are All Backed By Data And Evidence.....
Adam
oohoo
Mad
The real question is who programned the big bang, why are the laws of physics perfectly balanced to allow existence of matter. Is our universe just 1 possible universe in an infinite multiverse, or is it the only universe, but with deliberate nature?
Toby
god made our unirverse
1412
If That's What You Believe, That's Fine And Dandy..... But Proving A God Exist Or Doesn't Exist Is Impossible, Many Great Scientist Believed In A Personal Creator, But Not Even One Was Able To Prove The God Hypothesis..... Me Personally, I Believe That Beliefs Are Way Overrated, Even Mine.....
Adam
well you have the name of the first human being.
donot
and you say it's overrated. ofcourse scientist can never prove the God hypothesis. It's God made, non-human made.
donot
you all know about blackhole right? It's first said in the Holy Quran that given to Prophet Muhammad SAW. and that was on at-Takwir: 15-16, you can search it at google. and "black hole" is called Khunnas.
donot
I am not trying to make you all moeslem. But, I can't leave you while you denying God. Allah SWT. and many top-rated astronomers were change they religion to Islam.
donot
You Say We Can't Prove God, But In Your Next Sentence You're Saying Your Holy Book Proves Just That..... If A Creator Does Exist It's Of No Use To Us..... I Will Say This Before Islam Took Over That Region Of The World, They Were The Leaders Of The World When It Came To Math And Science.....
Adam
@Donot texteme relax im a muslim and astronomer too (well still on college)
1412
@1412 can you teach me... I want to particpate in National Astronomy Olimpiad next spring. btw Im Indonesian
donot
@adam what happen before you alive? what makes you, you? what happen if you dead?
donot
@Adam I don't want to argue, believe me. My heart, hurt painfully seeing you deny God. I pray for you, so you can believe the One and Only God. ALLAH SWT. aamiin.
donot
chill out guys. it's not a compitition. it's growing together. do not force upon others.
Brandon
I just want to clarify that I'm a native american. it's a humanity thing to help each other into a better understanding.
Brandon
Yes, you are absolutely correct @Brandon
donot
How I believe in Astronaut predicting my future by my natal date? Does it really work?
Dennis
no. absolutely. the future is God secret
donot
Have you ever experienced God works in your life? And how should I start to believe in God works?
Dennis
look around you... everything is God work. Including you and me and everyone.
donot
I have experienced it. It is me, I'm one of God works the smallest one. and by me, I mean human.
donot
No Arguing, Just Dialogue, If You're Going To Deal With Beliefs, Be Ready To Defend Said Beliefs, No Idea Is Safe From Scrutiny..... This Is Science Not Religion.....
Adam
well @Adam religion and science are connected.
donot
How Are They Connected?
Adam
Could the big bang have been programned by a sophisticated and advanced intelligence that emerged from a previous universe at the end of its lifespan, to create a new universe with the correct laws to allow physical reality to continue and intelligence to emerge again in a never ending cycle?
Toby
In An Uncertain Universe, Anything Is Possible, But For Some Superior Intelligence To Create The Universe We Find Ourselves In, It Would Have To Be More Complex Than It's Creation, And Who Created That Superior Intelligence?
Adam
i would say the cycle goes on beyond the superior intelligence
Tankia
thats the reason theories are possible in science because there are so many vast possibilities
Tankia
Science without religion is lame,religion without science is blind." So said Albert Einstein
donot
Complexity emerges from a simple code. Intelligence is an emergent property of the universe and the basic laws that govern it, and evolves over time.
Toby
I Don't Agree With That, Science Does Not Need Religion To Be Exciting..... But A Lot Of Amazing Scientist Believed In A Personal God.....
Adam
Well Said.....
Adam
I also don't agree. Some amazing scientist didn't even believe in a religion. For example, Stephen Hawking, he instead took his own beliefs and made them theories into his own. Some people think God is what started this world but what if it was something else?
Роза
A person in Boulder Colorado observes the planet Jupiter on the Eastern horizon right after sunset. Six hours later where will Jupiter be located?
Tig Reply
would the answer be high in the south
Tig
does all the multiverses should same particles I mean same feilds
Nanda Reply
what is astronomy
victor Reply
The Study Of Celestial Bodies.....
Adam
simple branch of science which includes study of space and and its existed bodies
BHAVAN
astronomy is the branch of science that deals with the study and understanding of universe
BHUMI
It is subject of science which deals with the study of space,and all the celestial bodies and apply the observation on thories or thought to explore new mysteries of Cosmos and it is also related to the study of cosmology
YOG
Practice Key Terms 3

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Source:  OpenStax, Astronomy. OpenStax CNX. Apr 12, 2017 Download for free at http://cnx.org/content/col11992/1.13
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