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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

something's like that maybe, the ways to know them
Dennis Reply
oh ok you can actually reply to your own comment by tapping it once
Tanmay
you should do this
Tanmay
what are laws of the universe
Dennis Reply
The law of attraction
Lambent
Are you talking about fundamental forces Dennis?
Tanmay
you can go to google and type 4 fundamental forces of the universe
Tanmay
let me give you gist of it there are 4 fundamental forces namely gravitational, electromagnetic, strong nuclear and weak nuclear
Tanmay
the came into being just after the bid bang
Tanmay
I mean big bang
Tanmay
you should watch this video for better understanding ***youtu.be/X9otDixAtFw
Tanmay
wow some more than information
Rajeshwari Reply
since space gets bigger dose it affect distance between the sun and earth
Swazi Reply
yes the distance between earth and sun increase at a rate of 15 cm per year
Tanmay
ohh really I didn't knew that , you learn something new everyday
NARUTO
true
Tanmay
thanks so much my friend
Youssef
Dear tanmay and other friends I want to ask that if both sun and earth are moving away from their center than why their inter relative distance is increasing rather squeezing taking in consideration of masses I am student so I apologize further and wanna guidance if possible
haseeb
What's difference between Astronomy and Astrophysics?
Gurjinder Reply
Actually astrophysics is one of the many branches of astronomy. It usually deals with the mathematical calculations of predicting the motions of heavenly bodies and also it studies the evolution of our universe by using physics.
Debabrata
So is there any observational astrophysics?
Gurjinder
Yes there are 2 types of astrophysicsist one is theoretical and other one is observational. I don't know about astrophysics though
Tanmay
Thanks
Gurjinder
welcome
Tanmay
😊
Gurjinder
Is there a way for us to find out that we are in a simulation or not?
Tanmay Reply
I think mathematics is a key
Arghyabindu
If we are in a simulation then I don't think that the super intelligent species which is controlling this simulation will give us any hint about how to know it.
Debabrata
There has to be some kind of bugs even a carefully designed app has some bugs in our world
Tanmay
Yeah.... There might be some loophole in their programme code.... And who knows.... We could find the bugs in a super massive black hole
Debabrata
But here we are talking about a very very very massive simulation by a very advanced species...... So they might ve already planned on how to deal with all the bugs and glitches
Debabrata
There's a really interesting theory that states even if we are in a simulation, it would be coded in such a way that as soon as one of us (a sentient being inside the simulation) had the slightest hint/evidence that we were in a simulation, the simulation would be edited to remove that information
ben
(I keep commenting on posts and they just dont post sometimes, does anyone else have this problem or should I just delete the app?)
ben
same happened to me but I see yours))
NARUTO
(ah well it must just be a little problem with the app, cheers for letting me know 🙌)
ben
(Well never happened to me though it takes some time to post large messages)
Tanmay
I saw a comment where he told that the universe is a game and finding it's nature is the level as soon as we find its nature the universe collapse and make another universe with more complex nature and this continues
Tanmay
(ahh that may be what it is actually because it is only the longer messages, thanks for letting us know)
ben
That was really a unique way of seeing the universe
Tanmay
Impractical way are there such as leaving your mortal body and entering to the astral body....cons of this idea is you can't tell us what you have saw or feel in that endemic confrontation
Arghyabindu
what a friend told me now
Arghyabindu
We are just a component of the universe trying to understand the other components of the universe...... So I guess that sometimes it makes the matter more and more complicated
Debabrata
what a friend told me now
Arghyabindu
Wait if we are in a simulation then does that means our future is predicted and we can't change it like some kind of rpg game
Tanmay
Yes IF we are in a simulation then definitely the future is already programmed..... But it may be in early access stage..... And the future might not be written at the moment.
Debabrata
so we can do time travel upto the point where our future is written
Tanmay
Maybe or may not be..... Depending on the script or program written in the simulation..... The intelligent species should be controlling every step we take and every thought that come into our mind.
Debabrata
Have you seen sword art online anime?
Tanmay
well never mind it's just repeated stuff
Tanmay
Nah.... I don't watch anime
Debabrata
ok
Tanmay
hii guyz
Lambent
Hey
Debabrata
BLM ✊🏾✊🏾✊🏾
Laila
?
Kilten
which is the biggest star in the universe? if anyone know answer,please reply.
Ciffee Reply
which is the biggest star. ?
Ciffee
u y scuti
Sunidhi
sun
Konica
for our galaxy
Konica
Konica UY Scuti is the biggest Star ever observed and it's located in our galaxy.
Gurjinder
what are the branches of astronomy?
SCIENCE Reply
So there are literary many branches of astronomy like- Radio astronomy, Ultraviolet astronomy, X ray astronomy, etc. (just imagine the electromagnetic spectrum) There's also Astrophysics (My favorite), astro chemistry, astrobiology, astro geology, planetary science, astrometry
Debabrata
factors that contribute to the development of ancient astronomy to modern astronomy
Andrea Reply
When will be we found them?I am so waiting.
Everything Changes when Galileo Galilee observed Sky with a telescope. There's no doubt that ancient astronomers knows a lot of things about sky , but there observation was with naked eye. i wanna share some of the glimpse of Indian ancient astronomy:
Gurjinder
1.They know the difference between the Star and Planets at that time. 2. They know which star is multiple star system and their rotation with respect to each other. 3. They know the value of speed of light. And their are lots of things which they knows even without telescope.
Gurjinder
why is a supernova
pooja Reply
well there are different types of supernovas. there is a type 1a supernova and that happens when a white dwarf reaches the mass of 1.4 of the sun. A type 2 supernova is when a high mass star starts to fuse iron in the core and the star collapse then expands to create that supernova
PopularHellboy
what is time.!
Samyak Reply
92 billion light years
The
4th Dimension
The
time is illusion
Ciffee
Time is a way of describing an event happened in our 3D world
Tanmay
Why are the largest visible-light telescopes in the world made with mirrors rather than lenses?
Nibha Reply
What is a charge-coupled device (CCD), and how is it used in astronomy?
Nibha
Why is it difficult to observe at infrared wavelengths? What do astronomers do to address this difficulty?
Nibha
not sure what a CCD.
PopularHellboy
(also, lenses have are more problematic over larger distances due to the way different wavelengths of light act within glass. Red and blue light wavelength differs by about 300nm, and so the refraction will affect them differently, whereas when reflecting on a mirror, this is not a problem)
ben
hi
Zalka
i'm from Indonesian
Zalka
(I tried posting this before but this app doesn't seem to work properly) A CCD essentially works as a camera. It's made from an array of capacitors (which make up the 'pixels'). When an incident photon hits the 'pixel', the charge generated is measured and can be translated into an image we can view
ben
the reason mirrors are more common than lenses (on large scale telescopes) is because it is a lot easier and cheaper to make a parabolic mirror than it is to make a perfect glass lens
ben
Because Refracting Telescope cause Cromatic abberetion.
Tushar
Just reading along. I can't see the end of the page so commenting to move it up.
Eva
same. but mirrors are also made with great efficiency and calculation for trapping the light
Konica
How might Venus’ atmosphere have evolved to its present state through a runaway greenhouse effect?
Nibha Reply
what is synchrotron radiation
Nibha
I am 15 and I got interested in astronomy. Can anyone tell me the basics that I must know?
Vikky Reply
you can start by studying the theories of astronomy. there is light and the spectrum of electromagnetic radiation. from there you learn about waves and how we as astronomers received information from space. then you can learn about the nebula hypothesis and also about our solar system
PopularHellboy
but if you learn about the foundation of light and the dually of nature with it and the Doppler effect, it will apply to most stuff in astronomy
PopularHellboy
heyy @populadHellboy can you tell me from where can I find this Light and The spectrum of electromagnetic radiation ? I mean is there any course ?
Sagar
I mean I learn astronomy in college with astronomy 101 and 102 I'm sure if you search online for YouTube videos or blogs they can help you with that. try crash course on YouTube for an introduction
PopularHellboy
Currently preparing for olympiad, is there any online resources for Astronomy, astrophysics, and cosmology? If there's any past question papers i'll be delighted. I'm currently using Principle and Practice and Introduction To Modern Astrophysics..
Aditya
what is time
Sourav
how big is a parsec
David Reply
I believe it's about 3.086 x 10^16 meters. You can try converting 1 radian to 1 arc secs, multiply with 1 AU, convert it to meter.
Aditya
Its 31 trillion km
Asim
very big
Ciffee
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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