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Cosmic recycling

The loss of mass by dying stars is a key step in the gigantic cosmic recycling scheme we discussed in Between the Stars: Gas and Dust in Space . Remember that stars form from vast clouds of gas and dust. As they end their lives, stars return part of their gas to the galactic reservoirs of raw material. Eventually, some of the expelled material from aging stars will participate in the formation of new star systems.

However, the atoms returned to the Galaxy by an aging star are not necessarily the same ones it received initially. The star, after all, has fused hydrogen and helium to form new elements over the course of its life. And during the red-giant stage, material from the star’s central regions is dredged up and mixed with its outer layers, which can cause further nuclear reactions and the creation of still more new elements. As a result, the winds that blow outward from such stars include atoms that were “newly minted” inside the stars’ cores. (As we will see, this mechanism is even more effective for high-mass stars, but it does work for stars with masses like that of the Sun.) In this way, the raw material of the Galaxy is not only resupplied but also receives infusions of new elements. You might say this cosmic recycling plan allows the universe to get more “interesting” all the time.

The red giant sun and the fate of earth

How will the evolution of the Sun affect conditions on Earth in the future? Although the Sun has appeared reasonably steady in size and luminosity over recorded human history, that brief span means nothing compared with the timescales we have been discussing. Let’s examine the long-term prospects for our planet.

The Sun took its place on the zero-age main sequence approximately 4.5 billion years ago. At that time, it emitted only about 70% of the energy that it radiates today. One might expect that Earth would have been a lot colder than it is now, with the oceans frozen solid. But if this were the case, it would be hard to explain why simple life forms existed when Earth was less than a billion years old. Scientists now think that the explanation may be that much more carbon dioxide was present in Earth’s atmosphere when it was young, and that a much stronger greenhouse effect kept Earth warm. (In the greenhouse effect, gases like carbon dioxide or water vapor allow the Sun’s light to come in but do not allow the infrared radiation from the ground to escape back into space, so the temperature near Earth’s surface increases.)

Carbon dioxide in Earth’s atmosphere has steadily declined as the Sun has increased in luminosity. As the brighter Sun increases the temperature of Earth, rocks weather faster and react with carbon dioxide, removing it from the atmosphere. The warmer Sun and the weaker greenhouse effect have kept Earth at a nearly constant temperature for most of its life. This remarkable coincidence, which has resulted in fairly stable climatic conditions, has been the key in the development of complex life-forms on our planet.

As a result of changes caused by the buildup of helium in its core, the Sun will continue to increase in luminosity as it grows older, and more and more radiation will reach Earth. For a while, the amount of carbon dioxide will continue to decrease. (Note that this effect counteracts increases in carbon dioxide from human activities, but on a much-too-slow timescale to undo the changes in climate that are likely to occur in the next 100 years.)

Eventually, the heating of Earth will melt the polar caps and increase the evaporation of the oceans. Water vapor is also an efficient greenhouse gas and will more than compensate for the decrease in carbon dioxide. Sooner or later (atmospheric models are not yet good enough to say exactly when, but estimates range from 500 million to 2 billion years), the increased water vapor will cause a runaway greenhouse effect.

About 1 billion years from now, Earth will lose its water vapor. In the upper atmosphere, sunlight will break down water vapor into hydrogen, and the fast-moving hydrogen atoms will escape into outer space. Like Humpty Dumpty, the water molecules cannot be put back together again. Earth will start to resemble the Venus of today, and temperatures will become much too high for life as we know it.

All of this will happen before the Sun even becomes a red giant. Then the bad news really starts. The Sun, as it expands, will swallow Mercury and Venus, and friction with our star’s outer atmosphere will make these planets spiral inward until they are completely vaporized. It is not completely clear whether Earth will escape a similar fate. As described in this chapter, the Sun will lose some of its mass as it becomes a red giant. The gravitational pull of the Sun decreases when it loses mass. The result would be that the diameter of Earth’s orbit would increase (remember Kepler’s third law). However, recent calculations also show that forces due to the tides raised on the Sun by Earth will act in the opposite direction, causing Earth’s orbit to shrink. Thus, many astrophysicists conclude that Earth will be vaporized along with Mercury and Venus. Whether or not this dire prediction is true, there is little doubt that all life on Earth will surely be incinerated. But don’t lose any sleep over this—we are talking about events that will occur billions of years from now.

What then are the prospects for preserving Earth life as we know it? The first strategy you might think of would be to move humanity to a more distant and cooler planet. However, calculations indicate that there are long periods of time (several hundred million years) when no planet is habitable. For example, Earth becomes far too warm for life long before Mars warms up enough.

A better alternative may be to move the entire Earth progressively farther from the Sun. The idea is to use gravity in the same way NASA has used it to send spacecraft to distant planets. When a spacecraft flies near a planet, the planet’s motion can be used to speed up the spacecraft, slow it down, or redirect it. Calculations show that if we were to redirect an asteroid so that it follows just the right orbit between Earth and Jupiter, it could transfer orbital energy from Jupiter to Earth and move Earth slowly outward, pulling us away from the expanding Sun on each flyby. Since we have hundreds of millions of years to change Earth’s orbit, the effect of each flyby need not be large. (Of course, the people directing the asteroid had better get the orbit exactly right and not cause the asteroid to hit Earth.)

It may seem crazy to think about projects to move an entire planet to a different orbit. But remember that we are talking about the distant future. If, by some miracle, human beings are able to get along for all that time and don’t blow ourselves to bits, our technology is likely to be far more sophisticated than it is today. It may also be that if humans survive for hundreds of millions of years, we may spread to planets or habitats around other stars. Indeed, Earth, by then, might be a museum world to which youngsters from other planets return to learn about the origin of our species. It is also possible that evolution will by then have changed us in ways that allow us to survive in very different environments. Wouldn’t it be exciting to see how the story of the story of the human race turns out after all those billions of years?

Key concepts and summary

After stars become red giants, their cores eventually become hot enough to produce energy by fusing helium to form carbon (and sometimes a bit of oxygen.) The fusion of three helium nuclei produces carbon through the triple-alpha process. The rapid onset of helium fusion in the core of a low-mass star is called the helium flash. After this, the star becomes stable and reduces its luminosity and size briefly. In stars with masses about twice the mass of the Sun or less, fusion stops after the helium in the core has been exhausted. Fusion of hydrogen and helium in shells around the contracting core makes the star a bright red giant again, but only temporarily. When the star is a red giant, it can shed its outer layers and thereby expose hot inner layers. Planetary nebulae (which have nothing to do with planets) are shells of gas ejected by such stars, set glowing by the ultraviolet radiation of the dying central star.

Questions & Answers

what is steral evolution (star evolution
meron Reply
hi
Nisha
when a star's mass changes over time
Joe
hi
Joe
hi
Lisette
Hii
Asim
hi
Nisha
what big bang
Nisha
yes joe over time chang star mass
Nisha
star prouduce nucluer fusion first stag ( hydroge fusion helium- carbon-neon-oxygen-silicon- last fusion iron hevy star mass not handle iron blast super nova
Nisha
what is the worm hole theory
Nisha Reply
it states that you can travel back through time by this. It's like folding a paper into half and making two points, and there states that you can bend spacetime but according to Einstein's equation that it can break easily and only really small particles can pass through it.
Dark
dark dream what is dark matter
Nisha
what is the great filter theory
Nisha
the great filter theory it's just like the literally filtering it says that when once a civilization achieved its highest state or let's say the highest technology for instance their civilization will end.
Dark
what is radio burst
Nisha
please answer
Nisha
what is the simulatin hypothies
Nisha
smart obsevatin
Nisha
In radio astronomy, a fast radio burst (FRB) is a transient radiopulse of length ranging from a fraction of a millisecond to a few milliseconds, caused by some high-energy astrophysical process not yet identified. We can say that this can be they way to at least know if there's other civilizations~
Dark
~out there
Dark
Simulation hypothesis it proposes that the earth, the universe and the reality you are in is just an artificial simulation or like you are living in a computer simulation.
Dark
sir possible time travel
Nisha
?
Nisha
Yes. Everything is possible.
Dark
replay
Nisha
thanks
Nisha
sir how to make neutron star
Nisha
replay
Nisha
?
Nisha
sir what is the white hole?
Nisha
hi good morning
Nisha
why does the matter of an objects density change the fabric of space time rather than the objects volume..? (hopefully I have expressed that question properly) thanks
Daijahrel Reply
because an objects density consists of it's energy & momentum. an objects volume, for example a photon can have no density (hopefully I expressed that answer properly)
Joe
I suppose each Individual has his or hers different laws and assumptions, so it can be difficult to ask and answer physics questions, but discussions are always positive
Joe
how
Melaku
which matter use rocket
Nisha
Does their is any procedure of star making
Asim Reply
Hope That Helps.....
Adam
how to produce star and how to dead star?
Nisha
waad mahad santnihiin dhamaan waxaan doonayaa inaan wax ka barto astronomyga waa maxay xidigis?
Abdicaroog Reply
understanding astronomy
ricardo Reply
What About Understanding Astronomy?
Adam
yap
Janmarc
what is astronomy?
Janmarc
define..
Janmarc
Currently, I'm studying in 10th grade. What should I do after my 10th so that I can get an astronomy career?
Chaya Reply
try jee exam and achieve a good score in jee advance to join in IIST(Space research institute)
Sri
okay.. thanks
Chaya
Hey there I want to be an astrophysicist... and I'm grade 9... what should I do to be an astrophysicist
Aymen
Know more about space,watch movies related to space ,and to become an astrophysicist u should be very good in physics,train urself to think everything logically. Start to focus on JEE Exam ,train urself or join any institute which is good in coaching for JEE ,then if u score high ,u can join IIST
Sri
Which is the best university for Astronomy
Asim
Probably Massachusetts Institute Of Technology.....
Adam
Math Math Math, Get Familiar With All Types Of Math.....
Adam
Which subject is most important for Astronomy
Asim
Geometry, Algebra, Calculus, Trigonometry, Do Alot Of It And Often.....
Adam
I Can't Say It Enough, Math Is The Language Of The Cosmos.....
Adam
Adam you are in which university?
Asim
I Went To University But Never Finished My Degree..... Had To Work And Couldn't Afford School.....
Adam
MaryMount University..... Philosophy Of Science Major.....
Adam
It ia a cathloic University. Am i write
Asim
And its main campas is in Arlington country
Asim
No, It's In New York City.....
Adam
It's Not A Catholic University.....
Adam
Ohh sorry
Asim
Are you interested in Astronomy
Asim
IIT ain't so good for Pure Astronomy. If you want to know how the universe works,go for pure science. If you want to make spacecraft,go for Aerospace Engineering
priyanshu
Your are in which university brother
Asim
I Love Astronomy, I'm An Active Amateur Astronomer.....
Adam
I also love Astronomy very much
Asim
And to help me to solve some puzzling questions
Asim
this famous person was the first to recognise earthshine on the moin
Rajan Reply
Leonardo Da Vinci.....
Adam
what is string theory?
sakshi Reply
A Cosmological Theory Based On The Exsistence Of Cosmic Vibrating Strings.....
Adam
Good Morning Asim Ali.....
Adam
I Can't Do That, You Can Ask Me What Ever You Want.....
Adam
If you don't mind can i ask why?
Asim
Do You Understand The Millions Of People Have Access To This Site, I Wouldn't Put My Information Out There, Knowing What People With Bad Intent Can Do With Personal Information.....
Adam
Ohh sorry
Asim
My question is that, there are many collision of stars in a day So that cause black hole. But is there any procedure of star making? Hopefully i ask my question properly.
Asim
No Need To Apologize, I Will Answer Anything You Need Answered And If I Can't Answer It I Will Guide You To The Answer.....
Adam
Thier Is Only One Way Stars Are Made, Gravity Makes Matter Come Together, And When The Amount Of Matter Gets Massive Enough Nuclear Fusion Starts Up And A Star Is Born.....
Adam
What is white drawft?
Asim
A White Dwarf Is A Low Mass Star That Has Exhausted All It's Central Nuclear Fuel And Lost It's Outer Layers As A Planetary Nebula.....
Adam
what is the great filter theory
Nisha
hi adam what is great filter theory
Nisha
Well First It's Not A Theory, It's A Hypothesis, The Great Filter Hypothesis States That What Ever Causes Dead Matter To Under Go Abiogenesis(Start Of Life) Must Be Very Hard And Very Rare In Our Universe, Because So Far We Only See 1 Civilisation That Made Through All The Requirements For.....
Adam
Intelligent Life, So Far Only Our Planet Has Intelligent Life, That We Know Of, And Again This Is Only A Hypothesis, No Evidence Exist To Back This Up.....
Adam
hi adam sir
Nisha
Good Day.....
Adam
Good to see you sir
Asim
hi
Nisha
good day
Nisha
hi
Nisha
Same Here.....
Adam
What's The Good Word For The Day?
Adam
Does MIT have good astrophysics courses ?
priyanshu Reply
Probably The Best In The United States.....
Adam
But Don't Get Caught Up On Who's The Best, You Can Be The Next Noble Winning Astrophysicist.....
Adam
hmmm..........that's nice one....Adam had said.....
Gospel
How did ASTRONOMY helped you understand yourself ? 🤔
Hussain Reply
why do you want to study ASTRONOMY?
Hussain Reply
It is one of the natural sciences and therefore worth exploring. You are a part of the universe and it is a part of you. The sky is my classroom. (student of cosmology, Oxford Uni)
SuperNova
because everything in the space is just beautiful...interesting and worth studying and exploring...
Memo
I have been studying astrophysics an love it
Carla
I love to learn what makes up our lives an heavens an how it works there us so much more out there than books an our veiw of thw heavens can reveal
Carla
How did ASTRONOMY helped you understand yourself ?
Hussain
Because it proves the impossibles and the limitless.
Dark
It helped me realize that there are like countless possibilities in life and get all through it.
Dark
It honestly showed me to view the world in a balanced way. Because space beautiful and calm yet violent, and so is the world, and we should still help, but there will always be violent people much like violent astrophysical jets.
Da
What does ASTRONOMY means?
Hussain
Does anyone know where can I study astronomy in Spain? My budget is too low for traveling out there...
Valerian Reply
How long the duration was when the laws of physics became active after the big bang?And why the time is called plank's time?
Mostak Reply
how many galaxies in universe?
Shaikh Reply
10 to the power 11
Wwe
testing
Ahmad
thnx
Shaikh
if u can count all the sands on the beaches and on the deserts then u will know how much it will be.......some said more than 1,000,000,000 galaxies are there in our universe...
Gospel
it's ok bro
Wwe
I hope you will become a member of nasa
Wwe
just new in this area, from art background not science
Ahmad
what's ur name wwe
Shaikh
The Observable Universe Contains Between 200 Billion To 2 Trillion Galaxies.....
Adam
are u sure?
Caleb
It actually hasn't been proven, people have just made estimations.
Ariana
the thing is u can't count,maybe the our number system will collapse there...who knows?
Abdullah
What's the exact time when the laws of physics became active after the big bang ?
Mostak
Actually we still don't know the exact number of galaxies in the universe, since the universe is bigger than we can imagine and it is still expanding even bigger today than yesterday
Ismaee
we didn't actually find the exact number but may be it is around 100 billion
Smridhi
why this universe is expanding?
ATUL
Science Does Not Concern It Self With Why Questions, Science Is Geared For How And What Questions.....
Adam
Why Questions Form And Endless Loop.....
Adam
According to the universal law of cause and effect .any phenomenon that occur in this universe should have any reason , nothing happen without any reason.
ATUL
Can you tell me the expanding speed of this universe.
ATUL
yes that would be a great question to have answered what is the expanding speed of the universe?
Daijahrel
Remember that most of what you can see is light years away. We're looking back in time, we can never know the current nature of our observations, only glimpse the galaxies and stars as they once were. Strange but true, and a little sad.
SuperNova
Correct, That's Why Telescopes Are Like Time Machines, You See The Past.....
Adam
really telescope can see the past?....i meant everything is in its place, though it rotates or revolve or whatever it is.......but how can this telescope can see the past.....can we see how our Universe was created,how it formed out of it? thats my question to all of you guys can you plz tell me.
Gospel
Because We Dont See Any Object In Space As It Is, We See It As It Was..... Hope This Clears That Up For You.....
Adam
And One Day We Might Have A Telescope That Will Show Us The Big Bang.....
Adam
ok....... that will be nice one
Gospel
ok....... that will be nice one
Gospel
Travel at light speed in a spaceship at 186,000 miles every SECOND. At this speed it will take you 100,000 years just to cross our Milky Way galaxy, which is just a dot in the sky. Next stop, the Andromeda galaxy, after 2.5 million years, still in the Local Group, Virgo Supercluster, still a dot.
SuperNova
Pretty Much.....
Adam
there are nearly 200 million I suppose.
Amit
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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