Stars don't "evolve" (APOD 12 Nov 2006)

[andres]

The November 12, 2006 APOD refers to "stellar evolution". Usually it's the biologists that have physics envy--I didn't realize that it went the other way! The public is confused enough about the concept of evolution without making it worse by applying it to unrelated concepts in other fields (a quick Google search suggests that astronomers use this a lot).

Evolution is a process in which species change over time, primarily as a result of the inheritance of traits which confer fitness (greater survival and/or reproduction) in an organism's current environment. It is a result of the interaction between populations of organisms and their environment. Unlike in the case of stars, there is no relentless progression between a beginning and end point. Please leave the use of the term "evolution" to biology, where it belongs.

[BMAONE23]

Consider this:
In the early universe there were many stars with 100+ solar masses and probably equally as many with twice that volume. Those gigantic 1st generation stars fuse their H quickly because of extreme heat and pressure, and supernova after only millions of years. The remnants of those 1st generation form 2nd generation stars that are smaller, fuse slower, and live longer because they are more evolved than their parent stars. Eventually the 2nd generation stars reach the end of their lifecycle and explode. The remnants of these spawn further generations of stars that are more evolved than their parent stars, being smaller and burning for tens of billions of years (like our sun).

This is a form of evolution as defined in Websters.

[harry]

Hello All

Andres said

Unlike in the case of stars, there is no relentless progression between a beginning and end point.

I think you should read more on star and galaxy formation and the relentless progression from the start to the end. Than you may understand what evolution means.

Evolution is my pet subject.

[Qev]

"Evolution", as a word, predates the theory of (biological) evolution. It simply describes a system changing over time. All sorts of systems evolve, it doesn't necessarily have anything to do with biology.

[harry]

Hello Qev

Well put.

[astro_uk]

Indeed Qev.

In this case evolution means the evolution of a single star during its lifetime. Its difficult to come up for a better term to describe this, as stars change dramatically as they age, in ways that depend on their intial mass and element abundance. A star like the sun will start the main sequence and gradually brighten for 10 Gyr then brighten dramatically and expand as it enters the red giant phase, which is followed by the much smaller dimmer white dwarf phase. Most stellar "evolution" occurs at points near the beginning and end of their lives as they move onto and off the main sequence.

Check out the wikipedia article for more details.
http://en.wikipedia.org/wiki/Stellar_evolution

[BMAONE23]

I would say the best phrase to describe stellar changes is "Stellar Maturity" when refering to the state of a single star at any given point within its lifetime and reserve "Stellar Evolution" to describe subsequent generations of stars, born from the supernovae of previous generation stars.

Just my $.02 worth

[iamlucky13]

On the other hand, maturity implies to me almost a plateau in development, so I associate that term when applied to a star as relating to the main sequence. I would suggest growth as a description of the process, but that term better applies to the accumulation of mass.

I guess "stellar development" could work? Still, evolution is a pretty well-accepted term.

[harry]

Hello All

Sometimes a mature star would go either Nova or supernova in either case we see it as a new star. When the star rejuvinates it confuses the dating process.

Our sun, over 5 Gyrs (Theoretical) ago was a mature star that went supernova creating our solar system. Lets assume that it was 10Gyrs old plus 5Gyrs makes it 15 Gyrs. I'm assuming its birth and did not go through rejuvination.

[ta152h0]

on the University of Washington Tv, the head of the vatican Observatory was commenting on star formation and claimed we are looking at the third generation stars in the skies and comparing the analogy to families that have grandfathers, fathers and sons living at the same time in the same family. The point was there is overlap in the age of stars. My next project is to discover how darkness became light immediately after the Big Bang. It is like taking a class in classical physics and finding out there is thermodynamics out there also.

[Wadsworth]

Stellar Phase Progression.

SPP.
duh! 8)

[Metallisoft]

Harry, our sun never went supernova, nor will it ever...supernovas do not create solar systems.

[Wadsworth]

Harry, our sun never went supernova, nor will it ever...supernovas do not create solar systems.

Yeah, I was thinking about this the other day, Harry if the sun's core is solid, how do you explain the 100 billion nuetrinos flowing through every square centimeter of your body right now?

[harry]

Hello All

I would advice some of you to look at the origin of our solar system.

I did not say that the core of our sun is solid.

please read these papers

http://www.omatumr.com/abstracts2001/nuc_sym3.pdf

http://www.thesurfaceofthesun.com/Plasm ... rFinal.pdf

http://www.omatumr.com/

Prof Oliver Manuel papers will expalin the functioning of the sun and its origin.

[Galactic Groove]

Hello Andres,
I think you are singling out astronomers here, as biologists do the same thing. A classic example??? The life cycle of a butterfly... egg to larva to pupa to adult... each stage evolves into the next as biologists love to say. As users of this forum are already saying, with respect to individuality, perhaps you bioligists should be reserving the term "evolution" and applying the term "maturity" instead!

So really the ideas are exactly the same, the life cycle of organisms and that of the stars. It's just the way we're using the term. Evolution can be defined in two ways: 1- It's a change in the genetic make-up from one generation to the next (biological evolution). 2 - It's a change of state within the lifespan of a particular body (lifecycles of stars, organisms, etc.)

No one is interpreting that when we say when a star evolves from one phase to the next that we are implying a new star altogether (except maybe Harry )... just as we don't interpret that a new life has been born when a butterfly evolves from one of its phases, it would just be reclassified based on its current state.

[andres]

Any biologist who uses "evolve" to describe developmental changes of an organism should be slapped up-side the head and stripped of all funding and/or teaching responsibilities.

I will grant you that biologists did not invent the term and do not have exclusive rights to it. But the lay public is confused enough about the biological concept (which is the context in which they are usually exposed to the term), and a popular website using it to describe a fairly deterministic process doesn't help.

[BMAONE23]

Maybe we should encourage the IAS to get together and further discuss appropriate terminology used to describe cretain astronomical events.

Oh and maybe determine what should and shouldn't be termed a "Planet"

[Keldor314]

... just as we don't interpret that a new life has been born when a butterfly evolves from one of its phases, it would just be reclassified based on its current state.

...There's a term for it - Stellar Metamorphosis!

[lewishb]

The ancients said that the star Sirius was a red star and
it is now blue-white....

this is stellar evolution......

a little observation shows that supernovas cannot create stars..... the shock wave would disperse stardust,, not condense it into stars.....

and Boyles law shows that stars cannot self-condense through gravity .... Boyles law says that as gas and dust collect and try to condence, they heat up and expand again.....

Science labels every dust cloud as a stellar nursery.... this is opinion
and has not yet been proven..........

[harry]

Hello All

Lewishb said

a little observation shows that supernovas cannot create stars..... the shock wave would disperse stardust,, not condense it into stars.....

Mate get more info in star formation and how neutron stars are formed.

and Boyles law shows that stars cannot self-condense through gravity .... Boyles law says that as gas and dust collect and try to condence, they heat up and expand again.....

This is quite true, but! degereated matter ejected from neutron stars and black holes (a compact star core that prevents light from escaping ) can form seeds for stars in my opinion. These seeds are high dense objects that grow from the surrounding matter colliding.

Science labels every dust cloud as a stellar nursery.... this is opinion

Many compact star cores in order for them to be rejuvinated they need matter and the nursery is a great spot.

Hey! thats my opinion.

[aichip]

It is true that when a supernova creates new elements and injects them into space, the cloud is extremely hot and spreads rapidly. However, it is radiating its heat to space until it is nearly as cold as space.

During the expansion phase, the material is driven outward by the explosion and inertia carries it, and since it is still very hot, it cannot contract until it has lost that heat. But when the gas spreads and cools, it can then be diffuse and reach temperatures almost down to 3 Kelvin.

At this point, a shock wave or even a gravitational disturbance can trigger the collapse and condensation of the cloud and this is when star formation begins. And consider that some of the material might already have begun to stick together into small dust particles, and that in this state it is much easier for the collapse to proceed. This is because in this compact state, the heat is more fully lost. Gas that is cold gains heat on compression, of course, but dust grains are already "compressed", being solid matter. At the same temperature, dust would more easily collapse than gas without "rebounding" due to heating.

I suspect that there may be a certain percentage of dust that must be present before star formation can proceed, or that more dust could translate to earlier star formation, due to the cooling that it represents.

[iamlucky13]

Good post aichip. One nitpick though in the context of the big bang theory, though. There have been several people discuss a need for dust to initiate star fusion.

According to the theory, the big bang left mostly hydrogen and a little bit of helium. No heavier elements to form dust. Yet, stars must have formed from these light gaseous elements or the theory has a major hole in it since stars clearly exist.

It is important to note that as gas pressure increases and it warms and re-expands, it becomes warmer than the surrounding, less dense gas, and therefore loses heat. As this progresses, further increases in density are possible, in fact, inevitable. As aichip noted, however, the presence of dust may simply accelerate the process by providing cool condensation nuclei.

[harry]

Hello All

Go back a little.

When I speak of degerated matter being ejected by jets from neutron stars and black holes. This is before anyform of supernova.

This degenerated matter forms knotts in the ejected jet stream. The seed need only be 400 mm in diameter.

M87's Energetic Jet
http://antwrp.gsfc.nasa.gov/apod/ap041211.html


In general for a star to form you need a gravity sink, a compact object.

=========================================

As for the Big Bang, it became the standard theory for the wrong reasons.
People have taken the theory as fact and now we have a situation that people think it actually happened.

[iamlucky13]

Well, discussions about the validity of the big bang theory have already been given a pretty thorough exercise here, so I don't intend to continue that. However, I subscribe to the mainstream acceptance of the BBT as the best guess we currently have for the formation of the universe.

That said, I maintain my position on the ability of a gas to condense into a star, although as I consider it further, it should be possible irregardless of the Big Bang Theory.


Harry, I'm interested in a general summary of your theories on the universe. I know you've linked to some lengthy papers suggesting the sun has a mostly iron core and that elliptical galaxies are older than we think, but I'm more interested in your theory on the origin and age of the universe and star formation. It will help me better understand some of your posts.