a reply to: tanka418
:On the age of Sirius A. I know that the "published" age is on the order of hundreds of millions of years, :however, I have talk to Astronomers who
seemed to indicate that Sirius could be much older, perhaps nearly :as old as Sol. While this is never confirmed, it does seem probable.
Well this is a complicated issue, but a well understood one. Google 'stellar evolution' and 'Hertzsprung Russell Diagram' for more detail.
Generally speaking Sirius A and Sirius B started out life about 300 million years ago, collapsing from a molecular cloud in about 10 million years
time. Sirius A is 2.02x as massive as the Sun and Sirius B started out life 5x as massive as the Sun.
Now Luminosity, the rate at which a Star burns up its fuel, is determined by its mass. This is known to be;
Lstar = Lsun * ( Mstar / Msun ) ^ 3.5
So, a star as large as Sirius A 25.4x as luminous as the Sun today. A star 5x as massive as the Sun is 279.5x as luminous as the Sun today.
So before Sirius B blew off its shell, Sirius would have been very bright in the night skies of Earth. It would have been incredibly bright to any
planet orbiting around the pair! You'd have to be 2.5 billion km away (the distance of Uranus from the Sun in solar system terms) to maintain
liquid water oceans on a planet. Of course, the star would radiate in the extreme UV or soft X-ray region mostly, as discussed previously.
Now lifetime is proportional to Mass divided by Luminosity, since Mass tells us how much nuclear fuel we have, and Luminosity tells us how much
nuclear fuel we're using per unit time. We've studied the Sun very closely, and it is has a lifetime of about 10 billion years fusing hydrogen.
So, astronomers estimate that Sirius B, being 2.02x as massive as the Sun will have a life cycle lasting 1,724.3 million years whilst Sirius B,
starting out with 5.00x more mass than the Sun will have a life cycle lasting 178.9 million years. That is, starting 300 million years ago, Sirius B
has already gone through its life cycle, and is now a White Dwarf cooling off. Sirius A has another 1,420 million years to go. In contrast the Sun
is 4.5 billion years old and has another 5.5 billion years to go before it becomes a White Dwarf like Sirius B after blowing off 45% of its mass into
a planetary nebula.
:Firstly, as I understand it there are two "ages" for any given star, though they nearly always agree more or :less. These would be the "movement"
or kinematic age, and the "color" age. If I understand correctly the 300 :million year age is the "color" age for Sirius A. That being the case;
what is it's kinematic age?
There are two ways to talk about the age of a star. The first is how far along its life cycle it is. The second is to talk about how old it is in
years. Stars that live fast and die young - like Sirius B and Sirius A - may be only 300 million years old, but be far in advance of the Sun through
their life cycle, even though the Sun is 4.5 billion years old.
Check out Hertzsprung Russell Diagram. This organizes our understanding of stellar evolution very well. The diagram plots a star according to its
luminosity on the Y-axis and according to its temperature on the X-axis.
Do this for all stars you see and you get a 'main sequence' of stars with 'branches' where they like to hang out.
Clouds of interstellar gas and dust that fall together to form stars, follow a specific path based on their initial mass. Here's the path of the
Sun. This path is determined by the physics of black bodies and the physics of nuclear fusion;
: Is there a way to find out what the "habitable zone" for Sirius A might be?
Yes, the circumstellar habitable zone is
CHZ = SQRT( Luminosity )
in Astronomical Units. So, Sirius A is 25.4x as bright as the Sun, so its CHZ(Sirius A) = 5.03 AU. Sirius B is 0.026 as luminous as the Sun so
CHZ(Sirius B) = 0.16 AU. At these distances liquid water could form on a planet's surface. Other factors may not be conducive to life as we know
it, however, life may evolve anyway, that thrives in these conditions as I pointed out. And, even other factors may apply, for example, a planet that
is inside the Roche Limit for a star would tend to have tidal effects so large as to pull the planet apart into a ring. This is the basis of Larry
Niven's 1984 sci-fi novel 'Integral Trees' which I recommend to anyone who wants to think creatively about the possibility of life around a White
:How difficult would it be for the kind of orbital resonance you speak of to occur naturally?
Not difficult at all. We see resonances of every type in the solar system.
: Could it be engineered?
Yet, if you are promoting the concept of life evolving in the Sirius star system I would say there isn't enough time - not for the sort of planet
bound evolution we see here on Earth - with the life forms we have.
Yet, we should always keep in mind, the comment of JBS Haldane, in his 1927 paper on the future, that the universe is not only stranger than we
imagine. The universe is stranger than we CAN imagine. Which is merely a re-statement of an even older statement of Shakespeare in his play Hamlet
in 1599 - where Hamlet talks to his school chum Horatio saying, "There are more things in Heaven and Earth, Horatio, than dreamed of in your
Life in the Molecular Cloud predating Sirius A and Sirius B
So, with an open mind, we can ask, how old is the Molecular cloud from which Sirius and the 200 other stars nearby were formed? The answer is, older
than the Sun. Now we have known since 2003 that these clouds possess amino acids and since 1998 that they have water
So, its not too difficult to imagine that they hold life. How old could this life be? Older than life on Earth!
In that context, it may be that life forms living in the cloud arrange the collapse of supermassive stars from the cloud, the same way we seed clouds
to produce rain. Why? To produce heavier elements needed for life and industry, along with energy.
Rapid Evolutionary Development around Hot Stars
Since the rate of evolution is proportional to the energy levels involved, and since UV and X-ray light is vastly more energetic, it may very well be
that once life gets started on worlds orbiting UV and X-ray emitters, that evolution proceeds far faster than it does on Earth. We may be slow-pokes
compared to the life forms that life around these stars. So, notwithstanding the shortened life span, it may very well be that life is vastly more
advanced in these systems than here on Earth.
Stupendously Rapid Evolutionary Development in Hot Stars
My friend Robert Forward wrote an excellent book in 1980 called Dragon's Egg. In the novel he described a star ship he designed and proposed to NASA
and Congress to be built actually. However, he also described a life form that evolved on the surface of a neutron star! Very similar to Sirius B.
Again, because the energy levels are so high, life evolved very rapidly indeed leaving us in the dust!