Posts Tagged ‘Supernovae’

Astronomy Domine

April 6, 2016

Astronomy domine is a song much played in philosophy, not just by Pink Floyd, ever since there are men, and they observe. (Homo Erectus probably observed the last fabulous Galactic Core Eruption, two million years ago.)

Before feeding the pocketbooks of the greedy, science feeds the imagination of poets.

Astronomy has been at the forefront of physics, at least since Buridan (14th Century). Buridan applied his notion of impetus to explain that planets went around in circles from what we now call inertia. In Greek Antiquity, a large, wagon sized meteorite landed in Northern Greece, and was visited for centuries (it may have been a piece of Halley’s comet, which whizzed by spectacularly close in 466 BCE).

A Place Of Great Eruptions, Past & Future. Eta Carinae Nebula, At Least A Couple of Giant Stars, The Lightest One At Least 30 Sun Masses, the Largest Maybe As Much As 220 Solar Masses, 7,500 Light Years Away. Five Million Times The Luminosity Of the Sun. Stellar Natures & Explosions Are Far From Fully Understood!

A Place Of Great Eruptions, Past & Future. Eta Carinae Nebula, At Least A Couple of Giant Stars, The Lightest One At Least 30 Sun Masses, the Largest Maybe As Much As 220 Solar Masses, 7,500 Light Years Away. Five Million Times The Luminosity Of the Sun. Stellar Natures & Explosions Are Far From Fully Understood!

Supernova explosions are awesome: the most luminous one ever detected had a peak luminosity 570 BILLION times the luminosity of the Sun (yes, (570) 10^9 Suns; that was seen in 2015).

Supernovae are us. Supernovae create most of chemistry: the extremely high temperatures of their explosions enable light nuclei to smash into each other, and fuse, making most elements of the periodic table.

There are two main types of stars which explode as supernovae: white dwarfs and massive giant stars. In the so-called Type Ia supernovae, gases falling onto a white dwarf raise its mass until it nears a critical level, the Chandrasekhar limit, resulting in an explosion when the mass approaches exactly 1.44 Solar Mass. In Type Ib/c and Type II supernovae, the progenitor star is a massive star which runs out of fuel to power its nuclear fusion reactions and collapses in on itself, reaching astounding temperatures as it implodes, and then explodes.

Supernova science is very far from finished knowledge. Even the nature of the Crab Nebula supernova, which was seen to explode in 1054 CE, is not clear (it is known it was a big star, more than 8 Solar Masses; it left a pulsar).

Even the Crab was philosophically interesting in devious ways: the explosion was duly recorded by Europeans and Chinese. However the Muslims tried very hard not to see it (a mention was recently found). Indeed, the heavens, for desert savages, are supposed to be messages from God, and God playing games with stars was apparently not kosher…

Type Ia supernovae have completely changed our idea of the universe in the last two decades. (According to your modest servant, other types of supernovae may change our view of the universe even more dramatically. See the conclusion!)

Eta Carinae is the only star known to produce ultraviolet laser emission!

There is some philosophy to be extracted from Eta Carinae: if a star, or a system of gravitationally bound stars, can be that exotic, how sure are we from the astrophysics we think we know?

I am not the only one who thought of this. The teams who determined the accelerating acceleration of the universe (“Dark Energy”), had to exclude weird, sort-of Type Ia Supernovae… from their statistics (pre-selecting the population of explosions they would apply statistics on…). There are now other ways to detect Dark Energy (and they give the same results as the pre-selected Type Ia supernovae studies). So the results have been confirmed.

However my position is more subtle, and general. How sure are we of the astrophysics we have, to the point that we can claim that stars are unable to create all the known elements? In the proportion observed?

I am no specialist of astrophysics. But, as a philosopher, I have seen the science evolve considerably, so I think we cannot be sure that we absolutely need the hellish temperatures of the Big Bang to generate all observed elements.

Very large stars (600 Solar masses) have now been observed. They don’t live very long. I don’t see why stars thousands of Solar Masses, living only for a few hundred years, before exploding, are not possible. During these so-far-unconceived apocalypses, nucleogenesis could well follow unexpected ways.

And that could well remove one of the main arguments for the Big Bang.

Patrice Ayme’

Where Is Everybody?

September 22, 2015

Where Is Everybody? This is the question Enrico Fermi asked in the 1950s, referring to the little green men who were supposed to inhabit the galaxy. This question is still with us. Efforts have been made to search for extraterrestrial life. Science Fiction books are full of worlds peopled by clever creatures.

It would be reassuring to know that the galaxy is full of clever creatures. After all, if we, human beings disappeared, well, we were just not good enough, no big deal: those out there, better than us, would pursue the mission we are named after, wisdom (sapiens in Latin).

Yet I see plenty of reasons why Earth’s advanced biosphere is unique. I go even further. In my opinion, the fact Earth has a radioactive, high density metallic core is crucial. I will reinforce this argument today (in light of just published research).

Weirder Planets Than We Ever Imagined Are Out There. Yet, Weirdest Of Them All Could Be The Earth

Weirder Planets Than We Ever Imagined Are Out There. Yet, Weirdest Of Them All Could Be The Earth

Fermi, Nobel for discovering the neutrino (“little neutron” in Italian), discovered the Fermi principle and statistics (which posits that matter does not collapse because Fermions refuse to be in the same “state” in the same place at the same time). Fermi, who had fled from fascist Italy, was also the scientific head of the Manhattan project.

Fermi was both a theoretician and an experimentalist. Thus immensely clever, but yet down to earth. He obviously found that the obvious absence of civilization out there in space was a striking fact. And it is.

The idea that the stars had little Earths orbiting them, graced with little green men, with their own little green Christs, came all the way back to another Italian, Giordano Bruno. Bruno had lectured in universities around Europe, and was a friar. However, to suggest the world was not exactly as Christianism described it, was a capital crime in places ruled by Christianism.

To punish Bruno’s mental exuberance, the Vatican imprisoned and tortured him for seven years. Then the Vatican and its horrid Fundamentalist Jihadists stripped Bruno naked, pierced his palate with iron (so that he could not address the public), and burned him alive after he refused to submit to infamy. I am still waiting for the excuses from the institution at fault, the world’s oldest, the Catholic Church.

Yet, although he was a genius, Bruno was probably wrong about the little green men. Why? Where is everybody? Indeed. I argued that the nuclear reactor at Earth’s core has been crucial for plate tectonics, and preserving Earth from the runaway greenhouse which destroyed venus as a potential biosphere. I even argued that said nuclear reactor may have generated the Moon, by far the largest satellite in the Solar System relatively to the size of the planet it orbits around. (The Moon is larger than Jupiter’s third largest satellite, Europa.)

To generate a large radioactive core to a planet, one needs, first of all, metals. Actually metals enable to make very complicated molecules central to the wealth of biology. Hemoglobin carries iron which is used to transport oxygen.

Where do metals come from? Supernovae.

Which type of planets do we expect to observe in the Habitable Zone?

Vardan Adibekyan, Pedro Figueira, Nuno C. Santos

(Submitted on 8 Sep 2015)

“We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth.”

So the (empirical) argument is that, if a planet has metal content similar to Earth, it orbits so close to its parent star that it will be too hot for life. Reciprocally, planets which orbit in the Habitable Zone are found to be metal poor.

Planets are built from the same elements as their stars. Most of the properties of planets of different types strongly depend on their host stars’ chemistry, and chemistry varies. It seems Habitable Zone planets were formed long ago. After supernovae formed and exploded, spewing heavy metals such as Iron and Uranium, second generation stars such as the Sun formed, and were metal rich. However, the observations on hundreds of planets tend to show that metal-rich stars like our sun have large rocky planets wrapped in huge gaseous envelopes (caveat: it may still be a bit of a statistical fluke, at this point!).

If not a fluke (and that’s a big if), it gives a new reason to doubt that Earth-like planets are frequent in the galaxy: I argued that not just metal, but the very heaviest metals, the ones which have such large nuclei that they fission, are indispensable for life. Now it turns out that Earth orbits a metal rich star, but at a respectable distance.

So it may well be that Earth is a very special case. Maybe some day the Galactic Human Empire will be able to colonize habitable planets in various Habitable Zones, because thanks to human technology, humans, or, rather, transhumans, will capable of synthesizing metals, as needed (one could do this, if one had a mastery of accelerator technology to fine-tuned nuclear fusion as needed).

Philosophically, this rarity of Earth’s circumstances tells us, once again, that life is more precious that we ever imagined. It’s not just our unborn great grandchildren who will suffer from the holocaust of the biosphere we are engaged in. It’s the universe itself, because we may well be that unique.

Patrice Ayme’