Gould’s Belt

29.2 – 27.7 million years ago

Logarithmic History has had a lot of geology and biology lately, not so much astronomy. But all is not peaceful in the heavens.

Benjamin Gould is a nineteenth century astronomer who noted that a lot of bright stars in the sky — especially the bright blue stars that we know are very young — seem to fall along a ring tilted at a 20 degree angle to the Milky Way. This ring has come to be called Gould’s Belt (or the Gould Belt). The Belt is an ellipse about 2400 by 1500 light years across where there has been a recent wave of star formation. Our Sun lies within the belt, somewhat off center; the center lies in the direction of the Pleiades.

The Belt began forming maybe thirty million years ago. We’re not sure what happened. A supernova may have set off a wave of star formation, but it would have to have been a huge one. Or it may be that a gas cloud or a clump of dark matter passed at an angle through our part of the Milky Way, and started stars forming with its shock wave. There are features resembling Gould’s Belt in other galaxies. In any case, the Belt is one of the really striking features of our part of the Milky Way.

Whatever its cause, no one disputes its magnificence. Gould’s belt is the most prominent starry feature in the Sun’s neighborhood, contributing most of the bright young stars nearby. Nearly two thirds of the massive stars within 2,000 light-years of the Sun belong to Gould’s belt. If I were kidnapped by an alien spaceship and taken to some remote corner of the Galaxy, Gould’s belt is what I’d look for to find my way back home.

Ken Crosswell. Gould’s Belt.

If you’re in the Northern hemisphere you can look at the sky tonight and see the Milky Way in an arc in the Western sky, stretching from North to South. West of the Milky Way you’ll see some of Gould’s belt, an arc of bright stars running north to south from the Pleiades, through Taurus and the bright stars of Orion, and Canis Major. So tonight look at the stars, and drink a toast if you want, to your ape ancestors, who were just on the cusp of splitting off from monkeys thirty million years ago.

A family tree for the Sun

7.45 – 7.06 billion years ago

Recently, some astronomers teamed up with some evolutionary biologists to produce a “family tree” of our Sun and some of its neighbors. The tree is based on the abundances of different chemical elements; these abundances don’t change much over the lifetime of a star, and can be thought of as a kind of inherited trait, something like DNA. The tree groups stars roughly according to their ages, with younger stars having more “metals” (elements other than hydrogen and helium), but only roughly, since other processes affect stellar chemistry.

Drawing a family tree for stars might seem like an odd thing to do. Stars aren’t really related as parent and offspring. On the other hand, we might at least call some bunches of stars “siblings,” if they originate from the same stellar neighborhood, and consequently have similar chemical makeup. As with galactic or mineral “evolution,” we’ve got something that borders on evolution, even if it’s not quite what gets biologists all het up.

Evolution and broken symmetries

8.34 – 7.89 billion years ago.

No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?

Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification.

However, people sometimes talk about evolution that doesn’t involve descent with modification, in contexts that have nothing much to do with biological evolution – cosmic evolution or stellar evolution in the history of the universe, for example, or mineral evolution in the history of the earth. Another Victorian writer, the sociologist and philosopher Herbert Spencer, offered a definition of evolution that might cover these cases.

Evolution is an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity.

It’s easy to make fun of this definition. It’s the sort of abstract word pile that style manuals tell you to avoid, and that gives sociology a bad name. For that matter, it’s easy to make fun of Herbert Spencer. He may be some of the inspiration for the character of Mr. Casaubon, the dried up, impotent pedant in George Eliot’s “Middlemarch.” (Spencer probably turned down a chance to marry George Eliot = Mary Ann Evans. You should be careful about offending a writer.) But it may be that Spencer was groping toward the important modern concepts of symmetry and symmetry breaking.

A simple example: imagine you’re holding a bicycle exactly upright. The bicycle is pretty much bilaterally (mirror image) symmetrical. (OK, not really, the gears are on the right side, so it’s not a perfect mirror image. But just pretend …) Now let go of the bike. It will fall to one side or the other. The symmetry is broken, and you need one extra “bit” of information to tell you which side the bicycle is on.

Symmetry breaking is a fundamental concept in physics. In the very early history of the universe, the four forces of nature — gravitational, strong, weak, and electromagnetic – were united, but then as the universe cooled, one by one, these forces broke the symmetry and turned into separate forces. More symmetry breaking generated elementary particles, and nuclei, and atoms. When atoms first formed, they were distributed symmetrically through the universe as a diffuse gas. But gravitation pulled atoms and other particles together into clumps, leaving other parts of space emptier, and the spatial symmetry was broken (a “translational” symmetry in this case).

Symmetry breaking will keep showing up throughout the history of the universe. Consider sexual reproduction. A simple early form of sex involved two equal sized gametes (sex cells) joining to produce a new organism. Some species still do it this way. But more commonly the symmetry is broken – some organs or organisms produce little gametes that move around easily (sperm or pollen), others produce big gametes that don’t move around so easily (eggs or ovules). We call the first sort of organs or organisms male and the second sort female. Sex in most multi-cellular organisms is a broken symmetry. This broken symmetry will go on to have a dramatic consequences for human social evolution. It entails, for example, that patrilineages can expand their size much more rapidly than matrilineages.

Or consider the rise of political stratification, the move from small-scale societies where “every man is a chief over himself” to large-scale societies of chiefs and commoners, rulers and ruled. Another broken symmetry. It may be more or less an accident (good or bad luck, Game of Thrones style) who ends up being king, but it’s not an accident that somebody is, past a certain social scale.

We don’t attach much moral significance to broken symmetries where the physical world is concerned. You’re being way too sensitive if you feel sorry for the poor weak nuclear force that missed its chance to be the strong nuclear force, or for the dwarf Gaia-Enceladus galaxy that got cruelly torn apart and cannibalized by the Milky Way. Broken symmetries in social life – males and females, kings and commoners – are another matter …

We are stardust

10.4 – 9.9 billion years ago

The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

Carl Sagan (h/t to commenter remanandhra)

There’s a long gap between the origin of the universe, the first stars, and early galaxies, and the origin of our Solar System and our planet Earth. If we were using a linear scale for our calendar, the Solar System would get started in September. Even on our logarithmic scale, Sun and Earth wait until late January. A spiral galaxy like the Milky Way is an efficient machine for turning dust into stars over many billions of years. But the earliest stars it produces are poor in “metals” (to an astronomer, anything heavier than helium is a metal). It takes generations of exploding stars producing heavier elements and ejecting them into space before a star like the Sun — 2% metal – can form.

And just a few years back, a spectacular discovery provided support for another mechanism of heavy element formation. Astronomers for the first time detected gravitational waves from the collision of two neutron stars, 300 million light-years away. Such collisions may be responsible for the formation of some of the heaviest atoms around, gold and silver in particular. So your gold ring may be not just garden-variety supernova stardust, but the relic of colliding neutron stars. Here’s a chart showing where the elements in our solar system come from:

Alchemists thought they could change one element into another – lead into gold, say. But it takes more extreme conditions than in any chemistry lab to transmute elements. The heart of a star makes heavy elements out of hydrogen and helium; it takes a supernova to make elements heavier than iron, and something even more spectacular, the collision of neutron stars, to make the heaviest elements. So it’s literally true, not just hippy poetry, that “we are stardust” (at least the part of us that isn’t hydrogen).

Gould’s belt

30.3 – 28.8 million years ago

Logarithmic History has had a lot of geology and biology lately, not so much astronomy. But all is not peaceful in the heavens.

Benjamin Gould is a nineteenth century astronomer who noted that a lot of bright stars in the sky — especially the bright blue stars that we know are very young — seem to fall along a ring tilted at a 20 degree angle to the Milky Way. This ring has come to be called Gould’s Belt (or the Gould Belt). The Belt is an ellipse about 2400 by 1500 light years across where there has been a recent wave of star formation. Our Sun lies within the belt, somewhat off center; the center lies in the direction of the Pleiades.

The Belt began forming maybe thirty million years ago. We’re not sure what happened. A supernova may have set off a wave of star formation, but it would have to have been a huge one. Or it may be that a gas cloud or a clump of dark matter passed at an angle through our part of the Milky Way, and started stars forming with its shock wave. There are features resembling Gould’s Belt in other galaxies. In any case, the Belt is one of the really striking features of our part of the Milky Way.

Whatever its cause, no one disputes its magnificence. Gould’s belt is the most prominent starry feature in the Sun’s neighborhood, contributing most of the bright young stars nearby. Nearly two thirds of the massive stars within 2,000 light-years of the Sun belong to Gould’s belt. If I were kidnapped by an alien spaceship and taken to some remote corner of the Galaxy, Gould’s belt is what I’d look for to find my way back home.

Ken Crosswell. Gould’s Belt.

If you’re in the Northern hemisphere you can look at the sky tonight and see the Milky Way in an arc in the Western sky, stretching from North to South. West of the Milky Way you’ll see some of Gould’s belt, an arc of bright stars running north to south from the Pleiades, through Taurus and the bright stars of Orion, and Canis Major. So tonight look at the stars, and drink a toast if you want, to your ape ancestors, who were just on the cusp of splitting off from monkeys thirty million years ago.

A family tree for the sun

7.44 – 7.04 billion years ago.

No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?

Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification. And Darwin argued that all living things belong to one or a few family trees linked by recent or remote common descent.

Recently, some astronomers teamed up with some evolutionary biologists to produce a “family tree” of our Sun and some of its neighbors. The tree is based on the abundances of different chemical elements; these abundances don’t change much over the lifetime of a star, and can be thought of as a kind of inherited trait, something like DNA. The tree groups stars roughly according to their ages, with younger stars having more “metals” (elements other than hydrogen and helium), but only roughly, since other processes affect stellar chemistry.

Drawing a family tree for stars might seem like an odd thing to do. In what sense are stars related as parent and offspring? Evolutionary biologists face a similar situation where group selection is concerned. Suppose you have a population of organisms. Those organisms form groups that last for a time and disband, with their members “seeding” the population at large, and influencing group formation in the next generation. Although there are ancestor-descendant relations between individual organisms, you can’t identify any one group in generation t+1 as the descendant of any particular group in generation t. Are the groups in this case meaningful evolutionary units? It depends on which biologist you talk to.

We are stardust

10.4 – 9.9 billion years ago

The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

Carl Sagan (h/t to commenter remanandhra)

There’s a long gap between the origin of the universe, the first stars, and early galaxies, and the origin of our Solar System and our planet Earth. If we were using a linear scale for our calendar, the Solar System would get started in September. Even on our logarithmic scale, Sun and Earth wait until late January. A spiral galaxy like the Milky Way is an efficient machine for turning dust into stars over many billions of years. But the earliest stars it produces are poor in “metals” (to an astronomer, anything heavier than helium is a metal). It takes generations of exploding stars producing heavier elements and ejecting them into space before a star like the Sun — 2% metal – can form.

And just a few years back, a spectacular discovery provided support for another mechanism of heavy element formation. Astronomers for the first time detected gravitational waves from the collision of two neutron stars, 300 million light-years away. Such collisions may be responsible for the formation of some of the heaviest atoms around, gold and silver in particular. So your gold ring may be not just garden-variety supernova stardust, but the relic of colliding neutron stars. Here’s a chart showing where the elements in our solar system come from:

Alchemists thought they could change one element into another – lead into gold, say. But it takes more extreme conditions than in any chemistry lab to transmute elements. The heart of a star makes heavy elements out of hydrogen and helium; it takes a supernova to make elements heavier than iron, and something even more spectacular, the collision of neutron stars, to make the heaviest elements. So it’s literally true, not just hippy poetry, that “we are stardust” (at least the part of us that isn’t hydrogen).

In the beginning

13.8 – 13.1 billion years ago

Logarithmic History is now rolling into its ninth year. We’ll continue with a mixture of blog posts and tweets, some recycled, some new, with favorite Logarithmic History holidays, celebrating the origins of seafood, first flowers, beer, bread, and more. Welcome! 

Knowing what happened at the very beginning of the Universe is speculative. It depends on what the theory of quantum gravity looks like, which is up in the air. The theory of inflation (insanely fast growth before 10^-32 seconds , after which the universe settled down to merely explosive growth with the Big Bang) may explain why the universe is flat, uniform, and not very lumpy. In 2014, it looked like we had direct evidence for gravity waves generated by inflation, going back just 10 sec from the beginning of the universe. But it looks like this doesn’t hold up.

Later developments are more generally agreed on, although some of the exact times may need revision in the future. The late (1933-1921) Steven Weinberg’s  The First Three Minutes is a classic summary. Strikingly, a lot of familiar astronomical objects, including stars and galaxies, are already around within 100’s of million of years. However early stars are short on metals (to astronomers, anything heavier than helium counts as a metal), and the early Milky Way is dispersed and fuzzy, not the barred spiral galaxy we know today.

Gould’s Belt

30.3 – 28.8 million years ago

Logarithmic History has had a lot of geology and biology lately, not so much astronomy. But all is not peaceful in the heavens.

Benjamin Gould is a nineteenth century astronomer who noted that a lot of bright stars in the sky — especially the bright blue stars that we know are very young — seem to fall along a ring tilted at a 20 degree angle to the Milky Way. This ring has come to be called Gould’s Belt (or the Gould Belt). The Belt is an ellipse about 2400 by 1500 light years across where there has been a recent wave of star formation. Our Sun lies within the belt, somewhat off center; the center lies in the direction of the Pleiades.

The Belt began forming maybe thirty million years ago. We’re not sure what happened. A supernova may have set off a wave of star formation, but it would have to have been a huge one. Or it may be that a gas cloud or a clump of dark matter passed at an angle through our part of the Milky Way, and started stars forming with its shock wave. There are features resembling Gould’s Belt in other galaxies. In any case, the Belt is one of the really striking features of our part of the Milky Way.

Whatever its cause, no one disputes its magnificence. Gould’s belt is the most prominent starry feature in the Sun’s neighborhood, contributing most of the bright young stars nearby. Nearly two thirds of the massive stars within 2,000 light-years of the Sun belong to Gould’s belt. If I were kidnapped by an alien spaceship and taken to some remote corner of the Galaxy, Gould’s belt is what I’d look for to find my way back home.

Ken Crosswell. Gould’s Belt.

If you’re in the Northern hemisphere you can look at the sky tonight and see the Milky Way in an arc in the Western sky, stretching from North to South. West of the Milky Way you’ll see some of Gould’s belt, an arc of bright stars running north to south from the Pleiades, through Taurus and the bright stars of Orion, and Canis Major. So tonight look at the stars, and drink a toast if you want, to your ape ancestors, who were just on the cusp of splitting off from monkeys thirty million years ago.

A family tree for the Sun

7.44 – 7.04 billion years ago.

No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?

Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification. And Darwin argued that all living things belong to one or a few family trees linked by recent or remote common descent.

Recently, some astronomers teamed up with some evolutionary biologists to produce a “family tree” of our Sun and some of its neighbors. The tree is based on the abundances of different chemical elements; these abundances don’t change much over the lifetime of a star, and can be thought of as a kind of inherited trait, something like DNA. The tree groups stars roughly according to their ages, with younger stars having more “metals” (elements other than hydrogen and helium), but only roughly, since other processes affect stellar chemistry.

Drawing a family tree for stars might seem like an odd thing to do. In what sense are stars related as parent and offspring? Evolutionary biologists face a similar situation where group selection is concerned. Suppose you have a population of organisms. Those organisms form groups that last for a time and disband, with their members “seeding” the population at large, and influencing group formation in the next generation. Although there are ancestor-descendant relations between individual organisms, you can’t identify any one group in generation t+1 as the descendant of any particular group in generation t. Are the groups in this case meaningful evolutionary units? It depends on which biologist you talk to.