[ The Vela Supernova exploded approximately 11,000-12,300 years ago about 800 light years away.]
I was watching The History Channel (now with the new H2 variation) and they were going on about Nemesis ( that in an earlier posting we showed was not near enough to be an issue in 2012, if it exists at all). That lead to looking at their claim that there was a 25 million year cycle of extinctions (which also lead to other folks claiming a 67 million year cycle and to the point that most of these ‘cycles’ have a few million year error bands on them…) In the end, that all led to looking at ‘nearby stuff’ with an emphasis on stars and similar. That led to something that is very old knowledge (late 1800s) but ‘new to me’… and with some newer insights into it.
Yes, that’s how my ‘day’ typically goes. An “interesting” leads to a “more?” leads to a “what?” leads to a “What the?”…
So here’s the deal: I ran into a couple of pages that just did a great job ( one could say ‘a stellar job’ if one didn’t mind moaning too much ;-) of laying this all out. I can not do as well, and I’m not willing to just copy their stuff, so I’m mostly just going to link to it.
What’s all this about?
Gould’s Belt ( a structure in our galaxy, or perhaps wandering into our galaxy), various ‘bubbles’ of star formation (some only a few million years old – practically brand new compared to our 4.5 Billion year age), and a tendency for things in the neighborhood to go BANG!
From the Ken Croswell link below, a small idea what Gould’s Belt is like:
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.
There is an odd structure, tilted to the general plane of the Galaxy by about 20 degrees, and holding many of our most interesting constellations. Our sun is ‘sort of in it’, in that we are located about where Gould’s Belt intersects the general plane of The Milky Way; but all the details are a bit murky with some folks even trying to decide if it is a ring or a disk. But what is very clear about it is this: It is an area of young star formation and it was formed about 30 to 60 Million years ago ( so ‘near’ the time of the dinosaur extinction, and with an error band that wide, I have to wonder if it might be just a bit older than 60 million years… that is the age of the stars, but might the ‘event’ have been earlier?)
OK, some links. This one has a GREAT visual of the belt. You can click on individual objects and find out more about them. A nice bit of ‘eye candy’ and fun to play with:
One bit to mention: Many of the stars are big blue ones with a short fast life cycle. Yet we are in a ‘hole’ of fewer than expected such blue stars. Might this be due to OUR sun having cleared the area of the needed gas for star formation during some earlier event? Could this argue for our sun being the ‘leftovers’ of it’s own nova event some billions of years back?
Look at that picture. The Sun is that yellow cross in the middle. Notice the blue stars all over the field… except near us. Curious, that…
I was particularly struck by “Gum 12” and “Gum 16”. Large gas clouds. Clicking on them gave this text:
Distance: 400 pc, Size: 291.2 pc
This vast 2.6 million year old supernova remnant is usually simply called “the Gum nebula”. Located at the collision between the Gould Belt and the Vela region, the Gum nebula is a major part of the local galaxy.
The Gum nebula is too large to easily create an image of it using either SuperCosmos or the Digitized Sky Survey, so this image was taken from Douglas Finkbeiner’s composite hydrogen-alpha image of the entire Milky Way.
Distance: 250 pc, Size: 35.0 pc
The ten thousand year old Vela supernova remnant is located at the front side of the Gum nebula (Gum 12)
In addition to the very nice pictures on the page: Notice the ages? Fairly young. This belt is a place of young fast lived stars and a surprising rate of supernova events.
Some Detail / Context
This next page has a great write up of Gould’s Belt. With nice pictures.
The “intro” part gives an idea just how much of our night sky and common constellations are, in fact, due to this one structure:
Although Gould’s belt was discovered in the southern sky, it’s a special treat to stargazers in the north. That’s because the bizarre 20-degree tilt allows many northerners to see bright stars that otherwise would elude them. Gould’s belt tilts above the plane of our Galaxy in the direction of the Milky Way’s center, toward Sagittarius and Scorpius, and below the Galactic plane in the opposite direction, toward Orion and Taurus.
Gould’s belt elevates stars that otherwise would be so far south as to be invisible from mid-northern latitudes. In particular, if you live at a northerly latitude, you can thank the odd tilt for providing your view of the spectacular constellation Scorpius. Without Gould’s belt, the constellation’s brightest stars would lurk in the murk of the southern horizon. Instead, the red supergiant Antares, the two blue stars on either side of it, and the Scorpion’s crooked head shine far to the north, visible even in Canada. All these stars are or were blue, and all belong to Gould’s belt. Antares, for example, hovers 15 degrees north of the Galactic plane. Gould’s belt likewise raises the bright stars of neighboring Lupus and Centaurus. All three constellations, plus Crux and Ophiuchus, feature the Scorpius-Centaurus OB association, the nearest group of massive, supernova-producing stars, 500 light-years away. Since Antares has evolved into a red supergiant, it likely will be the next to explode.
For anyone wondering if the ‘odd tilt’ of our solar system matches that 20 degree tilt of the Gould Belt, it doesn’t. We’re about 90 degrees tilted vs the Milky Way.
I’m especially fond of Ken Croswell’s treatment of “What made it?”. The short form?
Although Gould’s belt is a prominent fixture of the solar neighborhood, no one knows what caused it. Clearly something happened some 30 to 60 million years ago. That’s the age of the oldest surviving stars in Gould’s belt. It’s also the expansion age. Both the stars and the gas are redshifted, indicating that Gould’s belt is expanding like a ripple racing outward from a pebble tossed into the sea. The speed of the expansion implies that it began about 30 million years ago. The Galaxy’s rotation has stretched the original circle into an ellipse.
At first, a supernova might seem the way to explain Gould’s belt. Its shock waves could have piled up gas and dust in an expanding ring of star formation. But this won’t work. A single supernova doesn’t pack enough punch. And supernovae elsewhere, such as in the Scorpius-Centaurus association, haven’t created anything as grand as Gould’s belt.
So it’s big, really really big. It’s redshifted, so stuff is moving away from us. The oldest stars are about twice as old as the redshift would indicate for the starting age, and it is full of energetic objects and very young stars.
And it has a ‘center’ very near us.
“This is very much conjecture,” says Fernando Comerón of the European Southern Observatory in Germany, one of the astronomers who proposed the idea. “No mechanism–or combination of mechanisms–is ruled out.” He notes that the various ideas may have worked in tandem. A colliding gas cloud may have started the birth of stars, then supernova explosions enhanced the star-formation rate.
A logical place to look for the culprit is the center of Gould’s belt. As it turns out, not far from that point lies the Alpha Persei cluster, some 600 light-years from Earth. It’s about 50 million years old. Surrounding this cluster is the loose Cassiopeia-Taurus association of stars. Perhaps the stars here were the site of a Galactic “ground zero” that created Gould’s belt. Alpha Persei and the Cassiopeia-Taurus association may themselves have been created by a passing spiral arm or the collision of an intergalactic gas cloud.
600 light-years is just not very far away at all, in Galactic terms. In reality, it is even closer than that:
Still, Gould’s belt doesn’t come close enough to explain all the detections. Guillout therefore proposes that Gould’s belt is really a disk. In his view, the bright blue stars merely mark the outer boundary of Gould’s disk. Lesser stars shine at nearer distances, within range of ROSAT. At its closest, in Centaurus, the disk is only about 100 light-years from the Sun. In the future, Guillout will use x-ray data from the more sensitive XMM Newton satellite. Then he hopes to detect young, x-ray-emitting Gould-belt stars all around the sky.
Interstellar gas and dust–the raw materials from which new stars are born–also trace Gould’s belt. As early as 1922, Edwin Hubble noticed that many interstellar nebulae followed the path of Gould’s belt around the sky. In the 1960s, Swedish astronomer Per Olof Lindblad discovered a ring of neutral hydrogen gas that did the same. Indeed, the gas and dust account for most of the mass in Gould’s belt, outweighing its stars. Two of the best-known gaseous members are the Orion Nebula and the Rho Ophiuchi cloud.
Notice that the very young and very short lived blue stars are around the outside, and less short lived stars are nearer to us. Kind of looks like “something happened” and it spread out rapidly, but only started reaching those outer areas a bit later and causing star formation there, while the inner areas have had more stars already expire as supernova events and leaving only the smaller slower life cycle stars behind.
So, what happened? Nobody knows… But we know it was big (really really big, when even a supernova isn’t big enough to cause it) and we know it was about 60 million years ago. And we know it was ‘nearby’ in that 100 light-years is just down the block in space terms. Could it have been what knocked the impactors into earth and did-in the dinosaurs? Might the earlier partial die off have been from the radiation (and related effects) with a bit more time for the rock fall to wander in from the Oort Cloud? Could the shock of all this on the crust also explain the higher volcanism that happened at about the same time?
How MANY nova events were caused over that 60 millionish year interval as this process spread out?
The Sun lies inside Gould’s belt, but off-center. Most studies put the center of Gould’s belt around Perseus, several hundred light-years from the Sun. However, Perrot and Grenier say the center lies near neighboring Taurus, opposite the Milky Way’s center, at a distance of only 340 light-years. This is closer than the Pleiades, another Taurus resident.
When massive stars like those in Gould’s belt explode, they leave behind pulsars and black holes. In the late 1990s, Grenier noted that the Compton Gamma Ray Observatory recorded several dozen sources which track the path of Gould’s belt around the sky. No one knows what these gamma-ray sources are, but they may be pulsars or black holes–cinders left behind by the explosion of the first generation of brilliant stars that once illuminated Gould’s belt.
Now notice that we’re talking about an object that is only a few tens of millions of years old. Yet it’s got “dozens” of gamma ray sources in it? Dozens of potential black holes from nova events? We’re talking on the order of one per million years. Starting in our neighborhood and moving out. That has a reasonably high chance of having made the earth of the last 60 million years a much more interesting place and with a very spectacular sky every so often…
Much more in the article itself with the very nice pictures…
Sidebars and Footnotes
This then lead to some sidebars. One was the whole idea of local bubbles of stars. Seems that all sorts of places just suddenly make a batch of stars, often quite young ones. These come in a few different types of clusters, depending on local conditions and causes. Sometimes they hang together, sometimes the stars end up ‘wandering off’ to cruise around the galaxy. Not nearly as ‘orderly’ a place as we are lead to believe when shown the image of nice neat spiral arms with everything moving, but in rotation about the galactic center.
You can explore some of these at this rather nice site:
Which has a nice line drawing of the Gould Belt and a good ‘thumbnail sketch’ quoted here:
A partial ring or disk of hot, young stars, of types O and B, and star-forming molecular clouds, within which the Sun lies (approximately 40 light-years (12 parsecs) north of the Belt’s equatorial plane and about 325 light-years (100 parsecs) from its center). The Gould Belt has a diameter of about 3,000 light-years and is inclined to the galactic plane at about 20°. It appears to be a spur connected to the lower edge of the Orion Arm of the Galaxy. Among its most prominent components are the bright stars in Orion, Canis Major, Puppis, Carina, Centaurus, and Scorpius, including the Scorpius-Centaurus Association. It is thought to be 30 to 50 million years old but its origin is unclear. It is named after Stephen Gould, who established its existence in 1879.
Links take you to descriptions of various local clusters, associations, and bubbles of stars, like this one:
It has some really nice pictures too, along with helpful text like:
The nearest OB association to the Sun. The Scorpius-Centaurus Association is centered about 470 light-years away in the Gould Belt and contains several hundred stars, mostly of type B, including Shaula, Lesath, and Antares. Though born roughly at the same time, the association’s stars are not gravitationally bound, and the association is rapidly expanding.
Subcomponents of the Scorpius-Centaurus Association include the Upper Scorpius (the youngest), Upper Centaurus-Lupus (the oldest), and Lower Centaurus-Crux associations. The star formation process in Scorpius-Centaurus started in the Upper Centaurus-Lupus Association some 15 million years ago. About 12 million years ago the most massive star in Upper Centaurus-Lupus went supernova, creating a large shock wave. This shock wave passed through the Upper Scorpius cloud about 5 million years ago, and triggered the star formation process there. Shortly after, the strong winds of the numerous massive stars in Upper Scorpius started to disperse the molecular cloud and halted the star formation process. About 1.5 million years ago the most massive star in Upper Scorpius exploded as a supernova. This shock wave fully dispersed the Upper Scorpius molecular cloud and now passes through the Rho Ophiuchi Nebula, where it might well have started the star formation process about 1 million years ago. The superbubble known as Loop I, generated by supernovae around the Association is impinging on our own Local Bubble and directly affecting the environment in the solar neighborhood.
Supernova blowing bubbles? We live in a local bubble? And just HOW is it affecting our ‘environment’ and is that effect going to change much ( Is the ‘shock wave’ just arriving, just leaving, or ‘mid point’? And would we even notice?)
Instead of neat orderly orbiting, we have gas clouds, nebula blobs, star clusters forming and breaking up, supernova blowing holes in areas. The whole place is just a chaotic mess, really. Now I’d known about those things, but never looked at the time scale closely enough. It’s easy to think these things take on the order of Billions of Years (due to the age of the sun… and the fact that some stars are 15 billion years old). But here we find out it’s on the order of low 10s of Millions of years. Heck, humans evolved about 6 million years ago. One event was only 1 Million years ago. This is of the same order of magnitude as speciation and in some cases even faster.
It all just leaves me wondering how much we really do not know at all about our ‘galactic neighborhood’ and both the dust and cosmic ray environments (and how they change) over time. We can have whole star clusters born, supernova form, and dust clouds wandering by on surprisingly short time scales. So much for ‘settled science’…
Oh, and there may be a supernova left-over from about 300,000 years ago that is what cleared out the ‘local bubble’. Wonder if there’s any change in the ice cores reflective of any change from that lower dust level and / or changed radiation levels?
For nearly 20 years, the nature of Geminga was unknown, since it didn’t seem to show up at any other wavelengths. Then, in 1991, an exceptionally regular periodicity of 0.237 second was detected by the ROSAT satellite in soft X-ray emission, indicating that Geminga is almost certainly a pulsar (a flickering neutron star). Its invisibility at radio wavelengths – it’s the only known pulsar that is radio-quiet – may be because its beams of radio radiation don’t sweep past the Earth. It has also been identified optically with an extremely dim blue star, 100 million times fainter than anything visible to the naked eye. A comparison of images of the suspected optical counterpart taken over an eight-year period shows a proper motion that is consistent with a distance to Geminga of about 330 light-years, making it easily the closest known pulsar to Earth.
Geminga is believed to be the stellar remains of a supernova that took place some 300,000 years ago and which is, at least partly, responsible for clearing out a low density cavity in the interstellar medium in the vicinity of the solar system, known as the Local Bubble. High precision timing of Geminga, achieved by combining observations made by the COS-B satellite in the late 1970s and observations by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory, have indicated that the pulsar may have a companion planet (see pulsar planets).
Though I’m left wondering if it is 300 light-years away and happened just 300,000 years ago, is the effect from it “still on the way”? Or was it all light pressure mediated? In any case, clearing out local gases and changing cosmic ray flux ought to leave some evidence behind here on earth…
A Bit More Speculative
On a more speculative note, there was this somewhat more broad scope page:
The thesis here is that we are part of a ‘yellow cluster’ of stars and that as we wander in and out of various parts of the galaxy, we have extinction events. Oh, and eventually will get eaten by the galactic core or, as they call it, “the great attractor” (that I think is the galactic core…).
Astronomers detect a 62 million year cycle whereby the earth, instead of being part of the Orion Arm of the Milky Way, actually moves on a different plane entirely, I have talked about this in the past in several articles: the sun isn’t native to this galaxy but rather, was born within a small ‘hobbit’ star cluster/galaxy which was captured by the bigger galaxy and we go through vast changes in our stellar environment as our sun moves through various parts of the galactic plane.
There’s a lot more to this story there, and some interesting quotes and citations as well.
Our solar system travels through the disk-shaped Milky Way on a complicated circuit that takes about 225 million years to complete. At regular intervals, the system’s wanderings take it up and down through the thin central portion of the disk. The sun reaches its farthest distance from the central plane every 62 million years.
OK, at first blush I’m wondering if our tilt (as a galaxy orbital process) is aligned with the Gould Belt (even if our solar system internal ecliptic plane is at a different angle) then I notice that she is talking about a 225 Million year period for a single orbit. The whole Gould Belt thing is less than 1/4 of that, so “recent” in comparison.
Now I’m pondering just how many bits of other gas clouds, other “hobbit galaxies”, local clusters, et. al. have mushed into the Milky Way over the last few billion years, and how much their retained motions and momenta cause ‘odd things’ in the mixing and moving…
Are we looking at a ‘new guy’ gas cloud making the stars of our ‘recent’ night sky, yet we are just as alien to the older “locals” who where here billions of years before us? Was our sun and earth formed 4-5 Billion years ago in a similar event? Is that why we bob up and down vs the galactic plane and is that why we are so much younger than the older stars nearer the center?
Which all just leaves me wondering: How soon does the next one happen? Be it gas cloud or hypernova or ‘whatever’, just how often do these pot stirrers stir the pot?
And no one knows…