Mysteries of the galaxy

Continuing with the Astronomy Cast theme, here is their list of the top 10 mysteries of the Way, Milky.

The show notes are located here and here.

1.) Blue stragglers: are stars that appear to stay in their youth longer than expected, even regressing to their hotter youths. They're big and blue and given where they are located (in globular clusters), they should have burned more hydrogen than they seem to have. It seems they might be stealing mass from other stars although that's just speculation.

2.) Some of our supernovae are missing: The math says we should see 2-3 a century. The last one that occurred relatively close to us was in 1680.Chandra appears to have found remnants of supernova explosions in some dust clouds. What astronomers can say is there doesn't seem to be anything unique to our galaxy to explain why they can't see them. It may just be a question of not seeing them in the visible spectrum due to obstruction.

3.) The Small and Large Magellanic Clouds: these are the satellite galaxies that are...orbiting the Milky Way? Apparently, we don't quite know. They might be just be dwarf galaxies nonchalantly traveling past us. The explanation for why we can't tell is, once again, mathy but it has to do with factors like our inability to precisely estimate the Milky Way's mass. If they are orbiting us, it's possible the Milky Way will rip them up one day and gobble their stars. Andromeda is going to do the same thing to us, but it's billions of years away so I'll focus on worrying about Michelle Bachman actually winning the Republican nomination for now.

4.) Proxima Centauri's intimacy issues: Proxima is a red dwarf in the Alpha Centauri system, around 4 light years away. The problem is, it's awfully close to Alpha Centauri A&B. Some say it's a captured object that is orbiting this system. They all appear to be moving through the sky close together at around the same velocity.

5.) When is Eta Carinae going to blow already: this is one of the brightest stars in the sky, around 100 times the mass of the sun. It's located in the Homunculus Nebula (it's a great name, it just means "little man.") Stars in constellations are named according to their brightness. Thus, Alpha Centauri is the brightest star in Centauri, this Beta and so forth. Eta took the giant leap forward in 1843 when it brightened and appeared to be supernova-ing. There's no way to predict when. If you happen to be watching with the right kind of equipment, you can see the xray burst minutes before the eruption.

6.) One of our spiral arms is missing-or not: apparently when you study galaxy arms (and of course, such a specialized field exists), you are supposed to look at them all in the same color. But when you look at galaxies through different lights (radio, ultraviolet) the morphology changes. And parts of the arms could be obscured from us. I admit, I don't totally see the big deal about this one since part of it seems to apply to all galaxies.

7.) Where are the Sun's nebula buddies: Around 4.6 billion years, our solar system formed out of a solar nebula. When we look at other stellar nebulae (e.g. Orion, Carinae, Pleiades), we see clusters of stars. It could be due to gravitational effects that the rest were flung out of the system. You can't tell from looking at a star or its motions where it started out so to find out if another star was birthed with our sun, you'll need detailed chemical analysis. I gather this is a somewhat moot point because the answer, by present means anyways, it never much more than maybe and siblings could be on the other side of the Galaxy just as easily by now.

8.) The 60 million year extinction cycle: Here's some cheery reading--10 potential causes of mass extinctions from gamma rays to magnetic field reversals. UC Berkeley contends that around every 60 million or so years, some mass extinction event occurs that wipes out up to 90% of life on this planet. How old is that KT Boundary again? Yup, we're about due. There are some interesting theories about what is protecting us, at least most of the time including the Milky Way's proposed magnetic field.

9.) The case of the missing G-Dwarfs: G-dwarf are also called yellow dwarfs although that can be misleading (they range in color from white to yellow.) They are a subset of the main sequence stars, like all dwarfs. Our own sun is a G-dwarf, but the ones we are looking for would be a little smaller than the sun. Here's how the reasoning goes: the smaller the star, the longer it burns so the longer it hangs around burning through its hydrogen. There are a (at this point theoretical) group of stars formed just after the Big Bang called Population III. They should have little to no metal in them, as they should have formed before being polluted by supernovae. There should also be red dwarfs composed of this primordial hydrogen. It's possible the big stars (that form faster) just didn't leave room or resources for the smaller stars to develop. Or maybe the lack of metals in the primordiverse just prevented smaller stars from forming.

10.) The intermediate black hole quandary: an intermediate black hole would be greater than a stellar black hole but obviously not a supermassive black hole. The moniker "supermassive" always seems to me to indicate its kind of rare but in fact, the intermediate ones are the hard ones to find. They've tried looking in dwarf galaxies and globular clusters but no dice. Chandra has identified some extra-luminous x-ray sources  that might turn out to be the culprits.