Black Holes don’t suck

Last night I learned quite a bit about super massive black holes at the Mid Hudson Astronomy Association month meeting in a great presentation by Dr Barry McKernan.  His overwhelming theme of the evening was that “Black Holes Don’t Suck”, as he wanted to break that myth.  Everything you’ve seen in science fiction on black holes is pretty much wrong.

A black hole is just a dark star, so small (relative to mass) that the escape velocity from it’s surface is faster than the speed of light.  If you converted the earth into a black hole, it would be the size of a grape.  It would still have the mass of the earth.  The moon would still orbit it just the same.  But you’d be unable to see the thing you were orbiting.  The moon wouldn’t fall into the earth, as the celestial mechanics don’t change.

A very recent (last decade) discovery is that the hearts of most galaxies contain super massive black holes.  The one at the center of the milky way is 2 Million times the mass of the Sun, though only 10s of times as physically large.  That actually makes it smaller in radius than a lot of the brightest stars you can see at night, like Sirius and Betelgeuse.  Barry started the evening with a movie made of 10 years of observations of the center of the galaxy in which you could see stars moving around in arcs.  Zooming in on the data showed one star in particular whipping around something invisible, like it was a planet going around the sun.  This is part of the data that proved the existence of the super massive black hole in our galaxy.

A subset, less than 1%, of these galactic black holes are consuming dust.  Because dust clouds interact with themselves they effectively slow down over time (converting energy into light and heat).  This creates what are called Active Galactic Nuclei.  They are huge beacons of light at the center of galaxies.  Previously we call these things Quasars, Masars, Magnetars.  In the telescopes of 2 decades ago they look sort of like stars (they are point sources of light), but their light curves are all wrong to a be a star.  Now we can actually see both the “star” and the galaxy they are the center of.  If we get to see the disc top down, they outshine the rest of the galaxy by as much as 1000 times.

I asked the question, “if they outshine the rest of the galaxy, what would they look like if you were in their galaxy”.  I saw the speakers eyes light up when I asked the question, so I knew I’d hit on a good one.  The answer, there is so much dust in the discs of galaxies that all that optical, uv, and x-ray light would get absorbed, then re-emitted as infrared.  You’d see a big infrared glow in the direction of galactic center.  You’d also probably see radio jets shooting out like spikes perpendicular to the plane of the galaxy.

All in all this was one of my favorite talks at the group to date.  Very informative, and presenting some great science.  If you have any interest in the stars, and are in the Mid Hudson Valley, you should come check out the group.  Friendly folks, spreading science, what could be better.

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