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black holes, galaxies

What Happens in a Black Hole Stays in a Black Hole

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But the Matter Surrounding It? That’s Another Issue…

Schematic of a Black HoleBlack holes, as the old bumper sticker said, suck. They also don’t have any hair, as Stephen Hawking once said. They gobble up stuff like stars and gas and dust, and they don’t give anything back. You can’t tell anything about them by simply looking at them, although you can infer their masses by the gravitational influence they have on material around them. And, you can tell that one is around by the heat and x-rays and other signals given off by the material that spirals into a black hole. And, if the supermassive black hole has a jet, you can detect THAT. But, all of the mass they take in stays there and the information about it stays secret forever. It’s a sort of cosmic version of “what happens in Vegas stays in Vegas.”

It turns out there are some other interesting things about black holes besides the fact that they suck. For one thing, for a while, astronomers thought that there was a correlation between size of a galaxy’s central bulge (if it has one) and the size/mass of its central supermassive black hole. The more massive the black hole, the larger the bulge of stars at the center of a galaxy would be. That makes sense, since supermassive black holes have to have a lot of matter to eat to keep them hefty and massive, and big galaxy bulges would have a lot of stars and gas and dust to feed them.

Well, this relationship seems to work for some galaxies, but not all of them. Some galaxies, like M33 in Triangulum, have massive black holes, but don’t have central bulges. So, maybe there’s something else influencing black hole growth. Something as mysterious as a black hole: like, dark matter.

Now, that’s not to say that there are dark-matter-munching black holes out there in skinny galaxies. The relationship is something far more complex and so far, astronomers are still figuring out what it is.

Dark matter exists, but you can’t see it. You CAN, however (if you have the right methods) measure its influence on regular matter. It has a gravitational influence. And, how much influence it has depends on how much of it there is. So, maybe there are galaxies out there with huge dark matter components; some of them with bulges and some without. And, maybe all that dark matter is having some influence on the growth of the black holes at the hearts of those galaxies, whether they have bulges or not. Maybe the dark matter is influencing the bulge. And, maybe the black hole’s growth rate and size is telling us something about the dark matter surrounding it. If so, it may be the only message we get about matter from a black hole!

astronomy news, astrophysics, galaxies, Milky Way Galaxy

Gaining Clarity on the Milky Way

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Learning More about the Home Galaxy

Wow. I miss ONE AAS meeting, and they lose two spiral arms from our galaxy! This is what I get for staying home and working on two big projects with massive deadlines. I did manage to log in and watch the press conferences from the comfort of my overstuffed office, so I caught the gist of what has turned out to be a very cool story.

First, some background. For years, astronomers thought our galaxy probably had four spiral arms. But, it’s hard to tell because we can’t exactly SEE all of our galaxy in visible wavelengths. This is due to all the dust in the galactic plane, and since WE’RE in the galactic plane, it’s like trying to see through a dense fog when it comes to looking in various directions. Isaac Asimov put it best when he wrote, “In a sense, we are on a low roof on the outskirts of the city on a foggy day.”

Well, as it turns out, telescopes with infrared capability can look through that fog and see farther and sharper than visible-light counterparts. So, it makes sense to use such facilities when you want to see what’s out there.

Groups of astronomers from JPL/CalTech and the University of Wisconsin used the infrared-enabled Spitzer Space Telescope to look at the galaxy. Their survey, called the Galactic Legacy Infrared Midplane Extraordinaire (GLIMPSE), spanned 130 degrees in longitude (65 degrees on either side of the center of the galaxy), and 2-4 degrees in latitude. Since Earth is located about halfway out along the plane of a flattened spiral, this survey actually encompasses a large fraction of the volume of the Milky Way. The infrared views (shown below) show where the stars are, as well as the dust clouds in the plane, allowing a more complete star census to be done.

[GLIMPSE]

Here’s one of two views of the Milky Way from GLIMPSE, emphasizing wavelengths (3.6 – 8 microns) in the familiar blue-green-red that our eyes see, with the shortest wavelengths displayed in blue and the longest in red. For more technical details, check out the GLIMPSE page at the University of Wisconsin’s team site. They also have downloadable poster-size files of this and another view of the same data.

Milky Way Spiral StructureNow, if you could turn that image so we could see it from the “top down” this “artist’s concept” might be what our Milky Way really looks like. The survey showed, for the first time, that arms we thought were there, really aren’t. The Milky Way’s elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars.

Spitzer’s imagery of the galaxy comprises 800,000 snapshots, and when you piece them all together, they make the clearest view of the Milky Way ever produced. The team has created a poster that they showed at AAS that is 180 feet (289 meters) long and 3.5 feet (2.1 meters) wide. The poster is going on tour soon, apparently showing up at Griffith Observatory (where they have a similar large-scale image of a small part of the Virgo Cluster called “The Big Picture” on display), and then on to various other cities. You, however, can explore it from the comfort and privacy of your home or office by going to http://mipsgal.ipac.caltech.edu/p_map.html where they have a GoogleMaps zoomable map. Check it out!